Transport and thermoelectric properties of (Sr 1− x Eu x ) 3 Ti 2 O 7

The transport and thermoelectric properties of polycrystalline bulk samples (Sr 1− x Eu x ) 3 Ti 2 O 7 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 (Sr 1− x Eu x ) 3 Ti 2 O 7 ( x = 0.05, 0.1) increased linearly in tandem with an increase in temperature, whereas | S | for (Sr 1− x Eu x ) 3 Ti 2 O 7 ( x = 0.15) increased first, decreased next, and finally increased in tandem with an increase in temperature. The abnormality of | S | with temperature for (Sr 0.85 Eu 0.15 ) 3 Ti 2 O 7 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 (Sr 0.9 Eu 0.1 ) 3 Ti 2 O 7 at 1000 K.