Positive temperature coefficient of the thermal conductivity above room temperature in a perovskite cobaltite. Issue 1 (31st December 2022)

• Record Type: Journal Article
• Authors: Doi, Atsunori; Shimano, Satoshi; Kriener, Markus; Kikkawa, Akiko; Taguchi, Yasujiro; Tokura, Yoshinori
• Is Part Of: Science and technology of advanced materials. Volume 23:Issue 1(2022)
• Page Start: 858
• Page End: 865
• Publication Date: 2022-12-31
• Subjects: Strongly correlated electron materials -- spin state -- cobaltite -- thermal diode; Materials -- Technological innovations -- Periodicals; 620.112
• DOI: 10.1080/14686996.2022.2149035
• Languages: English
• ISSNs: 1468-6996

Abstract

ABSTRACT: The thermal conductivity above room temperature is investigated for LaCoO3 -based materials showing spin-state and insulator-metal crossovers. A positive temperature coefficient (PTC) of the thermal conductivity is observed during the insulator-metal crossover around 500 K. Our analysis indicates that the phononic thermal transport is also enhanced in addition to the electronic contribution as the insulator-metal crossover takes place. The enhancement of the phononic component is ascribed to the reduction of the incoherent local lattice distortion coupled with the spin/orbital state of each Co 3+ ion, which is induced by the enhanced spin-state fluctuation between low and excited spin-states. Moreover, fine tunability for the PTC of the thermal conductivity is demonstrated via doping hole-type carriers into LaCoO3 . The observed enhancement ratio of the thermal conductivity κ T (773 K) / κ T (323 K) = 2.6 in La0.95 Sr0.05 CoO3 is the largest value among oxide materials which exhibit a PTC of their thermal conductivity above room temperature. The thermal rectification ratio is estimated to reach 61% for a hypothetical thermal diode consisting of La0.95 Sr0.05 CoO3 and LaGaO3, the latter of which is a typical band insulator. These results indicate that utilizing spin-state and orbital degrees of freedom in strongly correlated materials is a useful strategy for tuning thermal transport properties, especially for designing thermal diodes. GRAPHICAL ABSTRACT: uf0001