Evidence for multiple phase transitions in La1-xCaxCoO3La1-xCaxCoO3

We report thermal-expansion and specific-heat data of the series La1-xCaxCoO3La1-xCaxCoO3 for 0⩽x⩽0.30⩽x⩽0.3. For x=0x=0 the thermal-expansion coefficient α(T)α(T) features a pronounced maximum around T=50K caused by a temperature-dependent spin-state transition from a low-spin state (S=0S=0) at low temperatures towards a higher spin state of the Co3+Co3+ ions. The partial substitution of the La3+La3+ ions by divalent Ca2+Ca2+ ions causes drastic changes in the macroscopic properties of LaCoO3LaCoO3. Around x≈0.125x≈0.125 the large maximum in α(T)α(T) has completely vanished. With further increasing x three different anomalies develop.