Sr0.9Ba0.1Ti0.8Nb0.2O3 ceramics （x=0, 0.01, 0.02 and 0.05） are prepared by solid state reaction, whose thermoelectric properties are investigated from 323K to 1073K. By introducing A-site nonstoichiometry, the absol...Sr0.9Ba0.1Ti0.8Nb0.2O3 ceramics （x=0, 0.01, 0.02 and 0.05） are prepared by solid state reaction, whose thermoelectric properties are investigated from 323K to 1073K. By introducing A-site nonstoichiometry, the absolute Seebeck coefficient is enhanced, while the electrical resistivity is surprisingly reduced due to the significantly enhanced carrier mobility. These results are dramatic in thermoelectric materials, effectively enhancing the power factor. Moreover, the thermal conductivity is reduced, thus the thermoelectric performance of Sr0.9Ba0.1Ti0.8Nb0.2O3 ceramic is significantly enhanced by A-site nonstoiehiometry.展开更多
Lead free 0.94(Bi_(0.5)Na_(0.5))TiO_(3)-0.06BaTiO_(3)ceramics were prepared by conventional solid-state mixed oxide route with the A-site stoichiometry modified to incorporate donor-doping(through Bi-excess)and accept...Lead free 0.94(Bi_(0.5)Na_(0.5))TiO_(3)-0.06BaTiO_(3)ceramics were prepared by conventional solid-state mixed oxide route with the A-site stoichiometry modified to incorporate donor-doping(through Bi-excess)and acceptor-doping(through Na-excess).Both stoichiometric and nonstoichiometric ceramics exhibited a single perovskite phase with pseudo-cubic symmetry.A significant improvement in the dielectric properties was observed in Bi-excess compositions and a deterioration in the dielectric properties was observed in Na-excess compositions.Impedance spectroscopy was utilized to analyze the effects of A-site nonstoichiometry on conduction mechanisms.Compositions with Bi-excess resulted in an electrically homogeneous microstructure with an increase in resistivity by3-4 orders of magnitude and an associated activation energy of 1.57 eV which was close to half of the optical bandgap.In contrast,an electrically heterogeneous microstructure was observed in both the stoichiometric and Na-excess compositions.In addition,the Na-excess compositions exhibited low resistivities(ρ-10^(3)Ω-cm)with characteristic peaks in the impedance data comparable to the recent observations of oxide ion conduction in(Bi_(0.5)Na_(0.5))TiO_(3).Long term annealing studies were also conducted at 800℃to identify changes in crystal structure and electrical properties.The results of this study demonstrates that the dielectric and electrical properties of 0.94(Bi_(0.5)Na_(0.5))TiO_(3)-0.06BaTiO_(3)ceramics are very sensitive to Bi/Na stoichiometry.展开更多
Rare-earth zirconate pyrochlores,which exhibit various interesting properties,especially low thermal conductivity,are of great interest.Nonstoichiometry is an effective strategy involving defect engineering to reduce ...Rare-earth zirconate pyrochlores,which exhibit various interesting properties,especially low thermal conductivity,are of great interest.Nonstoichiometry is an effective strategy involving defect engineering to reduce the thermal conductivity of materials.In this work,a long series of solid solutions,εSmO_(1.5)·(1−ε)ZrO_(2)(ε=0.200,0.250,0.350,0.400,0.450,0.500,0.525,0.550,0.600,and 0.650),were designed and synthesized to investigate the effects of nonstoichiometry on the structural evolution,defect chemistry,and thermal conductivity of SmO_(1.5)–ZrO_(2) system across the entire pyrochlore phase field and phase transition regions.The similarity of all the Raman spectra provides an incredible opportunity to confirm the structural details and evolution of pyrochlore and defective fluorite,as well as the emergence of the expected point defects.A new solution mechanism concerning nonstoichiometry was proposed and confirmed by analyzing the variations in the experimental density and Raman spectra.The thermal conductivities of all the samples were measured,and investigated in terms of the phonon-scattering theory.The results show that the nonstoichiometry with SmO1.5 excess is more effective in reducing the thermal conductivity to an extremely low value of approximately 1 W/(m·K),which can be attributed to the dramatic decrease in the average acoustic velocity in addition to the strong phonon scattering of Zr ion vacancies and oxygen vacancies.On the other hand,the nonstoichiometry with ZrO_(2) excess significantly reduces the thermal conductivity at room temperature,but conversely leads to a slight increase of it above 200°C.The former variation can be attributed to the phonon scattering of the 8a interstitial oxygen ions,which has a similar effectiveness to the defects on the SmO1.5-rich side.The latter variation may be attributed to the Umklapp scattering of phonons.展开更多
Ceramic-based dielectric capacitors are becoming more and more important in electronic devices.The ceramics of 0.93K_(0.5)Na_(0.5)NbO_(3)–0.07Bix(Mg_(1/3)Nb_(2/3))O_(3)(0.93KNN–0.07BixMN)(x?0:60,2/3,0.75 and 0.95)we...Ceramic-based dielectric capacitors are becoming more and more important in electronic devices.The ceramics of 0.93K_(0.5)Na_(0.5)NbO_(3)–0.07Bix(Mg_(1/3)Nb_(2/3))O_(3)(0.93KNN–0.07BixMN)(x?0:60,2/3,0.75 and 0.95)were successfully fabricated by virtue of the solid reaction process in this work.The results showed that the amount of Bi content has a significant impact on the ceramics of 0.93KNN–0.07BixMN.XRD indicates that all specimens exhibit a pure perovskite structure and existing oxygen vacancy in the specimens.The mean grain size for all specimens belong to submicron scale,and the sample of x=0.95 owns the smallest grain size is 0.11m.The maximum dielectric constant increases but the phase transition temperature Tm exhibits a contrary tendency at 1MHz with increasing Bi concentration.Besides,all ceramics are relaxor ferroelectric.The impedance analysis further revealed that the activation energy of the ceramics increases with Bi content.Eventually,the highestηof 58.8%and Wrec of 1.30 J/cm^(3) are simultaneously achieved in the sample with x=0.60.Overall,we demonstrate in this work that stoichiometry control of Bi in 0.93KNN–0.07BixMN ceramics is a practical method to obtain the desired structural,dielectric and energy storage properties.展开更多
The diffusion coefficient of hydrogen atoms in the studied alloys was electrochemically measured by chronoamperometry when the metallic hydride microelectrodes were completely discharged. It is found that the diffusio...The diffusion coefficient of hydrogen atoms in the studied alloys was electrochemically measured by chronoamperometry when the metallic hydride microelectrodes were completely discharged. It is found that the diffusion coefficient of hydrogen atoms decreases when cobalt is substituted for a minority of nickel. On the contrary, the diffusion coefficient increases with the partial substitution of manganese or aluminum for nickel, which is related to the lattice constant and cell volumes of hydrogen absorbing alloys. The lattice constant c is obviously affected by the substitute elements greatly. The result shows that the expansion of cell volume resulted from the increase of value c causes the increase of diffusion coefficient which is especially obvious when the lattice constant is relatively low. However, this relationship is not clear if the lattice constant increases to some extent. It is suggested that this phenomenon is related to the interaction of hydrogen atoms with metallic atoms.展开更多
Using compound energy model (CEM), the thermodynamic properties of <CeO2-y> and <Zr1_xCezO2-x> were evaluated. The evaluation was based on the optimization of ZrIO2-CeO2 and ZrO2-CeO1.5 systems, as well as...Using compound energy model (CEM), the thermodynamic properties of <CeO2-y> and <Zr1_xCezO2-x> were evaluated. The evaluation was based on the optimization of ZrIO2-CeO2 and ZrO2-CeO1.5 systems, as well as the miscibility gap in CeO1.5-CeO2 system. Except the cubic fluorite structure phase assessed with compound energy model, all the other solution phases were assessed with subsitutional solution model. The model parameters were evaluated through fitting the selected experimental data by means of thermodynamic optimization. A set of parameters with thermodynamics self-consistency was obtained and satisfactorily described the complex relation between y in <CeO2-y> and the partial pressure of oxygen at different temperatures, also the interdependence among miscellaneous factors such as temperature, oxygen partial pressure, the reduction amount of CeO2 as well as the nonstoichiometry in cubic phase <Zr1-xCezO2-x>- The calculated results seem to be reasonable when put into the explanation of pressureless sintering of Ce02-stabilized ZrO2 powder compacts at a controlled oxygen partial pressure.展开更多
A series of single-phase T-structured NdSrCu 1-x Co x O 4-δ with oxygen vacancies and T -structured Sm 1.8 Ce 0.2 Cu 1-x Co x O 4-δ （x： 0–0.4） with oxygen excess were prepared using ultrasound-assisted citric ac...A series of single-phase T-structured NdSrCu 1-x Co x O 4-δ with oxygen vacancies and T -structured Sm 1.8 Ce 0.2 Cu 1-x Co x O 4-δ （x： 0–0.4） with oxygen excess were prepared using ultrasound-assisted citric acid complexing method, and characterized by means of techniques such as thermogravimetric analysis and NO temperature-programmed desorption （NO-TPD）. The catalytic activities of these materials were evaluated for the decomposition of NO. It was found that the NdSrCu 1-x Co x O 4-δ catalysts were of oxygen vacancies whereas the Sm 1.8 Ce 0.2 Cu 1？x Co x O 4-δ ones possessed excessive oxygen （i.e., over-stoichiometric oxygen）; with a rise in Co doping level, the oxygen vacancy density of NdSrCu 1-x Co x O 4-δ decreased while the over-stoichiometric oxygen amount of Sm 1.8 Ce 0.2 Cu 1-x Co x O 4-δ increased. The NO-TPD results revealed that NO could be activated much easier over the oxygen-deficient perovskite-like oxides than over the oxygen-excessive perovskite-like oxides, with the NdSrCuO 3.702 catalyst showing the best efficiency in activating NO molecules. Under the conditions of 1.0% NO/helium, 2800 hr -1 , and 600–900°C, the catalytic activity of NO decomposition followed the order of NdSrCuO 3.702 〉 NdSrCu 0.8 Co 0.2 O 3.736 〉 NdSrCu 0.6 Co 0.4 O 3.789 〉 Sm 1.8 Ce 0.2 Cu 0.6 Co 0.4 O 4.187 〉 Sm 1.8 Ce 0.2 Cu 0.8 Co 0.2 O 4.104 〉 Sm 1.8 Ce 0.2 CuO 4.045 , in concord with the sequence of decreasing oxygen vacancy or oxygen excess density. Based on the results, we concluded that the higher oxygen vacancy density and the stronger Cu 3＋ /Cu 2＋ redox ability of NdSrCu 1-x Co x O 4-δ account for the easier activation of NO and consequently improve the catalytic activity of NO decomposition over the catalysts.展开更多
The La0.7Sr0.3CryMnzCo(1-y-z)O3-δ samples were prepared by solid state reaction.The phases,microstructure and properties of the samples were investigated by XRD,SEM,DC four-probe method and iodometry method.The singl...The La0.7Sr0.3CryMnzCo(1-y-z)O3-δ samples were prepared by solid state reaction.The phases,microstructure and properties of the samples were investigated by XRD,SEM,DC four-probe method and iodometry method.The single orthorhombic phase La0.7Sr0.3CryMnzCo(1-y-z)O3-δ perovskite oxides were obtained when sintered at l350 °C for 10 h.The oxygen nonstoichiometry of the materials varied inversely with the total electronic conductivity.The sample with composition of La0.7Sr0.3Cr0.5Mn0.35 Co0.15O3-δ had the maxima...展开更多
Ba_(1.03)Ce_(0.8)Eu_(0.2)O_(3-α) solid electrolyte with nonstoichiometric composition was prepared by high temperature solid-state reaction. Phase composition, surface and fracture morphologies of the specimen were c...Ba_(1.03)Ce_(0.8)Eu_(0.2)O_(3-α) solid electrolyte with nonstoichiometric composition was prepared by high temperature solid-state reaction. Phase composition, surface and fracture morphologies of the specimen were characterized by using XRD and SEM, respectively. Ionic conduction was researched by gas concentration cell, the performance of hydrogen-air fuel cell was measured in the temperature range of 600～1000 ℃, and compared them with those of BaCe_(0.8)Eu_(0.2)O_(3-α) and Ba_(0.98)Ce_(0.8)Eu_(0.2)O_(3-α). The results indicate that Ba_(1.03)Ce_(0.8)Eu_(0.2)O_(3-α) is a single-phase perovskite-type orthorhombic system. It is a pure proton conductor in the temperature range of 600～1000 ℃ in hydrogen atmosphere, and its proton conduction is superior to that of BaCe_(0.8)Eu_(0.2)O_(3-α) and Ba_(0.98)Ce_(0.8)Eu_(0.2)O_(3-α). It is a mixed conductor of oxide ion and electron hole in oxygen atmosphere. At 1000 ℃, the performance of the fuel cell in which Ba_(1.03)Ce_(0.8)Eu_(0.2)O_(3-α) as electrolyte is higher than that of BaCe_(0.8)Eu_(0.2)O_(3-α) or Ba_(0.98)Ce_(0.8)Eu_(0.2)O_(3-α).展开更多
The effects of some substituting elements on the specific discharge capacity, activation and cycling life of AB 5 non stoichiometric hydrogen absorbing alloys were studied electrochemically. Results show that the ch...The effects of some substituting elements on the specific discharge capacity, activation and cycling life of AB 5 non stoichiometric hydrogen absorbing alloys were studied electrochemically. Results show that the characteristics of hydrogen absorbing alloys under low current density are greatly improved through the substitution of Ni by Sn, Co, and Mn. Three hydrogen storage alloys, i.e., La(NiSn) 5.14 , La(NiSnCo) 5.12 and La(NiSnMn) 5.12 have the higher specific capacity and easy activation. However, Al in the alloy shows the opposite effect on the electrochemical properties. Under high current density, the discharge capacity and potential of La(NiSn) 5.14 is superior to La(NiSnCo) 5.12 and La(NiSnMn) 5.12 , but the cycling life of La(NiSn) 5.14 is very short. The addition of Mn, Co and Al to the alloys improves the cycling characteristics. In all these alloys, La(NiSnCo) 5.12 is considered as an ideal hydrogen storage alloy.展开更多
BaxCe0.8Pr0.2O3-α (x=0.98-1.03) ceramics were prepared by high temperature solid-state reaction. X-ray diffraction (XRD) patterns showed that the materials were perovskite-type orthorhombic single phase. By using gas...BaxCe0.8Pr0.2O3-α (x=0.98-1.03) ceramics were prepared by high temperature solid-state reaction. X-ray diffraction (XRD) patterns showed that the materials were perovskite-type orthorhombic single phase. By using gas concentration cell and AC impedance spectroscopy methods, the electrical conduction behavior of the materials was investigated in different gases at 500-900 °C. The influence of non-stoichiometry in the materials with x≠1 on conduction properties was studied and compared with that in the material with x=1. The results indicated that Ba1.03Ce0.8Pr0.2O3-α was a pure protonic conductor, and Ba0.98Ce0.8Pr0.2O3-α was a mixed conductor of protons and electrons in wet hydrogen at 500-900 °C. BaCe0.8Pr0.2O3-α was a pure protonic conductor in 500-600 °C, and a mixed conductor of protons and electrons above 600 °C in wet hydrogen. In 500-900 °C, they were all mixed conductors of oxide ions and electronic holes in dry air, and mixed conductors of protons, oxide ions and electronic holes in wet air. Both the protonic and oxide ionic conductivities increased with increasing barium content in the materials in wet hydrogen, dry air and wet air, respectively.展开更多
Perovskite stannates are promising semiconductors that are widely used in optoelectronic devices.Here,the composition dependent intrinsic point defects of stannate perovskites ASnO3(A=Ca,Sr,Ba)are studied by first-pri...Perovskite stannates are promising semiconductors that are widely used in optoelectronic devices.Here,the composition dependent intrinsic point defects of stannate perovskites ASnO3(A=Ca,Sr,Ba)are studied by first-principles calculations.The preferences of defects under stoichiometric and nonstoichiometric conditions are unsealed,meanwhile the charge states of each intrinsic defect varying with the change of electron Fermi energy are clarified.For stoichiometric BaSnO3 and SrSnO3,the Schottky defect complexes are predicted as the most stable defect structure,while the antisite defect complexes are the most stable one in CaSnO3.In nonstoichiometric ASnO3,excessive AO is beneficial to the formation of oxygen vacancies and A-Sn antisite defects in all ASnO3;while the Ca interstitial is another major defect existing in CaSnO3.In the case of SnO2 excess,the predominant defects are the Sn-A antisite defects and A vacancies.Since the functionality of these perovskite oxides is closely related to the types and concentrations of their point defects,the present results are expected to guide the future experiments to optimize the function of the perovskite oxides by tailoring the intrinsic defects through controlling the composition of AO and SnO2.展开更多
Gadolinium zirconate (GZ) is a promising candidate for next-generation thermal barrier coating (TBC) materials.Its corrosion resistance against calcium-magnesium-alumino-silicate(CMAS) needs to be further increased fo...Gadolinium zirconate (GZ) is a promising candidate for next-generation thermal barrier coating (TBC) materials.Its corrosion resistance against calcium-magnesium-alumino-silicate(CMAS) needs to be further increased for enhancing its in-service life.As the Gd element plays an important role in the CMAS resistance,three GZ coatings (GZ-0.75,GZ-1.0,and GZ-1.2) with different Gd/Zr atomic ratios are designed and deposited by laser enhanced chemical vapor deposition(LCVD) in this work.It is found that the generated Gd-apatite in GZ-1.2 would block micro-cracks inside the column structure and the inter-columnar gap more efficiently.Thus,the CMAS penetration rate (5.2 μm/h) of GZ-1.2 decreases over 27% comparing with GZ-1.0 and GZ-0.75,which is even lower than the Gd_(2)Zr_(2)O_(7) coatings fabricated by electron-beam physical vapor depositions (EB-PVDs).This work provides a feasible way to adjust the coating's corrosion resistance and may guide the development of future coating for long in-service life.展开更多
BaxCe0.8Tb0.2O3-a （x=0.98-1.03） solid electrolytes were synthesized and characterized by using X-ray diffraction （XRD）. By using AC impedance spectroscopy and gas concentration cell electromotive force （EMF） mea...BaxCe0.8Tb0.2O3-a （x=0.98-1.03） solid electrolytes were synthesized and characterized by using X-ray diffraction （XRD）. By using AC impedance spectroscopy and gas concentration cell electromotive force （EMF） measurements, the electrical conduction behavior of the specimens was investigated in different gases during 500-1000 ℃ The influence of nonstoichiometry in the specimens with x ≠ 1 on conduction properties was studied and compared with that in the specimen with x = 1. The results show that the specimens are all of perovskite-type orthorhombic structure. In 500-1000 ℃, electronic hole conduction is dominant in dry and wet oxygen, air or nitrogen. Protonic conduction is dominant in wet hydrogen and it is about two orders of magnitude higher than that in hydrogen-free atmospheres （oxygen, air and nitrogen）. The electrical conductivity of the same specimen in water vapor-saturated oxygen, air or nitrogen is slightly higher than that in corresponding gas without water vapor. The electrical conductivities of the nonstoichiometric specimens are higher than those of the stoichiometric one.展开更多
Charge nonstoichiometric 0.94Bi_(0.5+x)Na_(0.5-x)TiO_(3)-0.06BaTiO_(3)(BNT-BT)(x=-0.02,-0.01,0,0.01,0.02)ceramics were pre-pared and investigated.The depolarization temperature was dependent on composition and the fer...Charge nonstoichiometric 0.94Bi_(0.5+x)Na_(0.5-x)TiO_(3)-0.06BaTiO_(3)(BNT-BT)(x=-0.02,-0.01,0,0.01,0.02)ceramics were pre-pared and investigated.The depolarization temperature was dependent on composition and the ferroelectric property of x>0 was suppressed more significantly than the x<0,indicating the composition-sensitive electrical properties.Furthermore,the x=-0.02 was close to the insulator/conductor composition boundary while the x=0.02 was close to the ferroelectrics/relaxor boundary.These results were attributed to the complex effect of donor doping and acceptor doping on depolarization field.This work provides robust clues to tune and/or design electrical property and conductivity of Bi_(0.5)Na_(0.5)TiO_(3)-based materials.展开更多
1 Results Heterostructures,based on ternary CuInS(Se2) chalcogenides and related binary compounds (Cu2-xCh,CuCh,In2Ch3 and InCh; Ch=S,Se) are considered appear to be a matter of choice for producing promising optoelec...1 Results Heterostructures,based on ternary CuInS(Se2) chalcogenides and related binary compounds (Cu2-xCh,CuCh,In2Ch3 and InCh; Ch=S,Se) are considered appear to be a matter of choice for producing promising optoelectronic devices.In the present work we propose and consider a very simple way for the formation of sulfide and selenide heterostructures.The main idea is assumes a novel two-stage method of synthesis and nonstoichiometry control for heterostructures of InxS(Se)1-x/Si,CuInS(Se)2/Si and InxS1-...展开更多
基金Supported by the National Basic Research Program of China under Grant No 2013CB632506the National Natural Science Foundation of China under Grant Nos 51202132,51002087 and 11374186the Independent Innovation Foundation of Shandong University under Grant No IIFSDU 2012TS028
文摘Sr0.9Ba0.1Ti0.8Nb0.2O3 ceramics （x=0, 0.01, 0.02 and 0.05） are prepared by solid state reaction, whose thermoelectric properties are investigated from 323K to 1073K. By introducing A-site nonstoichiometry, the absolute Seebeck coefficient is enhanced, while the electrical resistivity is surprisingly reduced due to the significantly enhanced carrier mobility. These results are dramatic in thermoelectric materials, effectively enhancing the power factor. Moreover, the thermal conductivity is reduced, thus the thermoelectric performance of Sr0.9Ba0.1Ti0.8Nb0.2O3 ceramic is significantly enhanced by A-site nonstoiehiometry.
文摘Lead free 0.94(Bi_(0.5)Na_(0.5))TiO_(3)-0.06BaTiO_(3)ceramics were prepared by conventional solid-state mixed oxide route with the A-site stoichiometry modified to incorporate donor-doping(through Bi-excess)and acceptor-doping(through Na-excess).Both stoichiometric and nonstoichiometric ceramics exhibited a single perovskite phase with pseudo-cubic symmetry.A significant improvement in the dielectric properties was observed in Bi-excess compositions and a deterioration in the dielectric properties was observed in Na-excess compositions.Impedance spectroscopy was utilized to analyze the effects of A-site nonstoichiometry on conduction mechanisms.Compositions with Bi-excess resulted in an electrically homogeneous microstructure with an increase in resistivity by3-4 orders of magnitude and an associated activation energy of 1.57 eV which was close to half of the optical bandgap.In contrast,an electrically heterogeneous microstructure was observed in both the stoichiometric and Na-excess compositions.In addition,the Na-excess compositions exhibited low resistivities(ρ-10^(3)Ω-cm)with characteristic peaks in the impedance data comparable to the recent observations of oxide ion conduction in(Bi_(0.5)Na_(0.5))TiO_(3).Long term annealing studies were also conducted at 800℃to identify changes in crystal structure and electrical properties.The results of this study demonstrates that the dielectric and electrical properties of 0.94(Bi_(0.5)Na_(0.5))TiO_(3)-0.06BaTiO_(3)ceramics are very sensitive to Bi/Na stoichiometry.
基金supported by the National Natural Science Foundation of China(No.52172062)the YEQISUN Joint Funds of the National Natural Science Foundation of China(No.U2241279).
文摘Rare-earth zirconate pyrochlores,which exhibit various interesting properties,especially low thermal conductivity,are of great interest.Nonstoichiometry is an effective strategy involving defect engineering to reduce the thermal conductivity of materials.In this work,a long series of solid solutions,εSmO_(1.5)·(1−ε)ZrO_(2)(ε=0.200,0.250,0.350,0.400,0.450,0.500,0.525,0.550,0.600,and 0.650),were designed and synthesized to investigate the effects of nonstoichiometry on the structural evolution,defect chemistry,and thermal conductivity of SmO_(1.5)–ZrO_(2) system across the entire pyrochlore phase field and phase transition regions.The similarity of all the Raman spectra provides an incredible opportunity to confirm the structural details and evolution of pyrochlore and defective fluorite,as well as the emergence of the expected point defects.A new solution mechanism concerning nonstoichiometry was proposed and confirmed by analyzing the variations in the experimental density and Raman spectra.The thermal conductivities of all the samples were measured,and investigated in terms of the phonon-scattering theory.The results show that the nonstoichiometry with SmO1.5 excess is more effective in reducing the thermal conductivity to an extremely low value of approximately 1 W/(m·K),which can be attributed to the dramatic decrease in the average acoustic velocity in addition to the strong phonon scattering of Zr ion vacancies and oxygen vacancies.On the other hand,the nonstoichiometry with ZrO_(2) excess significantly reduces the thermal conductivity at room temperature,but conversely leads to a slight increase of it above 200°C.The former variation can be attributed to the phonon scattering of the 8a interstitial oxygen ions,which has a similar effectiveness to the defects on the SmO1.5-rich side.The latter variation may be attributed to the Umklapp scattering of phonons.
基金supported by National Science Foundation of China(Grant Nos.51572163,51577111 and 51607108)the Fundamental Research Funds for the Central Universities(Program Nos.GK201601003,GK201703016,GK201802007,201701011 and 2018CBLZ007).
文摘Ceramic-based dielectric capacitors are becoming more and more important in electronic devices.The ceramics of 0.93K_(0.5)Na_(0.5)NbO_(3)–0.07Bix(Mg_(1/3)Nb_(2/3))O_(3)(0.93KNN–0.07BixMN)(x?0:60,2/3,0.75 and 0.95)were successfully fabricated by virtue of the solid reaction process in this work.The results showed that the amount of Bi content has a significant impact on the ceramics of 0.93KNN–0.07BixMN.XRD indicates that all specimens exhibit a pure perovskite structure and existing oxygen vacancy in the specimens.The mean grain size for all specimens belong to submicron scale,and the sample of x=0.95 owns the smallest grain size is 0.11m.The maximum dielectric constant increases but the phase transition temperature Tm exhibits a contrary tendency at 1MHz with increasing Bi concentration.Besides,all ceramics are relaxor ferroelectric.The impedance analysis further revealed that the activation energy of the ceramics increases with Bi content.Eventually,the highestηof 58.8%and Wrec of 1.30 J/cm^(3) are simultaneously achieved in the sample with x=0.60.Overall,we demonstrate in this work that stoichiometry control of Bi in 0.93KNN–0.07BixMN ceramics is a practical method to obtain the desired structural,dielectric and energy storage properties.
文摘The diffusion coefficient of hydrogen atoms in the studied alloys was electrochemically measured by chronoamperometry when the metallic hydride microelectrodes were completely discharged. It is found that the diffusion coefficient of hydrogen atoms decreases when cobalt is substituted for a minority of nickel. On the contrary, the diffusion coefficient increases with the partial substitution of manganese or aluminum for nickel, which is related to the lattice constant and cell volumes of hydrogen absorbing alloys. The lattice constant c is obviously affected by the substitute elements greatly. The result shows that the expansion of cell volume resulted from the increase of value c causes the increase of diffusion coefficient which is especially obvious when the lattice constant is relatively low. However, this relationship is not clear if the lattice constant increases to some extent. It is suggested that this phenomenon is related to the interaction of hydrogen atoms with metallic atoms.
基金This paper is financially supported by the Flanders-China bilateral project (BIL 99/10)the Science and Technology Committee of Shanghai Municipality +1 种基金the State Key Lab of High Performance Ceramics Superfine Microstructure of Chinese Academy of Scien
文摘Using compound energy model (CEM), the thermodynamic properties of <CeO2-y> and <Zr1_xCezO2-x> were evaluated. The evaluation was based on the optimization of ZrIO2-CeO2 and ZrO2-CeO1.5 systems, as well as the miscibility gap in CeO1.5-CeO2 system. Except the cubic fluorite structure phase assessed with compound energy model, all the other solution phases were assessed with subsitutional solution model. The model parameters were evaluated through fitting the selected experimental data by means of thermodynamic optimization. A set of parameters with thermodynamics self-consistency was obtained and satisfactorily described the complex relation between y in <CeO2-y> and the partial pressure of oxygen at different temperatures, also the interdependence among miscellaneous factors such as temperature, oxygen partial pressure, the reduction amount of CeO2 as well as the nonstoichiometry in cubic phase <Zr1-xCezO2-x>- The calculated results seem to be reasonable when put into the explanation of pressureless sintering of Ce02-stabilized ZrO2 powder compacts at a controlled oxygen partial pressure.
基金supported by the Natural Science Foundation of Beijing Municipality Key Class B Project (No.KZ200610005004)the Beijing Municipal Commission of Education (No. PHR200907105)the Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipality(PHR (IHLB))
文摘A series of single-phase T-structured NdSrCu 1-x Co x O 4-δ with oxygen vacancies and T -structured Sm 1.8 Ce 0.2 Cu 1-x Co x O 4-δ （x： 0–0.4） with oxygen excess were prepared using ultrasound-assisted citric acid complexing method, and characterized by means of techniques such as thermogravimetric analysis and NO temperature-programmed desorption （NO-TPD）. The catalytic activities of these materials were evaluated for the decomposition of NO. It was found that the NdSrCu 1-x Co x O 4-δ catalysts were of oxygen vacancies whereas the Sm 1.8 Ce 0.2 Cu 1？x Co x O 4-δ ones possessed excessive oxygen （i.e., over-stoichiometric oxygen）; with a rise in Co doping level, the oxygen vacancy density of NdSrCu 1-x Co x O 4-δ decreased while the over-stoichiometric oxygen amount of Sm 1.8 Ce 0.2 Cu 1-x Co x O 4-δ increased. The NO-TPD results revealed that NO could be activated much easier over the oxygen-deficient perovskite-like oxides than over the oxygen-excessive perovskite-like oxides, with the NdSrCuO 3.702 catalyst showing the best efficiency in activating NO molecules. Under the conditions of 1.0% NO/helium, 2800 hr -1 , and 600–900°C, the catalytic activity of NO decomposition followed the order of NdSrCuO 3.702 〉 NdSrCu 0.8 Co 0.2 O 3.736 〉 NdSrCu 0.6 Co 0.4 O 3.789 〉 Sm 1.8 Ce 0.2 Cu 0.6 Co 0.4 O 4.187 〉 Sm 1.8 Ce 0.2 Cu 0.8 Co 0.2 O 4.104 〉 Sm 1.8 Ce 0.2 CuO 4.045 , in concord with the sequence of decreasing oxygen vacancy or oxygen excess density. Based on the results, we concluded that the higher oxygen vacancy density and the stronger Cu 3＋ /Cu 2＋ redox ability of NdSrCu 1-x Co x O 4-δ account for the easier activation of NO and consequently improve the catalytic activity of NO decomposition over the catalysts.
基金supported by the National Natural Science Foundation of China (50204007)Program for New Century Excellent Talents in University (NCET-07-0387)
文摘The La0.7Sr0.3CryMnzCo(1-y-z)O3-δ samples were prepared by solid state reaction.The phases,microstructure and properties of the samples were investigated by XRD,SEM,DC four-probe method and iodometry method.The single orthorhombic phase La0.7Sr0.3CryMnzCo(1-y-z)O3-δ perovskite oxides were obtained when sintered at l350 °C for 10 h.The oxygen nonstoichiometry of the materials varied inversely with the total electronic conductivity.The sample with composition of La0.7Sr0.3Cr0.5Mn0.35 Co0.15O3-δ had the maxima...
文摘Ba_(1.03)Ce_(0.8)Eu_(0.2)O_(3-α) solid electrolyte with nonstoichiometric composition was prepared by high temperature solid-state reaction. Phase composition, surface and fracture morphologies of the specimen were characterized by using XRD and SEM, respectively. Ionic conduction was researched by gas concentration cell, the performance of hydrogen-air fuel cell was measured in the temperature range of 600～1000 ℃, and compared them with those of BaCe_(0.8)Eu_(0.2)O_(3-α) and Ba_(0.98)Ce_(0.8)Eu_(0.2)O_(3-α). The results indicate that Ba_(1.03)Ce_(0.8)Eu_(0.2)O_(3-α) is a single-phase perovskite-type orthorhombic system. It is a pure proton conductor in the temperature range of 600～1000 ℃ in hydrogen atmosphere, and its proton conduction is superior to that of BaCe_(0.8)Eu_(0.2)O_(3-α) and Ba_(0.98)Ce_(0.8)Eu_(0.2)O_(3-α). It is a mixed conductor of oxide ion and electron hole in oxygen atmosphere. At 1000 ℃, the performance of the fuel cell in which Ba_(1.03)Ce_(0.8)Eu_(0.2)O_(3-α) as electrolyte is higher than that of BaCe_(0.8)Eu_(0.2)O_(3-α) or Ba_(0.98)Ce_(0.8)Eu_(0.2)O_(3-α).
文摘The effects of some substituting elements on the specific discharge capacity, activation and cycling life of AB 5 non stoichiometric hydrogen absorbing alloys were studied electrochemically. Results show that the characteristics of hydrogen absorbing alloys under low current density are greatly improved through the substitution of Ni by Sn, Co, and Mn. Three hydrogen storage alloys, i.e., La(NiSn) 5.14 , La(NiSnCo) 5.12 and La(NiSnMn) 5.12 have the higher specific capacity and easy activation. However, Al in the alloy shows the opposite effect on the electrochemical properties. Under high current density, the discharge capacity and potential of La(NiSn) 5.14 is superior to La(NiSnCo) 5.12 and La(NiSnMn) 5.12 , but the cycling life of La(NiSn) 5.14 is very short. The addition of Mn, Co and Al to the alloys improves the cycling characteristics. In all these alloys, La(NiSnCo) 5.12 is considered as an ideal hydrogen storage alloy.
基金Project supported by the National Natural Science Foundation of China (20771079)Qing Lan Project and the Natural Science Foundation of Education Department of Jiangsu Province (07KJB150126 and 08KJD150008)
文摘BaxCe0.8Pr0.2O3-α (x=0.98-1.03) ceramics were prepared by high temperature solid-state reaction. X-ray diffraction (XRD) patterns showed that the materials were perovskite-type orthorhombic single phase. By using gas concentration cell and AC impedance spectroscopy methods, the electrical conduction behavior of the materials was investigated in different gases at 500-900 °C. The influence of non-stoichiometry in the materials with x≠1 on conduction properties was studied and compared with that in the material with x=1. The results indicated that Ba1.03Ce0.8Pr0.2O3-α was a pure protonic conductor, and Ba0.98Ce0.8Pr0.2O3-α was a mixed conductor of protons and electrons in wet hydrogen at 500-900 °C. BaCe0.8Pr0.2O3-α was a pure protonic conductor in 500-600 °C, and a mixed conductor of protons and electrons above 600 °C in wet hydrogen. In 500-900 °C, they were all mixed conductors of oxide ions and electronic holes in dry air, and mixed conductors of protons, oxide ions and electronic holes in wet air. Both the protonic and oxide ionic conductivities increased with increasing barium content in the materials in wet hydrogen, dry air and wet air, respectively.
基金This work was supported financially by the National Natural Science Foundation of China(Nos.51602188 and 51972206)the Program for Professor of Special Appointment(Eastern Scholar)by Shanghai Municipal Education Commission(No.TP2015040)the Science and Technology Committee of Shanghai(No.19010500400).
文摘Perovskite stannates are promising semiconductors that are widely used in optoelectronic devices.Here,the composition dependent intrinsic point defects of stannate perovskites ASnO3(A=Ca,Sr,Ba)are studied by first-principles calculations.The preferences of defects under stoichiometric and nonstoichiometric conditions are unsealed,meanwhile the charge states of each intrinsic defect varying with the change of electron Fermi energy are clarified.For stoichiometric BaSnO3 and SrSnO3,the Schottky defect complexes are predicted as the most stable defect structure,while the antisite defect complexes are the most stable one in CaSnO3.In nonstoichiometric ASnO3,excessive AO is beneficial to the formation of oxygen vacancies and A-Sn antisite defects in all ASnO3;while the Ca interstitial is another major defect existing in CaSnO3.In the case of SnO2 excess,the predominant defects are the Sn-A antisite defects and A vacancies.Since the functionality of these perovskite oxides is closely related to the types and concentrations of their point defects,the present results are expected to guide the future experiments to optimize the function of the perovskite oxides by tailoring the intrinsic defects through controlling the composition of AO and SnO2.
基金This work was supported by the Natural Science Foundation of Shanghai(No.20ZR1419200)National Natural Science Foundation of China(Nos.52072232 and 52072231)the Program for Professor of Special Appointment(Eastern Scholar)by Shanghai Municipal Education Commission(No.TP2015040).
文摘Gadolinium zirconate (GZ) is a promising candidate for next-generation thermal barrier coating (TBC) materials.Its corrosion resistance against calcium-magnesium-alumino-silicate(CMAS) needs to be further increased for enhancing its in-service life.As the Gd element plays an important role in the CMAS resistance,three GZ coatings (GZ-0.75,GZ-1.0,and GZ-1.2) with different Gd/Zr atomic ratios are designed and deposited by laser enhanced chemical vapor deposition(LCVD) in this work.It is found that the generated Gd-apatite in GZ-1.2 would block micro-cracks inside the column structure and the inter-columnar gap more efficiently.Thus,the CMAS penetration rate (5.2 μm/h) of GZ-1.2 decreases over 27% comparing with GZ-1.0 and GZ-0.75,which is even lower than the Gd_(2)Zr_(2)O_(7) coatings fabricated by electron-beam physical vapor depositions (EB-PVDs).This work provides a feasible way to adjust the coating's corrosion resistance and may guide the development of future coating for long in-service life.
基金Project supported by the National Natural Science Foundation of China （No. 20171034） and the Natural Science Foundation of Education Department of Jiangsu Province （No. 04KJD150218）.
文摘BaxCe0.8Tb0.2O3-a （x=0.98-1.03） solid electrolytes were synthesized and characterized by using X-ray diffraction （XRD）. By using AC impedance spectroscopy and gas concentration cell electromotive force （EMF） measurements, the electrical conduction behavior of the specimens was investigated in different gases during 500-1000 ℃ The influence of nonstoichiometry in the specimens with x ≠ 1 on conduction properties was studied and compared with that in the specimen with x = 1. The results show that the specimens are all of perovskite-type orthorhombic structure. In 500-1000 ℃, electronic hole conduction is dominant in dry and wet oxygen, air or nitrogen. Protonic conduction is dominant in wet hydrogen and it is about two orders of magnitude higher than that in hydrogen-free atmospheres （oxygen, air and nitrogen）. The electrical conductivity of the same specimen in water vapor-saturated oxygen, air or nitrogen is slightly higher than that in corresponding gas without water vapor. The electrical conductivities of the nonstoichiometric specimens are higher than those of the stoichiometric one.
基金supported by the State Key Program for Basic Research of China(2015CB921203)the National Nature Science Foundation of China(11674156,51721001,11804150)the“Deng Feng B”of Nanjing University.
文摘Charge nonstoichiometric 0.94Bi_(0.5+x)Na_(0.5-x)TiO_(3)-0.06BaTiO_(3)(BNT-BT)(x=-0.02,-0.01,0,0.01,0.02)ceramics were pre-pared and investigated.The depolarization temperature was dependent on composition and the ferroelectric property of x>0 was suppressed more significantly than the x<0,indicating the composition-sensitive electrical properties.Furthermore,the x=-0.02 was close to the insulator/conductor composition boundary while the x=0.02 was close to the ferroelectrics/relaxor boundary.These results were attributed to the complex effect of donor doping and acceptor doping on depolarization field.This work provides robust clues to tune and/or design electrical property and conductivity of Bi_(0.5)Na_(0.5)TiO_(3)-based materials.
文摘1 Results Heterostructures,based on ternary CuInS(Se2) chalcogenides and related binary compounds (Cu2-xCh,CuCh,In2Ch3 and InCh; Ch=S,Se) are considered appear to be a matter of choice for producing promising optoelectronic devices.In the present work we propose and consider a very simple way for the formation of sulfide and selenide heterostructures.The main idea is assumes a novel two-stage method of synthesis and nonstoichiometry control for heterostructures of InxS(Se)1-x/Si,CuInS(Se)2/Si and InxS1-...
