Crystal structure and infrared spectra of Na2Al2B2O7

The structure of Na2Al2B2O7 has been refined on X-ray powder diffraction da ta collected in transmission mode by Rietveld techniques because the polycr ystalline samples exhibit a strong tendency of preferred orientation and th e single crystals are of poor quality. Final refinement on powder diffracti on data converged to agreement factors R-p=6.54%, R-wp=8.55% with R =5.24%. The title compound crystallizes in a trigonal space group P-31c. Lattice p arameters are refined to be a=4.8113(1) Angstrom and = 15.2781(3) Angstrom. The structure consists of infinite [Al2B2O7](x) sheets stacking along c-ax is and Na atoms in both the inter-sheets and intra-sheets. Infrared spectra of both Na2Al2B2O7 and Na2Ga2B2O7 are reported and a brief interpretation is given based on the structures. High quality X-ray powder diffraction dat a and results of thermal analysis are also presented. (C) 2001 Elsevier Sci ence B.V. All rights reserved.