Distribution of point defects in lithium niobate and defect-dependent electromechanical coupling

Abstract

The spectra of photoluminescence (PL) from a YZ-cut Lithium niobate (LN) plate reveal point defects of heavy metals Fe and Ba. The distribution of point defects (DPD) is nonuniform and exhibits peaks and valleys, in a direction parallel to the z-axis. The distance between consecutive peaks and consecutive valleys is not more than a few mm. The point defects are sensitive to local electric polarization and influence the electromechanical transformation (EMT) at the local point of the crystal. The EMT is estimated by reading an electric potential (V) generated while applying a constant mechanical stress, at steps of hundreds of microns parallel to the z-axis. The distribution of EMT in LN is nonuniform; the distance between consecutive peaks and consecutive valleys is similar to the DPD. Higher the concentration of point defects more is the EMT, and lower the concentration of point defects lower is the EMT. The point defects are manifested as peaks and valleys in the frequency dependence of admittance measurements. The presence of point defects excites ultrasonic modes in the crystal when radio-frequency current propagates through it.