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

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 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 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.