OXYGEN NONSTOICHIOMETRY AND DIFFUSION IN RBA2CU3O6+X (R=Y, GD, HO) INVESTIGATED BY TG METHOD

By means of thermogravimetry (TG) and chemical analysis equilibrium de pendencies of oxygen content in GdBa2Cu3O6+x and HoBa2Cu3O6+x on tempe rature and P-O2 were studied. It is found that at equal temperature an d P-O2 the oxygen content in RBa2Cu3O6+x increased in order Ho-Y-Gd. O n the basis of Fick 2nd law mathematical procedures to determine diffu sion coefficients of oxygen from ni data were developed. The oxygen di ffusion coefficients in RBa2Cu3O6+x (R=Y, Gd, Ho) were evaluated in a wide temperature (300-900 degrees C) range (at P-O2=0.21 bar). The dev eloped model rather satisfactory decribes oxygen diffusion processes i n phases under investigation. It is found that for all studied compoun ds oxygen diffusion in orthorhombic phase happened faster than in tetr agonal one. The values of diffusion coefficients increase in order Ho- Y-Gd with increasing of ionic radius of the rare earth element.