Specific heat and thermal expansion effects in LaCo1−xAxCoO3 (A = Mg, Rh, Ti and Nb)

Abstract

Rare-earth cobaltates LaCo1−xAxCoO3 (A = Mg, Rh, Ti, Nb and 0.02 ≤ x ≤ 1) have been systematically investigated to elucidate the effect of B site substitution on thermal and elastic properties. Specific heat, thermal expansion coefficient and bulk modulus of rare earth cobaltate LaCoO3 with Mg, Rh, Ti and Nb in the perovskite structure at B-site has been studied by means of a Modified Rigid Ion Model (MRIM) and AIM theory which has been found to be adequately suitable for such description for the rare earth cobaltates Ln1−xSrxCoO3 (Ln = Pr, Nd, Sm and Dy) materials [J. of Alloys Compd. 661 (2016) 257–267]. The partial replacement of rare earth cation by divalent, trivalent, tetravalent and pentavalent introduces large size and charge mismatch at B-site affecting the bulk modulus and thermal properties. The concentration dependence of the molecular force constant (f), Reststrahlen frequency (υ), cohesive energy (ϕ), Debye temperature (θD) and Gruneisen parameter (γ) are investigated for the first time. A fairly good agreement has been found between the observed and calculated values of the cohesive energy for these doped compounds. The trend of variation of specific heat, thermal expansion coefficient, Debye temperature with molar volume, temperature and concentration respectively are predicted probably for the first time for the doped rare earth cobaltates.