La1-XSrXCoO3-δ の熱容量測定

Abstract

Isobaric heat capacities, Cp, of La0.207Co0.207O0.586, La0.179Sr0.032Co0.210O0.579 and La0.109Sr0.109Co0.218O0.564 from near absolute zero Kelvin (2 K) to high temperature (1340 K) were measured by a relaxation method and differential scanning calorimetry. In the Cp values for La0.207Co0.207O0.586, two peaks at 628 K and 788 K were observed, consistent with the phase transition of from semi-conductor to metal and the phase transition at which magnetic moment increased as a function of temperature, respectively. Also, in the Cp values for La0.179Sr0.032Co0.210O0.579, such two-kinds of the phase transitions, that is the phase transition of semi-conductor to metal and the phase transition increasing the magnetic moment, were observed in the lower temperature ranges than in La0.207Co0.207O0.586. The phase transition from ferromagnetic- to paramagnetic-metal was caused at 239 K in La0.109Sr0.109Co0.218O0.564, while such two kinds of phase transitions observed in La0.207Co0.207O0.586 and La0.179Sr0.032Co0.210O0.579 were disappeared. The Debye temperature, ΘD, of La0.207Co0.207O0.586 was determined from the measured Cp values below 10 K. Its isochoric heat capacity, CV, was calculated by inserting ΘD into the Debye function, and the isochoric entropies of vibration, Δ0TSV, was determined, followed by calculating the entropy of vibration of oxygen vacancy, ΔfSTvib.V(Vö), by differentiation of Δ0TSV with the Vö content. The ΔfSTvib.V(Vö) obtained at 298 K and 800 K were 42.86 J·K-1·mol-1 and 44.00 J·K-1·mol-1, respectively. Such a large ΔfSTvib.V(Vö) appears to be one of important reason for foming Vö.