Heat Capacity of La<SUB>1−<I>X</I></SUB>Sr<I><SUB>X</SUB></I>FeO<SUB>3−δ</SUB> from 2 K to 1340 K

Abstract

Isobaric heat capacities, Cp, of La x sr 1-x FeO 3-δ solid solutions from near absolute zero Kelvin (2K) to high temperature (1340K) were measured by a relaxation method and differential scanning calorimetry. Also, their Debye temperatures, Θ D , were determined from the measured Cp values below 10 K and isochoric heat capacities, C v , were calculated by inserting the Θ D values into Debye functions, followed by calculating the isochoric entropies of vibration, Δ T 0 S v . From the measured C p values, it was found that oxygen vacancy (Vo) formed by a self-compensating reaction by doping of Sr' La decreased the onset temperatures of the magnetic and structure phase transitions, broadening the temperature ranges of such phase transitions. The entropies of vibration of oxygen vacancy, Δ f S vib Tv (Vo), estimated by differentiation of Δ T 0 S v with the Vo content at 298 K and 800 K were 58.65 J.K -1 ·mol -1 and 64.59 J.K -1 ·mol -1 , respectively. Such a large Δ f S vib Tv (Vo ) appears to be one of important reason for foming Vo.