Abstract

High-resolution neutron powder diffraction was used to study phase transitions in the leucite phases of KAISi2O6, RbAlSi2O6, CsAlSi2O6, and KFeSi2O6. The temperature-dependent structural behavior involves two mechanisms: relaxation of the tetrahedral framework about channel cations, and slowly changing T-O bond lengths. The high-temperature cubic phase is characterized by a fully-extended tetrahedral framework; thermal expansion occurs by an increase in mean T-O bond lengths. On decreasing temperature, a displacive phase transition to tetragonal symmetry is manifested by an optic instability; twisting of tetragonal prisms of comer-linked (Al,Si)O4 tetrahedra about [001] leads to collapse of the 〈111〉 structural channels and concomitant volume reduction.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.