Microwave Dielectric Properties of New Complex Perovskites: (Ba1/3Ln2/3)(Zn1/3Ti2/3)O3 ($\textit{Ln}=\text{La}$, Pr, and Nd) and (Ba(1+x)/3La(2-x)/3)(Zn1/3Ti(2-x)/3Nbx/3)O3

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Complex perovskites of the formula (Ba1/3Ln2/3)(Zn1/3Ti2/3)O3 ($\textit{Ln}=\text{La}$, Pr, and Nd) and (Ba(1+x)/3La(2-x)/3)(Zn1/3Ti(2-x)/3Nbx/3)O3 ($x=0.5,0.75,1.0,1.25$) have been synthesized by solid state reactions and are found to crystallize in the cubic structure (space group $Pm\bar{3}m$) from Rietveld refinement of powder X-ray data. The lattice parameter and the grain size increases with Nb substitution. Among the above oxides, (Ba1/3La2/3)(Zn1/3Ti2/3)O3 shows the best dielectric properties with quality factor ($Q$) of 3139 at 6.67 GHz and a temperature coefficient of resonant frequency ($\tau_{f}$) of $-10.8$ ppm/°C. Further, the temperature coefficient of resonant frequency ($\tau_{\text{f}}$) shows a large and systematic variation (with a continued decrease and a change of sign from positive to negative) with increase in Nb content.
2009-06-25