On the P-induced behavior of the zeolite phillipsite: an in situ single-crystal synchrotron X-ray diffraction study

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• 作者：Davide Comboni ; G. Diego Gatta ; Paolo Lotti…
• 关键词：Phillipsite ; High pressure ; Compressibility ; Elastic behavior ; Structure evolution ; Synchrotron X ; ray diffraction
• 刊名：Physics and Chemistry of Minerals
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：44
• 期：1
• 页码：1-20
• 全文大小：
• 刊物类别：Earth and Environmental Science
• 刊物主题：Mineralogy; Crystallography and Scattering Methods; Geochemistry; Mineral Resources;
• 出版者：Springer Berlin Heidelberg
• ISSN：1432-2021
• 卷排序：44

文摘

The elastic behavior and the structural evolution at high pressure of a natural phillipsite have been investigated by in situ single-crystal X-ray diffraction up to 9.44 GPa, using a diamond anvil cell and the nominally penetrating P-transmitting fluid methanol:ethanol:water (16:3:1) mix. Although no phase transition was observed within the P-range investigated, two different compressional regimes occur. Between 0.0001 and 2.0 GPa, the refined elastic parameters, calculated by a second-order Birch–Murnaghan equation of state (BM-EoS) fit, are V₀ = 1005(1) Å3, K₀ = 89(8) GPa for the unit-cell volume; a₀ = 9.914(7) Å, K_a = 81(12) GPa for the a-axis; b₀ = 14.201(9) Å, K_b = 50(5) GPa for the b-axis; and c₀ = 8.707(2) Å, K_c = 107(8) GPa for the c-axis (K_a:K_b:K_c ~1.62:1:2.14). Between 2.0 and 9.4 GPa, a P-induced change in the configuration of H₂O molecules, coupled with a change in the tilting mechanisms of the framework tetrahedra, gives rise to a second compressional regime, in which the phillipsite structure is softer if compared to the first compressional range. In the second compressional regime, the refined elastic parameters, calculated by a second-order BM-EoS fit, are V₀ = 1098 (7) Å3, K₀ = 18.8(7) GPa for the unit-cell volume; a₀ = 10.07(3) Å, K_a = 30(2) GPa for the a-axis; b₀ = 14.8(1) Å, K_b = 11(1) GPa for the b-axis; and c₀ = 8.94(2) Å, K_c = 21(1) GPa for the c-axis (K_a:K_b:K_c ~2.72:1:1.90). The evolution of the monoclinic β angle with pressure shows two distinct trends in the two compressional regimes: with a negative slope between 0.0001 and 2.0 GPa, and a positive slope between 2.0 and 9.4 GPa. The mechanisms, at the atomic scale, that govern the two compressional regimes of the phillipsite structure are described.