Determination of the absolute orientation of langatate crystals using X-ray diffraction

Acoustic wave propagation in piezoelectric crystals with point group 32 symmetry is strongly dependent on the specific crystal orientation. This paper reports an X-ray diffraction (XRD) method using pole figures and in-plane scattering measurements to precisely define the absolute orientation of crystal planes in langatate (LGT). XRD measurements were conducted on Z-cut and plusmn45deg Y-rotated LGT wafers whose absolute orientation had previously been determined by ultrasonic measurements. A large inequality in XRD intensity from certain LGT planes allows {hk middot l} crystal orientations to be distinguished from {hk middot lmacr} orientations. Specific Miller planes useful for LGT crystal alignment and absolute orientation by XRD are reported, along with the measured intensity ratios I_{{hk middot l}}/I_{{hk middot lmacr}}.