Energetics of the spin transition in LaCoO3

The heat capacity of LaCoO3 has been determined from 13 to 1000 K by adiabatic calorimetry. A spin transition, reported to occur between 20 and 100 K, is reflected in the heat capacity as a small, broad hump. A more substantial heat-capacity contribution, of electronic origin also, has its maximum at similar to 530 K. The excess heat capacity of the lower temperature transition corresponds to an excess entropy of similar to 4 J/K mol at 200 K. The excess heat capacity and entropy are discussed with reference to several models proposed for the electronic and structural phase transitions in LaCoO3. The experimental results comply with a spin transition taking place in more than one stage, due presumably in part to level splitting by spin-orbit coupling.