The structure and energy of He impurities and vacancy on （001） surface of bcc iron are investigated by an ab initio method. Three cases for stabilities of a He atom at the surface are found： some of He atoms at sur...The structure and energy of He impurities and vacancy on （001） surface of bcc iron are investigated by an ab initio method. Three cases for stabilities of a He atom at the surface are found： some of He atoms at surface atomic layers （SAL） relax into vacuum gap; some of surface He atoms at octahedral interstitial site relax into more stable tetrahedral interstitial site; some of surface He atoms still stay at tetrahedral interstitial site. The un-stability of the He atom at the surface system can be explained by deformation mechanism of charge densities and electronic densities of states. It is found that formation energy of the point defects from the topmost SAL to bulk-like atomic layer increase gradually, for example, the formation energies of a monovacancy at the first five topmost SALs are equal to 0.33, 1.56, 2.04, 2.02 and 2.11 eV, respectively. The magnetic moments of Fe atoms in the surface atomic layers are also calculated.展开更多
Based on density function theory （DFT） and the local density approximation （LDA）, the formation energy and transition levels of native point defects in LaBr3 were calculated under Br-rich conditions. From the calc...Based on density function theory （DFT） and the local density approximation （LDA）, the formation energy and transition levels of native point defects in LaBr3 were calculated under Br-rich conditions. From the calculated results, the following conclusions have been obtained： ① The dominant defect type is the triply positive lanthanum interstitial under p-type conditions. ② The triply negative lanthanum vacancy plays the most important role in n-type LaBr3.③ Neutral and singly positive bromine antisites are more stable in the middle of the band gap. ④ The singly positive （negative） bromine antisite can be a potential com- pensation source in n-type （p-type） LaBr3. ⑤ All the transition levels in LaBr3 belong to deep levels. The optimized geometric structures of bromine interstitials and antisites show that there is no formation of Br-Br covalent bond.展开更多
The formation energies and the equilibrium concentration of vacancies, interstitial H, K, P, O and antisite structural defects with P and K in KH2PO4 （KDP） crystals are investigated by ab initio total-energy calcula...The formation energies and the equilibrium concentration of vacancies, interstitial H, K, P, O and antisite structural defects with P and K in KH2PO4 （KDP） crystals are investigated by ab initio total-energy calculations. The formation energy of interstitial H is calculated to be about 2.06 eV and we suggest that it may be the dominant defect in KDP crystal. The formation energy of an O vacancy （5.25 eV） is much higher than that of interstitial O （0.60 eV）. Optical absorption centres can be induced by defects of O vacancies, interstitial O and interstitial H. We suggest that these defects may be responsible for the lowering of the damage threshold of the KDP. A K vacancy defect may increase the ionic conductivity and therefore the laser-induced damage threshold decreases.展开更多
When the GaAs/AlGaAs superlattice-based devices are used under irradiation environments, point defects may be created and ultimately deteriorate their electronic and transport properties. Thus, understanding the prope...When the GaAs/AlGaAs superlattice-based devices are used under irradiation environments, point defects may be created and ultimately deteriorate their electronic and transport properties. Thus, understanding the properties of point defects like vacancies and interstitials is essential for the successful application of semiconductor materials. In the present study, first-principles calculations are carried out to explore the stability of point defects in GaAs/Al_(0.5)Ga_(0.5)As superlattice and their effects on electronic properties. The results show that the interstitial defects and Frenkel pair defects are relatively difficult to form, while the antisite defects are favorably created generally. Besides, the existence of point defects generally modifies the electronic structure of GaAs/Al_(0.5)Ga_(0.5)As superlattice significantly, and most of the defective SL structures possess metallic characteristics. Considering the stability of point defects and carrier mobility of defective states,we propose an effective strategy that AlAs, GaAs, and AlGaantisite defects are introduced to improve the hole or electron mobility of GaAs/Al_(0.5)Ga_(0.5)As superlattice. The obtained results will contribute to the understanding of the radiation damage effects of the GaAs/AlGaAs superlattice, and provide a guidance for designing highly stable and durable semiconductor superlattice-based electronics and optoelectronics for extreme environment applications.展开更多
Ferroelectric materials have enormous potential applications in advanced techniques. However, there are still many problems in its practical application. Dielectric and mechanical (internal friction) measurements are ...Ferroelectric materials have enormous potential applications in advanced techniques. However, there are still many problems in its practical application. Dielectric and mechanical (internal friction) measurements are very sensitive to phase transitions, relaxation process of point defects, domain walls and their mobility, which have severe effect on ferroelectric properties. These make them become very good means to investigate substantial information on structural features and to explore the fundamental principles in ferroelectric materials and their applications. In this paper, the dielectric and internal friction measurement were used to investigate the behaviors for point defects and phase transition in ferroelectric ceramics such as Bi_ 4-x La_ x Ti_ 3 O_ 12 , Bi_ 4 Ti_ 3-y Nb_ y O_ 12 , SrBi_ 2 Ti_ 2 O_ 9 , PbZr_ x Ti_ 1-x O_ 3 ,_ PMN-PT. They were used to clarify the mechanism for some ferroelectric behaviors.展开更多
Using the first-principles method, we investigate the thermal stability of cation point defects in LaAlO3 bulk and films. The calculated densities of states indicate that cation vacancies and antisites act as acceptor...Using the first-principles method, we investigate the thermal stability of cation point defects in LaAlO3 bulk and films. The calculated densities of states indicate that cation vacancies and antisites act as acceptors. The formation energies show that cation vacancies are energetically favorable in bulk LaAIO3 under O-rich conditions, while the AILa antisites are stable in reducing atmosphere. However, the same behavior does not appear in the case of LaAlO3 films. For LaO-terminated LaAlOa fihns, La or AI vacancies remain energetically favorable under O-rich and O-deficient conditions. For an AlO2-terminated surface, under O-rich condition the La interstitial atom is repelled from the outmost layer after optimization, which releases more stress leading to the decrease of total energy of the system. An AI interstitial atom has a smaller radius so that it can stay in distorted films and becomes more stable under O-deficient conditions, and the Al interstitial atoms can be another possible carrier source contribution to the conductivity of n-type interface under an ultrahigh vacuum. La and Al antisites have similar formation energy regardless of oxygen pressure. The results would be helpful to understand the defect structures of LaAlOa-related materials.展开更多
The Curie point of barium titanate(BaTiO_(3))has been a focal point of research since the discovery of its ferroelectric properties.Exploring methods to elevate the Curie point without relying on Pb as a dopant presen...The Curie point of barium titanate(BaTiO_(3))has been a focal point of research since the discovery of its ferroelectric properties.Exploring methods to elevate the Curie point without relying on Pb as a dopant presents fresh opportunities for lead-free dielectric and/or piezoelectric materials.It is essential to avoid introducing ions like K^(+)and Na^(+),which could jeopardize the functional ceramic characteristics.This study delves into the stoichiometry of barium titanate,examining how impurities,point defects and doping techniques influence its Curie point,focus on the potential of doping and processing to enhance this property.BaTiO_(3)nanopowders were synthesized directly with varyingBa:Ti ratios in an ethanol-water solution at 60°C,followed by sintering at 1280°C and characterization through dielectric spectroscopy.A comparison was made with samples doped with Si,vapor-doped with Bi and vapor-doped with Pb.Results revealed that even minimal Si doping could boost the ferroelectric properties and elevate the Curie point,while vapor-doping with trace amounts of PbO or Bi_(2)O_(3)significantly increased the Curie point,particularly in samples with higher Ti content.The impact of vapor dopants of PbO and Bi_(2)O_(3)was similar,with a nominal doping level of 1 mol%shifting the Curie point above 140°C.Notably,in samples with a Ba:Ti ratio of 0.95 vapor-doped with PbO,the Curie point rose to 146°C.a notable increase of 16°C.surpassing the traditional doping efficiency.This study offers fresh insights into enhancing the Curie point of barium titanate-based materials,exploring the intricate connections among chemical stoichiometry,dopants,point defects and dielectric properties.It highlights the significant influence of chemical composition,impurities,defects and doping strategies on the dielectric characteristics of barium titanate.展开更多
We study radial symmetric point defects with degree k/2 in the 2-D disk or R^(2) in the Q-tensor framework with a singular bulk energy,which is defined by Bingham closure.First,we obtain the existence of solutions for...We study radial symmetric point defects with degree k/2 in the 2-D disk or R^(2) in the Q-tensor framework with a singular bulk energy,which is defined by Bingham closure.First,we obtain the existence of solutions for the profiles of radial symmetric point defects with degree k/2 in the 2-D disk or R^(2).Then,we prove that the solution is stable for |k| = 1 and unstable for |k| > 1.Some identities are derived and utilized throughout the proof of existence and stability/instability.展开更多
Point defect engineering endows catalysts with novel physical and chemical properties,elevating their electrocatalytic efficiency.The introduction of defects emerges as a promising strategy,effectively modifying the e...Point defect engineering endows catalysts with novel physical and chemical properties,elevating their electrocatalytic efficiency.The introduction of defects emerges as a promising strategy,effectively modifying the electronic structure of active sites.This optimization influences the adsorption energy of intermediates,thereby mitigating reaction energy barriers,altering paths,enhancing selectivity,and ultimately improving the catalytic efficiency of electrocatalysts.To elucidate the impact of defects on the electrocatalytic process,we comprehensively outline the roles of various point defects,their synthetic methodologies,and characterization techniques.Importantly,we consolidate insights into the relationship between point defects and catalytic activity for hydrogen/oxygen evolution and CO_(2)/O_(2)/N_(2) reduction reactions by integrating mechanisms from diverse reactions.This underscores the pivotal role of point defects in enhancing catalytic performance.At last,the principal challenges and prospects associated with point defects in current electrocatalysts are proposed,emphasizing their role in advancing the efficiency of electrochemical energy storage and conversion materials.展开更多
The structural features and real compositions with point defects of Bi+-doped TlCdCl_3 and TlCdI_3 single crystals, grown by the Bridgman-Stockbarger technique, are first studied using the X-ray diffraction, X-ray syn...The structural features and real compositions with point defects of Bi+-doped TlCdCl_3 and TlCdI_3 single crystals, grown by the Bridgman-Stockbarger technique, are first studied using the X-ray diffraction, X-ray synchrotron radiation, and EXAFS/XANES spectroscopy. In the structures of Bi^+-doped TlCdCl_3 and TlCdI_3 crystals, the Cd, Cl, and I sites are found to be defect-free. The vacancies in the Tl sites and interstitial Bi atoms located in the vicinity of the Tl sites are detected in the structures of both samples. In the Bi^+-doped TlCdCl_3, the presence of a small amount of Bi^+ ions in the Tl^+ sites is possible. The correlation between photoluminescence bands and point defects in the refined structures are determined. Photoluminescence spectra and decay kinetics of the Bi+-doped TlCdCl_3 and TlCdI_3 demonstrate that they are attractive materials for potential applications in photonics.展开更多
Photocatalytic reduction of CO_(2) with water by photocatalysts such as TiO_(2) to produce solar fuels is an attractive approach to alleviate the environmental influences of greenhouse gases and in the meantime produc...Photocatalytic reduction of CO_(2) with water by photocatalysts such as TiO_(2) to produce solar fuels is an attractive approach to alleviate the environmental influences of greenhouse gases and in the meantime produce valuable carbon-neutral fuels.Among the materials properties that affect catalytic activity of CO_(2) photoreduction,the point defect on TiO_(2) is one of the most important but not frequently addressed and well understood in the literature.In this review,we have examined the major influences of TiO_(2) point defects on CO_(2)photoreduction with H_(2)O,by changing the catalysts'gas adsorption capabilities,optical properties,and electronic structures.In addition,the performances of various defective TiO_(2) toward CO_(2) photoreduction are summarized and compared in terms of productivity,selectivity,and stability.We hope this review can contribute to understanding the mechanism of CO_(2) photoreduction on defective TiO_(2) and provide insights to the design of highly efficient defect-rich TiO_(2) to boost the CO_(2) utilization.展开更多
The point defects and their related physical properties in L10 FePt are investigated by molecular dynamics simulations based on an analytic bond-order potential. The calculated results agree well with the experimental...The point defects and their related physical properties in L10 FePt are investigated by molecular dynamics simulations based on an analytic bond-order potential. The calculated results agree well with the experimental value, indicating that the analytic bond-order potential is suitable to describe the structural properties and surface energies of the FePt alloy in the L10 phase. However, the calculated vacancy formation energy of an Fe atom is higher than that of a Pt atom, which disagrees with some other previously calculated results. This result indicates that the analytic bond-order potential is unable to describe the related point defect properties. The analytic bond-order potential needs to be modified in order to study these defect properties of an FePt alloy.展开更多
The close-to-optimal band gap,large absorption coefficient,low manufacturing cost and rapid increase in power conversion efficiency make the organic-inorganic hybrid halide（CH3NH3PbI3）and related perovskite solar ce...The close-to-optimal band gap,large absorption coefficient,low manufacturing cost and rapid increase in power conversion efficiency make the organic-inorganic hybrid halide（CH3NH3PbI3）and related perovskite solar cells very promising for commercialization.The properties of point defects in the absorber layer semiconductors have important influence on the photovoltaic performance of solar cells,so the investigation on the defect properties in the perovskite semiconductors is necessary for the optimization of their photovoltaic performance.In this work,we give a brief review to the first-principles calculation studies on the defect properties in a series of perovskite semiconductors,including the organic-inorganic hybrid perovskites and inorganic halide perovskites.Experimental identification of these point defects and characterization of their properties are called for.展开更多
Despite the long history of research that has focused on the role of defects on device performance, the studies have not always been fruitful. A major reason is because these defect studies have typically been conduct...Despite the long history of research that has focused on the role of defects on device performance, the studies have not always been fruitful. A major reason is because these defect studies have typically been conducted in a parallel mode wherein the semiconductor wafer was divided into multiple pieces for separate optical and structural characterization, as well as device fabrication and evaluation. The major limitation of this approach was that either the defect being investigated by structural characterization techniques was not the same defect that was affecting the device performance or else the defect was not characterized under normal device operating conditions. In this review, we describe a more comprehensive approach to defect study, namely a series mode, using an array of spatially-resolved optical, electrical, and structural characterization techniques, all at the individual defect level but applied sequentially on a fabricated device. This novel sequential approach enables definitive answers to key questions, such as:(ⅰ) how do individual defects affect device performance?(ⅱ) how does the impact depend on the device operation conditions?(ⅲ) how does the impact vary from one defect to another? Implementation of this different approach is illustrated by the study of individual threading dislocation defects in GaAs solar cells. Additionally,we briefly describe a 3-D Raman thermometry method that can also be used for investigating the roles of defects in high power devices and device failure mechanisms.展开更多
The existence and its movement rule of crystalline structure defect are closely related to the diffusion, solid phase reaction, sintering, phase transformation as well as the physical and chemical properties of materi...The existence and its movement rule of crystalline structure defect are closely related to the diffusion, solid phase reaction, sintering, phase transformation as well as the physical and chemical properties of materials. Point defect theory has been widely applied in material mineralization research, unfavorable transformation controlling, material modification, the research and development of new materials and so on. Point defect theory is one of the important theories for new material research and development. Herein we mainly discuss the application of point defect theory in some structural material researches.展开更多
In this study, we report the effect of Zn doping on the thermoelectric properties of CO1-xZnxSbS0.85Se0.15 solid solutions （x = 0, 0.02, 0.05, 0.08）. The results show the dimensionless figure of merit （zT） increas...In this study, we report the effect of Zn doping on the thermoelectric properties of CO1-xZnxSbS0.85Se0.15 solid solutions （x = 0, 0.02, 0.05, 0.08）. The results show the dimensionless figure of merit （zT） increases from 0.17 to 0.34 at 875 K for Co0.95Zn0.05SbS0.85Se0.15 sample, due to the noticeable decrease in the lattice thermal conductivity by introducing point defect, which is further confirmed by an analysis based on the Debye-Callaway- Klemens model. Meanwhile, the thermoelectric power factor is maintained at high temperatures. This work highlights the important role of point defect in improving the thermoelectric performance of CoSbS-based compounds.展开更多
The roles of different point defects in persistent luminescence of SrAl2O4：Eu,Dy phosphors were investigated. The research results showed that Dyer plays an important role in the persistent luminescence of SrA1EO4：E...The roles of different point defects in persistent luminescence of SrAl2O4：Eu,Dy phosphors were investigated. The research results showed that Dyer plays an important role in the persistent luminescence of SrA1EO4：Eu, Dy phosphors. It can serve as the electron trap of suitable depth for persistent luminescence. V~ does not serve as the electron trap of suitable depth, but its existence can increase the depth of electron traps. There is interaction between the Dy^3＋（ DySr ） and the Eu^2＋（Eu^x Sr ）, and only if the distance between the Dy^3＋（DySr） and the Eu^2＋ （Eu^x Sr） is close enough, the Dyer can work as an effective electron trap. The point defect of V＂ Sr can be hole trap, but the change of its density in crystal matrix does not arouse the obvious change of persistent luminescence.展开更多
The point defect concentrations of L12-A13X（Sc, Zr, Er） were systematically investigated using the first- principle calculations with thermodynamics approach. The results show that the constitutional point defects o...The point defect concentrations of L12-A13X（Sc, Zr, Er） were systematically investigated using the first- principle calculations with thermodynamics approach. The results show that the constitutional point defects of off- stoichiometric L12-A13X（Sc, Zr, Er） prefer to occur in X sublattice, that is X anti-site in X-rich alloy and X vacancy in Al-rich alloy, respectively. And A1 anti-site also has a high density in Al-rich Llz-A13X（Sc, Er）. It is found that the point defect concentrations of stoichiometric L12-A/3X（Sc, Zr） follow in the sequence as： A1 vacancies （VA0 〉 X vacancies （Vx） 〉 X anti-sites （XA1） 〉 A1 anti- sites （Alx）. The point defect concentration of stoichio- metric A13Er is similar to that of L12-A13X（Sc, Zr）. The result suggests that the A1 vacancy （VA1） is a dominant point defect in L12-A13X（Sc, Zr, Er）. A simple parameter Hvx-HVA1 can be used for a rough estimation of the point defect concentrations in L12-A13X structure. Some rules of point defect concentrations for L12-A13X（Sc, Zr, Er） are also revealed.展开更多
Doping- and alloying-induced point defects lead to mass and strain field fluctuations which can be used as effective strategies to decrease the lattice thermal conductivity and consequently boost the performance of th...Doping- and alloying-induced point defects lead to mass and strain field fluctuations which can be used as effective strategies to decrease the lattice thermal conductivity and consequently boost the performance of thermoelectric materials. Herein, we report the effects of Sm and S co-doping on thermoelectric transport properties of copper antimony selenides in the temperature range of 300 K 〈 T〈 650 K. Through the Callaway model, it demonstrates that Sm and S co-doping induces strong mass differences and strain field fluctuations in Cu3SbSe4. The results prove that doping with suitable elements can increase point defect scattering of heat-carrying phonons, leading to a lower thermal conductivity and a better ther- moelectric performance. The highest figure of merit （ZT） of - 0.55 at 648 K is obtained for the Sm and S co-doped sample with nominal composition of Cu2.995Sm0.005Sb- Se3.95S0.05, which is about 55% increase compared to the ZT of pristine Cu3SbSe4.展开更多
Photoluminescence （PL） measurement is used to study the point defect distribution in a GaN terahertz Gunn diode, which is able to the degrade high-field transport characteristic during further device operation. PL, ...Photoluminescence （PL） measurement is used to study the point defect distribution in a GaN terahertz Gunn diode, which is able to the degrade high-field transport characteristic during further device operation. PL, secondary ion mass spectroscopy （SIMS）, transmission electron microscope （TEM）, and capacitance-voltage （C-V） measurements are used to discuss the origin of point defects responsible for the yellow luminescence in structures. The point defect densities of about 1011 cm-2 in structures are extracted by analysis of C-V characterization. After thermal annealing treatment, diminishments of point defect densities in structures are efficiently demonstrated by PL and C-V results.展开更多
基金supported by National Basic Research Program of China (No.2007CB209803)the National Natural Science Foundation of China (No.51231002)the Applied Basic Research Program from Hebei Province
文摘The structure and energy of He impurities and vacancy on （001） surface of bcc iron are investigated by an ab initio method. Three cases for stabilities of a He atom at the surface are found： some of He atoms at surface atomic layers （SAL） relax into vacuum gap; some of surface He atoms at octahedral interstitial site relax into more stable tetrahedral interstitial site; some of surface He atoms still stay at tetrahedral interstitial site. The un-stability of the He atom at the surface system can be explained by deformation mechanism of charge densities and electronic densities of states. It is found that formation energy of the point defects from the topmost SAL to bulk-like atomic layer increase gradually, for example, the formation energies of a monovacancy at the first five topmost SALs are equal to 0.33, 1.56, 2.04, 2.02 and 2.11 eV, respectively. The magnetic moments of Fe atoms in the surface atomic layers are also calculated.
基金Supported by the National Nature Science Foundation of China(11275142)
文摘Based on density function theory （DFT） and the local density approximation （LDA）, the formation energy and transition levels of native point defects in LaBr3 were calculated under Br-rich conditions. From the calculated results, the following conclusions have been obtained： ① The dominant defect type is the triply positive lanthanum interstitial under p-type conditions. ② The triply negative lanthanum vacancy plays the most important role in n-type LaBr3.③ Neutral and singly positive bromine antisites are more stable in the middle of the band gap. ④ The singly positive （negative） bromine antisite can be a potential com- pensation source in n-type （p-type） LaBr3. ⑤ All the transition levels in LaBr3 belong to deep levels. The optimized geometric structures of bromine interstitials and antisites show that there is no formation of Br-Br covalent bond.
基金Project supported by the Program for New Century Excellent Talents at the University of China (Grant No.NCET-08-0722)
文摘The formation energies and the equilibrium concentration of vacancies, interstitial H, K, P, O and antisite structural defects with P and K in KH2PO4 （KDP） crystals are investigated by ab initio total-energy calculations. The formation energy of interstitial H is calculated to be about 2.06 eV and we suggest that it may be the dominant defect in KDP crystal. The formation energy of an O vacancy （5.25 eV） is much higher than that of interstitial O （0.60 eV）. Optical absorption centres can be induced by defects of O vacancies, interstitial O and interstitial H. We suggest that these defects may be responsible for the lowering of the damage threshold of the KDP. A K vacancy defect may increase the ionic conductivity and therefore the laser-induced damage threshold decreases.
基金Project supported by the NSAF Joint Foundation of China (Grant No. U1930120)the Key Natural Science Foundation of Gansu Province, China (Grant No. 20JR5RA211)the National Natural Science Foundation of China (Grant No. 11774044)。
文摘When the GaAs/AlGaAs superlattice-based devices are used under irradiation environments, point defects may be created and ultimately deteriorate their electronic and transport properties. Thus, understanding the properties of point defects like vacancies and interstitials is essential for the successful application of semiconductor materials. In the present study, first-principles calculations are carried out to explore the stability of point defects in GaAs/Al_(0.5)Ga_(0.5)As superlattice and their effects on electronic properties. The results show that the interstitial defects and Frenkel pair defects are relatively difficult to form, while the antisite defects are favorably created generally. Besides, the existence of point defects generally modifies the electronic structure of GaAs/Al_(0.5)Ga_(0.5)As superlattice significantly, and most of the defective SL structures possess metallic characteristics. Considering the stability of point defects and carrier mobility of defective states,we propose an effective strategy that AlAs, GaAs, and AlGaantisite defects are introduced to improve the hole or electron mobility of GaAs/Al_(0.5)Ga_(0.5)As superlattice. The obtained results will contribute to the understanding of the radiation damage effects of the GaAs/AlGaAs superlattice, and provide a guidance for designing highly stable and durable semiconductor superlattice-based electronics and optoelectronics for extreme environment applications.
文摘Ferroelectric materials have enormous potential applications in advanced techniques. However, there are still many problems in its practical application. Dielectric and mechanical (internal friction) measurements are very sensitive to phase transitions, relaxation process of point defects, domain walls and their mobility, which have severe effect on ferroelectric properties. These make them become very good means to investigate substantial information on structural features and to explore the fundamental principles in ferroelectric materials and their applications. In this paper, the dielectric and internal friction measurement were used to investigate the behaviors for point defects and phase transition in ferroelectric ceramics such as Bi_ 4-x La_ x Ti_ 3 O_ 12 , Bi_ 4 Ti_ 3-y Nb_ y O_ 12 , SrBi_ 2 Ti_ 2 O_ 9 , PbZr_ x Ti_ 1-x O_ 3 ,_ PMN-PT. They were used to clarify the mechanism for some ferroelectric behaviors.
基金Supported by the Hebei Provincial Young Top-Notch Talent Support Program under Grant No BJRC2016the Innovative Funding Project of Graduates of Hebei University under Grant No hbu2018ss62the Midwest Universities Comprehensive Strength Promotion Project
文摘Using the first-principles method, we investigate the thermal stability of cation point defects in LaAlO3 bulk and films. The calculated densities of states indicate that cation vacancies and antisites act as acceptors. The formation energies show that cation vacancies are energetically favorable in bulk LaAIO3 under O-rich conditions, while the AILa antisites are stable in reducing atmosphere. However, the same behavior does not appear in the case of LaAlO3 films. For LaO-terminated LaAlOa fihns, La or AI vacancies remain energetically favorable under O-rich and O-deficient conditions. For an AlO2-terminated surface, under O-rich condition the La interstitial atom is repelled from the outmost layer after optimization, which releases more stress leading to the decrease of total energy of the system. An AI interstitial atom has a smaller radius so that it can stay in distorted films and becomes more stable under O-deficient conditions, and the Al interstitial atoms can be another possible carrier source contribution to the conductivity of n-type interface under an ultrahigh vacuum. La and Al antisites have similar formation energy regardless of oxygen pressure. The results would be helpful to understand the defect structures of LaAlOa-related materials.
文摘The Curie point of barium titanate(BaTiO_(3))has been a focal point of research since the discovery of its ferroelectric properties.Exploring methods to elevate the Curie point without relying on Pb as a dopant presents fresh opportunities for lead-free dielectric and/or piezoelectric materials.It is essential to avoid introducing ions like K^(+)and Na^(+),which could jeopardize the functional ceramic characteristics.This study delves into the stoichiometry of barium titanate,examining how impurities,point defects and doping techniques influence its Curie point,focus on the potential of doping and processing to enhance this property.BaTiO_(3)nanopowders were synthesized directly with varyingBa:Ti ratios in an ethanol-water solution at 60°C,followed by sintering at 1280°C and characterization through dielectric spectroscopy.A comparison was made with samples doped with Si,vapor-doped with Bi and vapor-doped with Pb.Results revealed that even minimal Si doping could boost the ferroelectric properties and elevate the Curie point,while vapor-doping with trace amounts of PbO or Bi_(2)O_(3)significantly increased the Curie point,particularly in samples with higher Ti content.The impact of vapor dopants of PbO and Bi_(2)O_(3)was similar,with a nominal doping level of 1 mol%shifting the Curie point above 140°C.Notably,in samples with a Ba:Ti ratio of 0.95 vapor-doped with PbO,the Curie point rose to 146°C.a notable increase of 16°C.surpassing the traditional doping efficiency.This study offers fresh insights into enhancing the Curie point of barium titanate-based materials,exploring the intricate connections among chemical stoichiometry,dopants,point defects and dielectric properties.It highlights the significant influence of chemical composition,impurities,defects and doping strategies on the dielectric characteristics of barium titanate.
基金supported by the Basque Government through the BERC PRO-GRAMME 2022-2025 and by the Spanish State Research Agency through Basque Center for Applied Mathematics Severo Ochoa excellence accreditation SEV-2017-0718 and through Project PID2020-114189RB-I00 funded by Agencia Estatal de Investigacion(Grant No.PID2020-114189RB-I00/AEI/10.13039/501100011033)supported by National Natural Science Foundation of China(Grant Nos.11931010 and 12271476)。
文摘We study radial symmetric point defects with degree k/2 in the 2-D disk or R^(2) in the Q-tensor framework with a singular bulk energy,which is defined by Bingham closure.First,we obtain the existence of solutions for the profiles of radial symmetric point defects with degree k/2 in the 2-D disk or R^(2).Then,we prove that the solution is stable for |k| = 1 and unstable for |k| > 1.Some identities are derived and utilized throughout the proof of existence and stability/instability.
基金supported by the National Natural Science Foundation of China(U21A20281)the Special Fund for Young Teachers from Zhengzhou University(JC23557030,JC23257011)+1 种基金the Key Research Projects of Higher Education Institutions of Henan Province(24A530009)the Project of Zhongyuan Critical Metals Laboratory(GJJSGFYQ202336).
文摘Point defect engineering endows catalysts with novel physical and chemical properties,elevating their electrocatalytic efficiency.The introduction of defects emerges as a promising strategy,effectively modifying the electronic structure of active sites.This optimization influences the adsorption energy of intermediates,thereby mitigating reaction energy barriers,altering paths,enhancing selectivity,and ultimately improving the catalytic efficiency of electrocatalysts.To elucidate the impact of defects on the electrocatalytic process,we comprehensively outline the roles of various point defects,their synthetic methodologies,and characterization techniques.Importantly,we consolidate insights into the relationship between point defects and catalytic activity for hydrogen/oxygen evolution and CO_(2)/O_(2)/N_(2) reduction reactions by integrating mechanisms from diverse reactions.This underscores the pivotal role of point defects in enhancing catalytic performance.At last,the principal challenges and prospects associated with point defects in current electrocatalysts are proposed,emphasizing their role in advancing the efficiency of electrochemical energy storage and conversion materials.
文摘The structural features and real compositions with point defects of Bi+-doped TlCdCl_3 and TlCdI_3 single crystals, grown by the Bridgman-Stockbarger technique, are first studied using the X-ray diffraction, X-ray synchrotron radiation, and EXAFS/XANES spectroscopy. In the structures of Bi^+-doped TlCdCl_3 and TlCdI_3 crystals, the Cd, Cl, and I sites are found to be defect-free. The vacancies in the Tl sites and interstitial Bi atoms located in the vicinity of the Tl sites are detected in the structures of both samples. In the Bi^+-doped TlCdCl_3, the presence of a small amount of Bi^+ ions in the Tl^+ sites is possible. The correlation between photoluminescence bands and point defects in the refined structures are determined. Photoluminescence spectra and decay kinetics of the Bi+-doped TlCdCl_3 and TlCdI_3 demonstrate that they are attractive materials for potential applications in photonics.
基金The authors acknowledge the financial support from National Science Foundation CAREER Award(CBET#1538404).
文摘Photocatalytic reduction of CO_(2) with water by photocatalysts such as TiO_(2) to produce solar fuels is an attractive approach to alleviate the environmental influences of greenhouse gases and in the meantime produce valuable carbon-neutral fuels.Among the materials properties that affect catalytic activity of CO_(2) photoreduction,the point defect on TiO_(2) is one of the most important but not frequently addressed and well understood in the literature.In this review,we have examined the major influences of TiO_(2) point defects on CO_(2)photoreduction with H_(2)O,by changing the catalysts'gas adsorption capabilities,optical properties,and electronic structures.In addition,the performances of various defective TiO_(2) toward CO_(2) photoreduction are summarized and compared in terms of productivity,selectivity,and stability.We hope this review can contribute to understanding the mechanism of CO_(2) photoreduction on defective TiO_(2) and provide insights to the design of highly efficient defect-rich TiO_(2) to boost the CO_(2) utilization.
基金supported by the National Natural Science Foundation of China (Grant No. 50971011)the Beijing Natural Science Foundation (Grant No. 1102025)the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20091102110038)
文摘The point defects and their related physical properties in L10 FePt are investigated by molecular dynamics simulations based on an analytic bond-order potential. The calculated results agree well with the experimental value, indicating that the analytic bond-order potential is suitable to describe the structural properties and surface energies of the FePt alloy in the L10 phase. However, the calculated vacancy formation energy of an Fe atom is higher than that of a Pt atom, which disagrees with some other previously calculated results. This result indicates that the analytic bond-order potential is unable to describe the related point defect properties. The analytic bond-order potential needs to be modified in order to study these defect properties of an FePt alloy.
基金Project supported by the National Natural Science Foundation of China(No.61574059)the Shanghai Rising-Star Program(No.14QA1401500)+1 种基金the Shu-Guang Program(15SG20)the CC of ECNU
文摘The close-to-optimal band gap,large absorption coefficient,low manufacturing cost and rapid increase in power conversion efficiency make the organic-inorganic hybrid halide（CH3NH3PbI3）and related perovskite solar cells very promising for commercialization.The properties of point defects in the absorber layer semiconductors have important influence on the photovoltaic performance of solar cells,so the investigation on the defect properties in the perovskite semiconductors is necessary for the optimization of their photovoltaic performance.In this work,we give a brief review to the first-principles calculation studies on the defect properties in a series of perovskite semiconductors,including the organic-inorganic hybrid perovskites and inorganic halide perovskites.Experimental identification of these point defects and characterization of their properties are called for.
基金supported by ARO/Electronics (Grant No. W911NF-16-1-0263)the support of Bissell Distinguished Professorship at UNC-Charlotte。
文摘Despite the long history of research that has focused on the role of defects on device performance, the studies have not always been fruitful. A major reason is because these defect studies have typically been conducted in a parallel mode wherein the semiconductor wafer was divided into multiple pieces for separate optical and structural characterization, as well as device fabrication and evaluation. The major limitation of this approach was that either the defect being investigated by structural characterization techniques was not the same defect that was affecting the device performance or else the defect was not characterized under normal device operating conditions. In this review, we describe a more comprehensive approach to defect study, namely a series mode, using an array of spatially-resolved optical, electrical, and structural characterization techniques, all at the individual defect level but applied sequentially on a fabricated device. This novel sequential approach enables definitive answers to key questions, such as:(ⅰ) how do individual defects affect device performance?(ⅱ) how does the impact depend on the device operation conditions?(ⅲ) how does the impact vary from one defect to another? Implementation of this different approach is illustrated by the study of individual threading dislocation defects in GaAs solar cells. Additionally,we briefly describe a 3-D Raman thermometry method that can also be used for investigating the roles of defects in high power devices and device failure mechanisms.
基金This work was supported by the "863" program (No. 2003AA322020)
文摘The existence and its movement rule of crystalline structure defect are closely related to the diffusion, solid phase reaction, sintering, phase transformation as well as the physical and chemical properties of materials. Point defect theory has been widely applied in material mineralization research, unfavorable transformation controlling, material modification, the research and development of new materials and so on. Point defect theory is one of the important theories for new material research and development. Herein we mainly discuss the application of point defect theory in some structural material researches.
基金financially supported by the National Natural Science Foundation of China (Nos. 11344010. 11404044 and 51472036)the Fundamental Research Funds for the Central Universities (No. 106112016CDJZR308808)
文摘In this study, we report the effect of Zn doping on the thermoelectric properties of CO1-xZnxSbS0.85Se0.15 solid solutions （x = 0, 0.02, 0.05, 0.08）. The results show the dimensionless figure of merit （zT） increases from 0.17 to 0.34 at 875 K for Co0.95Zn0.05SbS0.85Se0.15 sample, due to the noticeable decrease in the lattice thermal conductivity by introducing point defect, which is further confirmed by an analysis based on the Debye-Callaway- Klemens model. Meanwhile, the thermoelectric power factor is maintained at high temperatures. This work highlights the important role of point defect in improving the thermoelectric performance of CoSbS-based compounds.
基金This study is financially supported by the Jiangxi University of Finance and Economy (Project No. 0421205) Jiangxi Provincial Department of Education (Project No. (2007) 260)
文摘The roles of different point defects in persistent luminescence of SrAl2O4：Eu,Dy phosphors were investigated. The research results showed that Dyer plays an important role in the persistent luminescence of SrA1EO4：Eu, Dy phosphors. It can serve as the electron trap of suitable depth for persistent luminescence. V~ does not serve as the electron trap of suitable depth, but its existence can increase the depth of electron traps. There is interaction between the Dy^3＋（ DySr ） and the Eu^2＋（Eu^x Sr ）, and only if the distance between the Dy^3＋（DySr） and the Eu^2＋ （Eu^x Sr） is close enough, the Dyer can work as an effective electron trap. The point defect of V＂ Sr can be hole trap, but the change of its density in crystal matrix does not arouse the obvious change of persistent luminescence.
基金financially supported by the National Natural Science Foundation of China(Nos.51401093 and 51341010)the Natural Science Foundation of Jiangsu Province (No.BK20130233)
文摘The point defect concentrations of L12-A13X（Sc, Zr, Er） were systematically investigated using the first- principle calculations with thermodynamics approach. The results show that the constitutional point defects of off- stoichiometric L12-A13X（Sc, Zr, Er） prefer to occur in X sublattice, that is X anti-site in X-rich alloy and X vacancy in Al-rich alloy, respectively. And A1 anti-site also has a high density in Al-rich Llz-A13X（Sc, Er）. It is found that the point defect concentrations of stoichiometric L12-A/3X（Sc, Zr） follow in the sequence as： A1 vacancies （VA0 〉 X vacancies （Vx） 〉 X anti-sites （XA1） 〉 A1 anti- sites （Alx）. The point defect concentration of stoichio- metric A13Er is similar to that of L12-A13X（Sc, Zr）. The result suggests that the A1 vacancy （VA1） is a dominant point defect in L12-A13X（Sc, Zr, Er）. A simple parameter Hvx-HVA1 can be used for a rough estimation of the point defect concentrations in L12-A13X structure. Some rules of point defect concentrations for L12-A13X（Sc, Zr, Er） are also revealed.
基金financially supported by the German Research Foundation within the DFG Priority Program SPP 1386 (No.WE 2803/2-2)Federal Ministry for Economics Affairs and Energy (BMWI)(No. Nr 19U15006F)
文摘Doping- and alloying-induced point defects lead to mass and strain field fluctuations which can be used as effective strategies to decrease the lattice thermal conductivity and consequently boost the performance of thermoelectric materials. Herein, we report the effects of Sm and S co-doping on thermoelectric transport properties of copper antimony selenides in the temperature range of 300 K 〈 T〈 650 K. Through the Callaway model, it demonstrates that Sm and S co-doping induces strong mass differences and strain field fluctuations in Cu3SbSe4. The results prove that doping with suitable elements can increase point defect scattering of heat-carrying phonons, leading to a lower thermal conductivity and a better ther- moelectric performance. The highest figure of merit （ZT） of - 0.55 at 648 K is obtained for the Sm and S co-doped sample with nominal composition of Cu2.995Sm0.005Sb- Se3.95S0.05, which is about 55% increase compared to the ZT of pristine Cu3SbSe4.
基金supported by the National Natural Science Foundation of China(Grant Nos.61076079 and 61274092)the Doctoral Program Fund of the Ministry of Education of China(Grant No.20090203110012)the Major Program and State Key Program of the National Natural Science Foundation of China(GrantNo.60890191)
文摘Photoluminescence （PL） measurement is used to study the point defect distribution in a GaN terahertz Gunn diode, which is able to the degrade high-field transport characteristic during further device operation. PL, secondary ion mass spectroscopy （SIMS）, transmission electron microscope （TEM）, and capacitance-voltage （C-V） measurements are used to discuss the origin of point defects responsible for the yellow luminescence in structures. The point defect densities of about 1011 cm-2 in structures are extracted by analysis of C-V characterization. After thermal annealing treatment, diminishments of point defect densities in structures are efficiently demonstrated by PL and C-V results.
