Thermodynamic evidence for phase transition in MoO2-δ

Jacob, K. T. ; Saji, V. S. ; Gopalakrishnan, J. ; Waseda, Y. (2007) Thermodynamic evidence for phase transition in MoO2-δ Journal of Chemical Thermodynamics, 39 (12). pp. 1539-1545. ISSN 0021-9614

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The standard Gibbs free energy of formation of MoO2-δ, ΔfG(MoO2-δ), has been measured over a wide temperature range (925 to 1925) K using an advanced version of bi-electrolyte solid-state electrochemical cell incorporating a buffer electrode: Pt|Mo + MoO2-δ||(Y2O3)ThO2||(CaO)ZrO2||O2(0.1MPa)|Pt The Gibbs free energy of formation of MoO2-δ, which is directly related to the measured cell e.m.f., can be represented by two linear segments: ΔfG°(MoO2-δ)±570(Jmol-1)=-579,821+170.003(T/K) in the temperature range(925 to 1533)K, and ΔfG°(MoO2-δ)±510(Jmol-1)=-564,634+160.096(T/K) in the temperature range (1533 to 1925) K. The change in slope at T = 1533 K is probably related to the phase transition of MoO2 from monoclinic structure with space group P21/c to tetragonal structure characteristic of rutile with space group P42/mnm. The enthalpy and entropy change for the phase transition are: ΔHtr = (15.19 ± 2.1) kJ · mol-1; ΔStr = (9.91 ± 1.27) J · mol-1· K-1. The standard enthalpy of formation of MoO2-δ at T = 298.15 K assessed by the third-law method is: δfH(M±O2-δ) = (-592.28 ± 0.33) kJ· mol-1. The new measurements refine thermodynamic data for MoO2.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:MoO2; Gibbs Free Energy Of Formation; Phase Transition; E.M.F. Measurement; Enthalpy Of Formation
ID Code:12519
Deposited On:13 Nov 2010 13:25
Last Modified:16 May 2016 21:51

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