Imaging of inversion twin boundaries in potassium titanyl phosphate (KTP) by liquid–crystal surface decoration and X–ray diffraction topography

Abstract

An extended inversion boundary separating two large 180 • domains of a flux-grown KTP crystal is studied by nematic liquid-crystal (NLC) surface decoration and by X-ray projection and section topography using Mo-Kα radiation. Although a nonpolar (100) cleavage plate was used for NLC decoration, the domains appeared by bright optical contrast. The boundary exhibits a mainly irregular zigzag course with an-on average-charged orientation and is clearly visualized by both methods. It appears by strong contrast in X-ray reflection 004 (normal to the polar axis) and is completely invisible in reflection 040. A large uncharged planar boundary segment parallel to the polar axis and inclined by ca. 40 • to the normal of the specimen surface shows in reflection 004 dynamical fringe contrast of the stacking fault type. A section topograph of this segment exhibits an ideal 'hourglass' contrast pattern, proving the absence of long-range strain and of any tilt of the reflecting (001) planes across the inversion boundary.