Accurate Refinement of the Crystal Structure of Ba3TaGa3Si2O14 from Langasite Family and Analysis of Structural Transformations Due to Isomorphous Cation Substitutions

An accurate structure analysis of a Ba3TaGa3Si2O14 single crystal from langasite family was performed using four X-ray diffraction data sets collected on a diffractometer equipped with a CCD area detector (sp. gr. P321, Z = 1, sin theta/lambda <= 1.35 angstrom(-1); at 295 K a = 8.516(1) angstrom, c = 5.1910(6) angstrom, R/wR = 0.58/0.56%, Delta rho(min)/Delta rho(max) = -0.73/0.42 e/angstrom(3), 4414 independent reflections; at 106 K a = 8.5109(9) angstrom , c = 5.1861(9) angstrom , R/wR = 0.75/0.86%, Delta rho(min)/Delta rho(max) = -0.81/1.06 e/angstrom(3), 4382 reflections). The distinguishing feature of the Ba3TaGa3Si2O14 structure is a strong disorder of the Ga atom at the 3f site. Structural transformations in the series of Ca3TaGa3Si2O14-Sr3TaGa3Si2O14-Ba3TaGa3Si2O14-Ba3TaFe3Si2O14 crystals were analyzed.