Tb2Co(B2O5)2 and Tb2Cu(B2O5)2 – two new borates with gadolinite-type structures

Abstract Using high-pressure/high-temperature synthesis methods, it was possible to increase the number of known borates with a crystal structure derived from gadolinite. Syntheses of Tb2Co(B2O5)2 (8 GPa, 1000 °C) and Tb2Cu(B2O5)2 (11 GPa, 650 °C) were carried out in a Walker-type multianvil device. The crystal structures were determined by single-crystal X-ray diffraction methods and Rietveld refinements of the powder patterns. The new compounds were further characterized by their infrared spectra. The lanthanoid cobalt and copper borates Tb2Co(B2O5)2 and Tb2Cu(B2O5)2 crystallize in the monoclinic space group P21/c (no. 14) with the unit cell parameters a = 4.5630(1), b = 7.2991(2), c = 9.4161(2) Å, and β = 91.14(1)° for the cobalt and a = 4.5757(1), b = 7.3078(2), c = 9.3771(3) Å, β = 90.73(1)° for the copper compound.