Journal of Phase Equilibria

, Volume 24, Issue 5, pp 431–440 | Cite as

Thermodynamic properties of SmFeO3(s) and Sm3Fe5O12(s)

  • S. C. Parida
  • V. Venugopal
  • K. T. Jacob
Basic And Applied Research

Abstract

The enthalpy increments and the standard molar Gibbs energy (G) of formation of SmFeO3(s) and Sm3Fe5O12(s) have been measured using a Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. A λ-type transition, related to magnetic order-disorder transformation (antiferromagnetic to paramagnetic), is apparent from the heat capacity data at ∼673 K for SmFeO3(s) and at ∼560 K for Sm3Fe5O12(s). Enthalpy increment data for SmFeO3(s) and Sm3Fe5O12(s), except in the vicinity of λ-transition, can be represented by the following polynomial expressions:
$$\begin{gathered} \{ H^0 _m (T) - H^0 _m (298.15K)\{ /J mol^{ - 1} ( \pm 1.2\% ) = - 54532.8 + 147.4 \cdot (T/K) + 1.2 \cdot 10^{ - 4} \cdot (T/K)^2 \hfill \\ + 3.154 \cdot 10^6 \cdot (T/K)^{ - 1} ;(298.15 \leqslant T/K \leqslant 1000) \hfill \\ \end{gathered} $$
for SmFeO3(s), and
$$\begin{gathered} \{ H^0 _m (T) - H^0 _m (298.15K)\} /J mol^{ - 1} ( \pm 1.4\% ) = - 192763 + 554.7 \cdot (T/K) + 2.0 \cdot 10^{ - 6} \cdot (T/K)^2 \hfill \\ + 8.161 \cdot 10^6 \cdot (T/K)^{ - 1} ;(298.15 \leqslant T/K \leqslant 1000) \hfill \\ \end{gathered} $$
for Sm3Fe5O12(s).
The reversible emf of the solid-state electrochemical cells, (−)Pt/{SmFeO3(s)+Sm2O3(s)+Fe(s)} // YDT / CSZ // {Fe(s)+Fe0.95O(s)} / Pt(+) and (−)Pt/{Fe(s)+Fe0.95O(s)} // CSZ // {SmFeO3(s)+Sm3Fe5O12(s)+Fe3O4(s)} / Pt(+), were measured in the temperature ranges of 1005–1259 K and 1030–1252 K, respectively. The standard molar G of formation of solid SmFeO3 and Sm3Fe5O12 calculated by the least squares regression analysis of the data obtained in the current study, and data for Fe0.95O and Sm2O3 from the literature, are given by:
$$\Delta _f G^0 _m (SmFeO_3 ,s)/kJ \cdot mol^{ - 1} ( \pm 2.0) = - 1355.2 + 0.2643 \cdot \langle T/K);(1005 \leqslant T/K \leqslant 1570)$$
and
$$\Delta _f G^0 _m (Sm_3 Fe_5 O_{12} ,s)/kJ \cdot mol^{ - 1} ( \pm 3.1) = - 4891.0 + 1.0312 \cdot (T/K);(1030 \leqslant T/K \leqslant 1252)$$

The uncertainty estimates for Δ f G° m include the standard deviation in the emf and uncertainty in the data taken from the literature. Based on these thermodynamic data, the oxygen potential diagram for the system Sm-Fe-O was constructed at 1250 K.

Keywords

Ternary Oxide Enthalpy Increment Standard Molar Gibbs Energy Oxygen Potential Diagram Enthalpy Increment Measurement 

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Copyright information

© ASM International 2003

Authors and Affiliations

  • S. C. Parida
    • 1
  • V. Venugopal
    • 1
  • K. T. Jacob
    • 2
  1. 1.Fuel Chemistry DivisionBhabha Atomic Research CentreMumbaiIndia
  2. 2.Department of MetallurgyIndian Institute of ScienceBangaloreIndia

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