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

An extended inversion boundary separating two lar ge 180 degrees domains of a flux-grown KTP crystal is studied by nematic liquid-crystal (NLC) surfac e decoration and by X-ray projection and section topography using Mo-K alph a radiation. Although a nonpolar (100) cleavage plate was used for NLC deco ration, the domains appeared by bright optical contrast. The boundary exhib its a mainly irregular zigzag course with an-on average-charged orientation and is clearly visualized by both methods. It appears by strong contrast i n X-ray reflection 004 (normal to the polar axis) and is completely invisib le in reflection 040. A large uncharged planar boundary segment parallel to the polar axis and inclined by ca. 40 degrees to the normal of the specime n surface shows in reflection 004 dynamical fringe contrast of the stacking fault type. A section topograph of this segment exhibits an ideal 'hourgla ss' contrast pattern, proving the absence of long-range strain and of any t ilt of the reflecting (001) planes across the inversion boundary.