UV irradiation effect on the electrical properties of Pb2MoO5 single crystal

Abstract

Electrical properties of Pb₂MoO₅ single crystal were studied in AC field (f=1 kHz) after irradiation with UV light (290 K). It was found that UV irradiation caused appearance of maximums on permittivity ε and conductivity σ temperature dependences, which were observed around 530 K. The anomalies of ε and σ vanished after annealing at 700 K and could be restored by subsequent UV irradiation performed at room temperature. The magnitude of ε and σ peaks increased for higher exposition time. Above 600 K conductivity σ was practically independent on irradiation. It is proposed that photoelectrons induced by UV light, are trapped by Mo located -within the oxygen tetrahedrons with vacancy VO in one of the vertexes. The dipole moments of (MoO₃) groups reorient at VO hopping through the tetrahedron vertexes. Annealing at 700 K thermally decomposes (MoO₃)^- complexes. For T>600 K behavior of σ(T) is determined by conduction currents and nearly insensitive to UV irradiation. At high temperatures the photoelectrons do not contribute to conductivity since they are bound in (MoO₃)^- centers, recombine with holes or re-captured by more deep traps.