Solid Solutions between PbVO and BiCoO.

(1 - )PbVO-BiCoO solid solutions with 0 ≤ ≤ 1 were prepared at a high pressure of 5-6 GPa and a high temperature of 1223-1473 K. They adopt a polar tetragonal 4 structure for the 0 ≤ ≤ 0.3 and 0.75 ≤ ≤ 1 ranges with giant tetragonal distortions and a cubic 3̅ structure for the 0.4 ≤ ≤ 0.7 range. High-temperature structural studies with synchrotron X-ray powder diffraction showed that polarization, calculated by the point-charge model, and the tetragonal distortion remained nearly constant in the = 0.8 sample from 295 K up to the decomposition temperature of about 700 K. Magnetic and differential scanning calorimetry measurements showed that the Néel temperature, , nearly linearly decreased from 470 K for = 1 to 250 K for = 0.75 (with = 395 K for = 0.9 and = 295 K for = 0.8). Long-range magnetic ordering also takes place at = 44 K for = 0. All other samples with 0.1 ≤ ≤ 0.7 demonstrated spin-glass-like magnetic properties and notably reduced Weiss temperatures. Effective magnetic moments estimated for the = 0.6, 0.65, and 0.7 cubic samples gave evidence that cobalt is present in the +2 and +3 oxidation states, and Co cations take the low-spin state.