Bulk ${\mathrm{SrTiO}}_3$ is a quantum paraelectric in which an antiferrodistortive distortion below $\approx 105$ K and quantum fluctuations at low temperature preclude the stabilization of a long-range ferroelectric state. However, biaxial mechanical stress, impurity doping, and Sr nonstoichiometry, among other mechanisms, are able to stabilize a ferroelectric or relaxor ferroelectric state at room temperature, which develops into a longer-range ferroelectric state below 250 K. In this paper, we show that epitaxial ${\mathrm{SrTiO}}_3$ thin films grown under tensile strain on ${\mathrm{DyScO}}_3$ exhibit a large reduction of thermal conductivity, of $\approx 60\%$ at room temperature, with respect to identical strain-free or compressed films. The thermal conductivity shows a further reduction below 250 K, a temperature concurrent with the peak in the dielectric constant [J. H. Haeni et al., Nature (London) 430, 758 (2004)]. These results suggest that strain gradients in the relaxor and ferroelectric phase of ${\mathrm{SrTiO}}_3$ are very effective phonon scatterers, limiting the thermal transport in this material.

• Received 19 November 2019
• Revised 27 March 2020
• Accepted 16 April 2020

DOI:https://doi.org/10.1103/PhysRevMaterials.4.054002