HIGH-PRESSURE SYNTHESIS AND STRUCTURAL STUDY OF R2CUO4 COMPOUNDS WITH R = Y, TB, DY, HO, ER, TM

The title compounds have been prepared by high pressure/high temperature reaction. Thermogravimetric measurements indicate that they decompose above almost-equal-to 350-degrees-C in He flow. Electron microscopy and X-ray powder and single crystal diffraction data are presented. They all reveal the presence of three types of superstructure, corresponding to different unit cells, which can be observed in different grains of the same sample. The results of an average structure refinement carried out with the unit cell, and symmetry of the T' phase are presented for the Tm2CuO4 compound. These results are compared with those obtained for Gd2CuO4.