H. Charalambous, S. Jha, K. Vikrant, R. García, X. L. Phuah, Han Wang, Haiyan Wang, A. Mukherjee, T. Tsakalakos
Abstract The degradation mechanism of flash sintering 8 mol% yttria stabilized zirconia, which results in poor densification and crumbling of the samples under direct current, was investigated. Microstructure analysis revealed highly strained grain boundaries and nanopore formation at the grain boundaries after flash sintering with a direct current. A higher current density experiment gave a varied microstructure with internal grain dimpling near the negative electrode, a highly porous “swiss-cheese” like microstructure in the pellet interior, and melting and recrystallization near the positive electrode. These characteristics were not observed under an alternating current. Phase field simulations predicted an oxygen vacancy buildup and potential reduced phases along the grain boundaries, which lead to the depletion of free holes and dramatic increase of free electrons. This results in high tensile stresses at the grain boundaries, which explains the degradation along the grain boundaries after flash sintering under direct current.
{"title":"Electric Field-Induced Grain Boundary Degradation Mechanism in Yttria Stabilized Zirconia","authors":"H. Charalambous, S. Jha, K. Vikrant, R. García, X. L. Phuah, Han Wang, Haiyan Wang, A. Mukherjee, T. Tsakalakos","doi":"10.2139/ssrn.3831032","DOIUrl":"https://doi.org/10.2139/ssrn.3831032","url":null,"abstract":"Abstract The degradation mechanism of flash sintering 8 mol% yttria stabilized zirconia, which results in poor densification and crumbling of the samples under direct current, was investigated. Microstructure analysis revealed highly strained grain boundaries and nanopore formation at the grain boundaries after flash sintering with a direct current. A higher current density experiment gave a varied microstructure with internal grain dimpling near the negative electrode, a highly porous “swiss-cheese” like microstructure in the pellet interior, and melting and recrystallization near the positive electrode. These characteristics were not observed under an alternating current. Phase field simulations predicted an oxygen vacancy buildup and potential reduced phases along the grain boundaries, which lead to the depletion of free holes and dramatic increase of free electrons. This results in high tensile stresses at the grain boundaries, which explains the degradation along the grain boundaries after flash sintering under direct current.","PeriodicalId":237724,"journal":{"name":"EngRN: Materials Chemistry (Topic)","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122580815","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lu Zhang, H. Tian, S. Dong, Dong Yang, Xiaoguang Li, J. Li, Jianqi Li, Huaixin Yang
Abstract The coexistence and coupling between alternatively stacked layers with different functional properties often give rise to exotic physical phenomena, such as high-temperature superconductivity, multiferroic behavior, and giant thermoelectric performance, which are tightly linked with the intrinsic microstructures. Here we unambiguously uncover the structural modulations in multiferroic Bi4.2K0.8Fe2O9+δ (BKFO) nanobelts with a magnetoelectric–dielectric superlattice by scanning transmission electron microscopy (STEM). The octahedrons in the perovskite layers are identified as FeO6 and the ordered arrangements of the Bi and K cations are clearly determined. Quantitative measurements of the positions of the Bi columns indicate that the displacive modulations can be decomposed into a transverse wave and a longitudinal wave, whose amplitudes and phases are layer-dependent. This study may help to understand and optimize the magnetoelectric coupling effect in BKFO.
{"title":"Direct Observation of Modulation Structure in Room Temperature Multiferroic Bi 4.2K 0.8Fe 2O 9+δ","authors":"Lu Zhang, H. Tian, S. Dong, Dong Yang, Xiaoguang Li, J. Li, Jianqi Li, Huaixin Yang","doi":"10.2139/ssrn.3708675","DOIUrl":"https://doi.org/10.2139/ssrn.3708675","url":null,"abstract":"Abstract The coexistence and coupling between alternatively stacked layers with different functional properties often give rise to exotic physical phenomena, such as high-temperature superconductivity, multiferroic behavior, and giant thermoelectric performance, which are tightly linked with the intrinsic microstructures. Here we unambiguously uncover the structural modulations in multiferroic Bi4.2K0.8Fe2O9+δ (BKFO) nanobelts with a magnetoelectric–dielectric superlattice by scanning transmission electron microscopy (STEM). The octahedrons in the perovskite layers are identified as FeO6 and the ordered arrangements of the Bi and K cations are clearly determined. Quantitative measurements of the positions of the Bi columns indicate that the displacive modulations can be decomposed into a transverse wave and a longitudinal wave, whose amplitudes and phases are layer-dependent. This study may help to understand and optimize the magnetoelectric coupling effect in BKFO.","PeriodicalId":237724,"journal":{"name":"EngRN: Materials Chemistry (Topic)","volume":"8 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127808753","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
O. Yıldırım, A. Borzì, C. Falub, H. Rohrmann, D. Jaeger, Marco Rechsteiner, D. Schneider, A. Neels, Hans Josef Hug, Miguel Marioni
Abstract High-quality epitaxial Pt films are usually grown by molecular beam evaporation (MBE) techniques, where the deposited atoms reach the substrate with typical thermal energies. To obtain a good epitaxial growth, the substrate is kept at elevated temperatures ranging between few hundred to thousand degrees. While the epitaxial quality improves at higher substrate temperatures, above a critical temperature Volmer-Weber growth mode starts and causes a rough film morphology. Here, we use a new type of facing target cathode (FTC) to grow Pt onto Al 2 O 3 (0001) substrates. In contrast to conventional sputtering sources, FTC sources provide adatoms with lower kinetic energies, but higher growth rates compared to MBE. In this study, the crystal structure of Pt films is compared for different substrate temperatures. Using FTC, flat Pt films with low strain and a morphology that is either nanocrystalline or highly epitaxial could be grown through proper choice of substrate temperature.
{"title":"Tuning the Microstructure of the Pt Layers Grown on Al 2O 3 (0001) by Different Sputtering Methods","authors":"O. Yıldırım, A. Borzì, C. Falub, H. Rohrmann, D. Jaeger, Marco Rechsteiner, D. Schneider, A. Neels, Hans Josef Hug, Miguel Marioni","doi":"10.2139/ssrn.3742929","DOIUrl":"https://doi.org/10.2139/ssrn.3742929","url":null,"abstract":"Abstract High-quality epitaxial Pt films are usually grown by molecular beam evaporation (MBE) techniques, where the deposited atoms reach the substrate with typical thermal energies. To obtain a good epitaxial growth, the substrate is kept at elevated temperatures ranging between few hundred to thousand degrees. While the epitaxial quality improves at higher substrate temperatures, above a critical temperature Volmer-Weber growth mode starts and causes a rough film morphology. Here, we use a new type of facing target cathode (FTC) to grow Pt onto Al 2 O 3 (0001) substrates. In contrast to conventional sputtering sources, FTC sources provide adatoms with lower kinetic energies, but higher growth rates compared to MBE. In this study, the crystal structure of Pt films is compared for different substrate temperatures. Using FTC, flat Pt films with low strain and a morphology that is either nanocrystalline or highly epitaxial could be grown through proper choice of substrate temperature.","PeriodicalId":237724,"journal":{"name":"EngRN: Materials Chemistry (Topic)","volume":"96 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127159999","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The plastic deformation behavior of single crystals of Fe3Ge with the L12 structure has been investigated at room temperature as a function of crystal orientation by micropillar compression tests. In addition to slip on (010), slip on (111) is observed to occur in Fe3Ge for the first time. The CRSS (critical resolved shear stress) for (111)[10‾1] slip, estimated by extrapolating the size-dependent strength variation to the ‘bulk’ size, is ~240 MPa, which is almost 6 times that (~40 MPa) for (010)[101] slip similarly estimated. The dissociation scheme for the superlattice dislocation with b=[10‾1] is confirmed to be of the APB (anti-phase boundary)-type both on (010) and on (111), in contrast to the previous prediction for the SISF (superlattice intrinsic stacking fault) scheme on (111) because of the expected APB instability. While superlattice dislocations do not have any preferential directions to align when gliding on (010) (indicative of low frictional stress at room temperature), the alignment of superlattice dislocations along their screw orientation is observed when gliding on (111). This is proved to be due to thermally-activated cross-slip to form Kear-Wilsdorf locks, indicative of the occurrence of yield stress anomaly that is observed in many other L12 compounds such as Ni3Al. Some important deformation characteristics expected to occur in Fe3Ge (such as the absence of SISF-couple dissociation and the occurrence of yield stress anomaly) will be discussed in the light of the experimental results obtained (APB energies on (111) and (010) and CRSS values for slip on (111) and (010)).
{"title":"Micropillar Compression Deformation of Single Crystals of Fe 3Ge with the L1 2 Structure","authors":"Zhenghao Chen, H. Inui","doi":"10.2139/ssrn.3762209","DOIUrl":"https://doi.org/10.2139/ssrn.3762209","url":null,"abstract":"The plastic deformation behavior of single crystals of Fe3Ge with the L12 structure has been investigated at room temperature as a function of crystal orientation by micropillar compression tests. In addition to slip on (010), slip on (111) is observed to occur in Fe3Ge for the first time. The CRSS (critical resolved shear stress) for (111)[10‾1] slip, estimated by extrapolating the size-dependent strength variation to the ‘bulk’ size, is ~240 MPa, which is almost 6 times that (~40 MPa) for (010)[101] slip similarly estimated. The dissociation scheme for the superlattice dislocation with b=[10‾1] is confirmed to be of the APB (anti-phase boundary)-type both on (010) and on (111), in contrast to the previous prediction for the SISF (superlattice intrinsic stacking fault) scheme on (111) because of the expected APB instability. While superlattice dislocations do not have any preferential directions to align when gliding on (010) (indicative of low frictional stress at room temperature), the alignment of superlattice dislocations along their screw orientation is observed when gliding on (111). This is proved to be due to thermally-activated cross-slip to form Kear-Wilsdorf locks, indicative of the occurrence of yield stress anomaly that is observed in many other L12 compounds such as Ni3Al. Some important deformation characteristics expected to occur in Fe3Ge (such as the absence of SISF-couple dissociation and the occurrence of yield stress anomaly) will be discussed in the light of the experimental results obtained (APB energies on (111) and (010) and CRSS values for slip on (111) and (010)).","PeriodicalId":237724,"journal":{"name":"EngRN: Materials Chemistry (Topic)","volume":"114 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115141606","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Guojing Wang, Fengqi Wang, Shuo Liu, Mingyang Li, Mingzheng Xie, Zhilong Yang, Yunjie Xiang, Shasha Lv, W. Han
To overcome the recombination issue of photocarriers, TiO2 quantum dots (QDs, nanoparticles in a few nanometers) were used to form heterojunctions with graphene oxide nanosheets. This combination has significantly enhanced the photocatalytic activity by providing more active reaction sites at the nanoscale surface and suppressing photocarrier recombination through fast separating the photocarriers by the internal electric field in the TiO2/graphene oxide heterojunctions. The enhancement in photocatalytic activity has been evidenced by the improved hydrogen generation rate in photoelectrochemical water splitting, about 30% higher than that of bare TiO2 QDs in the same situation. Moreover, the TiO2/graphene oxide composite also exhibits a lower flat band potential, which means a higher reducing potential of photo-excited electrons.
{"title":"Construction of Heterojuncted Photocatalyst with TiO 2 Quantum Dots and Graphene Oxide Nanosheets for High-Efficient Photocatalysis","authors":"Guojing Wang, Fengqi Wang, Shuo Liu, Mingyang Li, Mingzheng Xie, Zhilong Yang, Yunjie Xiang, Shasha Lv, W. Han","doi":"10.2139/ssrn.3737310","DOIUrl":"https://doi.org/10.2139/ssrn.3737310","url":null,"abstract":"To overcome the recombination issue of photocarriers, TiO2 quantum dots (QDs, nanoparticles in a few nanometers) were used to form heterojunctions with graphene oxide nanosheets. This combination has significantly enhanced the photocatalytic activity by providing more active reaction sites at the nanoscale surface and suppressing photocarrier recombination through fast separating the photocarriers by the internal electric field in the TiO2/graphene oxide heterojunctions. The enhancement in photocatalytic activity has been evidenced by the improved hydrogen generation rate in photoelectrochemical water splitting, about 30% higher than that of bare TiO2 QDs in the same situation. Moreover, the TiO2/graphene oxide composite also exhibits a lower flat band potential, which means a higher reducing potential of photo-excited electrons.","PeriodicalId":237724,"journal":{"name":"EngRN: Materials Chemistry (Topic)","volume":"78 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117306803","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-10-23DOI: 10.15587/1729-4061.2020.214507
N. Korovnikova, O. Dubyna, V. Oliinik, Yana Svishchova
The studies reported here have made it possible to determine the optimal ways of fire protection, in which the samples of modified complexite have reduced flammability. The sample with the ions of molybdenum (VI), treated with phosphoric acid, had the highest magnitude of oxygen index among five modified samples of the fiber. This is the most fire-protected sample, which contains three types of flame retardants: nitrogen (amidoxime groups of complexite, phosphorus (treatment with phosphoric acid) and molybdenum (VI). The obtained data indicate the chemical interaction of flame retardant with complexite. The morphology of fibers and the process of their destruction are influenced by the introduction of flame retardants. Scanning electronic microphotographs show the existence of a morphological change of the surface at modification of the complexite samples with flame retardant. The introduction of flame retardant into complexite affects the process of thermal destruction of the samples in the air and argon media. At the same time, the introduction of molybdenum (VI) significantly reduces the thermal stability of fibers. It is likely that processes of thermal destruction can be catalyzed by metals both in the air medium and in the argon medium. The magnitudes of order of reaction of thermal decomposition at the transition from a fiber sample treated only with acids to the samples of complexite containing molybdenum (VI) decreases up to 0.38. At the same time, the values of activation energies E, kcal/mol, and the enthalpy of the process of thermal destruction of complexite DH, kcal/mole also decrease. The mechanical properties of fibers at the introduction of flame retardants into the fiber composition change insignificantly. Depending on the composition of flame retardants, rupture load decreases by 6–11 %, lengthening of the samples decreases by 6–16 %. Thus, there are some grounds to suggest that it is possible to create fibrous materials based on cellulose with predetermined properties of reduced flammability.
{"title":"Chemical Cellulose-Based Fibers of Decreased Flammability","authors":"N. Korovnikova, O. Dubyna, V. Oliinik, Yana Svishchova","doi":"10.15587/1729-4061.2020.214507","DOIUrl":"https://doi.org/10.15587/1729-4061.2020.214507","url":null,"abstract":"The studies reported here have made it possible to determine the optimal ways of fire protection, in which the samples of modified complexite have reduced flammability. The sample with the ions of molybdenum (VI), treated with phosphoric acid, had the highest magnitude of oxygen index among five modified samples of the fiber. This is the most fire-protected sample, which contains three types of flame retardants: nitrogen (amidoxime groups of complexite, phosphorus (treatment with phosphoric acid) and molybdenum (VI). The obtained data indicate the chemical interaction of flame retardant with complexite. The morphology of fibers and the process of their destruction are influenced by the introduction of flame retardants. Scanning electronic microphotographs show the existence of a morphological change of the surface at modification of the complexite samples with flame retardant. The introduction of flame retardant into complexite affects the process of thermal destruction of the samples in the air and argon media. At the same time, the introduction of molybdenum (VI) significantly reduces the thermal stability of fibers. It is likely that processes of thermal destruction can be catalyzed by metals both in the air medium and in the argon medium. The magnitudes of order of reaction of thermal decomposition at the transition from a fiber sample treated only with acids to the samples of complexite containing molybdenum (VI) decreases up to 0.38. At the same time, the values of activation energies E, kcal/mol, and the enthalpy of the process of thermal destruction of complexite DH, kcal/mole also decrease. The mechanical properties of fibers at the introduction of flame retardants into the fiber composition change insignificantly. Depending on the composition of flame retardants, rupture load decreases by 6–11 %, lengthening of the samples decreases by 6–16 %. Thus, there are some grounds to suggest that it is possible to create fibrous materials based on cellulose with predetermined properties of reduced flammability.","PeriodicalId":237724,"journal":{"name":"EngRN: Materials Chemistry (Topic)","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116079605","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-10-22DOI: 10.15587/1729-4061.2020.213892
B. Pospelov, V. Kovrehin, E. Rybka, O. Krainiukov, O. Petukhova, T. Butenko, Pavlo Borodych, I. Morozov, O. Horbov, Inna Hrachova
A method has been developed to detect hazardous conditions of contaminated air in urban areas in real time for an arbitrary number of pollutants. The method is based on restoring the hidden dynamics of the combined risk of instantaneous action on the basis of the current measurements of the concentration of pollutants at the point of control. Other data on current conditions at the point of control are not used in the developed method. Therefore, the method, in contrast to known analogs, is universal and can be applied for arbitrary conditions and control points. At the same time, the restored dynamics of the level of the combined risk of instantaneous action makes it possible not only to identify dangerous conditions relating to contaminated atmospheric air but, on the basis of the current recurrence of combined risk levels, to assess the probability of detecting and predicting dangerous levels in the combined risk of instantaneous action in real time at the predefined point of control. Using the developed method at several control points in an arbitrary area would make it possible to determine the space-time distribution of the levels of the combined risk of instantaneous action of atmospheric pollution on the population within a territory. Experimental measurements of the concentration of formaldehyde, ammonia, and nitrogen dioxide in the atmosphere have been performed at the point of control within an industrial city with an air pollution level of 37 units on the AQC scale (USA). Based on the measurements, the method has been confirmed to be feasible. It was established that at the time of a credible dangerous event, the level of the combined risk of instantaneous action was approximately 10 -3 with a single probability of this level. This level of the combined risk is about 10 5 times higher than the corresponding upper limit of permissible individual risk. It is shown that the maximum forecast time of the dangerous level of combined risk under the considered conditions does not exceed 18 hours
{"title":"Development of a Method for Detecting Dangerous States of Polluted Atmospheric Air Based on the Current Recurrence of the Combined Risk","authors":"B. Pospelov, V. Kovrehin, E. Rybka, O. Krainiukov, O. Petukhova, T. Butenko, Pavlo Borodych, I. Morozov, O. Horbov, Inna Hrachova","doi":"10.15587/1729-4061.2020.213892","DOIUrl":"https://doi.org/10.15587/1729-4061.2020.213892","url":null,"abstract":"A method has been developed to detect hazardous conditions of contaminated air in urban areas in real time for an arbitrary number of pollutants. The method is based on restoring the hidden dynamics of the combined risk of instantaneous action on the basis of the current measurements of the concentration of pollutants at the point of control. Other data on current conditions at the point of control are not used in the developed method. Therefore, the method, in contrast to known analogs, is universal and can be applied for arbitrary conditions and control points. At the same time, the restored dynamics of the level of the combined risk of instantaneous action makes it possible not only to identify dangerous conditions relating to contaminated atmospheric air but, on the basis of the current recurrence of combined risk levels, to assess the probability of detecting and predicting dangerous levels in the combined risk of instantaneous action in real time at the predefined point of control. Using the developed method at several control points in an arbitrary area would make it possible to determine the space-time distribution of the levels of the combined risk of instantaneous action of atmospheric pollution on the population within a territory. Experimental measurements of the concentration of formaldehyde, ammonia, and nitrogen dioxide in the atmosphere have been performed at the point of control within an industrial city with an air pollution level of 37 units on the AQC scale (USA). Based on the measurements, the method has been confirmed to be feasible. It was established that at the time of a credible dangerous event, the level of the combined risk of instantaneous action was approximately 10 -3 with a single probability of this level. This level of the combined risk is about 10 5 times higher than the corresponding upper limit of permissible individual risk. It is shown that the maximum forecast time of the dangerous level of combined risk under the considered conditions does not exceed 18 hours","PeriodicalId":237724,"journal":{"name":"EngRN: Materials Chemistry (Topic)","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129077230","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Sypek, S. Vijayan, I. Bakst, Shuyang Xiao, M. Kramer, P. Canfield, M. Aindow, C. Weinberger, S. Lee
Micropillar compression experiments on [001]-oriented CaFe 2 As 2 single crystals have recently revealed the existence of superelasticity with a remarkably high elastic limit over 10%. The collapsed tetragonal phase transition, which is a uni-axial contraction process in which As-As bonds are formed across an intervening Ca-plane, is the main mechanism of superelasticity. Usually, superelasticity and the related structural transitions are affected strongly by both the microstructure and the temperature. In this study, therefore, we investigated how the microstructure and temperature affect the superelasticity of [001]-oriented CaFe 2 As 2 micropillars cut from solution-grown single crystals, by performing a combination of in-situ cryogenic micromechanical testing and transmission electron microscopy studies. Our results show that the microstructure of CaFe 2 As 2 is influenced strongly by the crystal growth conditions and by subsequent heat treatment. The presence of Ca and As vacancies and FeAs nanoprecipitates affect the mechanical behavior significantly. In addition, the onset stress for the collapsed tetragonal transition decreases gradually as the temperature decreases. These experimental results are discussed primarily in terms of the formation of As-As bonds, which is the essential feature of this mechanism for superelasticity. Our research outcomes provide a more fundamental understanding of the superelasticity exhibited by CaFe 2 As 2 under uni-axial compression.
最近在[001]取向的caf2as2单晶上进行的微柱压缩实验揭示了超弹性的存在，其弹性极限非常高，超过10%。崩塌的四方相变是一种单轴收缩过程，在此过程中，As-As键在中间的ca平面上形成，是超弹性的主要机制。通常，超弹性和相关的结构转变受微观结构和温度的强烈影响。因此，在本研究中，我们通过原位低温微力学测试和透射电镜研究相结合的方法，研究了微观结构和温度如何影响从溶液生长单晶中切割出来的[001]取向CaFe 2 As 2微柱的超弹性。结果表明，caf2as2的微观结构受晶体生长条件和后续热处理的强烈影响。Ca、As空位和FeAs纳米沉淀物的存在显著影响了材料的力学行为。此外，随着温度的降低，坍塌的四方相变的起始应力逐渐减小。这些实验结果主要是根据As-As键的形成来讨论的，这是这种超弹性机制的基本特征。我们的研究结果为caf2as 2在单轴压缩下表现出的超弹性提供了更基本的理解。
{"title":"Uniaxial Compression of [001]-Oriented CaFe 2As 2 Single Crystals: The Effects of Microstructure and Temperature on the Superelasticity, Part I: Experimental Observations","authors":"J. Sypek, S. Vijayan, I. Bakst, Shuyang Xiao, M. Kramer, P. Canfield, M. Aindow, C. Weinberger, S. Lee","doi":"10.2139/ssrn.3693596","DOIUrl":"https://doi.org/10.2139/ssrn.3693596","url":null,"abstract":"Micropillar compression experiments on [001]-oriented CaFe 2 As 2 single crystals have recently revealed the existence of superelasticity with a remarkably high elastic limit over 10%. The collapsed tetragonal phase transition, which is a uni-axial contraction process in which As-As bonds are formed across an intervening Ca-plane, is the main mechanism of superelasticity. Usually, superelasticity and the related structural transitions are affected strongly by both the microstructure and the temperature. In this study, therefore, we investigated how the microstructure and temperature affect the superelasticity of [001]-oriented CaFe 2 As 2 micropillars cut from solution-grown single crystals, by performing a combination of in-situ cryogenic micromechanical testing and transmission electron microscopy studies. Our results show that the microstructure of CaFe 2 As 2 is influenced strongly by the crystal growth conditions and by subsequent heat treatment. The presence of Ca and As vacancies and FeAs nanoprecipitates affect the mechanical behavior significantly. In addition, the onset stress for the collapsed tetragonal transition decreases gradually as the temperature decreases. These experimental results are discussed primarily in terms of the formation of As-As bonds, which is the essential feature of this mechanism for superelasticity. Our research outcomes provide a more fundamental understanding of the superelasticity exhibited by CaFe 2 As 2 under uni-axial compression.","PeriodicalId":237724,"journal":{"name":"EngRN: Materials Chemistry (Topic)","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127931655","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Luo, Wei Peng, Yang Zhao, J. Lan, Ming Peng, Jiuhui Han, Hongju Li, Yongwen Tan
Abstract The development of earth-abundant, non-noble, high-performance hydrogen evolution reaction (HER) electrocatalysts is still a highly challenging but vitally important issue for energy conversion system. Herein, we reported a self-supported Mo modified hierarchical nanoporous Cu as an efficient electrocatalyst for hydrogen evolution. The optimized nanoporous Cu-Mo electrocatalysts with extremely dilute Mo content exhibits a high HER activity with a negligible onset potential, a small Tafel slope, and an excellent durability in alkaline solution. The dealloying process provides nanoporous Cu-Mo electrocatalysts a unique three-dimensional interconnected bicontinuous nanoporous architecture, which can not only offer high-density catalytic active sites for HER, but also accelerate the desorption of hydrogen molecule from catalysts surface. Density functional theory (DFT) calculations reveal that the introducing of Mo into Cu matrix can accelerate water adsorption and dissociation and optimize adsorption-desorption energetics of H intermediates, thus improving the intrinsic HER activity of nanoporous Cu-Mo electrocatalysts.
{"title":"Dilute Molybdenum Atoms Embedded in Hierarchical Nanoporous Copper Accelerate the Hydrogen Evolution Reaction","authors":"M. Luo, Wei Peng, Yang Zhao, J. Lan, Ming Peng, Jiuhui Han, Hongju Li, Yongwen Tan","doi":"10.2139/ssrn.3661930","DOIUrl":"https://doi.org/10.2139/ssrn.3661930","url":null,"abstract":"Abstract The development of earth-abundant, non-noble, high-performance hydrogen evolution reaction (HER) electrocatalysts is still a highly challenging but vitally important issue for energy conversion system. Herein, we reported a self-supported Mo modified hierarchical nanoporous Cu as an efficient electrocatalyst for hydrogen evolution. The optimized nanoporous Cu-Mo electrocatalysts with extremely dilute Mo content exhibits a high HER activity with a negligible onset potential, a small Tafel slope, and an excellent durability in alkaline solution. The dealloying process provides nanoporous Cu-Mo electrocatalysts a unique three-dimensional interconnected bicontinuous nanoporous architecture, which can not only offer high-density catalytic active sites for HER, but also accelerate the desorption of hydrogen molecule from catalysts surface. Density functional theory (DFT) calculations reveal that the introducing of Mo into Cu matrix can accelerate water adsorption and dissociation and optimize adsorption-desorption energetics of H intermediates, thus improving the intrinsic HER activity of nanoporous Cu-Mo electrocatalysts.","PeriodicalId":237724,"journal":{"name":"EngRN: Materials Chemistry (Topic)","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125173259","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lu Jiang, V. Radmilović, J. Sabisch, Liang Qi, A. Minor, D. Chrzan, M. Asta
Twinning plays an important role in governing the balance between strength and ductility in hexagonal-close-packed (HCP) metals. Here, we report a combined experimental and theoretical study of twin nucleation from a single
{"title":"Twin Nucleation From a Single (c+a) Disclocation in Hexagonal Close-packed Crystals","authors":"Lu Jiang, V. Radmilović, J. Sabisch, Liang Qi, A. Minor, D. Chrzan, M. Asta","doi":"10.2139/ssrn.3659800","DOIUrl":"https://doi.org/10.2139/ssrn.3659800","url":null,"abstract":"Twinning plays an important role in governing the balance between strength and ductility in hexagonal-close-packed (HCP) metals. Here, we report a combined experimental and theoretical study of twin nucleation from a single","PeriodicalId":237724,"journal":{"name":"EngRN: Materials Chemistry (Topic)","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130014820","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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