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 <i>X</i>, <i>Y</i>, <i>M</i>, and <i>T</i> in the general formula <i>XY</i> ₂[<i>M</i>(<i>T</i>O₄)₂] are fully occupied by atoms of different elements. The crystal structures of the title compounds were refined in space group <i>P</i>3 under consideration of a two-component twin model. The SiO₄ tetra-hedra are rotated approximately ±10.2° from the mirror plane of space group <i>P</i>3<i>m</i> around an axis parallel to [001].