Heat Capacity of La_1-XSr_XFeO_3-δ from Near Absolute Zero Kelvin to High Temperature

Abstract

  Isobaric heat capacities, C_p, of La_XSr_1-XFeO_3-δ solid solutions from near absolute zero Kelvin (2 K) to high temperature (1340 K) were measured by a relaxation method and differential scanning calorimetry. Also, their Debye temperatures, Θ_D, were determined from the measured C_p 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, Δ₀^TS_V. From the measured C_p values, it was found that oxygen vacancy (V_o) 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_fS_T^vib._V(V_o), estimated by differentiation of Δ₀^TS_V with the V_o 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_fS_T^vib._V(V_o) appears to be one of important reason for foming V_o.