Data di Pubblicazione:
2005
Citazione:
Thermal expansion and phase transitions in akermanite and gehlenite / M. Merlini, M. Gemmi, G. Artioli. - In: PHYSICS AND CHEMISTRY OF MINERALS. - ISSN 0342-1791. - 32:3(2005), pp. 189-196.
Abstract:
Thermal expansion has been measured by laboratory and synchrotron X-ray powder diffraction for end-member (a) over circle kermanite (ak, Ca2MgSi2O7) and gehlenite (ge, Ca2Al2SiO7) in the range 20-1,500 K. In ak in the range 340-390 K, there is a negative linear thermal expansion in [001] direction. This is related to the phase transition from an incommensurate modulated structure (IC) to a normal one (N). The volumetric mean thermal expansion coefficients for ak and ge, obtained with a linear fit of the experimental data in the temperature range 298-1,400 K, are respectively 32.1x10(-6) and 28.3x10(-6) K-1. The variation of the c/a ratio with temperature, due to different thermal expansion along the crystallographic axes, can be related to the different behaviour of the tetrahedral layers in the N and IC phases. Analysis of the variation of the superstructure peaks intensity across the phase transition confirms the tricritical behaviour of the IC/N transition in ak.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
X-ray powder diffraction; akermanite; gehlenite; thermal expansion; incommensurate modulated structure; phase transition
Elenco autori:
M. Merlini, M. Gemmi, G. Artioli
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