Abnormal thermal expansion coefficients in(Nd_(1−x)Dy_(x))_(2)Zr_(2)O_(7) pyrochlore:The effect of low-lying optical phonons  

作　　者：Zesheng Yang Yi Li Wei Pan Chunlei Wan 

机构地区：[1]State Key Laboratory of New Ceramics&Fine Processing,Tsinghua University,Beijing 100084,China [2]College of Mathematics and Physics,Beijing University of Chemical Technology,Beijing 100029,China

出　　处：《Journal of Advanced Ceramics》2023年第5期1001-1014,共14页先进陶瓷（英文）

基　　金：supported by the National Natural Science Foundation of China(No.52022042);the National Key R&D Program of China(No.2021YFB3702300);National Science and Technology Major Project(No.J2019-VII-0008-0148).

摘　　要：Chemical doping is a normal strategy to tune thermal expansion coefficient(TEC)of ceramics in engineering applications,but the resultant TEC values usually follow Vegard’s law,as doping does not modify the nature of chemical bonding in ceramics and its anharmonicity.In this paper,we report abnormal TEC behavior in(Nd_(1−x)Dy_(x))_(2)Zr_(2)O_(7) ceramics,where the TEC values remarkably exceed the values predicted by Vegard’s law and even exceed the values obtained for two constituents Nd_(2)Zr_(2)O_(7) and Dy_(2)Zr_(2)O_(7).In addition to a reduction in lattice energy with an increasing molar fraction of Dy(x)value,we attribute the additional increase in the TEC to the high concentration of Dy dopants in a pyrochlore(P)region,which can soften low-lying optical phonon modes and induce strongly avoided crossing with acoustic phonon branches and enhanced anharmonicity.We believe that this finding can provide a new route to break through the restriction imposed by the conventional Vegard’s law on the TEC values and bring new opportunities for thermal barrier coatings(TBCs)or ceramic/metal composites towards realizing minimized thermal mismatch and prolonged service life during thermal cycling.

关 键 词：thermal barrier coating(TBC) thermal expansion first-principles calculations avoided crossing 

分 类 号：TQ174.1[化学工程—陶瓷工业]