Studies on rare earth trisoxalatochromates (III), rare earth chromates (V) and rare earth chromites (III)

Abstract

Rare earth trisoxalatochromates (III), LnCr(C₂O₄)₃·nH₂O (n = 9 for La, and N = 8 for Ce, Pr and Nd) have been isolated and characterized by a number of physicochemical studies. These compounds (except for Ce) serve as precursors for the rare earth chromates (V) and chromites (III). LnCrO₄ may be obtained by heating LnCr(C₂O₄)₃·nH₂O at 520°C for 4 hr and LnCrO₃ at 900°C for a similar period. CeCr(C₂O₄)₃·8H₂O decomposes to a mixture of CeO₂ and Cr₂O₃. The EPR spectra of LaCrO₄ are consistent with a tetrahedral geometry of the CrO₄ group. Although the unit cell of LaCrO₄ is monoclinic and of NdCrO₄ is tetragonal, compounds of composition La_1-xNd_xCrO₄ show the presence of only monoclinic phase for x up to 0.23. The electronic spectra of LnCrO₃ are compatible with the perovskite structure of these compounds.