Effects of variations in crystal structure on microwave dielectric properties of Y2BaCuO5 system

The dielectric properties of (Y2–xRx)BaCuO5 (R=Sm, Gd, Dy, Ho, Er and Tm) solid solutions were measured for the application as a new microwave resonator. Moreover, the relationships between the results of the dielectric properties obtained and variation in the crystal structure of (Y2−xRx)BaCuO5 solid solutions have been studied in some detail using the results of Reitveld analysis. The result is that εr changes from 12.7 to 19.6 and depend on the ionic radii of the rare-earth which composed the R2O11 polyhedron. Then, τf was largely improved by substituting R for Y, and in the case of Dy2BaCuO5 compound, the value was −6.4ppm/°C. Using the results of Rietveld analysis obtained at 20 and 80oC, negative values of τε were considered to be caused by a decrease in the atomic distances of the R2O11 polyhedron in the direction of the b-axis. As for the Q·f value, it suggests that the difference of Q·f value between x=1 and 2 is reduced by the strain of R2O11 polyhedron which is caused by the difference of ionic radii of Y and R.