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High-entropy perovskite RETa_(3)O_(9) ceramics for high-temperature environmental/thermal barrier coatings

Journal of Advanced Ceramics 2022年第4期11卷 556-569页

作者： Lin CHEN Baihui LI Jun GUO Yuke ZHU Jing FENG Faculty of Material Science and Engineering Kunming University of Science and TechnologyKunming 650093China

Four high-entropy perovskite(HEP)RETa_(3)O_(9) samples were fabricated via a spark plasma sintering(SPS)method,and the corresponding thermophysical properties and underlying mechanisms were investigated for environmental/thermal barrier coating(E/TBC)*** prepared samples maintained low thermal conductivity(1.50 W·m^(−1)·K^(−1)),high hardness(10 GPa),and an appropriate Young’s modulus(180 GPa),while the fracture toughness increased to 2.5 MPa·m^(1/2).Nanoindentation results showed the HEP ceramics had excellent mechanical properties and good component *** analysed the influence of different parameters(the disorder parameters of the electronegativity,ionic radius,and atomic mass,as well as the tolerance factor)of A-site atoms on the thermal *** thermal expansion coefficients,combined with a high melting point and extraordinary phase stability,expanded the applications of the HEP RETa_(3)O_(9).The results of this study had motivated a follow-up study on tantalate high-entropy ceramics with desirable properties.

关键词： high-entropy ceramics(HECs) tantalates thermal conductivity nanoindentation fracture toughness

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Influence of HfO2 alloying effect on microstructure and thermal conductivity of HoTaO4 ceramics

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Journal of Advanced Ceramics 2019年第4期8卷 537-544页

作者： Lin CHEN Jing FENG Faculty of Material Science and Engineering Kunming University of Science and Technology

HfO2 alloying effect has been applied to optimize thermal insulation performance of HoTaO4 ceramics.X-ray diffraction,Raman spectroscopy,and X-ray photoelectron spectroscopy are employed to decide the crystal *** electronic microscopy is utilized to detect the influence of HfO2 alloying effect on *** paper indicates that the same numbers of Ta5+and Ho3+ions of HoTaO4 are substituted by Hf4+cations,and it is defined as alloying *** crystal structural transition is introduced by HfO2 alloying effect,and circular pores are produced in ***2 alloying effect is efficient in decreasing thermal conductivity of HoTaO4 and it is contributed to the differences of ionic radius and atomic weight between Hf4+ions and host cations(Ta5+and Ho3+).The least experimental thermal conductivity is 0.8 W·K–1·m–1 at 900℃,which is detected in 6 and 9 mol%-HfO2 HoTaO4 *** results imply that HfO2–HoTaO4 ceramics are promising thermal barrier coatings(TBCs)due to their extraordinary thermal insulation performance.

关键词： thermal barrier coating(TBC) thermal conductivity rare earth tantalates microstructure alloying effect optical property

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High Dielectric Constant and Low-loss Dielectric Ceramics of Sr_5 LnTi_3Ta_7O_(30)(Ln=La,Nd,Sm and Y)

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Journal of Wuhan University of Technology(Materials Science) 2008年第2期23卷 218-221页

作者： TU Wenmao CHEN Pu PENG Xiyang LIU Ting School of Resource and Environmental Engineering Wuhan University of Technology Wuhan 430070 China

Polycrystalline Sr5LnTi3Ta7O30 （Ln=La, Nd, Sm and Y） ceramics were prepared as single-phase materials through conventional solid-state ceramics method. The structure was characterized by X-ray diffraction method and scanning electron microscopy （SEM）. The dielectric properties were measured from room temperature to 400℃. All compounds are paraelectric phases adopting the filled tetragonal tungsten bronze （TB） structure at room temperature. At 1 MHz their dielectric constant （ετ） varied from 109 to 139, dielectric loss changed from 0.003 3 to 0.005 8, and the temperature coefficients of the dielectric constant （τε） moved from -710 to -880×10^-6℃^-1.

关键词： dielectric properties paraelectric tungsten bronze tantalates

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Dielectric Properties and the Phase Transition of Pure and Cerium Doped Calcium-Barium-Niobate

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World Journal of Condensed Matter Physics 2012年第2期2卷 80-84页

作者： Alexander Niemer Rainer Pankrath Klaus Betzler Manfred Burianek Manfred Muehlberg Department of Physics University of Osnabrück Osnabrück Germany Institute of Crystallography University of Cologne Cologne Germany

The complex dielectric constant of pure and cerium doped calcium-barium-niobate (CBN) was studied at frequencies 20 Hz ≤ f ≤ 1 MHz in the temperature range 300 K ≤ T ≤ 650 K and compared with the results for the well known ferroelectric relaxor strontium-barium-niobate (SBN). By the analysis of the systematically taken temperature and frequency dependent measurements of the dielectric constant the phase transition characteristic of the investigated materials was evaluated. From the results it must be assumed that CBN shows a slightly diffuse phase transition without relaxor behavior. Doping with cerium yields a definitely different phase transition characteristic with some indications for a relaxor type ferroelectric material, which are common from SBN.

关键词： 77.80.-e Ferroelectricity and Antiferroelectricity 77.80.Jk Relaxor Ferroelectrics 77.84.Ek Niobates and tantalates 77.22.Ch Permittivity (Dielectric Function)

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