Rietveld Refinement Strategy of CaTa<sub>4-x</sub>Nb<sub>x</sub>O<sub>11</sub> Solid Solutions Using GSAS-EXPGUI Software Package

Crystal structures of CaTa 4-x Nb x O 11 solid solutions ( x = 0, 1 and 2) in space group P 6 3 22, have been refined by application of the Rietveld method X-ray powder diffraction profile. Refinement were carried out using GSAS software and EXPGUI interface. The unit cell parameters and cell volume increase with increasing Nb content; all samples contain random distribution of Ta/Nb. Strategy and procedures for CaTa 4-x Nb x O 11 solid solutions refinement are reported. The structure consists of layers of tantalum-oxygen bipyramids sharing-edges alternating with layers of octahedra.