Electrical Properties of the Ln$_{\mathrm{3-x}}$Y$_{\mathrm{x}}$TaO$_7$ (Ln$=$Dy, Gd) solid solution

Systems with the formula Ln$_{\mathrm{3-x}}$Y$_{\mathrm{x}}$TaO$_7$ (Ln$=$Dy, Gd) crystallizing in the weberite relatedstructure (SG C222, No. 20) were synthesizedby the solid-state reaction method. Structural characterization through Rietveld refinements indicates that a solid solution in the whole range 0$\le $x$\le $3 exist in both Gd and Dy systems. Structural cell parameters as a function of the rare-earth content areshown in this work, as well as the AC electrical properties in the 30-700$^o$C range. We have performed impedance (400-600$^{\circ}$C)and electric polarizability measurements (at room temperature); the results indicate that the polarizability reaches its maximum values at x$=$0.67, 1.67 and 2.33 for the Gd samples, meanwhile these values were x$=$0.67 and 2.0 for the Dy samples. In intermediate composition values, the Ln$_{\mathrm{3-x}}$Y$_{\mathrm{x}}$TaO$_7$ samples exhibit null polarization.