Hydroxide precursors to produce nanometric YCrO3: Characterization and conductivity analysis

A precursor to produce perovskite-type YCrO3 was precipitated by bubbling gaseous ammonia into an yttrium/chromium salts solution. X-ray diffraction showed that the as-prepared powders were amorphous. Thermal treatment between 1273 and 1373 K, leads to formation of polycrystalline YCrO3 with crystal sizes around 20 nm. High resolution X-ray photoelectron spectra showed uniform chemical environment for yttrium and chromium in the amorphous hydroxide and crystalline YCrO3. Shifts between Y 3d5/2 and Cr 2p3/2 binding energy suggest redistribution or charge transfer between yttrium and chromium ions in the YCrO3 structure. The electrical properties of YCrO3, whose precursors were precipitated with gaseous ammonia are different than those prepared by combustion synthesis. Electrical conductivity presents a sudden increase at ∼473 K, which is associated to the grain size and morphology of the crystallites. The redistribution of charge between Y(III) and Cr(III) is thermally activated by the hopping of small-polarons, which are characterized by the Arrhenius law as the conductive mechanism.