Rare-earth tantalates and niobates(REjTaO7 and REjNbO7)have been considered as promising candidate thermal barrier coating(TBC)materials in next generation gas-turbine engines due to their ultra-low thermal conductivi...Rare-earth tantalates and niobates(REjTaO7 and REjNbO7)have been considered as promising candidate thermal barrier coating(TBC)materials in next generation gas-turbine engines due to their ultra-low thermal conductivity and better thermal stability than yttria-stabilized zirconia(YSZ).However,the low Vickers hardness and toughness are the main shortcomings of RE;TaO-and REjNbOr that limit their applications as TBC materials.To increase the hardness,high entropy(Yu3Ybu3Er/3)sTaOr,(Y13YbnErns)NbO,and(Sm1/6Eu1/6Y 1/6Yb1/6Lu1/6Er1/6)3(Nb1/2Ta1/2)O7 are designed and synthesized in this study.These high entropy ceramics exhibit high Vickers hardness(10.912.0 GPa),close thermal expansion coefficients to that of single-principal-component RE3TaO,and RE;NbO,(7.9×10^-6-10.8×10-6 C-1 at room temperature),good phase stability,and good chemical compatibility with thermally grown Al2O3,which make them promising for applications as candidate TBC materials.展开更多
Thermal barrier coating(TBC)materials perform an increasingly important role in the thermal or chemical protection of hot components in a gas turbine.In this study,a novel high entropy hafnate(Y_(0.2)Gd_(0.2)Dy_(0.2)E...Thermal barrier coating(TBC)materials perform an increasingly important role in the thermal or chemical protection of hot components in a gas turbine.In this study,a novel high entropy hafnate(Y_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Hf_(2)O_(7) was synthesized by solution combustion method and investigated as a potential TBC layer.The as-synthesized(Y_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Hf_(2)O_(7) possesses a pure single disordered fluorite phase with a highly homogeneous distribution of rare earth(RE)cations,exhibiting prominent phase stability and excellent chemical compatibility with Al_(2)O_(3) even at 1300°C.Moreover,(Y_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Hf_(2)O_(7) demonstrates a more sluggish grain growth rate than Y_(2)Hf_(2)O_(7).The thermal conductivity of(Y_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Hf_(2)O_(7)(0.73-0.93 W m^(-1)K^(-1))is smaller than those of components RE_(2)Hf_(2)O_(7) and many high entropy TBC materials.Beside,the calculated thermal expansion coefficient(TEC)of(Y_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Hf_(2)O_(7)(10.68×10^(-6)/K,1100°C)is smaller than that of yttriastabilized zirconia(YSZ).Based on the results of this work,(Y_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Hf_(2)O_(7) is suitable for the next generation TBC materials with outstanding properties.展开更多
The discovery of ferroelectricity in hafnium oxide (HfO_(2)) based thin films in 2011 renewed the interest inferroelectrics. These new ferroelectrics possess completely different crystal morphology with conventional p...The discovery of ferroelectricity in hafnium oxide (HfO_(2)) based thin films in 2011 renewed the interest inferroelectrics. These new ferroelectrics possess completely different crystal morphology with conventional perovskiteferroelectrics, and present more robust ferroelectric properties upon aggressive scaling and compatibility withstandard integrated circuit fabrication processes. In this article, we give a brief introduction to the conventionalferroelectric memories, then review the basic properties, recent progress, and memory applications of theseHfO_(2)-based ferroelectrics.展开更多
Environmental barrier coatings(EBCs)with excellent chemical resistance and good high-temperature stability are of great significance for their applications in next-generation turbine engines.In this work,a new type of...Environmental barrier coatings(EBCs)with excellent chemical resistance and good high-temperature stability are of great significance for their applications in next-generation turbine engines.In this work,a new type of high-entropy fluorite-structured oxide(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2))O_(2−δ)(HEFO-1)with different Ti^(4+)contents were successfully synthesized.Minor addition of Ti4+could be dissolved into a high-entropy lattice to maintain the structure stable,effectively reducing the phase formation temperature and promoting the shrinkage of bulk samples.Heat treatment experiments showed that all the samples remained a single phase after annealing at 1200–1600℃for 6 h.In addition,high-entropy(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2)Ti_(0.2x)O_(2−δ)demonstrated great resistance to calcium–magnesium–alumina–silicate(CMAS)thermochemical corrosion.When the content of Ti was increased to x=0.5,the average thickness of the reaction layer was about 10.5µm after being corroded at 1300℃for 10 h.This study reveals that high-entropy(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2)Ti_(0.2x)O_(2−δ)is expected to be a candidate for the next-generation EBC materials with graceful resistance to CMAS corrosion.展开更多
Perovskite structure La_（0.75）Sr_（0.25）Cr_（0.5）Mn_（0.5）O_（3-δ）（LSCM） cathode with unique structure can electrolyze CO_2 to CO in solid oxide electrolysers（SOEs）.However,the cell performance is restricte...Perovskite structure La_（0.75）Sr_（0.25）Cr_（0.5）Mn_（0.5）O_（3-δ）（LSCM） cathode with unique structure can electrolyze CO_2 to CO in solid oxide electrolysers（SOEs）.However,the cell performance is restricted by its electro-catalysis activity.In this work,fluorite structure nanoparticles（CeO_（2-δ）） are impregnated on LSCM cathode to improve the electro-catalysis activity.X-ray diffraction（XRD）,scanning electron microscope（SEM） and X-ray photoelectron spectroscopy（XPS） together approve that the fluorite structure nanoparticles are uniformly distributed on the perovskite structure LSCM scaffold.Electrochemical measurements illustrate that direct CO_2 electrolysis with 10%mol CeO_（2-δ） impregnated LSCM cathode exhibits excellent performance for current density（0.5 A×cm^（-2）） and current efficiency（～95%） at 800 ℃ under 1.6 V.It is believed that the enhanced performance of directed CO_2 electrolysis may be due to the synergetic effect of fluorite structure CeO_（2-δ） nanoparticles and perovskite structure LSCM ceramic electrode.展开更多
基金This study was financially supported by the National Natural Science Foundation of China(Nos.51672064 and 51972089).
文摘Rare-earth tantalates and niobates(REjTaO7 and REjNbO7)have been considered as promising candidate thermal barrier coating(TBC)materials in next generation gas-turbine engines due to their ultra-low thermal conductivity and better thermal stability than yttria-stabilized zirconia(YSZ).However,the low Vickers hardness and toughness are the main shortcomings of RE;TaO-and REjNbOr that limit their applications as TBC materials.To increase the hardness,high entropy(Yu3Ybu3Er/3)sTaOr,(Y13YbnErns)NbO,and(Sm1/6Eu1/6Y 1/6Yb1/6Lu1/6Er1/6)3(Nb1/2Ta1/2)O7 are designed and synthesized in this study.These high entropy ceramics exhibit high Vickers hardness(10.912.0 GPa),close thermal expansion coefficients to that of single-principal-component RE3TaO,and RE;NbO,(7.9×10^-6-10.8×10-6 C-1 at room temperature),good phase stability,and good chemical compatibility with thermally grown Al2O3,which make them promising for applications as candidate TBC materials.
基金financially supported by the National Natural Science Foundation of China (Nos. 51872234, 51502242, 51432008, 51802244, and 51821091)the Key R&D Program of Shaanxi Provence (No. 2019ZDLGY04-02)。
文摘Thermal barrier coating(TBC)materials perform an increasingly important role in the thermal or chemical protection of hot components in a gas turbine.In this study,a novel high entropy hafnate(Y_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Hf_(2)O_(7) was synthesized by solution combustion method and investigated as a potential TBC layer.The as-synthesized(Y_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Hf_(2)O_(7) possesses a pure single disordered fluorite phase with a highly homogeneous distribution of rare earth(RE)cations,exhibiting prominent phase stability and excellent chemical compatibility with Al_(2)O_(3) even at 1300°C.Moreover,(Y_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Hf_(2)O_(7) demonstrates a more sluggish grain growth rate than Y_(2)Hf_(2)O_(7).The thermal conductivity of(Y_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Hf_(2)O_(7)(0.73-0.93 W m^(-1)K^(-1))is smaller than those of components RE_(2)Hf_(2)O_(7) and many high entropy TBC materials.Beside,the calculated thermal expansion coefficient(TEC)of(Y_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Hf_(2)O_(7)(10.68×10^(-6)/K,1100°C)is smaller than that of yttriastabilized zirconia(YSZ).Based on the results of this work,(Y_(0.2)Gd_(0.2)Dy_(0.2)Er_(0.2)Yb_(0.2))_(2)Hf_(2)O_(7) is suitable for the next generation TBC materials with outstanding properties.
基金This work was supported by the National Key Basic R&D Program of China(Nos.2016YFA0200400 and 2018YFC2001202)the National Natural Science Foundation of China(Nos.U20A20168,61874065,and 51861145202)the Research Fund from Tsinghua University Initiative Scientific Research Program,the Beijing Innovation Center for Future Chip,and the Tsinghua-Fuzhou Institute for Date Technology(No.TFIDT2018008).
文摘The discovery of ferroelectricity in hafnium oxide (HfO_(2)) based thin films in 2011 renewed the interest inferroelectrics. These new ferroelectrics possess completely different crystal morphology with conventional perovskiteferroelectrics, and present more robust ferroelectric properties upon aggressive scaling and compatibility withstandard integrated circuit fabrication processes. In this article, we give a brief introduction to the conventionalferroelectric memories, then review the basic properties, recent progress, and memory applications of theseHfO_(2)-based ferroelectrics.
基金supported by the National Natural Science Foundation for Young Scientists of China(Grant No.51802213)Program of Applied Basic Research Program of Shanxi Province(Grant No.201901D211118)Key R&D Program of Shanxi Province(Grant No.202102030201006).
文摘Environmental barrier coatings(EBCs)with excellent chemical resistance and good high-temperature stability are of great significance for their applications in next-generation turbine engines.In this work,a new type of high-entropy fluorite-structured oxide(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2))O_(2−δ)(HEFO-1)with different Ti^(4+)contents were successfully synthesized.Minor addition of Ti4+could be dissolved into a high-entropy lattice to maintain the structure stable,effectively reducing the phase formation temperature and promoting the shrinkage of bulk samples.Heat treatment experiments showed that all the samples remained a single phase after annealing at 1200–1600℃for 6 h.In addition,high-entropy(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2)Ti_(0.2x)O_(2−δ)demonstrated great resistance to calcium–magnesium–alumina–silicate(CMAS)thermochemical corrosion.When the content of Ti was increased to x=0.5,the average thickness of the reaction layer was about 10.5µm after being corroded at 1300℃for 10 h.This study reveals that high-entropy(Ce_(0.2)Hf_(0.2)Y_(0.2)Pr_(0.2)Gd_(0.2)Ti_(0.2x)O_(2−δ)is expected to be a candidate for the next-generation EBC materials with graceful resistance to CMAS corrosion.
基金supported by the National Natural Science Foundation of China(91545123)Natural Science Foundation of Fujian Province(2016J01275)
文摘Perovskite structure La_（0.75）Sr_（0.25）Cr_（0.5）Mn_（0.5）O_（3-δ）（LSCM） cathode with unique structure can electrolyze CO_2 to CO in solid oxide electrolysers（SOEs）.However,the cell performance is restricted by its electro-catalysis activity.In this work,fluorite structure nanoparticles（CeO_（2-δ）） are impregnated on LSCM cathode to improve the electro-catalysis activity.X-ray diffraction（XRD）,scanning electron microscope（SEM） and X-ray photoelectron spectroscopy（XPS） together approve that the fluorite structure nanoparticles are uniformly distributed on the perovskite structure LSCM scaffold.Electrochemical measurements illustrate that direct CO_2 electrolysis with 10%mol CeO_（2-δ） impregnated LSCM cathode exhibits excellent performance for current density（0.5 A×cm^（-2）） and current efficiency（～95%） at 800 ℃ under 1.6 V.It is believed that the enhanced performance of directed CO_2 electrolysis may be due to the synergetic effect of fluorite structure CeO_（2-δ） nanoparticles and perovskite structure LSCM ceramic electrode.
