Syntheses and structures of BAPr_xBi_(1-x)O_3 perovskites

摘要

The perovskite-type BaPr_(0.75)Bi_(0.25)O_(2.69) and BaPr_xBi_(1-x)O_3 (x = 0.025, 0.10, 0.25, 0.33, 0.5, 0.67, 0.75) solid solutions containing mixed valent praseodymium and bismuth ions have been synthesized via a two-stage synthetic procedure. The crystal structure of BaPr_(0.67)Bi_(0.33)O_3 has been refined from X-ray data by the Rietveld method and was found to be orthorhombic (Pnma) with a = 6.1650(2) A, b = 8.7069(2) A, c = 6.2014(1) A. The Rietveld refinement of BaPr_(0.75)Bi_(0.25)O_3 has revealed an orthorhombic cell (Pnma) with a = 6.1713(3) A, b = 8.7145(3) A, c = 6.2106(2) A. Magnetic transitions at 4.4 K and 9.1 K in a low magnetic field (0.001 T) were observed for BaPr_(0.75)Bi_(0.25)O_(2.69) and BaPr Pr_(0.75)Bi_(0.25)O_3 respectively. Divergences between the ZFC and FC measurements of magnetic susceptibility were observed for BaPr_(0.025)Bi_(0.975)O_3 and BaPr_(0.25)Bi_(0.75)O_3. Two regions of different valence situations in BaP_xBi_(1-x)O_3 were established. Interestingly, the readiness of praseodymium to adopt the tetravalent state increases with growing x.