Convenient, rapid synthesis of rare earth orthochromites LnCrO 3 by self-propagating high-temperature synthesis

Abstract

Lanthanide orthochromites of general formula LnCrO 3 (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, Lu) and YCrO 3 have been made by self-propagating high-temperature synthesis (SHS). Four different SHS reactions were found to form LnCrO 3: reaction of Ln 2O 3, Cr and CrO 3 with NaClO 4 or Ba (ClO 4) 2 in air; reaction of Ln 2O 3, Cr and CrO 3 in oxygen; reaction of LnCl 3, CrCl 3 and NaO 2 or Na 2O 2 in air and reaction of Ln (NO 3) 3, Cr and melamine in air. Reactions were studied by DTA and TGA experiments which showed exotherms and weight losses associated with the initiation temperatures ( ca. 350°C) of the SHS reactions. Maximum reaction temperature T c and propagation velocity U c were measured for selected reactions. X-ray powder diffraction showed a single phase orthorhombic perovskite structure was produced in all reactions. Systematic changes in the lattice parameters, cell volume and pycnometrical densities were seen as a function of lanthanide atomic number. SHS prepared LnCrO 3 samples were all shown to be weak antiferromagnets. IR spectra for the LnCrO 3 materials showed bands at 635, 480, 440, 350 and 180 cm −1.