Orthosilicates with glaserite-type crystal structures: Na2BaZr[SiO4]2 and Na2BaHf[SiO4]2.

Single crystal particles of Na2BaZr[SiO4]2 [systematic name: disodium barium zirconium bis-(orthosilicate)] and Na2BaHf[SiO4]2 [disodium barium hafnium bis-(orthosilicate)] were extracted from grain-grown polycrystals obtained by heating compacts of binary oxide mixtures at 1473 K. Single crystal X-ray diffraction analysis revealed that these are isostructural orthosilicates with a glaserite-type crystal structure, in which all sites of X, Y, M, and T in the general formula XY 2[M(TO4)2] are fully occupied by atoms of different elements. The crystal structures of the title compounds were refined in space group P3 under consideration of a two-component twin model. The SiO4 tetra-hedra are rotated approximately ±10.2° from the mirror plane of space group P3m around an axis parallel to [001].