CRYSTAL-STRUCTURES AND MAGNETIC-PROPERTIES OF THE HIGH-PRESSURE MODIFICATIONS OF COMOO4 AND NIMOO4

The wolframite structure with beta < 90 degrees instead of beta > 90 degrees is observed for the high-pressure modifications of CoMoO4(II) and NiMoO4(II). Atomic parameters are reported as derived from X-ray powder diffraction with Rietveld refinement. Both compounds were prepared at a pressure of 50 kbar at 873 K from their alpha-phases. Antiferromagnetic ordering is observed below 68(1) K for CoMoO4(II) and 83(1)K for NiMoO4(II). At higher temperatures both compounds obey a Curie-Weiss law with Theta = - 125(5) K and \mu\(Co2+)= 5.4(1)mu(B) for CoMoO4(II) and Theta = - 145(5) K and \mu\(Ni2+)= 3.7(1)mu(B) for NiMoO4(II).