Dielectric property–microstructure relations in Co-O doped (Y2−xSmx)BaCuO5 ceramics

The effect of CoO doping on the microwave dielectric property and the microstructure of (Y2−xSmx)BaCuO5 ceramics have been investigated. The limits of the (Y2−xSmx)Ba(Cu1−yCoy)O5 (x=0,1 and 2) solid solutions were approximately y=0.1 and the deviations of the valences in cations determined by using bond valence sum may be related to the formation of the solid solutions. It was found that high Q·f values were obtained by the Co substitution for Cu in the (Y2−xSmx)BaCuO5 ceramics, whereas the τf values were not improved. In the Sm-substituted (Y2−xSmx)Ba(Cu1−yCoy)O5 ceramics, the optimum value of τf which was closest to 0 ppm/°C was −6.3 ppm/°C for x=2. The reduction of porosity in the Sm2Ba(Cu1−yCoy)O5 ceramics at compositions lower than y=0.01 was recognized; it was found that these morphological changes in the ceramics were closely related to the increase of the Q·f values. Thus, the optimum dielectric properties, i.e. εr=16.8, Q·f =90732 GHz and τf=−9.2 ppm/°C, were obtained in the Sm2Ba(Cu0.99Co0.01)O5 ceramics by using cold isotropic pressing (CIP).