Crystal structure of (KNa)CaSiO.

Single crystals of (KNa)CaSiO [idealized (KNa)CaSiO, di(pot-assium, sodium) tricalcium tris-ilicate], were obtained from the crystallization of a glass with a molar oxide ratio of KO:NaO:CaO:SiO = 1.5:0.5:6:6 that was annealed at 1273 K. The crystal structure can be characterized as a mixed-anion oxidosilicate with isolated [SiO] tetra-hedra as well as [SiO] single rings. The insular and cyclic silicate anions occur in the ratio 2:1, resulting in the idealized crystallochemical formula KNaCa[SiO][SiO]. Charge compensation is provided by K, Na (occupying the same sites) and Ca cations. The two unique Ca cations are coordinated by six O atoms, forming distorted octa-hedra. By sharing common corners, edges and faces, these [CaO] polyhedra build up octa-hedral layer-like motifs parallel to (010). (K/Na) ions reside in voids between the the silicate anions and the calcium centered octa-hedra and are coordinated by eight to nine oxygen ligands. (KNa)CaSiO is isotypic with KCaSiO indicating the existence of a solid-solution series K Na CaSiO