Abstract
We present results from low-temperature heat capacity measurements of spinels along the solid solution between MgAl2O4 and MgCr2O4. The data also include new low-temperature heat capacity measurements for MgAl2O4 spinel. Heat capacities were measured between 1.5 and 300 K, and thermochemical functions were derived from the results. No heat capacity anomaly was observed for MgAl2O4 spinel; however, we observe a low-temperature heat capacity anomaly for Cr-bearing spinels at temperatures below 15 K. From our data we calculate standard entropies (298.15 K) for Mg(Cr,Al)2O4 spinels. We suggest a standard entropy for MgAl2O4 of 80.9 ± 0.6 J mol−1 K−1. For the solid solution between MgAl2O4 and MgCr2O4, we observe a linear increase of the standard entropies from 80.9 J mol−1 K−1 for MgAl2O4 to 118.3 J mol−1 K−1 for MgCr2O4.
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Acknowledgments
Our thanks go to E. Schmitt (Stuttgart), H. Kleinschmidt and I. Glass (Heidelberg) for technical support in the laboratories. This work was supported by the Deutsche Forschungsgemeinschaft and the Leverhulme Trust. We would like to thank Prof A. Navrotsky and an anonymous reviewer for reviews which helped to improve the manuscript substantially.
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Klemme, S., Ahrens, M. Low-temperature heat capacities of MgAl2O4 and spinels of the MgCr2O4–MgAl2O4 solid solution. Phys Chem Minerals 34, 59–72 (2007). https://doi.org/10.1007/s00269-006-0128-4
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DOI: https://doi.org/10.1007/s00269-006-0128-4