Abstract
Double perovskite Nd2Co1-xCrxMnO6 (x = 0, 0.1, 0.2, 0.3) samples were synthesized by a sol-gel method, and their structural, magnetic and thermoelectric properties were investigated. X-ray diffraction analysis showed that all crystallized in a monoclinic P21/n structure. The lattice parameters and unit cell volume increase with increasing Cr content. Two ferromagnetic transitions were observed in the Cr-doped samples, which can be attributed to the exchange interactions of the ordered Co2+–O–Mn4+ and the disordered Cr3+/Co3+–O–Mn3+ clusters, respectively. A large coercive field of 10.6 kOe was achieved at 10 K for the sample with x = 0.2. The magnetic transition temperatures and the magnetic moments decrease with increasing Cr content, which combined with the Raman analysis indicated a decrease in the degree of the B-site ordering. Both the electrical conductivity (σ) and Seebeck coefficient (S) increase over the temperature range of 190–1100 K with Cr doping. The undoped Nd2CoMnO6 exhibits a colossal S of 2273 μV/K at 220 K and has a negative S between 300 and 700 K with a maximum of − 24 μV/K at 325 K. All the Cr-doped samples are p-type semiconductors. The conduction mechanism follows the small polaron hopping model.
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