Abstract
This paper reports electrical transport studies of rare-earth vanadates (RVO4 with R = Ce, Pr, Nd, Sm, Eu and Gd), prepared by solid state reaction and characterized by X-ray diffraction studies. TGA study (300 to 1200 K) shows no weight loss; possible phase transitions in the range 1075 to 1300 K have been indicated by DTA studies. All these vanadates are typical semiconducting compounds with room temperature electrical conductivity (σ) lying between 10−4 and 10−2Ω−1m−1. Measurements of σ and the Seebeck coefficient (S) are reported in the temperature interval 400 to 1200 K. Two linear regions 400 to T 1K and T 1 to T 2K have been obtained from the log σ against T −1 as well as the S against T −1 plots followed by a peak around T 3 and minima around T 4K. T 4>T 3>T 2>T 1, are different for different vanadates. It has been concluded that in the interval 400 to T 1K, conduction is of the extrinsic hopping type with Ce4+ in CeVO4, Pr4+ in PrVO4 and V4+ in Nd to Gd vanadates as dominant defect centres. In the temperature interval T 1, to T 2K, the conduction has been shown to be of the intrinsic band type in all vanadates with polarons of intermediate coupling strength as the dominant charge carriers. Above T 2 all vanadates tend to become metallic, but before this is achieved the phase change makes the conductivity smaller. T 4 is close enough to the temperature corresponding to the DTA peak to be termed the phase transition temperature.
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Gaur, K., Lal, H.B. Electrical transport in light rare-earth vanadates. J Mater Sci 20, 3167–3176 (1985). https://doi.org/10.1007/BF00545182
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DOI: https://doi.org/10.1007/BF00545182