Crystal and Magnetic Structure of PbCrO3

Abstract

PbCrO₃ has been synthesized in the high‐pressure ``belt'' apparatus from PbO and CrO₂ at 1150°C and a pressure in excess of 50 kbar. Single‐crystal and powder x‐ray diffraction at room temperature show the compound has the cubic perovskite structure with a₀=4.00 Å. No deformation of the cubic structure was discerned in neutron diffraction patterns at 77° and 4.2°K. At low temperature the magnetic moments of the chromium atoms are ordered in the antiferromagnetic G‐type structure in which the spins on each Cr are antiparallel to those of the six nearest neighbors. Assuming the magnetic form factor of chromium can be approximated by that of Cr³⁺, the magnetic intensities give a moment of 1.9 μ_B per chromium atom, approximately the spin value for Cr⁴⁺ (3d²). The temperature dependence of the (111) magnetic peak was measured and the results fitted to a Brillouin function with T_N≈240°K. The magnetic susceptibility does not show a maximum at the Néel point but does obey a Curie‐Weiss law above T_N, consistent with the neutron‐diffraction results.