Seebeck coefficient in the system (Gd1-xCax)MnO2.98 (0.6≤x≤0.95)

The Seebeck coefficient (S) of the perovskite system (Gd1-xCax)MnO2.98(0.6≤x≤0.95) was measured in the temperature range 100 to 350 K. S is negative and temperature-independent at high temperature. The temperature-independent region extends to lower temperatures with increasing x. In the region 0.8≤x≤0.95, the low- and the high-spin states of Mn3+ coexist. The temperature independence of S is explained by the hopping model. In the range 0.6≤x<0.8, the spi state of the Mn3+ ion changes from low to high at a metal-insulator transition temperature (Tt). A monotonous change of S corresponds to the change from a semiconductor to a metal