The low-temperature behavior of balliranoite (CAN topology): An in situ single-crystal X-ray diffraction study

The thermoelastic behavior and structural evolution of a natural balliranoite (Na4.47Ca2.86K0.11)(Si5.96Al6.04O24)Cl-2.03(CO3)(0.78)(SO4)(0.33), a = 12.6701(3) angstrom, c = 5.3178(1) angstrom, and V = 739.30(3) angstrom(3), space group P6(3), the CO32- analogue of davyne, a cancrinite-group mineral, have been studied within the range 108 <= T (K) <= 293 by in situ single-crystal X-ray diffraction. No evidences of phase transition or change of the "compressional" behavior have been observed. The refined volume thermal expansion coefficient is alpha(V) = 4.6(4)*10(-5) K-1, whereas the refined unit-cell edges linear thermal expansion coefficients are alpha(a) = 1.4(2)*10(-5) K-1 and alpha(c) = 1.7(2)*10(-5) K-1. The structural evolution at T <= 293 K is driven by the rotation of the rigid TO4 framework tetrahedra. A description of the main deformation mechanisms is carried out along with a comparison with the cancrinite behavior at the same temperature conditions. Significant differences pertaining to the mechanisms acting on the (0001) plane are observed between these isotypic materials. These results suggest that the coordination environment of cations within the can unit could influence the magnitude of the [CAN] framework deformation at low-T. (C) 2013 Elsevier Inc. All rights reserved.