Co₃O₄-Co₂ZnO₄ spinels: The case for a solid solution

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• 作者：Nicola H. Perry^a ; Thomas O. Mason^a ; ^{t-mason@northwestern.edu} ; Chengcheng Ma^b ; Alexandra Navrotsky^b ; Yezhou Shi^c ; Joanna S. Bettinger^c ; Michael F. Toney^c ; Tula R. Paudel^d ; Stephan Lany^d ; Alex Zunger^e
• 关键词：Co3O4 ; ZnCo2O4 ; Calorimetry ; Diffraction ; Mixing thermodynamics ; Electrical conductivity
• 刊名：Journal of Solid State Chemistry
• 出版年：2012
• 期刊代码：130_00224596
• 类别：ch
• 出版时间：June, 2012
• 卷：190
• 期：Complete
• 页码：143-149
• 文件大小：526 K

摘要

In prior first-principles theoretical work we predicted a complete solid solution in the Co₃O₄-Co₂ZnO₄ system, with a negligibly small mixing enthalpy. In this work we tested this prediction on bulk, large-grained specimens across the Co₃O₄-Co₂ZnO₄ join, combining oxide melt solution calorimetry, differential scanning calorimetry, precise lattice parameter measurements, anomalous X-ray and neutron diffraction, and in situ electrical measurements. The calorimetric results confirm the presence of a solid solution at high temperatures, but with a large enthalpy of mixing that exceeds the predicted value. Because Co₃O₄ and Co₂ZnO₄ have essentially identical lattice parameters, this energetic destabilization must arise from factors other than the strain energy resulting from size mismatch. Changes in Co³⁺ spin states vs. temperature and zinc content are proposed to account for the positive excess enthalpy, and may also provide additional entropy to stabilize the solid solution at high temperature.