Transport and magnetic properties of PrCo1-xNixO3 (x = 0.0-0.7)

The influence of Ni substitution on the transport and magnetic properties of the perovskite PrCo1-xNixO3 (x = 0.0-0.7) has been investigated by synthesizing and characterizing different samples. The unit cell volume of orthorhombic crystal structure expands with increasing Ni content, affecting the distortion of M-O (I, II)-M bond angles (M = Co, Ni). The expansion of the unit cell volume can be attributed to the larger ionic radii of Ni2+ and to the stabilization of the intermediate-spin state in the low-spin cobalt matrix. The electrical conduction mechanism varies with the Ni content with noticeable change from variable range hopping to nearest neighbour hopping in compositions 0.07 ≤ x ≤ 0.29. The Seebeck coefficient is positive for samples with 0.0 < x < 0.49. Only PrCo0.3Ni0.7O3 has a negative Seebeck coefficient. The ZFC/FC curves and M (H) hysteresis loops reveal both a spin-glass behaviour and ferromagnetic ordering below the Curie temperature (TC) for Ni-substituted samples. By the combination of Seebeck coefficient data and the measured effective magnetic moment μeff, the mixed valences of Co3+/Co4+ and Ni2+/Ni3+ in PrCo1-xNixO3 compounds were determined and the values are in agreement with x-ray photoemission spectroscopy measurements.