Growth, characterization, and high-pressure optical studies of CuWO₄

Abstract

Copper tungstate (CuWO₄) crystals grown by the top-seeded solution growth method were characterized by X-ray diffraction, Raman scattering, and optical measurements. CuWO₄ has a triclinic structure (P 1¯) with a = 4.709 Å, b = 5.845 Å, c = 4.884 Å, α = 88.3°, β = 92.5°, and γ = 97.2°. It consists of corner-linked CuO₆ and WO₆ octahedra, the former having a pseudo-tetragonally elongated geometry caused by the Cu²⁺ Jahn–Teller effect. Fifteen out of the eighteen Raman modes of CuWO₄ are reported, discussed, and compared with those of other tungstates. We also determined the indirect band-gap energy of CuWO₄ (2.3 eV) and its negative pressure coefficient up to 25 GPa. The pressure evolution of the band-gap is discussed in terms of the electronic structure of CuWO₄. Finally, no clear evidence of structural changes were found in our high-pressure experiments, but large amounts of defects are apparent beyond 18 GPa.

Keywords:

• CuWO₄
• tungstates
• scintillating material
• crystal structure
• electronic properties

Acknowledgements

Research supported by the Spanish MICINN (Grants MAT2007-65990-C03-01, MAT2006-02279, and CSD-2007-00045) and the Science & Technology Plan Project of Fujian, China (Grants 2005HZ1026, 2007H0037, and SZD08001-2). The authors thank F. Rey (ITQ, CSIC-UPV) for giving access to diffraction and Raman setups.

Additional information

Notes on contributors

D. Errandonea

Presently at the Fundación General de la Universidad de Valencia.