Monoclinic-to-orthorhombic phase transition in Cu2(AsO4)(OH) olivenite at high temperature: strain and mode decomposition analyses

Tarantino, Serena C. and Zema, Michele and Callegari, Athos M. and Boiocchi, Massimo and Carpenter, Michael A. (2018) Monoclinic-to-orthorhombic phase transition in Cu2(AsO4)(OH) olivenite at high temperature: strain and mode decomposition analyses. Mineralogical Magazine, 82 (02). pp. 347-365. ISSN 0026-461X DOI https://doi.org/10.1180/minmag.2017.081.048

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Official URL: https://doi.org/10.1180/minmag.2017.081.048

Abstract

A natural olivenite single crystal was submitted to in situ high-temperature single-crystal X-ray diffraction from room temperature (RT) to 500°C. Unit-cell parameters were measured at regular intervals of 25°C, and complete datasets collected at T = 25, 50, 100, 150, 200, 250, 300, 400 and 500°C. Evolution of unit-cell parameters and structure refinements indicates that olivenite undergoes a structural phase transition from P21/n to Pnnm at ~200°C, and eventually becomes isostructural with the other members of the olivenite-mineral group. Volume expansion with temperature is larger in the monoclinic phase – where it follows a non-linear trend – than in the orthorhombic one. Axial and volume expansion coefficients of the orthorhombic olivenite phase are positive and linear and similar to those of the other Cu-bearing member of the mineral family, namely libethenite, but rather different from those of the Zn-analogue arsenate adamite. Distortion of Cu polyhedra is quite high in the olivenite monoclinic phase at RT and goes towards a relative regularization with increasing T until the phase transition occurs. In the orthorhombic phase, no significant variation of the polyhedral distortion parameters is observed with increasing temperature, and maximum expansion is along the b direction and governed by corner-sharing. Landau potential provides a good representation of the macroscopic changes associated with the phase transition, coupling between the strains and the order parameter is responsible for the nearly tricritical character of the transition.

Item Type: Article
Uncontrolled Keywords: 2018AREP; IA72
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
Journal or Publication Title: Mineralogical Magazine
Volume: 82
Page Range: pp. 347-365
Identification Number: https://doi.org/10.1180/minmag.2017.081.048
Depositing User: Sarah Humbert
Date Deposited: 11 Apr 2019 13:58
Last Modified: 11 Apr 2019 13:58
URI: http://eprints.esc.cam.ac.uk/id/eprint/4467

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