2015 Volume 56 Issue 6 Pages 864-871
In this study, polycrystalline samples of Pr1−xSrxMnO3 (0.1 ≦ x ≦ 0.7) were synthesized using a conventional solid-state reaction method. We investigated crystal structure, magnetic susceptibility (χ), and thermoelectric properties, such as electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ), as a function of temperature (T) or Sr content (x). The crystal structure at room temperature changed from orthorhombic Pbnm phases, with x ≦ 0.4, to tetragonal I4/mcm phases, with x ≧ 0.5. The samples for x ≦ 0.5 showed the ferromagnetic-like ground state below Curie temperature. Conversely, the samples for x = 0.5, 0.6, and 0.7 showed the charge-ordering ground state below 160 K, the A-type antiferromagnetic ground state below 310 K, and the C-type antiferromagnetic ground state below 318 K, respectively. Above room temperature, all the samples exhibited adiabatic small polaron conduction in a competition between the double exchange interaction and the Jahn-Teller distortion. Although the samples for x = 0.1 and 0.2 showed a large positive S below room temperature, the carrier type changed from hole-like to electron-like behavior above 1000 K and 500 K, respectively. Thus, all the samples for 0.1 ≦ x ≦ 0.7 showed a negative S at a high temperature. The largest dimensionless figure of merit (ZT) of all the samples above room temperature was 0.085 at 1073 K for x = 0.7, by a decrease in both ρ and lattice κ, and an increase in S. In addition, we obtained the largest ZT in the p-type specimens for x = 0.1, thus, attaining a maximum value of 0.0035 at 468 K. We discuss this behavior in terms of the potentiality to fabricate the oxide thermoelectric modules consisting of the same type of elements.
