The reversible a ? ß phase transition of Cu 2As2O7
- Autor(en)
- Matthias Weil, Christian Lengauer, Ekkehard Füglein, Enrique J. Baran
- Abstrakt
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(en)
- Institut für Mineralogie und Kristallographie
- Externe Organisation(en)
- Technische Universität Wien, Netzsch-Gerätebau GmbH., Universidad Nacional de La Plata
- Journal
- Crystal Growth & Design
- Band
- 4
- Seiten
- 1229-1235
- Anzahl der Seiten
- 7
- ISSN
- 1528-7483
- Publikationsdatum
- 2004
- Peer-reviewed
- Ja
- ÖFOS 2012
- 1051 Geologie, Mineralogie
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/3ba47946-c0fa-42db-9558-f23c9648c7cf