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 +/- 45 degrees 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 - l} crystal orientations to be distinguished from {hk - (l) over bar} orientations. Specific Miller planes useful for LGT crystal alignment and absolute orientation by XRD are reported, along with the measured intensity ratios I{hk - l}/I{hk - (l) over bar}.