Abnormally low thermal conductivity of Co2MnO4 spinel induced by cation inversion†

Abstract

The relationship between crystal structure and lattice thermal conductivity (LTC) is of great importance for material development. Herein, we reveal the substantial effect of cation inversion on the LTC of spinels. Although the theoretical LTC of a normal cubic-phased spinel Co₂MnO₄ is much higher than that of the tetragonal-phased spinel CoMn₂O₄, we experimentally observe a significantly lower thermal conductivity in the prepared Co₂MnO₄ samples than that of CoMn₂O₄ samples. The abnormally low thermal conductivity results from the cation inversion in the prepared Co₂MnO₄ samples. Further theoretical calculations indicate that the cation inversion of Co₂MnO₄ triggers an about 80% LTC decrease from 26.56 W m⁻¹ K⁻¹ to 4.14 W m⁻¹ K⁻¹ at 300 K. We further reveal that the LTC has a negative relation with the degree of cation inversion, which is also validated for other spinels such as NiCo₂O₄ and NiFe₂O₄. Furthermore, we found that the thermal conductivity of Co–Mn–O spinels could be decreased ulteriorly by cation occupation disorder in Co_xMn_3−xO₄, and the lowest thermal conductivity was observed for Co_1.8Mn_1.2O₄. The results provide an advanced understanding of the structure–performance relationship between cation occupation and LTC in spinel materials and demonstrate a potential method for LTC regulation.