Thermodynamic studies on LaFeO3(s)

Abstract

The enthalpy increments and the standard molar Gibbs energies in the formation of LaFeO3(s) have been measured using a high-temperature Calvet micro-calorimeter and a solid oxide galvanic cell, respectively. The corresponding expression for enthalpy increments is given as:H°(T)−H°(298.15K)(Jmol−1)(±1.2%)=−36887.27+103.53T(K)+25.997×10−3T2(K)+11.055×105/T(K).The heat capacity, the first differential of H°(T)−H°(298.15 K) with respect to temperature, is given as:Cp,m°(T)(JK−1mol−1)=103.53+51.994×10−3T(K)−11.055×105/T2(K).From the measured e.m.f. of the cell, (−)Pt/(LaFeO3(s)+La2O3(s)+Fe(s))//CSZ//(Ni(s)+NiO(s))/Pt(+), and the relevant ΔfGm°(T) values from the literature, the ΔfGm°(LaFeO3, s, T) was calculated, and is given as:ΔfGm°(LaFeO3,s,T)(kJmol−1)(±0.72)=−1319.2+0.2317T(K).The calculated ΔfHm°(LaFeO3, s, 298.15 K) and S°(298.15 K) values obtained using the second law method are −1334.7 kJmol−1 and 128.9 JK−1mol−1, respectively.