Abstract
Helium atom di raction experiments have been carried out on the (001) surface of KTaO3 doped
with 30% Nb. The surfaces were produced by cleaving single crystals of the material in situ. After
the samples were thermally cycled, the angular distributions measured in the <100> azimuth, but
not those in the <110> azimuth, revealed half-order di raction peaks. These indicate the formation
of small (21) surface domains. The scans of the specular and Bragg di raction peak intensities as
the sample temperatures were varied from about 325K to 60-80K and back to 325K showed large
hysteresis particularly in the <100> azimuth. In addition, these scans showed a distinct intensity
dip at about 85K, which is far removed from any bulk phase transition temperature of this material.
Most curious, the specular re
ectivity of the surface was found to be a strong function of the He
wavevector, decreasing rapidly as the wavevector was varied above or below an optimum value.