The reversible a ? ß phase transition of Cu 2As2O7

Author(s)
Matthias Weil, Christian Lengauer, Ekkehard Füglein, Enrique J. Baran
Abstract

Single crystals of copper(II) pyroarsenate(V), Cu2As 2O7, were prepared by chemical transport reactions in sealed and evacuated silica ampules starting from stoichiometric mixtures of the component oxides and chlorine as transport agent (temperature gradient 880 ? 800°C, 5 days). Cu2As2O7 is dimorphous and shows a reversible a (low-temperature) ? ß (high-temperature) phase transition at 356(2)°C detected by differential scanning calorimetry (DSC) and high-temperature X-ray powder diffraction (XRPD) measurements. The crystal structure of a-Cu2As 2O7 (C2/c, Z = 4, a = 7.237(3), b = 8.2557(17), c = 9.780(3) A°, ß = 111.03(2)°, R[F2 > 2s(F 2)] = 0.028) was determined from single-crystal data at room temperature. It crystallizes isotypically with a-Cu2P 2O7 and ß-Cu2V2O7. The thortveitite-type crystal structure of ß-Cu2As 2O7 (C2/m, Z = 2, a = 7.0987(3), b = 8.2777(4), c = 4.8666(2) A°, ß = 110.206(4)°, R(Bragg) = 0.1056) was determined by means of high-temperature XRPD recorded at 400°C. The crystal structures of both polymorphs are closely related and consist of infinite sheets of [CuOx] polyhedra (a: x = 5; ß: x = 6) and interjacent As2O7 anions that occur either in a bent (As-O-As) configuration (a-Cu2As2O7, bridging angle 145.9(2)°) or in a linear (As-O-As) configuration (ß-Cu 2As2O7). a-Cu2As 2O7 was further characterized by vibrational spectroscopy. Its IR and Raman spectra are discussed on the basis of a factor group analysis.

Organisation(s)
Department of Mineralogy and Crystallography
External organisation(s)
Technische Universität Wien, Netzsch-Gerätebau GmbH., Universidad Nacional de La Plata
Journal
Crystal Growth & Design
Volume
4
Pages
1229-1235
No. of pages
7
ISSN
1528-7483
Publication date
2004
Peer reviewed
Yes
Austrian Fields of Science 2012
1051 Geology, Mineralogy
Portal url
https://ucrisportal.univie.ac.at/en/publications/3ba47946-c0fa-42db-9558-f23c9648c7cf