Altermagnets,a new type of collinear antiferromagnet,exhibiting non-degenerate electron and magnon dispersion in momentum space have attracted intensive research attention.We theoretically analyze the origin and featu...Altermagnets,a new type of collinear antiferromagnet,exhibiting non-degenerate electron and magnon dispersion in momentum space have attracted intensive research attention.We theoretically analyze the origin and feature of chiral magnon splitting in representative altermagnets including tetragonal RuO_(2),hexagonal MnTe,and orthorhombic LaMnO_(3).The magnon spin transport properties including spin Seebeck and spin Nernst coefcients have been investigated.Through these materials,we demonstrate the diference of chiral splitting in d-wave and g-wave antiferromagnet on magnon transport.RuO2with planar magnon splitting exhibits signifcant magnon spin Nernst and magnon spin Seebeck anisotropy in(110)and(001)planes,whereas MnTe,due to its bulk-like magnon splitting,is incapable of producing magnon spin Nernst efect.Our work may provide in-depth understanding on the mechanisms of nonrelativistic magnon splitting and thermal spin transport in altermagnets.展开更多
Martensite is one of the most important structures determining the ability to tailor the performance of steel and several other engineering materials.In previous studies,the face-centered cubic(FCC)to hexag-onal close...Martensite is one of the most important structures determining the ability to tailor the performance of steel and several other engineering materials.In previous studies,the face-centered cubic(FCC)to hexag-onal close-packed(HCP)(or body-centered cubic(BCC))martensitic transformation and the FCC to body-centered tetragonal(BCT)(or BCC)martensitic transformation during deformation and quenching were widely investigated;these transformations usually improve the plasticity and strength of steel,respec-tively.In this work,detailed transmission electron microscopy(TEM)observations and electron diffraction pattern analyses of the BCT and BCC twins are performed along the[110],[131],and[¯153]zone axes.The transformation of BCT twins into BCC twins along the[131]zone axis is also analyzed through in situ heating during the TEM observations.The high-resolution TEM observations of mutually perpendicular BCT variants are consistent with the atomic arrangement obtained for the quenching pathway during the martensitic transformation.In addition,different orientation relationships between austenite and marten-site are explained in terms of the atomic migration occurring during the deformation pathway and the quenching pathway of the martensitic transformation.展开更多
Platinum-based alloy nanoparticles are the most attractive catalysts for the oxygen reduction reaction at present,but an in-depth understanding of the relationship between their short-range structural information and ...Platinum-based alloy nanoparticles are the most attractive catalysts for the oxygen reduction reaction at present,but an in-depth understanding of the relationship between their short-range structural information and catalytic performance is still lacking.Herein,we present a synthetic strategy that uses transition-metal oxide-assisted thermal diffusion.PtCo/C catalysts with localized tetragonal distortion were obtained by controlling the thermal diffusion process of transition-metal elements.This localized structural distortion induced a significant strain effect on the nanoparticle surface,which further shortened the length of the Pt-Pt bond,improved the electronic state of the Pt surface,and enhanced the performance of the catalyst.PtCo/C catalysts with special short-range structures achieved excellent mass activity(2.27 Amg_(Pt)^(-1))and specific activity(3.34 A cm^(-2)).In addition,the localized tetragonal distortion-induced surface compression of the Pt skin improved the stability of the catalyst.The mass activity decreased by only 13% after 30,000 cycles.Enhanced catalyst activity and excellent durability have also been demonstrated in the proton exchange membrane fuel cell configuration.This study provides valuable insights into the development of advanced Pt-based nanocatalysts and paves the way for reducing noble-metal loading and increasing the catalytic activity and catalyst stability.展开更多
Taking Pd_(2)MnTi as a representative example,we systematically investigate and theoretically reveal the electronic structure evolution during martensitic phase transition in all-d-metal Heusler compounds.The calculat...Taking Pd_(2)MnTi as a representative example,we systematically investigate and theoretically reveal the electronic structure evolution during martensitic phase transition in all-d-metal Heusler compounds.The calculation and theoretical analysis suggest that Pd_(2)MnTi is not stable in cubic structure and prone to transform to lowsymmetric tetragonal structure.By tetragonal deformation,the shrinkage of lattice parameters and the decrease of symmetry promote the electron accumulation between Pd and its first nearest neighboring Ti atom,resulting in the increasing covalent hybridization.The occurrence of pseudogap in density of states of tetragonal Pd_(2)MnTi near the Fermi level also verifies the enhancement of covalent bond.Comparatively,the stronger interatomic bond in tetragonal Pd_(2)MnTi,i.e.,covalent bond here,would strengthen interatomic coupling and consequently lower the energy of the material.By the martensitic phase transition,more stable states in energy are achieved.Thus,based on the analysis of electronic structure evolution,the nature of martensitic phase transition is a process wherein symmetry breaking weakens the original weak chemical bonds in high-symmetric parent phase and induces the strong chemical bond to lower the energy of the materials and to achieve a more stable state.This study could help to deepen the understanding of martensitic phase transition and the exploration of novel materials for potential technical applications.展开更多
Tetragonal barium titanate was synthesized from barium hydroxide octahydrate and titanium tetrachloride through a simple one-step hydrothermal method.The effect of different solvents on the crystal structure and morph...Tetragonal barium titanate was synthesized from barium hydroxide octahydrate and titanium tetrachloride through a simple one-step hydrothermal method.The effect of different solvents on the crystal structure and morphology of barium titanate nanoparticles during the hy-drothermal process was investigated.Except for ethylene glycol/water solvent,impurity-free barium titanate was synthesized in pure water,methanol/water,ethanol/water,and isopropyl alcohol/water mixed solvents.Compared with other alcohols,ethanol promotes the formation of a tetragonal structure.In addition,characterization studies confirm that particles synthesized in methanol/water,ethanol/water,and isopropyl al-cohol/water mixed solvents are smaller in size than those synthesized in pure water.In the case of alcohol-containing solvents,the particle size decreases in the order of isopropanol,ethanol,and methanol.Among all the media used in this study,ethanol/water is considered the optimum reaction media for barium titanate with high tetragonality(defined as the ratio of two lattice parameters c and a,c/a=1.0088)and small aver-age particle size(82 nm),which indicates its great application potential in multilayer ceramic capacitors.展开更多
Yttria-stabilized zirconia ceramics were prepared by using different raw materials in order to compare commercially available optical ferrule. Injection-molded cylindrical green compacts were sintered in air at 1350&#...Yttria-stabilized zirconia ceramics were prepared by using different raw materials in order to compare commercially available optical ferrule. Injection-molded cylindrical green compacts were sintered in air at 1350°C, 1400°C and 1450°C for 2 hrs, followed by furnace cooling. Crystallinity, microstructure and mechanical strength of the sintered body were evaluated by using an X-ray diffraction analyses, a field emission-scanning electron microscope, a universal tester, and a micro-hardness tester, respectively. For practical usage, the sample B sintered at 1350°C was favorable because of high tetragonality and good mechanical strength.展开更多
Abstract： Lead-free piezoelectric ceramics of （1 - x） Bi0.5K0.5TiO3-BaTiO3 （BKT-BT） were fabricated by the solid state reaction method with normal sintering. The influence of BT addition on the crystal structure,...Abstract： Lead-free piezoelectric ceramics of （1 - x） Bi0.5K0.5TiO3-BaTiO3 （BKT-BT） were fabricated by the solid state reaction method with normal sintering. The influence of BT addition on the crystal structure, phase transition and dielectric properties was investigated. The crystal structure and ferroelectric phase transition were studied by XRD （X-ray diffraction） and dielectric measurements. The complete solid solution of BKT-BT was observed for all compositions. In XRD results, all compositions showed a single phase perovskite structure with tetragonal symmetry at room temperature. With increasing BT content, the separation between diffraction peaks corresponded to increasing tetragonality. The phase transition temperature of ferroelectric tetragonal-paraelectric cubic （Tc） decreased with increasing BT content. As the amount of BT concentration increased, the ceramic became denser, and almost no porosity was finally obtained.展开更多
Zirconia-based bioceramics have been widely applied in the field of prosthodontics owing to its desir- able mechanical performance, biocompatibility and aesthetics. However, the low-temperature degradation （LTD） of ...Zirconia-based bioceramics have been widely applied in the field of prosthodontics owing to its desir- able mechanical performance, biocompatibility and aesthetics. However, the low-temperature degradation （LTD） of tetragonal zirconia （ZrOJ under intraoral condition can lead to the deterioration of mechanical properties of ZrO2 dental crowns, which contribute to many clinical failures in long-term observations. The long-term tetragonal phase stability and mechanical properties of yttria-stabilized tetragonal zir- conia polycrystal （Y-TZP） are influenced by grain size of ZrO2 crystals, distribution and properties of stabilizers, the humid environment, etc. However, it is still difficult to control the abovementioned factors at the same time. This review summarizes the major advances in researches dealing with LTD and clari- fies the obstacles to stabilization of the tetragonal ZrO2. Furthermore, the suggestions on improving the LTD resistance of tetragonal ZrO2 are proposed, which is the catalyst to promote the long-term stability of ZrO2-based all-ceramic crowns.展开更多
Zirconia powders doped with yttrium prepared by special liquid-phase precipitation method were sintered by spark plasma sintering （SPS） to obtain high performance samples. The microstructure, phase composition, and ...Zirconia powders doped with yttrium prepared by special liquid-phase precipitation method were sintered by spark plasma sintering （SPS） to obtain high performance samples. The microstructure, phase composition, and mechanical properties of the samples were studied. The results of X-ray diffraction （XRD）, Raman spectrum, and transmission electron microscope （TEM） show that the phase is tetragonal. The powders with large surface area and high sintering activity, due to small crystallite size, could be densified at 1100℃. The highest relative density of the sample obtained at 1300℃ is higher than 99% （the tetragonal phase is 6.08 g/cm^3）. The Hv and KIC are 13.76 GPa and 15.4 MPa.m^1/2, respectively.展开更多
Tailoring microstructure and microchemistry by altering elemental compositions and thermomechanical treatment parameters enables superior corrosion performance in zirconium alloys for nuclear applications.However,our ...Tailoring microstructure and microchemistry by altering elemental compositions and thermomechanical treatment parameters enables superior corrosion performance in zirconium alloys for nuclear applications.However,our understanding of the relationship between various defects and the corrosion process remains limited in the newly developed zirconium alloys.Here we report the oxide formation mechanism of a CZ1 zirconium alloy with corrosion resistance surpassing many other zirconium alloy systems,such as Zircaloy-4 and Zr-1Nb-1Sn alloys.Autoclave experiments of CZ1 alloy and Zr1Nb-1Sn model alloy were performed in 360°C water for up to 820 d.We quantitively determined oxide phases by transmission Kikuchi diffraction(TKD)and examined lateral cracks,nano-porosity,and second-phase particles in oxide scales by transmission electron microscopy(TEM).Compared to the Zr-1Nb-1Sn model alloy,CZ1 alloy with lower Nb and Sn concentrations has shown smaller and lower-density lateral cracks but slightly larger oxide grains,reducing the diffusion route for oxidating species.Using analytical scanning and transmission electron microscopy,we demonstrate that due to the lower content of Sn(∼0.9 wt.%),there is less tetragonal ZrO_(2) phase formed in the oxide,and the level of tetragonal to the monoclinic phase transition is reduced.Although the Nb content(0.1 wt.%–0.3 wt.%)is lower than the solid solution limit of Nb in Zr,by introducing minor elements such as Fe,Cr,and Cu,there are still a reasonable number of second-phase particles to relieve the high stress associated with the metal-to-oxide transformation.These mechanisms have substantially changed the density and distribution of lateral cracks in the oxide,thus reducing the corrosion rate of zirconium alloys.展开更多
Nanocrystalline zirconia powder with high surface area and high tetragonal phase percentage is prepared by the precipitation method using ammonium hydroxide as a precipitating agent. The pH of precipitation, preparati...Nanocrystalline zirconia powder with high surface area and high tetragonal phase percentage is prepared by the precipitation method using ammonium hydroxide as a precipitating agent. The pH of precipitation, preparation temperature and calcinations＇ temperature are optimized.Crystallite size, specific surface area, tetragonal phase percentage and the thermal stability of the prepared samples are identified by diferent characterization tools such as X-ray difraction（XRD）, thermo gravimetric analysis（TGA）, diferential scanning calorimetry（DSC）, BET surface area, scanning electron microscopy（SEM） and transmission electron microscopy（TEM）. The optimum preparation parameters for obtaining nanocrystalline zirconia with high percentage of tetragonal phase and high surface area are pH 9, preparation temperature of 80℃ and calcinations＇ temperature of 400℃. The sample prepared under optimized conditions showed a high specific surface area of 179.2 m2/g, high tetragonal phase percentage of 81% and high catalytic activity（60%） for synthesis of butyl acetate ester.展开更多
The recently discovered tetragonal, monoclinie and orthorhombic polymorphs of M3N4 （M=C, Si, Sn） are in- vestigated by using first-principles calculations. A set of anisotropic elastic quantities, i.e., the bulk and...The recently discovered tetragonal, monoclinie and orthorhombic polymorphs of M3N4 （M=C, Si, Sn） are in- vestigated by using first-principles calculations. A set of anisotropic elastic quantities, i.e., the bulk and shear moduli, Young＇s modulus, Poisson ratio, H/G ratio and rickets hardness of M3N4 （M=C, Si, Sn） are predicted. The quasi-harmonic Debye model, assuming that the solids are isotopic, may lead to large errors for the non-cubic crystals. The thermal effects are obtained by the traditional quasi-harmonic approach. The dependences of heat capacity, thermal expansion coefficient and Debye temperature on temperature and pressure are systematically discussed in the pressure range of 0 IOGPa and in the temperature range of 0-1100 K. More importantly, o- C3N4 is a negative thermal expansion material. Our results may have important consequences in shaping the understanding of the fundamental properties of these binary nitrides.展开更多
The Y 2O 3-CeO 2-ZrO 2 powders were prepared using a co-precipitation process and the corresponding coatings were prepared by plasma spraying. The results show that an optimal composition exists in Y 2O 3-doped ...The Y 2O 3-CeO 2-ZrO 2 powders were prepared using a co-precipitation process and the corresponding coatings were prepared by plasma spraying. The results show that an optimal composition exists in Y 2O 3-doped CeO 2-ZrO 2, but not in CeO 2-doped Y 2O 3-ZrO 2. The powders mainly contain tetragonal phase and a trace amount of monoclinic phase. The homogeneity in composition, large agglomerate size, ideal particle size distribution and high flowability were obtained. The as-sprayed coatings are composed of non-transformable tetragonal phase, tz′structure, and resistant to transformation under thermal or mechanical stresses.展开更多
The aim of this study was to determine if accelerated aging of porcelain veneering had an effect on the surface properties specific to a tetragonal-to-monoclinic transformation（TMT） of zirconia restorations. Thirty-...The aim of this study was to determine if accelerated aging of porcelain veneering had an effect on the surface properties specific to a tetragonal-to-monoclinic transformation（TMT） of zirconia restorations. Thirty-six zirconia samples were milled and sintered to simulate core fabrication followed by exposure to various combinations of surface treatments including as-received（control）,hydrofluoric acid（HF）, application of liner plus firings, application of porcelain by manual layering and pressing with firing, plus accelerated aging. The quantity of transformed tetragonal to monoclinic phases was analyzed utilized an X-ray diffractometer and one-way analysis of variance was used to analyze data. The control samples as provided from the dental laboratory after milling and sintering process had no TMT（X m5 0）. There was an effect on zirconia samples of HF application with TMT（X m5 0.8%） and liner plus HF application with TMT（X m5 8.7%）. There was an effect of aging on zirconia samples（no veneering） with significant TMT（X m5 70.25%）. Both manual and pressing techniques of porcelain applications reduced the TMT（manual, X m5 4.41%, pressing,X m5 11.57%）, although there was no statistical difference between them. It can be concluded that simulated applications of porcelain demonstrated the ability to protect zirconia from TMT after aging with no effect of a liner between different porcelain applications.The HF treatment also caused TMT.展开更多
Novel Bi2S3/BiOCl photocatalysts were successfully synthesized via a facile biomoleculeassisted solvothermal method and biomolecule L-cysteine was used as the sulfur source.The structures,morphology,and optical proper...Novel Bi2S3/BiOCl photocatalysts were successfully synthesized via a facile biomoleculeassisted solvothermal method and biomolecule L-cysteine was used as the sulfur source.The structures,morphology,and optical properties of the synthesized samples were characterized by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,Raman spectroscopy,transmission electron microscopy（TEM）,and UV-vis diffuse reflectance spectroscopy（DRS）.The presence of Bi2S3 in the Bi2S3/BiOCl composites could not only improve the optical properties but also enhance the photocatalytic activities for the degradation of Rhodamine B（Rh B） under visible-light irradiation（λ〉420 nm） as compared with single Bi2S3 and BiOCl.Especially,the sample displayed the best performance of the photodegradation when the feed molar ratio of BiCl3 and L-cysteine was 2.4：1,which was about 10 times greater than that of pure Bi OCl.The enhanced photocatalytic activities could be ascribed to the effective separation of photoinduced electrons and holes and the photosensitization of dye.Moreover,the possible photodegradation mechanism was also proposed,and the results revealed that the active holes（h＋） and superoxide radicals（·O2-） were the main reactive species during photocatalytic degradation.展开更多
A series of cobalt catalysts with different supports were prepared for the selective conversion of biomassderived furfural to cyclopentanol（CPL） in one step.The best CPLyield was 82 mol%at 160 ℃,2 MPa H2,4 h when c...A series of cobalt catalysts with different supports were prepared for the selective conversion of biomassderived furfural to cyclopentanol（CPL） in one step.The best CPLyield was 82 mol%at 160 ℃,2 MPa H2,4 h when cobalt was supported on ZrO2-La2O3.The supports were characterized by X-ray diffraction（XRD）and temperature-programmed desorption of ammonia（NH3-TPD）.The XRD results indicated that the more stable t-ZrO2 formed by doping La2O3.The amount of acid sites of the catalyst increased,too.The influences of parameters such as reaction temperature,hydrogen pressure,and reaction time on the catalytic activity were also investigated.The polymer formed during the reaction may cause the deactivation of the Co/ZrO2-La2O3 catalyst.This work provides a possibility to prepare the stable t-ZrO2and apply with cobalt metal for biomass valorization.展开更多
A convenient method for synthesis of tetragonal FeS using iron powder as iron source, is reported. Nanocrystalline tetragonal FeS samples were successfully synthesized by reacting metallic iron powder with sodium sulf...A convenient method for synthesis of tetragonal FeS using iron powder as iron source, is reported. Nanocrystalline tetragonal FeS samples were successfully synthesized by reacting metallic iron powder with sodium sulfide in acetate buffer solution. The obtained sample is single-phase tetragonal FeS with lattice parameters a = 0.3767 nm and c = 0.5037 nm, as revealed by X-ray diffraction. The sample consists of fiat nanosheets with lateral dimensions from 20 nm up to 200 nm and average thickness of about 20 nm. We found that tetragonal FeS is a fairly good conductor from the electrical resistivity measurement on a pellet of the nanosheets. The temperature dependence of conductivity of the pellet was well fitted using an empirical equation wherein the effect of different grain boundaries was taken into consideration. This study provides a convenient, economic way to synthesize tetragonal FeS in a large scale and reports the first electrical conductivity data for tetragonal FeS down to liquid helium temperature.展开更多
This paper gives the general expressions for the compliance s′ijkl, Young＇s modulus E（hkl） and Poisson＇s ratio v（hkl, θ） along arbitrary loading direction [hkl] for tetragonal crystals. The representation surf...This paper gives the general expressions for the compliance s′ijkl, Young＇s modulus E（hkl） and Poisson＇s ratio v（hkl, θ） along arbitrary loading direction [hkl] for tetragonal crystals. The representation surface for which the length of the radius vector in the [hkl] direction equals E（hkl） and representation curve for which the length of the radius vector with angle θ deviated from the reference directions [001^-], [100], [001^-], [101^-] and [112^-] equals v（100, θ）, v（001, θ）, v（110,θ）, v（101,θ） and v（111, θ） respectively, are constructed for nine tetragonal crystals （ammonium dihydrogen arsenate, ammonium dihydrogen phosphate, barium titanate, indium, nickel sulfate, potassium dihydrogen arsenate, potassium dihydrogen phosphate, tin and zircon）. The characteristics of them are analysed in detail.展开更多
High performance solid electrolytes have been widely used in many devices, such as intermediate temperature（650–850 oC） solid oxide fuel cells, oxygen sensors, super capacitors, etc. In order to solve the problem o...High performance solid electrolytes have been widely used in many devices, such as intermediate temperature（650–850 oC） solid oxide fuel cells, oxygen sensors, super capacitors, etc. In order to solve the problem of phase stability and high grain boundary resistance during the working process, the novel core/shell structure ScSZ nanocomposites were successfully prepared by fractional-precipated method. Non core/shell composites were also prepared by co-precipitation at the same Sc/Zr ratio for comparison. high-resolution transmission electron microscopy（HRTEM）, X-ray photoelectron spectroscopy（XPS）, Raman characterization were performed to identify the microstructure and phase configuration of the obtained composites. According to HRTEM, clear rich scandia shell layer of 2–4 nm existed at the edge of each core/shell particle. The HRTEM figures of non core/shell composites were homogeneous without the shell structure. XPS element analysis for core/shell composite indicated that scandium ratio increased and zirconium ratio decreased when heat treatment temperature fell. When the heating temperature fell down to 450 oC, scandium ratio reached nearly 35 mol.%. EIS and DC measurement were taken for both kinds of electrolytes to study the electrochemical properties. The ionic conductivity were 178.2 and 154.4 mS/cm at 850 oC for core/shell and non core/shell electrolytes, respectively. The mechanism of conductivity improvement was also studied. It was predicted that the core/shell interface could improve ionic conductivity by modifying the space-charge regions. This result outlines a novel and potential direction for high-end electrolytes to enhance ionic conductivity.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12174129,T2394475,and T2394470)。
文摘Altermagnets,a new type of collinear antiferromagnet,exhibiting non-degenerate electron and magnon dispersion in momentum space have attracted intensive research attention.We theoretically analyze the origin and feature of chiral magnon splitting in representative altermagnets including tetragonal RuO_(2),hexagonal MnTe,and orthorhombic LaMnO_(3).The magnon spin transport properties including spin Seebeck and spin Nernst coefcients have been investigated.Through these materials,we demonstrate the diference of chiral splitting in d-wave and g-wave antiferromagnet on magnon transport.RuO2with planar magnon splitting exhibits signifcant magnon spin Nernst and magnon spin Seebeck anisotropy in(110)and(001)planes,whereas MnTe,due to its bulk-like magnon splitting,is incapable of producing magnon spin Nernst efect.Our work may provide in-depth understanding on the mechanisms of nonrelativistic magnon splitting and thermal spin transport in altermagnets.
基金supported by the National Natural Science Foundation of China(Grant Nos.51931005 and 51901235).
文摘Martensite is one of the most important structures determining the ability to tailor the performance of steel and several other engineering materials.In previous studies,the face-centered cubic(FCC)to hexag-onal close-packed(HCP)(or body-centered cubic(BCC))martensitic transformation and the FCC to body-centered tetragonal(BCT)(or BCC)martensitic transformation during deformation and quenching were widely investigated;these transformations usually improve the plasticity and strength of steel,respec-tively.In this work,detailed transmission electron microscopy(TEM)observations and electron diffraction pattern analyses of the BCT and BCC twins are performed along the[110],[131],and[¯153]zone axes.The transformation of BCT twins into BCC twins along the[131]zone axis is also analyzed through in situ heating during the TEM observations.The high-resolution TEM observations of mutually perpendicular BCT variants are consistent with the atomic arrangement obtained for the quenching pathway during the martensitic transformation.In addition,different orientation relationships between austenite and marten-site are explained in terms of the atomic migration occurring during the deformation pathway and the quenching pathway of the martensitic transformation.
基金supported by the National Natural Science Foundation of China (Grant No.22278123).
文摘Platinum-based alloy nanoparticles are the most attractive catalysts for the oxygen reduction reaction at present,but an in-depth understanding of the relationship between their short-range structural information and catalytic performance is still lacking.Herein,we present a synthetic strategy that uses transition-metal oxide-assisted thermal diffusion.PtCo/C catalysts with localized tetragonal distortion were obtained by controlling the thermal diffusion process of transition-metal elements.This localized structural distortion induced a significant strain effect on the nanoparticle surface,which further shortened the length of the Pt-Pt bond,improved the electronic state of the Pt surface,and enhanced the performance of the catalyst.PtCo/C catalysts with special short-range structures achieved excellent mass activity(2.27 Amg_(Pt)^(-1))and specific activity(3.34 A cm^(-2)).In addition,the localized tetragonal distortion-induced surface compression of the Pt skin improved the stability of the catalyst.The mass activity decreased by only 13% after 30,000 cycles.Enhanced catalyst activity and excellent durability have also been demonstrated in the proton exchange membrane fuel cell configuration.This study provides valuable insights into the development of advanced Pt-based nanocatalysts and paves the way for reducing noble-metal loading and increasing the catalytic activity and catalyst stability.
基金supported by the special fund for introduced talent to initiate scientific research in Nanjing Tech Universitythe National Natural Science Foundation of China(Grant Nos.52088101 and 52325201)the National Key Research and Development Program of China(Grant No.2023YFA1607400)。
文摘Taking Pd_(2)MnTi as a representative example,we systematically investigate and theoretically reveal the electronic structure evolution during martensitic phase transition in all-d-metal Heusler compounds.The calculation and theoretical analysis suggest that Pd_(2)MnTi is not stable in cubic structure and prone to transform to lowsymmetric tetragonal structure.By tetragonal deformation,the shrinkage of lattice parameters and the decrease of symmetry promote the electron accumulation between Pd and its first nearest neighboring Ti atom,resulting in the increasing covalent hybridization.The occurrence of pseudogap in density of states of tetragonal Pd_(2)MnTi near the Fermi level also verifies the enhancement of covalent bond.Comparatively,the stronger interatomic bond in tetragonal Pd_(2)MnTi,i.e.,covalent bond here,would strengthen interatomic coupling and consequently lower the energy of the material.By the martensitic phase transition,more stable states in energy are achieved.Thus,based on the analysis of electronic structure evolution,the nature of martensitic phase transition is a process wherein symmetry breaking weakens the original weak chemical bonds in high-symmetric parent phase and induces the strong chemical bond to lower the energy of the materials and to achieve a more stable state.This study could help to deepen the understanding of martensitic phase transition and the exploration of novel materials for potential technical applications.
基金supported by Chongqing Newcent New Materials Co.,Ltd.,China (No.2021GKF-0708).
文摘Tetragonal barium titanate was synthesized from barium hydroxide octahydrate and titanium tetrachloride through a simple one-step hydrothermal method.The effect of different solvents on the crystal structure and morphology of barium titanate nanoparticles during the hy-drothermal process was investigated.Except for ethylene glycol/water solvent,impurity-free barium titanate was synthesized in pure water,methanol/water,ethanol/water,and isopropyl alcohol/water mixed solvents.Compared with other alcohols,ethanol promotes the formation of a tetragonal structure.In addition,characterization studies confirm that particles synthesized in methanol/water,ethanol/water,and isopropyl al-cohol/water mixed solvents are smaller in size than those synthesized in pure water.In the case of alcohol-containing solvents,the particle size decreases in the order of isopropanol,ethanol,and methanol.Among all the media used in this study,ethanol/water is considered the optimum reaction media for barium titanate with high tetragonality(defined as the ratio of two lattice parameters c and a,c/a=1.0088)and small aver-age particle size(82 nm),which indicates its great application potential in multilayer ceramic capacitors.
文摘Yttria-stabilized zirconia ceramics were prepared by using different raw materials in order to compare commercially available optical ferrule. Injection-molded cylindrical green compacts were sintered in air at 1350°C, 1400°C and 1450°C for 2 hrs, followed by furnace cooling. Crystallinity, microstructure and mechanical strength of the sintered body were evaluated by using an X-ray diffraction analyses, a field emission-scanning electron microscope, a universal tester, and a micro-hardness tester, respectively. For practical usage, the sample B sintered at 1350°C was favorable because of high tetragonality and good mechanical strength.
文摘Abstract： Lead-free piezoelectric ceramics of （1 - x） Bi0.5K0.5TiO3-BaTiO3 （BKT-BT） were fabricated by the solid state reaction method with normal sintering. The influence of BT addition on the crystal structure, phase transition and dielectric properties was investigated. The crystal structure and ferroelectric phase transition were studied by XRD （X-ray diffraction） and dielectric measurements. The complete solid solution of BKT-BT was observed for all compositions. In XRD results, all compositions showed a single phase perovskite structure with tetragonal symmetry at room temperature. With increasing BT content, the separation between diffraction peaks corresponded to increasing tetragonality. The phase transition temperature of ferroelectric tetragonal-paraelectric cubic （Tc） decreased with increasing BT content. As the amount of BT concentration increased, the ceramic became denser, and almost no porosity was finally obtained.
基金?nancially supported by the National Natural Science Foundation of China(No.81500897)China Scholarship Council(No.201408210385)+1 种基金Foundation of the Education Department of Liaoning Province in China(No.L2013285)Science and Technology Planning Project of Shenyang City(No.F11-262-9-16)
文摘Zirconia-based bioceramics have been widely applied in the field of prosthodontics owing to its desir- able mechanical performance, biocompatibility and aesthetics. However, the low-temperature degradation （LTD） of tetragonal zirconia （ZrOJ under intraoral condition can lead to the deterioration of mechanical properties of ZrO2 dental crowns, which contribute to many clinical failures in long-term observations. The long-term tetragonal phase stability and mechanical properties of yttria-stabilized tetragonal zir- conia polycrystal （Y-TZP） are influenced by grain size of ZrO2 crystals, distribution and properties of stabilizers, the humid environment, etc. However, it is still difficult to control the abovementioned factors at the same time. This review summarizes the major advances in researches dealing with LTD and clari- fies the obstacles to stabilization of the tetragonal ZrO2. Furthermore, the suggestions on improving the LTD resistance of tetragonal ZrO2 are proposed, which is the catalyst to promote the long-term stability of ZrO2-based all-ceramic crowns.
文摘Zirconia powders doped with yttrium prepared by special liquid-phase precipitation method were sintered by spark plasma sintering （SPS） to obtain high performance samples. The microstructure, phase composition, and mechanical properties of the samples were studied. The results of X-ray diffraction （XRD）, Raman spectrum, and transmission electron microscope （TEM） show that the phase is tetragonal. The powders with large surface area and high sintering activity, due to small crystallite size, could be densified at 1100℃. The highest relative density of the sample obtained at 1300℃ is higher than 99% （the tetragonal phase is 6.08 g/cm^3）. The Hv and KIC are 13.76 GPa and 15.4 MPa.m^1/2, respectively.
文摘Tailoring microstructure and microchemistry by altering elemental compositions and thermomechanical treatment parameters enables superior corrosion performance in zirconium alloys for nuclear applications.However,our understanding of the relationship between various defects and the corrosion process remains limited in the newly developed zirconium alloys.Here we report the oxide formation mechanism of a CZ1 zirconium alloy with corrosion resistance surpassing many other zirconium alloy systems,such as Zircaloy-4 and Zr-1Nb-1Sn alloys.Autoclave experiments of CZ1 alloy and Zr1Nb-1Sn model alloy were performed in 360°C water for up to 820 d.We quantitively determined oxide phases by transmission Kikuchi diffraction(TKD)and examined lateral cracks,nano-porosity,and second-phase particles in oxide scales by transmission electron microscopy(TEM).Compared to the Zr-1Nb-1Sn model alloy,CZ1 alloy with lower Nb and Sn concentrations has shown smaller and lower-density lateral cracks but slightly larger oxide grains,reducing the diffusion route for oxidating species.Using analytical scanning and transmission electron microscopy,we demonstrate that due to the lower content of Sn(∼0.9 wt.%),there is less tetragonal ZrO_(2) phase formed in the oxide,and the level of tetragonal to the monoclinic phase transition is reduced.Although the Nb content(0.1 wt.%–0.3 wt.%)is lower than the solid solution limit of Nb in Zr,by introducing minor elements such as Fe,Cr,and Cu,there are still a reasonable number of second-phase particles to relieve the high stress associated with the metal-to-oxide transformation.These mechanisms have substantially changed the density and distribution of lateral cracks in the oxide,thus reducing the corrosion rate of zirconium alloys.
文摘Nanocrystalline zirconia powder with high surface area and high tetragonal phase percentage is prepared by the precipitation method using ammonium hydroxide as a precipitating agent. The pH of precipitation, preparation temperature and calcinations＇ temperature are optimized.Crystallite size, specific surface area, tetragonal phase percentage and the thermal stability of the prepared samples are identified by diferent characterization tools such as X-ray difraction（XRD）, thermo gravimetric analysis（TGA）, diferential scanning calorimetry（DSC）, BET surface area, scanning electron microscopy（SEM） and transmission electron microscopy（TEM）. The optimum preparation parameters for obtaining nanocrystalline zirconia with high percentage of tetragonal phase and high surface area are pH 9, preparation temperature of 80℃ and calcinations＇ temperature of 400℃. The sample prepared under optimized conditions showed a high specific surface area of 179.2 m2/g, high tetragonal phase percentage of 81% and high catalytic activity（60%） for synthesis of butyl acetate ester.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61475132 and 61501392
文摘The recently discovered tetragonal, monoclinie and orthorhombic polymorphs of M3N4 （M=C, Si, Sn） are in- vestigated by using first-principles calculations. A set of anisotropic elastic quantities, i.e., the bulk and shear moduli, Young＇s modulus, Poisson ratio, H/G ratio and rickets hardness of M3N4 （M=C, Si, Sn） are predicted. The quasi-harmonic Debye model, assuming that the solids are isotopic, may lead to large errors for the non-cubic crystals. The thermal effects are obtained by the traditional quasi-harmonic approach. The dependences of heat capacity, thermal expansion coefficient and Debye temperature on temperature and pressure are systematically discussed in the pressure range of 0 IOGPa and in the temperature range of 0-1100 K. More importantly, o- C3N4 is a negative thermal expansion material. Our results may have important consequences in shaping the understanding of the fundamental properties of these binary nitrides.
文摘The Y 2O 3-CeO 2-ZrO 2 powders were prepared using a co-precipitation process and the corresponding coatings were prepared by plasma spraying. The results show that an optimal composition exists in Y 2O 3-doped CeO 2-ZrO 2, but not in CeO 2-doped Y 2O 3-ZrO 2. The powders mainly contain tetragonal phase and a trace amount of monoclinic phase. The homogeneity in composition, large agglomerate size, ideal particle size distribution and high flowability were obtained. The as-sprayed coatings are composed of non-transformable tetragonal phase, tz′structure, and resistant to transformation under thermal or mechanical stresses.
基金supported in part by Deanship of Research, Taibah University, Kingdom of Saudi Arabia, and Matt Winstead, CDT, Vice President, Oral Arts Dental Labs, Huntsville, AL, USA
文摘The aim of this study was to determine if accelerated aging of porcelain veneering had an effect on the surface properties specific to a tetragonal-to-monoclinic transformation（TMT） of zirconia restorations. Thirty-six zirconia samples were milled and sintered to simulate core fabrication followed by exposure to various combinations of surface treatments including as-received（control）,hydrofluoric acid（HF）, application of liner plus firings, application of porcelain by manual layering and pressing with firing, plus accelerated aging. The quantity of transformed tetragonal to monoclinic phases was analyzed utilized an X-ray diffractometer and one-way analysis of variance was used to analyze data. The control samples as provided from the dental laboratory after milling and sintering process had no TMT（X m5 0）. There was an effect on zirconia samples of HF application with TMT（X m5 0.8%） and liner plus HF application with TMT（X m5 8.7%）. There was an effect of aging on zirconia samples（no veneering） with significant TMT（X m5 70.25%）. Both manual and pressing techniques of porcelain applications reduced the TMT（manual, X m5 4.41%, pressing,X m5 11.57%）, although there was no statistical difference between them. It can be concluded that simulated applications of porcelain demonstrated the ability to protect zirconia from TMT after aging with no effect of a liner between different porcelain applications.The HF treatment also caused TMT.
基金Funded by the National Natural Science Foundation of China(No.51272107)the Natural Science Foundation of Jiangsu Province,China(No.BK2011024)the Specialized Research Fund for the Doctoral Program of Higher Education(No.20133219110015)
文摘Novel Bi2S3/BiOCl photocatalysts were successfully synthesized via a facile biomoleculeassisted solvothermal method and biomolecule L-cysteine was used as the sulfur source.The structures,morphology,and optical properties of the synthesized samples were characterized by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,Raman spectroscopy,transmission electron microscopy（TEM）,and UV-vis diffuse reflectance spectroscopy（DRS）.The presence of Bi2S3 in the Bi2S3/BiOCl composites could not only improve the optical properties but also enhance the photocatalytic activities for the degradation of Rhodamine B（Rh B） under visible-light irradiation（λ〉420 nm） as compared with single Bi2S3 and BiOCl.Especially,the sample displayed the best performance of the photodegradation when the feed molar ratio of BiCl3 and L-cysteine was 2.4：1,which was about 10 times greater than that of pure Bi OCl.The enhanced photocatalytic activities could be ascribed to the effective separation of photoinduced electrons and holes and the photosensitization of dye.Moreover,the possible photodegradation mechanism was also proposed,and the results revealed that the active holes（h＋） and superoxide radicals（·O2-） were the main reactive species during photocatalytic degradation.
基金financial support from the NSFC(No.21572213)the National Basic Research Program of China(No.2013CB228103)+1 种基金Program for Changjiang Scholars and Innovative Research Team in University of the Ministry of Education of Chinathe Fundamental Research Funds for the Central Universities(No.wk 2060190040)
文摘A series of cobalt catalysts with different supports were prepared for the selective conversion of biomassderived furfural to cyclopentanol（CPL） in one step.The best CPLyield was 82 mol%at 160 ℃,2 MPa H2,4 h when cobalt was supported on ZrO2-La2O3.The supports were characterized by X-ray diffraction（XRD）and temperature-programmed desorption of ammonia（NH3-TPD）.The XRD results indicated that the more stable t-ZrO2 formed by doping La2O3.The amount of acid sites of the catalyst increased,too.The influences of parameters such as reaction temperature,hydrogen pressure,and reaction time on the catalytic activity were also investigated.The polymer formed during the reaction may cause the deactivation of the Co/ZrO2-La2O3 catalyst.This work provides a possibility to prepare the stable t-ZrO2and apply with cobalt metal for biomass valorization.
基金Project supported by the National Natural Science Foundation of China(Grant No.21271183)the National Basic Research Program of China(Grant Nos.2011CBA00112 and 2011CB808202)
文摘A convenient method for synthesis of tetragonal FeS using iron powder as iron source, is reported. Nanocrystalline tetragonal FeS samples were successfully synthesized by reacting metallic iron powder with sodium sulfide in acetate buffer solution. The obtained sample is single-phase tetragonal FeS with lattice parameters a = 0.3767 nm and c = 0.5037 nm, as revealed by X-ray diffraction. The sample consists of fiat nanosheets with lateral dimensions from 20 nm up to 200 nm and average thickness of about 20 nm. We found that tetragonal FeS is a fairly good conductor from the electrical resistivity measurement on a pellet of the nanosheets. The temperature dependence of conductivity of the pellet was well fitted using an empirical equation wherein the effect of different grain boundaries was taken into consideration. This study provides a convenient, economic way to synthesize tetragonal FeS in a large scale and reports the first electrical conductivity data for tetragonal FeS down to liquid helium temperature.
基金supported by the State Key Development Program for Basic Research of China (Grant No 2004CB619302)the National Natural Science Foundation of China (Grant No 50271038)
文摘This paper gives the general expressions for the compliance s′ijkl, Young＇s modulus E（hkl） and Poisson＇s ratio v（hkl, θ） along arbitrary loading direction [hkl] for tetragonal crystals. The representation surface for which the length of the radius vector in the [hkl] direction equals E（hkl） and representation curve for which the length of the radius vector with angle θ deviated from the reference directions [001^-], [100], [001^-], [101^-] and [112^-] equals v（100, θ）, v（001, θ）, v（110,θ）, v（101,θ） and v（111, θ） respectively, are constructed for nine tetragonal crystals （ammonium dihydrogen arsenate, ammonium dihydrogen phosphate, barium titanate, indium, nickel sulfate, potassium dihydrogen arsenate, potassium dihydrogen phosphate, tin and zircon）. The characteristics of them are analysed in detail.
基金Project supported by the National Science and Foundation of China(51504034)
文摘High performance solid electrolytes have been widely used in many devices, such as intermediate temperature（650–850 oC） solid oxide fuel cells, oxygen sensors, super capacitors, etc. In order to solve the problem of phase stability and high grain boundary resistance during the working process, the novel core/shell structure ScSZ nanocomposites were successfully prepared by fractional-precipated method. Non core/shell composites were also prepared by co-precipitation at the same Sc/Zr ratio for comparison. high-resolution transmission electron microscopy（HRTEM）, X-ray photoelectron spectroscopy（XPS）, Raman characterization were performed to identify the microstructure and phase configuration of the obtained composites. According to HRTEM, clear rich scandia shell layer of 2–4 nm existed at the edge of each core/shell particle. The HRTEM figures of non core/shell composites were homogeneous without the shell structure. XPS element analysis for core/shell composite indicated that scandium ratio increased and zirconium ratio decreased when heat treatment temperature fell. When the heating temperature fell down to 450 oC, scandium ratio reached nearly 35 mol.%. EIS and DC measurement were taken for both kinds of electrolytes to study the electrochemical properties. The ionic conductivity were 178.2 and 154.4 mS/cm at 850 oC for core/shell and non core/shell electrolytes, respectively. The mechanism of conductivity improvement was also studied. It was predicted that the core/shell interface could improve ionic conductivity by modifying the space-charge regions. This result outlines a novel and potential direction for high-end electrolytes to enhance ionic conductivity.
