Executive Summary : | In this project, nonlinear optical imaging setup will be developed to study the structural dynamics of ferroelectric materials over wide temperature range (~2K to 1000K). Ferroelectric materials are non-centrosymmetric crystalline structures and second order nonlinear processes like second harmonic generation (SHG) are only allowed in non-centrosymmetric materials. This fact allowed SHG method to probe the ferroelectric and multiferroic transitions and dynamics of the ferroelectric and multiferroic materials with temperature and or external field. Although SHG measurements for ferroelectric materials were done in BaTiO₃ just a few years after the invention of SHG in 1961, the polarized SHG imaging got a significant attention in recent years. This is recently emerging because of the possibility to probe non-distructively the crystalline symmetry and mapping of domain structures etc. Also, SHG technique is very sensitive to inversion breaking and possible to measure the lattice deformations and smaller polarization variations by detecting the low-intensity SHG signals using high sensitivity detectors. In this proposed work, polarized SHG technique will be employed to study thermal dynamics of various ferroelectric materials such as CuO, Pr doped SrTiO₃ and NdGaO₃ in bulk and thin films. This study will clarify the anomalies in the literature regarding the crystalline symmetries, accurate phase transition temperatures, localized polarization and domain structures in a wide temperature range. To complement these evidences by SHG, polarized Raman measurements will be also carried out over the same temperature range and correlate both measurements to support the revealed findings. I believe, studying the thermal dynamics, accurate phase transitions, mapping of localized polarization and lattice deformations of ferroelectric and multiferroic materials are up most important for two primary reasons: one is to clear anomalies that exist in the literature and second, the most important one is to increase their wide application prospect and scope. For instance, a clear understanding of these materials can enhance their applicability in pyroelectric sensors, piezoelectric actuators, electrooptic modulators, memory devices and superconducting substrates. |