In this study,perovskite-type La_(0.7)Ca_(0.3)Co_(0.3)Fe_(0.6)M_(0.1)O_(3-δ)(M=Cu,Zn)powders were synthesized using a scalable reverse co-precipitation method,presenting them as novel materials for oxygen transport m...In this study,perovskite-type La_(0.7)Ca_(0.3)Co_(0.3)Fe_(0.6)M_(0.1)O_(3-δ)(M=Cu,Zn)powders were synthesized using a scalable reverse co-precipitation method,presenting them as novel materials for oxygen transport membranes.The comprehensive study covered various aspects including oxygen permeability,crystal structure,conductivity,morphology,CO_(2) tolerance,and long-term regenerative durability with a focus on phase structure and composition.The membrane La_(0.7)Ca_(0.3)Co_(0.3)Fe_(0.6)M_(0.1)O_(3-δ)exhibited high oxygen permeation fluxes,reaching up to 0.88 and 0.64 mL·min^(−1)·cm^(−2) under air/He and air/CO_(2) gradients at 1173 K,respectively.After 1600 h of CO_(2) exposure,the perovskite structure remained intact,showcasing superior CO_(2) resistance.A combination of first principles simulations and experimental measurements was employed to deepen the understanding of Cu/Zn substitution effects on the structure,oxygen vacancy formation,and transport behavior of the membranes.These findings underscore the potential of this highly CO_(2)-tolerant membrane for applications in high-temperature oxygen separation.The enhanced insights into the oxygen transport mechanism contribute to the advancement of next-generation membrane materials.展开更多
Cubic silicon nitride(-Si_(3)N_(4))is superhard and one of the hardest materials after diamond and cubic boron nitride(cBN),but has higher thermal stability in an oxidizing environment than diamond,making it a competi...Cubic silicon nitride(-Si_(3)N_(4))is superhard and one of the hardest materials after diamond and cubic boron nitride(cBN),but has higher thermal stability in an oxidizing environment than diamond,making it a competitive candidate for technological applications in harsh conditions(e.g.,drill head and abrasives).Here,we report the high-pressure synthesis and characterization of the structural and mechanical properties of a γ-Si_(3)N_(4)/Hf_(3)N_(4) ceramic nanocomposite derived from single-phase amorphous silicon(Si)-hafnium(Hf)-nitrogen(N)precursor.The synthesis of the-Si_(3)N_(4)/Hf_(3)N_(4) nanocomposite is performed at~20 GPa and ca.1500 ℃ in a large volume multi anvil press.The structural evolution of the amorphous precursor and its crystallization to-Si_(3)N_(4)/Hf_(3)N_(4) nanocomposites under high pressures is assessed by the in situ synchrotron energy-dispersive X-ray diffraction(ED-XRD)measurements at~19.5 GPa in the temperature range of ca.1000-1900℃.The fracture toughness(K_(IC))of the two-phase nanocomposite amounts~6/6.9 MPa·m^(1/2) and is about 2 times that of single-phaseγ-Si_(3)N_(4),while its hardness of ca.30 GPa remains high.This work provides a reliable and feasible route for the synthesis of advanced hard and tough-Si_(3)N_(4)-based nanocomposites with excellent thermal stabililty.展开更多
The thermoelectric transport properties of Zr0.43Hf0.57 NiSn half-Heusler compounds were investigated for samples sintered with different spark plasma sintering(SPS)periods:8,32 and 72 min.By means of scanning transmi...The thermoelectric transport properties of Zr0.43Hf0.57 NiSn half-Heusler compounds were investigated for samples sintered with different spark plasma sintering(SPS)periods:8,32 and 72 min.By means of scanning transmission electron microscopy with a highangular annular dark-field detector(STEM-HAADF),it was found that sintering time affected the defect concentration,namely the amount of Ni interstitial atoms,and created locally ordered inclusions of full-Heusler phase.The structural information,phase composition and electrical transport properties could be consistently explained by the assumption that Ni interstitials give rise to an impurity band situated about 100 meV below the bottom of the conduction band via a self-doping behavior.The impurity band was found to merge with the conduction band for the sample with intermediate SPS time.The effect was ascribed to the gradual dissolution of full-Heusler phase inclusions and production of interstitial Ni defects,which eventually vanished for the sample with the longest sintering time.It was demonstrated that the modification of the density of states near the edge of the conduction band and enhanced overall charge carrier concentration provided by defect engineering led to overall 26%increase in the thermoelectric figure of merit(ZT)with respect to the other samples.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
A series of novel dense mixed conducting ceramic membranes based on K2NiF4-type(La1-xCax)2(Ni0.75Cu0.25)O4+δwas successfully prepared through a sol-gel route.Their chemical compatibility,oxygen permeability,CO and CO...A series of novel dense mixed conducting ceramic membranes based on K2NiF4-type(La1-xCax)2(Ni0.75Cu0.25)O4+δwas successfully prepared through a sol-gel route.Their chemical compatibility,oxygen permeability,CO and CO2 tolerance,and long-term CO2 resistance regarding phase composition and crystal structure at different atmospheres were studied.The results show that higher Ca contents in the material lead to the formation of CaCO3.A constant oxygen permeation flux of about 0.63 mL·min−1·cm−2 at 1173 K through a 0.65 mm thick membrane was measured for(La0.9Ca0.1)2(Ni0.75Cu0.25)O4+δ,using either helium or pure CO2 as sweep gas.Steady oxygen fluxes with no sign of deterioration of this membrane were observed with increasing CO2 concentration.The membrane showed excellent chemical stability towards CO2 for more than 1360 h and phase stability in presence of CO for 4 h at high temperature.In addition,this membrane did not deteriorate in a high-energy CO2 plasma.The present work demonstrates that this(La0.9Ca0.1)2(Ni0.75Cu0.25)O4+δmembrane is a promising chemically robust candidate for oxygen separation applications.展开更多
文摘In this study,perovskite-type La_(0.7)Ca_(0.3)Co_(0.3)Fe_(0.6)M_(0.1)O_(3-δ)(M=Cu,Zn)powders were synthesized using a scalable reverse co-precipitation method,presenting them as novel materials for oxygen transport membranes.The comprehensive study covered various aspects including oxygen permeability,crystal structure,conductivity,morphology,CO_(2) tolerance,and long-term regenerative durability with a focus on phase structure and composition.The membrane La_(0.7)Ca_(0.3)Co_(0.3)Fe_(0.6)M_(0.1)O_(3-δ)exhibited high oxygen permeation fluxes,reaching up to 0.88 and 0.64 mL·min^(−1)·cm^(−2) under air/He and air/CO_(2) gradients at 1173 K,respectively.After 1600 h of CO_(2) exposure,the perovskite structure remained intact,showcasing superior CO_(2) resistance.A combination of first principles simulations and experimental measurements was employed to deepen the understanding of Cu/Zn substitution effects on the structure,oxygen vacancy formation,and transport behavior of the membranes.These findings underscore the potential of this highly CO_(2)-tolerant membrane for applications in high-temperature oxygen separation.The enhanced insights into the oxygen transport mechanism contribute to the advancement of next-generation membrane materials.
基金Part of this research was carried out at PETRA III LVP at beamline P61B(beamtime I-20200434)and P02.1Shrikant Bhat and Robert Farla acknowedge the support from the Federal Ministry of Education and Research,Germany(BMBF,Nos.05K16WC2 and 05K13WC2)+2 种基金Wei Li and Leonore Wiehl also acknowledge the travel support from DESY.Zhaoju Yu thanks the National Natural Science Foundation of China(Nos.51872246 and 52061135102)for financial supportMarc Widenmeyer and Anke Weidenkaff are grateful for the financial support by the German Ministry of Education and Research(No.03SF0618B)Wei Li acknowledges the financial support from China Scholarship Council(No.201907040060).
文摘Cubic silicon nitride(-Si_(3)N_(4))is superhard and one of the hardest materials after diamond and cubic boron nitride(cBN),but has higher thermal stability in an oxidizing environment than diamond,making it a competitive candidate for technological applications in harsh conditions(e.g.,drill head and abrasives).Here,we report the high-pressure synthesis and characterization of the structural and mechanical properties of a γ-Si_(3)N_(4)/Hf_(3)N_(4) ceramic nanocomposite derived from single-phase amorphous silicon(Si)-hafnium(Hf)-nitrogen(N)precursor.The synthesis of the-Si_(3)N_(4)/Hf_(3)N_(4) nanocomposite is performed at~20 GPa and ca.1500 ℃ in a large volume multi anvil press.The structural evolution of the amorphous precursor and its crystallization to-Si_(3)N_(4)/Hf_(3)N_(4) nanocomposites under high pressures is assessed by the in situ synchrotron energy-dispersive X-ray diffraction(ED-XRD)measurements at~19.5 GPa in the temperature range of ca.1000-1900℃.The fracture toughness(K_(IC))of the two-phase nanocomposite amounts~6/6.9 MPa·m^(1/2) and is about 2 times that of single-phaseγ-Si_(3)N_(4),while its hardness of ca.30 GPa remains high.This work provides a reliable and feasible route for the synthesis of advanced hard and tough-Si_(3)N_(4)-based nanocomposites with excellent thermal stabililty.
基金financially supported by German Research Foundation Priority Programme 1386(No.WE 2803/2-2)the European Union under Marie Sklodowska-Curie Program(W.J.X.)。
文摘The thermoelectric transport properties of Zr0.43Hf0.57 NiSn half-Heusler compounds were investigated for samples sintered with different spark plasma sintering(SPS)periods:8,32 and 72 min.By means of scanning transmission electron microscopy with a highangular annular dark-field detector(STEM-HAADF),it was found that sintering time affected the defect concentration,namely the amount of Ni interstitial atoms,and created locally ordered inclusions of full-Heusler phase.The structural information,phase composition and electrical transport properties could be consistently explained by the assumption that Ni interstitials give rise to an impurity band situated about 100 meV below the bottom of the conduction band via a self-doping behavior.The impurity band was found to merge with the conduction band for the sample with intermediate SPS time.The effect was ascribed to the gradual dissolution of full-Heusler phase inclusions and production of interstitial Ni defects,which eventually vanished for the sample with the longest sintering time.It was demonstrated that the modification of the density of states near the edge of the conduction band and enhanced overall charge carrier concentration provided by defect engineering led to overall 26%increase in the thermoelectric figure of merit(ZT)with respect to the other samples.
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This work is part of the project “Plasma-induced CO2-conversion”(PiCK,project number:03SFK2S3B)and financially supported by the German Federal Ministry of Education and Research in the framework of the“Kopemikus projects for the Energiewende”.The authors are thankfUl to B.Sc.Laura Steinle(University of Stuttgart)for her assistance during the CO stability tests,and Christine Stefani and Prof.Dr.Robert Dinnebier(Max Planck Institute for Solid State Research,Stuttgart)for the in situ PXRD measurements,respectively.G.C.thanks Frank Hack and Dr.Angelika Veziridis for their kind support during experiments and discussions.
文摘A series of novel dense mixed conducting ceramic membranes based on K2NiF4-type(La1-xCax)2(Ni0.75Cu0.25)O4+δwas successfully prepared through a sol-gel route.Their chemical compatibility,oxygen permeability,CO and CO2 tolerance,and long-term CO2 resistance regarding phase composition and crystal structure at different atmospheres were studied.The results show that higher Ca contents in the material lead to the formation of CaCO3.A constant oxygen permeation flux of about 0.63 mL·min−1·cm−2 at 1173 K through a 0.65 mm thick membrane was measured for(La0.9Ca0.1)2(Ni0.75Cu0.25)O4+δ,using either helium or pure CO2 as sweep gas.Steady oxygen fluxes with no sign of deterioration of this membrane were observed with increasing CO2 concentration.The membrane showed excellent chemical stability towards CO2 for more than 1360 h and phase stability in presence of CO for 4 h at high temperature.In addition,this membrane did not deteriorate in a high-energy CO2 plasma.The present work demonstrates that this(La0.9Ca0.1)2(Ni0.75Cu0.25)O4+δmembrane is a promising chemically robust candidate for oxygen separation applications.