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Origin of stability of the high-temperature, low-pressure Rh 2O 3 III form of rhodium sesquioxide
Journal article   Peer reviewed

Origin of stability of the high-temperature, low-pressure Rh 2O 3 III form of rhodium sesquioxide

Shuping Zhuo and Karl Sohlberg
Journal of solid state chemistry, v 179(7), pp 2126-2132
2006

Abstract

First-principles calculations Free energy Phase diagram Phase transformation Rhodium sesquioxide Structure
We present a first principles study of the equilibrium structures and relative thermodynamic stability of the three observed polymorphs of rhodium(III) sesquioxide. The thermodynamic Gibbs free energies for each phase are calculated as a function of P and T based on the electronic total energy, as well as vibrational energy and vibrational entropy contributions in the local harmonic (LH) approximation. The results confirm that Rh 2O 3 I is a low-temperature, low-pressure form and Rh 2O 3 II is a high-pressure form. A breakdown in the LH approximation at high T is then discussed and to address this breakdown an empirically corrected local harmonic (ECLH) approximation is introduced. ECLH demonstrates that the high-temperature, low-pressure form Rh 2O 3 III is entropically stabilized and produces a partitioning of phase space that is consistent with published experimental investigations. Calculations of the Gibbs free energies for three phases of Rh sesquioxide, including estimates of the vibrational energy and vibrational entropy contributions, show that this Rh 2O 3 III phase is entropically stabilized.

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Collaboration types
Domestic collaboration
International collaboration
Web of Science research areas
Chemistry, Inorganic & Nuclear
Chemistry, Physical
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