Original paper

Thermally induced reversible phase transformations of boroleucite, KBSi2O6

Krzhizhanovskaya, Maria G.; Bubnova, Rimma S.; Derkacheva, Elena S.; Depmeier, Wulf; Filatov, Stanislav K.

Abstract

The high-temperature structural behaviour of the monoclinic and cubic phases of ANA-type boroleucite, KBSi2 O6, was studied by X-ray powder diffraction. Boroleucite crystallizes with different symmetry depending on the method of preparation: the P 21/a monoclinic modification was obtained by dry high-pressure synthesis at 600°C and 0.5 GPa, whereas the cubic I43d phase was prepared by solid-state reaction at 700°C, 1 bar, for 72 h. Both modifications undergo reversible transformations at higher temperatures, viz. P21/a↔ (at 800°C) Ia3 d and I4 3 d↔ (at 300°C) P 2 1/ a↔ (at 550°C) Ia3 d, respectively. The values of the thermal-expansion coefficients are reported. The high-temperature Ia3 d modification of KBSi 2O6 exhibits the lowest thermal expansion (6–10 x 10-6°C-1); it decomposes above 1000°C with formation of SiO2.

Keywords

high-temperature powder diffractionborosilicateshigh-temperature polymorphic transformationphase transitionana typeleucitethermal expansion