Ushakov Sergey V, Hayun Shmuel, Gong Weiping, Navrotsky Alexandra
School of Molecular Sciences, and Center for Materials of the Universe, Arizona State University, Tempe, AZ 85287, USA.
Department of Materials Engineering at the Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
Materials (Basel). 2020 Jul 14;13(14):3141. doi: 10.3390/ma13143141.
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)O, where all oxides are in equimolar ratios and RE is Nd or Gd or Y. After annealing at 800 °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 °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)O sample as 2456 ± 12 °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 SmO-DyO, SmO-ErO, and DyO-ErO systems.
通过熔体急冷、高温差热分析以及对激光加热样品进行同步辐射X射线衍射，研究了多组分稀土 sesquioxides 中的相变。采用溶液燃烧法制备了三种成分：(La,Sm,Dy,Er,RE)O，其中所有氧化物的摩尔比相等，RE为Nd或Gd或Y。在800°C退火后，所有粉末主要包含C型方铁锰矿结构的相。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°C范围内有三个可逆相变，被确定为向A、H和X型稀土 sesquioxides 结构类型的转变。通过X射线衍射测量了C - B、B - A和H - X转变时的晶胞体积和体积变化，与纯稀土 sesquioxides 中的趋势一致。通过相图计算预测了单相固溶体的形成。测定了(La,Sm,Dy,Er,Nd)O样品的熔点为2456 ± 12°C，高于任何一种组成氧化物的熔点。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，并促使对SmO - DyO、SmO - ErO和DyO - ErO体系的液相线表面进行进一步研究。
