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Thermodynamical Behaviour of Quartz Around the Transitions Between α, Incommensurate and β Phases
Published online by Cambridge University Press: 21 February 2011
Abstract
Recently an intermediate incommensurate phase has been found around 846 K in a small temperature range of 1.3 K between the usual α and β phases of quartz. In the neighborhood of these transitions most physical properties show drastic variations which has remained a puzzle. We shall present some measurements of the heat capacity Cp and of thermal expansion coefficients αi which present very large variations in the incommensurate phase. These divergences can be related by Pippard-Garland relations in the 3 phases. Furthermore in the low temperature α phase this result can be explained by the existence of a macroscopic order parameter η related to SiO4 tetrahedra, and varying as predicted by the Landau theory of 1st order phase transition. While in the high temperature phases (β and incommensurate) η vanishes, it takes a finite value in α phase, increasing continuously upon further cooling. However at the microscopic level, the discontinuity is reduced by the existence of the incommensurate phase, which corresponds probably to modulated tilting of SiO4 tetrahedra.
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- Copyright © Materials Research Society 1984
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