Suppression of intrinsic thermal conductivity in Sr1−xGdxTiO3 ceramics via phonon-point defect scattering for enhanced thermoelectric application

Abstract

A substantial reduction in the thermal conductivity for strontium titanate (ABO₃) perovskite structure was realized for the A-site substitution of gadolinium (rare earth element) in SrTiO₃ ceramics. The effect of Gd³⁺ substitution on the structure, composition, and thermoelectric properties of SrTiO₃ was investigated. The substitution of Gd³⁺ in the SrTiO₃ matrix resulted in the minimalization of thermal conductivity. The thermal conductivity followed a similar trend as that of thermal diffusivity, but specific heat capacity exhibited a non-monotonic trend. The thermal conductivity is reduced to 1.05 W m⁻¹ K⁻¹ for the minimal substitutional composition (Sr_0.99Gd_0.01TiO₃) which is 30% less than that of SrTiO₃ at 303 K. The variation in the ionic radii and atomic mass of the heavier rare earth Gd³⁺ substituted over Sr²⁺ resulted in the reduction of thermal conductivity of SGTO ceramics caused by the corresponding boundary scattering at low temperatures and temperature-independent phonon-impurity scattering at high temperatures.