STRUCTURAL CHANGE OF C-RARE EARTH SESQUIOXIDES Yb//2O//3 AND Er//2O//3 AS A FUNCTION OF TEMPERATURE.

The high temperature structures of C-rare earth sesquioxides, Yb//2O//3 and Er//2O//3, were studied by the single crystal X-ray diffractometry. The intensity data were collected at 296, 378, 598, 834, 1032 and 1245 K for Yb//2O//3, and 296, 514, 724, 931, 1123 and 1260 K for Er//2O//3. The structure at each temperature was refined by the full-matrix least-squares procedure, providing the final R values falling within 0. 034 to 0. 050 for Yb//2O//3 and within 0. 036 to 0. 051 for Er//2O//3. The effect of temperature and oxygen vacancies on the distortion in RO//6 polyhedra is discussed.