Thermoelectric figure of merit enhancement of solid solutions based on SrTiO$_3$ by mechanical activation

The influence of high-energy mechanical activation on the thermoelectric properties of polycrystalline Dy$_{0.075}$Sr$_{0.925}$Ti$_{1-x}$P$_x$O$_3$ ($x$ = 0, 0.01, 0.025) samples has been studied. The synthesized solid solutions have a negative Seebeck coefficient, increasing almost linearly in absolute value with increasing temperature. For all samples, a change in the type of electrical conductivity from semiconductor to metallic is observed. A comparative analysis of the results obtained in the temperature range of 300–800 K showed a significant decrease in electrical resistivity with a slight change in the Seebeck coefficient, increasing the thermoelectric power factor to 12.2 $\mu$W/(cm $\cdot$ K$^2$) at $x$ = 0. Despite the increase in thermal conductivity measured at temperature 300–673 K, thermoelectric figure of merit $ZT$ of mechanically activated samples at $T$ = 670 K is higher than that of those not subjected to mechanical activation. The value of figure of merit $ZT$ = 0.31 obtained for $x$ = 0 is one of the highest reported in the literature for thermoelectrics based on SrTiO$_3$ at this temperature. Replacing titanium with phosphorus does not improve thermoelectric characteristics. A tendency towards a decrease in electrical resistance and an increase in thermal conductivity as a result of mechanical activation is observed for all studied samples.