Comparative Study of Single Crystals and Laser-grown Films of V 2 O 5
- PDF / 251,024 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 47 Downloads / 248 Views
L. Na´nai Department of Physics, JCYTFK, H-6720 Szeged, Dom t. 9, Hungary
W. Marine Department of Physics, University of Marseille, Marseille, F-13288 Cedex 9, France
S.P. Souto and M. Balkanski Laboratory of Solids, University of P. and M. Curie, Paris, F-75252 Cedex 05, France
Thomas F. George Office of the Chancellor/Departments of Chemistry and Physics & Astronomy, University of Wisconsin—Stevens Point, Stevens Point, Wisconsin 54481 (Received 24 October 2001; accepted 14 February 2002)
Comparative investigations are carried out for spectral (Raman) electrical and structural properties of V2O5 single crystals and polycrystalline samples obtained by IR laser light illumination of pure metallic samples in an oxidizing atmosphere (air). It is shown that the structures grown on metallic plates in the field of laser light are predominantly V2O5 polycrystals. Raman measurements reveal that the main peaks, which are characteristic for single crystals, are also present in laser-driven samples but with different intensities. Some peaks are attributed to laser-grown thick films, which are not present in the single-crystalline phase. There are shifts in the peak positions indicating the existence of different force constants for films as compared with crystals. The activation energies obtained from the electrical properties (conductivity, impedance versus temperature) yield similar values except for the anisotropic characteristics of the single crystal where the values are a bit different along different crystallographic axes (unlike the polycrystalline oxide films made by the laser). The single-crystalline phase has a well-defined layered structure with well-defined shapes showing formed units of truncated oktaeders, while the film structure shows randomly distributed tubular micron-size structures with empty holes at the peripheral part of the irradiated area, and nanoscaled long and thin tubes well oriented along the direction of the incoming laser light in the central part of the irradiation spot.
I. INTRODUCTION
Vanadium oxide crystals, including V2O5, have been widely examined, while the oxides grown under nonisothermal conditions, e.g., in the field of laser light, have received much less attention.1– 4 These oxides are of great interest for technological applications in the chemical and pharmaceutical industries.5,6 Vanadium pentoxide crystals and their xerogels and aerogels are especially used in catalysis and in sensor and nuclear technics.7 Oxides of vanadium and some other metals grown under special circumstances are of interest for chemical reactors and even for microelectronics as thin oxide gate layers on semiconducting supports.8–10 A characteristic feature of vanadium oxides and their amorphous 1096
http://journals.cambridge.org
J. Mater. Res., Vol. 17, No. 5, May 2002 Downloaded: 15 Mar 2015
structures is a nonstoichiometric randomness, which is important for chemical applications.11–14 The vanadium pentoxide single crystal has a well-expressed layered structure with high anisotropy of some electr
Data Loading...
