Transport and thermoelectric properties of (Sr1−xEux)3Ti2O7

Abstract

The transport and thermoelectric properties of polycrystalline bulk samples (Sr1−xEux)3Ti2O7 with different Eu-doped contents x were investigated. The experiments revealed that electrical resistivity ρ and the absolute value of Seebeck coefficient |S| decreased as x increased from 0.05 to 0.1 at temperatures ranging from 300 to 1000 K. However, electrical resistivity ρ increased instead when x further increased from 0.1 to 0.15, whereas |S| dropped below 450 K and then rose above 450 K. |S| for (Sr1−xEux)3Ti2O7 (x = 0.05, 0.1) increased linearly in tandem with an increase in temperature, whereas |S| for (Sr1−xEux)3Ti2O7 (x = 0.15) increased first, decreased next, and finally increased in tandem with an increase in temperature. The abnormality of |S| with temperature for (Sr0.85Eu0.15)3Ti2O7 may be attributed to the existence of mixed conduction in this sample. Moreover, mobile charge-carrier thermal conductivity is somewhat negligible compared with that of phononic contribution, suggesting that phonon contribution is predominant in these oxides. Thermal conductivity κ for all compounds decreased gradually with increasing temperature. The dimensionless figure of merit (ZT) values of Eu-doped compounds increased with an increase in temperature. The maximum ZT is 0.061, which was obtained in compound (Sr0.9Eu0.1)3Ti2O7 at 1000 K.