Istituto di Geoscienze e Georisorse     
Camara F., Gatta G. D., Meven M., Pasqual D. Thermal expansion and high temperature structure evolution of zoisite by single-crystal X-ray and neutron diffraction. In: Physics and Chemistry of Minerals, vol. 39 (1) pp. 27 - 45. Springer, 2012.
The thermo-elastic behaviour and the temperature-induced structure evolution of a natural Fe-free zoisite have been investigated by in situ single-crystal X-ray and neutron diffraction. Neither discontinuities in volume expansion nor changes in symmetry have been observed up to 1,023 K. Zoisite shows a negative thermal expansion along [100] at T > 700 K, while a continuous positive expansion occurs on the (100) plane. Two different regimes in the anisotropic thermal behaviour of zoisite can be distinguished (i.e. at T < 700 K and T > 700 K), corresponding to an increase in the volumetric thermal expansion at T > 700 K. The structure evolution with temperature has been described by a series of X-ray and neutron refinements at different temperatures. In particular, the M(3) polyhedra show a significant octahedral flattening and expansion in the equatorial plane with T. All [SiO4] tetrahedra show a regularization with increasing T. The neutron refinements show no change in the configuration of the hydrogen bonding at least up to 873 K. The effects of the T-induced main deformation mechanisms on the anisotropic elastic behaviour of zoisite are discussed. A comparison with the thermal behaviour of epidote has been carried out.
URL: http://https://link.springer.com/journal/269
Subject zoisite
thermal expansion
single-crystal X ray diffraction
single-crystal neutron diffraction
hydrogen bonding

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