Low-temperature behavior of natural kalsilite with P31c symmetry: An in situ single-crystal X-ray diffraction study

Gatta, G. Diego and Angel, Ross J. and Carpenter, Michael A. (2010) Low-temperature behavior of natural kalsilite with P31c symmetry: An in situ single-crystal X-ray diffraction study. American Mineralogist, 95 (7). pp. 1027-1034. DOI 10.2138/am.2010.3478

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Abstract

The low-temperature behavior of a natural kalsilite (ideal formula KAlSiO4) with P31c symmetry has been investigated by in situ single-crystal diffraction. A series of intensity data collections and structural refinements have been performed at 298, 250, 200, 150, and 100 K on decreasing temperature, and 175, 225, and 275 K on increasing T. The variations of the unit-cell parameters of kalsilite as a function of T are continuous, and show no evidence of any phase transitions or thermo-elastic anomalies in this temperature range. An expansion is observed along [0001] with decreasing temperature. The axial and volume thermal expansion coefficients ({alpha}j = lj-1{middle dot}{partial}lj/{partial}T, {alpha}V = V-1{middle dot}{partial}V/{partial}T) between 298 and 100 K, calculated by weighted linear regression through the data points, are {alpha}a = {alpha}b = 1.30(6){middle dot}10-5, {alpha}c = -1.5(1){middle dot}10-5, {alpha}V = 1.1(2){middle dot}10-5 K-1. The main structural change on decreasing temperature is a cooperative anti-rotation of tetrahedra forming the six-membered rings lying parallel to (0001). This tetrahedral rotation is coupled with a change in the distances between the extra-framework cations and the framework O atoms. A small decrease in the tetrahedral tilts perpendicular to [0001] is responsible for the negative thermal expansion along [0001]; the implications of these mechanisms for thermal expansion in nephelines and kalsilites are discussed.

Item Type:	Article
Uncontrolled Keywords:	2010AREP; IA61;
Subjects:	03 - Mineral Sciences
Divisions:	03 - Mineral Sciences
Journal or Publication Title:	American Mineralogist
Volume:	95
Page Range:	pp. 1027-1034
Identification Number:	10.2138/am.2010.3478
Depositing User:	Sarah Humbert
Date Deposited:	09 Sep 2010 14:16
Last Modified:	23 Jul 2013 10:00
URI:	http://eprints.esc.cam.ac.uk/id/eprint/1932

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