| Lithium niobate (LiNbO3 or LN) is a versatile material with widespread applications. Thus its fundamental properties continue to be of interest. At the same time, LN contains impurities and point defects, which affect its physical properties. This in turn could influence the performance of the practical devices using the specific properties. Thus it is important to identify these impurities, and predict what properties they might influence. This research aims at finding new crystal characteristics including the identification of point defects, and finding the distribution of the defects parallel to the optical crystallographic z-axis, and in a direction normal to the z-axis. Bulk crystals, wafers and ferroelectric phononic crystals such as periodically poled LN (PPLN) are studied. The spectra of photoluminescence (PL) reveal both charged and neutral impurities. The impurities may be classified as heavy metals, noble gases, color centers and antisite defects. The band scheme of LN is developed with the presence of intraband donor or acceptor levels. The impurities show a peak and valley distribution both parallel and normal to the z-axis. The distribution of the impurities and point defects in PPLN, can be used to identify the ferroelectric domain walls. Engineering application of these findings may be non-destructive characterization of phononic crystals.;The impurities and point defects affect crystal properties including conductivity, electromechanical transformation (EMT) and others. The charged defects are sensitive to local electric polarization, thus they affect the EMT at local points of the crystal. The EMT distribution reveals peaks and valleys. The distance between consecutive peaks and valleys of the EMT distribution is similar to those obtained from PL measurements. Frequency dependence of the radio frequency admittance reveals peaks and valleys, which corresponds to specific ultrasonic modes in a plate. The revealed correlation between defects and EMT is a basis for nonlinear phenomena involving piezoelectricity including nonclassical nonlinearity, acoustical memory and others. |
