Thermodynamic Properties of L S CoO 3

We have investigated the bulk modulus and thermal properties of () at temperatures probably for the first time by incorporating the effect of lattice distortions using the modified rigid ion model (MRIM). The calculated specific heat, thermal expansion, bulk modulus, and other thermal properties reproduce well with the available experimental data, implying that MRIM represents properly the nature of the pure and doped cobaltate. The specific heats are found to increase with temperature and decrease with concentration (x) for the present. The increase in Debye temperature () indicates an anomalous softening of the lattice specific heat because increase in T3-term in the specific heat occurs with the decrease of concentration (x). 1. Introduction Cobaltites of rare-earth elements with the chemical formula LnCoO3 are important agile and multifunctional materials, which are very promising for high temperature oxygen separation membranes and cathodes in solid oxide fuel cells (SOFCs), heterogeneous catalysts, and gas sensors [1, 2]. The LaCoO3 ceramic is at present the best studied representative of the rare-earth cobaltite family. LaCoO3 exhibits two spin state transitions as the temperature increases. The first transition is from low temperature low spin (LS) to intermediate spin (IS) state near 100？K characterized by a steep jump of magnetization at the transition [3–5] and the second one is from IS to high spin (HS) state leading to an insulator-metal (I-M) transition around 500？K [3, 5]. Throughout the ACoO3 series, only LaCoO3 has been analyzed with rhombohedral symmetry [6]; the rest of the members of the family with the ionic radius of the rare-earth smaller than the ionic radius of La exhibit an orthorhombic crystallographic structure [7]. A structural transition from rhombohedral () to orthorhombic (Pbnm) symmetry with Sm doping level is found from the X-ray diffraction data in CoO3 [8]. Recently, we have applied the modified rigid ion model (MRIM) to study the specific heat of cobaltates and manganites [9, 10]. Motivated from the applicability and versatility of MRIM, we have applied MRIM to investigate the temperature dependence of the specific heat, thermal expansion, and elastic and thermal properties of CoO3 (0 ≤ ≤ 0.2). It is found that the model is successful in describing temperature dependent (1？K < < 300？K) specific heat (), cohesive energy (), molecular force constant (), Reststrahlen frequency (), Debye temperature (), and Gruneisen parameter () of CoO3 (0 ≤ ≤ 0.2). The various properties in LSCoO3 (0 ≤ ≤ 0.2) are affected by the