Nanocomposites ang nanomaterials

Effect of nanoscale defects on photoconductivity and optical absorption of silicosillenite crystals
Panchenko T.V1, Karpova L.M.2
 1 Oles Honchar Dnipro National University, Faculty of Physics, Electronics and Computer Systems. Gagarin ave, 72, Dnipro-49010, Ukraine. 
E-mail: email.of. corresponding__panchtv141@gmail.com
2 Ukrainian State University of Chemical Technology, Faculty of Mechanics, Gagarin ave., 8, Dnipro-49010, Ukraine. 

Photorefractive сrystals of silicosillenite Bi12SiO20 (BSO) are successfully used in various fields of functional electronics [1]. It is of interest to modify the properties of BSO for the purpose of their application in nanoelectronics.
In this paper, the effect of nanosized nonstoichiometric defects caused by an excess or deficit of Bi ions (in BSO + Bi or BSO-Bi crystals, respectively) on the surface photoconductivity, edge optical absorption, and vibrational spectra of BSO is investigated.
It is found that nonstoichiometric defects manifest themselves near the edge of fundamental optical absorption and in vibrational IR absorption spectra. In BSO + Bi and BSO-Bi crystals, they cause an increase and, accordingly, a weakening of absorption and photoconductivity relative to BSO in the light photon energy range 2.5–3.5 eV. For this range, the effect of annealing in vacuum and oxygen on the structure and intensity of the absorption and photoconductivity bands of BSO crystals of stoichiometric and non-stoichiometric composition was studied.
The IR absorption spectra of BSO + Bi and BSO-Bi crystals in the region of two phonon processes differ from the BSO spectra by a change in the intensity ratio of two main peaks with frequencies ω1 = 1603.1 and ω2 = 1656.7 cm-1. In BSO + Bi crystals, the peak intensity with ω1 is higher, and in BSO-Bi crystals, with ω2. In addition, in BSO + Bi crystals, both peaks have a larger spectral broadening.
Analysis of the results allows us to propose a model of nanoscale defects of nonstoichiometry BSO in the form of oxygen SiO4 tetrahedra with partial substitution of Si ions by anti-structural Bi ions and charge compensation in the oxygen sublattice.
1. Gunter P., Huignard J. Photorefractive Materials and Their Applications. Part1. Springer Science+Business Media New York –2006.