Thermal Analysis of High Entropy Rare Earth Oxides
Thermal Analysis of High Entropy Rare Earth Oxides
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DOI：
10.3390/ma13143141
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发表时间：
2020-07-01
期刊：
影响因子：
3.4
通讯作者：
Navrotsky, Alexandra
中科院分区：
文献类型：
--
作者：
Ushakov, Sergey, V;Hayun, Shmuel;Navrotsky, Alexandra
通过熔体溅射淬火、高温差热分析和激光加热样品的同步加速器 X 射线衍射研究了多组分稀土三氧化物的相变。采用溶液燃烧法制备了三种成分：(La,Sm,Dy,Er,RE)(2)O-3，其中所有氧化物均等摩尔比，RE为Nd或Gd或Y。在800℃退火后，所有粉末均主要含有C型方铁锰矿结构相。激光熔化后，所有样品均淬火成单相单斜 B 型结构。热分析表明在 1900-2400 摄氏度范围内发生了三种可逆相变，指定为 A、H 和 X 稀土倍半氧化物结构类型的转变。通过 X 射线衍射测量了 C-B、B-A 和 H-X 变换的晶胞体积和体积变化，与纯稀土三氧化物的趋势一致。通过 Calphad 计算预测单相固溶体的形成。 (La,Sm,Dy,Er,Nd)(2)O(3) 样品的熔点测定为 2456 +/- 12 摄氏度，高于任何组成氧化物。熔化温度的升高可能与固体和/或熔体中的非理想混合有关，并促使未来对 Sm2O3-Dy2O3、Sm2O3-Er2O3 和 Dy2O3-Er(2)O(3) 系统中的液相线表面进行研究。
Phase transformations in multicomponent rare earth sesquioxides were studied by splat quenching from the melt, high temperature differential thermal analysis and synchrotron X-ray diffraction on laser-heated samples. Three compositions were prepared by the solution combustion method: (La,Sm,Dy,Er,RE)(2)O-3, where all oxides are in equimolar ratios and RE is Nd or Gd or Y. After annealing at 800 degrees C, all powders contained mainly a phase of C-type bixbyite structure. After laser melting, all samples were quenched in a single-phase monoclinic B-type structure. Thermal analysis indicated three reversible phase transitions in the range 1900-2400 degrees C, assigned as transformations into A, H, and X rare earth sesquioxides structure types. Unit cell volumes and volume changes on C-B, B-A, and H-X transformations were measured by X-ray diffraction and consistent with the trend in pure rare earth sesquioxides. The formation of single-phase solid solutions was predicted by Calphad calculations. The melting point was determined for the (La,Sm,Dy,Er,Nd)(2)O(3)sample as 2456 +/- 12 degrees C, which is higher than for any of constituent oxides. An increase in melting temperature is probably related to nonideal mixing in the solid and/or the melt and prompts future investigation of the liquidus surface in Sm2O3-Dy2O3, Sm2O3-Er2O3, and Dy2O3-Er(2)O(3)systems.