Yakhnevych U. Modifications of LiNbO3 crystals by heat treatment in the presence of metal ions for devices of micro-and nanosystem technology

Thesis is devoted to establishing regularities of metal ion diffusion processes in LiNbO3 crystals and determining optimal conditions of thermochemical treatments for the application of modified materials in functional electronics devices. In the thesis, important scientific tasks have been solved, namely: changes in the structural, optical, mechanical, and pyroelectric properties of LiNbO3 caused by high-temperature annealing of crystals in the presence of metal ions were studied; the spatial distributions of the impurity ions concentrations incorporated into the crystals by diffusion were determined in different crystallographic directions, using methods of local control and scanning of changes in the physical properties of lithium niobate samples caused by thermochemical treatments; the influence of the modes of thermochemical treatments of LiNbO3 crystals in the presence of metal ions on the diffusion processes has been investigated; the processes of incorporation of metal ions into LiNbO3 crystals caused by thermochemical treatments were described on the basis of mathematical diffusion models; modeling was performed and a working model of precise positioning actuator based on the lithium niobate bimorph plate was created; the dependences of the displacement value on the applied electric voltage were experimentally investigated; the optimal crystallographic orientations of bimorph plates were determined; the application of methods of purposefully thermochemical nanostructural modification of lithium niobate crystals is proposed for practical use in devices of micro- and nanosystem technology, for example, in actuators.