Suppression of intrinsic thermal conductivity in Sr 1- x Gd x TiO 3 ceramics via phonon-point defect scattering for enhanced thermoelectric application.

A substantial reduction in the thermal conductivity for strontium titanate (ABO 3 ) perovskite structure was realized for the A-site substitution of gadolinium (rare earth element) in SrTiO 3 ceramics. The effect of Gd 3+ substitution on the structure, composition, and thermoelectric properties of SrTiO 3 was investigated. The substitution of Gd 3+ in the SrTiO 3 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 0.99 Gd 0.01 TiO 3 ) which is 30% less than that of SrTiO 3 at 303 K. The variation in the ionic radii and atomic mass of the heavier rare earth Gd 3+ substituted over Sr 2+ 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.