Comparative Study of Single Crystals and Laser-grown Films of V2O5

Abstract

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.