Local structure of LuBO3 prepared via sol-gel process and its transformation with temperature:: 11B-NMR and L-edge XAS studies

The present work deals with the temperature effect on the stability range of LuBO3 prepared by sol-gel synthesis. Structural modifications from vaterite to calcite form versus the thermal treatments have been measured by X-ray diffraction and infrared spectroscopy. Several samples derived from the xerogel annealed at 400, 800 and 1200 degreesC were studied by B-11 solid state NMR and at the lutetium. L-I-L-III edges by X-ray absorption spectroscopy to determine the local atomic arrangement around the rare earth and the boron ions. The predominance of BO4 groups and the eightfold coordination of lutetium atoms in the LuBO3 xerogel in samples treated up to 800 degreesC indicate an evolution of the xerogel to vaterite form after thermal treatment instead of the expected calcite form as established for samples prepared by solid state reaction. (C) 2002 Elsevier Science B.V. All rights reserved.