The physical properties, especially dielectric properties, of pseudobinary $\frac{1-x}{2} Pb_2BiNbO_6-x Pb (Fe_{\frac{1}{2}}Nb_{\frac{1}{2}})O_3$ ceramic system were studied.
X-ray structure studies show that pure $Pb_2BiNbO_6$ has defected fluorite structure with small distortion and there is virtually no $Fe^{3+}$ solubility substituting $Bi^{3+}$ with $Fe^{3+}$ and vice versa.
Even though $Pb_2BiNbO_6$ can become ferroelectric from structural standpoint, E-P hysteresis, D.C. resistivity and D.S.C. behaviours have shown it is not ferroelectric.
The imaginary part of dielectric permittivity of pure $Pb(Fe_{\frac{1}{2}}Nb_{\frac{1}{2}})O_3$ exhibited an anomalous dielectric behaviour near the critical temperature which was contradictory to the so-called Kramers-Kronig relation.
The dielectric critical temperature of x=0.8 was abnormal 15℃ lower than that of x=0.9. Because defected fluorite structured $Pb_2BiNbO_6$ begins to show up at x=0.9 in the X-ray diffraction patterns, the $Pb_2BiNbO_6$ solubility in $Pb(Fe_{\frac{1}{2}}Nb_{\frac{1}{2}})O_3$ is not expected to exceed by more than 0.9 in composition. The anomalous critical temperature drop by 15℃ at x=0.8 from the value at x=0.9 is quite unexpected since the critical temperature characteristics will be only exhibited by $Pb(Fe_{\frac{1}{2}}Nb_{\frac{1}{2}})O_3$ phase in addition to the negligible contribution from the remaining non-ferroelectric $Pb_2BiNbO_6$. An attempt was made to explain the anomalous behavior in this study.
