Control of non-linear self-localization phenomena of strongly coupling charge carriersin LiNb_(1-x)Ta_xO_3 (LNT) - solid solutions

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The proposal is part of the research group 'Periodic low-dimensional defect structures in polar oxides', which is dedicated to the correlation of defect structure, electron and ion transport and electromechanical properties using the model system lithium niobate-lithium tantalate (LiNb_(1-x)Ta_x)O_3, LNT). The focus of this subproject is the interaction of strongly coupling charge carriers with (i) the structural, atomistic properties of the solid solution system, (ii) the dielectric and structural properties of ferroelectric domain walls, and (iii) the transport properties of ionic diffusion at elevated temperatures. Thus, the project aims to address the question of the role of structural, electronic and ionic properties in self-localization mechanisms in dielectric, oxide solid state materials in general. Specifically for the solid solution system LNT, it is expected that with the extended knowledge, possibilities for a tailored control of the self-localization of charge carriers by adjusting the composition, by domain structuring and temperature can be worked out. From an application-oriented point of view, e.g. non-linear photonics or nano-optoelectronics, this is connected with the question of possibilities for extensive control of (non-)linear optical and electronic properties. From a methodological point of view, the processing of this objective requires (a) the systematic application of established methods of nonlinear optical, time-resolved spectroscopy in the ultraviolet and visible spectral range on time scales from sub-picoseconds to the second range, (b) their extension by the aspect of spatially resolved studies on the micrometer length scale and (c) their application at temperatures above room temperature. This is associated with the correlative combination of nonlinear optical wide-field and confocal microscopy with excitation-scan spectroscopy and the installation of a temperature cell with a controllable oxygen content. The experimental results on LNT crystals of different composition and doping, ferroelectrically monodomain or periodically poled crystal samples, will be reproduced with numerical model calculations on the dynamics of self-localization, transport and recombination processes in the dielectric environment with composition gradients, extended phonon spectrum, lattice defects, domain walls and ionic diffusion. By comparison with atomistic model calculations as well as statistical transport models a correlation between material-specific, experimental and nonlinear optical or electronic parameters will be developed. The project ends with the identification of control possibilities of nonlinear optical, electronic and electromechanical properties based on the self-localization of charge carriers.