Barocaloric and magnetocaloric effects in the A-site layer-ordered double perovskite YBaCo2O5.5

Abstract

Searching for novel caloric materials is essential for realizing environmentally friendly, energy-efficient refrigeration systems. The A-site layer-ordered double perovskite oxide YBaCo₂O_5.5, which had a degree of freedom for the Co³⁺-spin state, was found to exhibit caloric effects by applying multiple external fields regarding three observed phase transitions. Large latent heat of 8.8 J g⁻¹ is observed near the first-order metal–insulator–transition temperature (close to room temperature), where a negative-thermal-expansion-like volume change and a change in the Co³⁺-spin state are accompanied. Significantly, the corresponding entropy change of 29.8 J K⁻¹ kg⁻¹ can be utilized through an inverse barocaloric effect. The ferrimagnetic and antiferromagnetic transitions below the metal–insulator transition temperature can be controlled by applying magnetic fields, inducing normal and inverse magnetocaloric effects, respectively. In addition, when a high magnetic field above 10 kOe is applied, the second-order ferrimagnetic transition merges with the first-order metal–insulator transition as a single first-order transition, potentially enhancing the barocaloric effect. These thermal properties provide valuable insight into the development of efficient refrigeration by means of transition-metal oxides.