Evidence for Multiple Phase Transitions in La_1-xCa_xCoO_3

TL;DR

This study investigates La_1-xCa_xCoO_3, revealing multiple phase transitions through thermal-expansion and specific-heat measurements, highlighting how calcium doping influences spin states and phase behavior.

Contribution

It provides experimental evidence for multiple phase transitions in La_1-xCa_xCoO_3 related to spin-state changes and doping effects, expanding understanding of its complex phase diagram.

Findings

Spin-state transition at T ≈ 50 K in x=0

Suppression of maximum in thermal expansion at x≈0.125

Emergence of multiple anomalies with increased Ca doping

Abstract

We report thermal-expansion and specific-heat data of the series La_1-xCa_xCoO_3 for 0 <= x <= 0.3. For x = 0 the thermal-expansion coefficient alpha(T) features a pronounced maximum around T = 50 K caused by a temperature-dependent spin-state transition from a low-spin state (S=0) at low temperatures towards a higher spin state of the Co^3+ ions. The partial substitution of the La^3+ ions by divalent Ca^2+ ions causes drastic changes in the macroscopic properties of LaCoO_3. Around x ~ 0.125 the large maximum in alpha(T) has completely vanished. With further increasing x three different anomalies develop.