Anomalous and non-monotonic strain dependent thermal conductivity of typical negative thermal expansion material ScF3

It is well known that the lattice thermal conductivity of the vast majority of bulk materials increases under compressive strain and decreases under tensile strain. In this paper, taking the typical negative thermal expansion material ScF3 as an example, we systematically investigate the effect of strain on the phonon transport properties by means of first-principles calculation combined with the Boltzmann transport equation. The results show that the thermal conductivity of ScF3 exhibits an anomalous strain dependence, where the thermal conductivity decreases under compressive strain while increasing as the tensile strain is smaller than −4.2 GPa. When the tensile strain increases further (larger than −4.2 GPa), however, the thermal conductivity of ScF3 decreases with tensile strain, presenting a non-monotonic behavior. Through analyzing the phonon mode information, we demonstrate that such anomalous and non-monotonic strain dependent thermal transport in ScF3 mainly originated from the intrinsic character of the negative Grüneisen parameter (negative thermal expansion). Moreover, the root mean square displacement is also utilized to further demonstrate the variation of phonon anharmonicity and thermal conductivity of ScF3 with strain. The findings shed light on the underlying association between thermal expansion and thermal conductivity and provide a feasible strategy for searching for materials with anomalous strain dependent thermal conductivity.