Thermoelectric properties of the Pr0.8Na0.2MnO3 manganite at ultrahigh pressures of up to 20 GPa

The pressure dependences of the thermopower and electrical resistance of the Pr_0.8Na_0.2MnO₃ manganite are measured in the pressure range 0–20 GPa at room temperature. The thermopower varies nonmonotonically with pressure: the magnitude of the thermopower increases in the range of comparatively low pressures P < 5 GPa and decreases at higher pressures, whereas the electrical resistance decreases throughout the pressure range studied. The pressure at which the pressure coefficient dS/dP reverses sign is close to the value at which the Pr_0.8Na_0.2MnO₃ manganite undergoes a magnetic phase transition in the low-temperature range. The correlation between the specific features in the behavior of the thermopower with variations in pressure and the transformations of the magnetic and crystal structures of Pr_0.8Na_0.2MnO₃ at high pressures is discussed.