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Crystal chemistry and phase equilibria of the CaO-½Ho2O3-CoOz system at 885 °C in air
Solid State Sciences ( IF 3.4 ) Pub Date : 2020-07-02 , DOI: 10.1016/j.solidstatesciences.2020.106348
W. Wong-Ng , W. Laws , Q. Huang , J. Hou , S.H. Lapidus , L. Ribaud , J.A. Kaduk

The phase equilibrium diagram of the CaO-½Ho2O3-CoOz system was determined at 885 °C in air. This diagram offers compatibility relationships in the ternary oxide system that are essential for processing and for the understanding of properties of several thermoelectric phases in the system. Four three-phase regions and three solid solution tie-line regions were determined in the CaO-½Ho2O3-CoOz system. In the CaO-Ho2O3 system, while a small solid solution region was identified for (Ho1-xCax)O(3-z)/2 (0 ≤x ≤ 0.14), Ho was not present in the Ca site of CaO. Neither the reported Ho2CoO4 phase in the Ho2O-CoOz system nor the Ca-doped (Ho1+xCa1-x)CoO4-z phase was present at 885 °C. No solid solution of the distorted perovskite, (Ho1-xCax)CoO3-z, was established at this temperature. The CaO-CoOz system consists of two calcium cobaltate thermoelectric compounds. The 2D thermoelectric oxide, (Ca3-xHox)Co4O9-z (0 ≤x ≤ 0.5), has a misfit layered structure, and the 1D Ca3Co2O6 consists of chains of alternating CoO6 trigonal prisms and CoO6 octahedra. Ca3Co2O6 was found to be a stoichiometric compound. A comparison of the phase diagrams of the CaO-½R2O3-CoOz (R = La, Nd, Eu, and Ho) systems is given.



中文翻译:

CaO-1 / 2Ho 2 O 3 -CoO z系统在885°C的空气中的晶体化学和相平衡

CaO-1 / 2Ho 2 O 3 -CoO z系统的相平衡图在空气中于885°C下确定。该图提供了三元氧化物系统中的相容性关系,这对于处理和理解系统中多个热电相的性质至关重要。在CaO-1 / 2Ho 2 O 3 -CoO z系统中确定了四个三相区域和三个固溶联系线区域。在CaO-Ho 2 O 3系统中,虽然对(Ho 1-x Ca x)O (3-z)/ 2的固溶区很小(0≤x≤0.14),在CaO的Ca部位不存在Ho。在Ho 2 O-CoO z系统中报道的Ho 2 CoO 4相和在885°C下都不存在Ca掺杂(Ho 1 + x Ca 1-x)CoO 4-z相。在该温度下未形成变形的钙钛矿(Ho 1-x Ca x)CoO 3-z的固溶体。CaO-CoO z系统由两种钴酸钙热电化合物组成。二维热电氧化物(Ca 3-x Ho x)Co 4 O 9-z(0≤x≤0.5)具有错配的分层结构,一维Ca 3 Co 2 O 6由交替的CoO 6三角棱镜和CoO 6八面体链组成。发现Ca 3 Co 2 O 6是化学计量的化合物。给出了CaO-1 / 2R 2 O 3 -CoO z(R = La,Nd,Eu和Ho)系统的相图的比较。

更新日期:2020-07-02
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