The thermodynamics and phase behaviour of Tb₂Pd₂O₅ and Er₂Pd₂O₅

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• 作者：Jacob ; K. Thomas ; Lwin ; Kay Thi ; Waseda ; Yoshio
• 关键词：phase diagrams ; systems Tb&ndash ; Pd&ndash ; O and Er&ndash ; Pd&ndash ; O ; thermodynamic properties of Tb₂Pd₂O₅ and Er₂Pd₂O₅
• 刊名：Journal of Chemical Thermodynamics
• 出版年：2002
• 期刊代码：123_00219614
• 类别：ch
• 出版时间：October, 2002
• 卷：34
• 期：10
• 页码：1509-1529
• 文件大小：389 K

摘要

Isothermal sections of the phase diagrams for the systems Ln–Pd–O (with Ln=Tb or Er) have been established by equilibration of samples at T=1223K, and phase identification after quenching by optical and scanning electron microscopy (OM, SEM), energy dispersive spectroscopy (EDS), and X-ray powder diffraction (XRPD). Two oxide phases were stable along the binary Tb–O: Tb₂O_3+x, a phase of variable composition, and Tb₇O₁₂ at T=1223K. The oxide PdO was not stable at this temperature. Only one ternary oxide Tb₂Pd₂O₅ was identified in the Tb–Pd–O system. No ternary compound was found in the system Er–Pd–O at T=1223K. However, the compound Er₂Pd₂O₅ could be synthesized at T=1075K by the hydrothermal route. In both systems, the alloys and inter-metallic compounds were all found to be in equilibrium with the lanthanide sesquioxide Ln₂O₃ (where Ln is either Tb or Er). Two solid-state cells, each incorporating a buffer electrode, were designed to measure the Gibbs energy of formation of the ternary oxides, using yttria-stabilized zirconia as the solid electrolyte and pure oxygen gas as the reference electrode. Electromotive force measurements were conducted in the temperature range (900–1275)K for Tb–Pd–O system, and at temperatures from (900–1075)K for the system Er–Pd–O. The standard Gibbs energy of Δ_fG_m, formation of the inter-oxide compounds from their component binary oxides Ln₂O₃ and PdO Δ_fG_m, are represented by equations linear in temperature. Isothermal chemical potential diagrams for the systems Ln–Pd–O (with Ln=Tb or Er) are developed based on the thermodynamic information.