Nanocomposites and nanomaterials

The elastic-optical effect in Na0.5Bi0.5TiO3 crystals 
Kruzina T.V.1, Popov S.A.1, Suchanicz J.2, Potapovich Yu.N.1, Rutskiy A.S.1
1 Department of Physics, electronics and computer systems, Oles’ Honchar Dnipro National University. prosp. Gagarina, 72, Dnipro, Ukraine.
E-mail: tkruz@meta.ua
2Institute of Physics, Pedagogical University, ul. Podchorazych 2, Krakow, Poland, 30-84

Among ferroelectric-relaxors the Na0,5Bi0,5TiO3 (NBT) is considered as a base for thin films and nano-composite materials promising advantages for piezoelectric applications. NBT exhibits unusual electrical and optical properties which are associated with both disordering of Na+ and Bi3+ cations in the crystal lattice and existence of nanoscale polar regions in wide temperature range. 
In this work we report some aspects of axial pressure influence on birefringence in NBT crystals grown by Czhochralskii method. Macroscopic monodomain crystals (001) are used in the investigations. The stable monodomain state is achieved in two ways: for ~500 µm thick samples - application of axial pressure <100 bar, for ~100 µm samples - annealing in air (tann=600°C for 2h) [1]. 
The birefringence is measured by polarization-optical method at wavelength 632.8 nm in temperature interval 25-500°C. The axial pressure (10-40 bar range) is applied to samples along [100] and [110] directions. The peculiarities of the temperature behavior of birefringence ∆n in NBT are associated with the structure phase transitions and the “izotropisation point”, where the sign of birefringence changes. It is discovered that value of axial pressure in [100] direction almost does not influence the birefringence ∆n. While the birefringence significantly increases with an increase of applied axial pressure along [110] direction. It is observed that the birefringence linearly depends on the axial pressure, and the temperature changes the line slope angle. 
It is supposed, that both the increase of Δn with application of axial pressure along [110] direction and the influence of temperature on the slope of the Δn = f(p) are associated with change of orientation of nanoscale polar regions, contributing to the elastic-optical effect.

1.	Suchanicz J., Kruzina T.V. The effect of axial pressure on domain state and dielectric properties of Na0.5Bi0.5TiO3 and related materials // Ferroelectrics.-2005.-317.-P. 109-113.