Self-Propagating High-Temperature Synthesis of Lanthanide Orthochromites LnCrO<sub>3</sub>

Abstract

Lanthanide orthochromites of general formula LnCrO(3) (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, Lu) have been made by Self-propagating High-temperature Synthesis (SHS). Four different series of SHS samples were produced; series 1 - SHS of Ln(2)O(3), Cr and CrO3 with NaClO4 or Ba(CLO4)(2) in air; series 2 - SHS of Ln(2)O(3), Cr and CrO3 in oxygen; series 3 - SHS of LnCl(3), CrCl3 and NaO2 or Na2O2 in air; series 4 - SHS of Ln(NO3)(3), Cr and melamine in air. Maximum reaction temperature T-c and propagation velocity Uc were measured for all reactions. Selected series 1 reactions were studied by DTA these showed an exotherm at 450 degrees C. X-ray powder diffraction showed, that in all series of SHS reactions a single phase orthorhombic perovskite structure was produced. 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 reflection spectra for the LnCrO(3) materials gave four broad absorbtions in the region 800-200 cm(-1).