| Abstract: | Lanthanide orthochromites of general formula LnCrO3 (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, Lu) and YCrO3 have been made by self-propagating high-temperature synthesis (SHS). Four different SHS reactions were found to form LnCrO3: reaction of Ln2O3, Cr and CrO3 with NaClO4 or Ba (ClO4)2 in air; reaction of Ln2O3, Cr and CrO3 in oxygen; reaction of LnCl3, CrCl3 and NaO2 or Na2O2 in air and reaction of Ln (NO3)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 Tc and propagation velocity Uc 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 LnCrO3 samples were all shown to be weak antiferromagnets. IR spectra for the LnCrO3 materials showed bands at 635, 480, 440, 350 and 180 cm−1. |
