Nanooptics and photonics

Variations of the initial charge composition and physical properties of the single crystals of PbO – MoO3 system 
Bochkova T.M.1, Bondar D.S.1, Trubitsyn M.P.1, Volnyanskii M.D.1, Volnyanskaya I.P.2 
1 Physics of Active Dielectric Crystals Laboratory, Oles Honchar Dnipro National University, prosp. Gagarina 72, Dnipro, 49010, Ukraine 
E-mail: tbochkova@meta.ua
2 Prydniprovs’ka State Academy of Civil Engineering and Architecture, str. Chernyshevsky 24A, Dnipro, 49600, Ukraine 

Lead molybdate (PbMoO4) and double lead molybdate (Pb2MoO5) are perspective materials for acousto-optical devices. These applications require good optical quality and high radiation resistance. However, the crystals grown from the melt in air by the conventional Czochralskii technique, as a rule, have specific color and demonstrate photochromism after irradiation with UV light. Such undesirable phenomena can be associated with nanometer sized phase inclusions, coordination complexes based on intrinsic defects and/or impurities. Comprehensive study of the typical defects is of high importance to obtain PbO – MoO3 single crystals more suitable for practical applications. It is known that PbMoO4 exhibits vacancy disorder due to violation of stoichiometry and oxygen exchange with surrounding atmosphere. One can expect that an increase in the volatile component in the composition of the charge helps to prevent the formation of cation vacancies. Regarding Pb2MoO5, there is no any information on this issue.
Lead molybdate possess the scheelite-type crystal structure of the tetragonal system (space group I 41/a). The lattice of Pb2MoO5 is monoclinic (space group C 2/m). Both crystals contain the characteristic molecular anionic groups (MoO4)2- with almost the same Mo – O distance. The similarity and differences in the structure of crystals determine the features in their optical and electrical properties.
In this work we report the data on study of PbMoO4 and Pb2MoO5 single crystals grown by Czochralskii method using of the initial charge composition with deviations from the stoichiometric ratio of components. The influence of some excess of lead, as well as of molybdenum in the charge, on the optical absorption, photochromic and photodielectric effects in the crystals is discussed. The effect of growing conditions, doping, and high temperature annealing on the properties of crystals PbMoO4 and Pb2MoO5 is also considered.