Dielectric properties, field induced strain and sintering behavior in $Pb (Mg_{1/3}Nb_{2/3})O_3-Ba(Mg_{1/3}Nb_{2/3})O_3-PbTiO_3$ ternary ceramic system have been investigated. Dielectric and X-ray diffraction measurements were used to determine the phase diagram of $Pb(Mg_{1/3}Nb_{2/3})O_3-Ba(Mg_{1/3}Nb_{2/3})O_3-PbTiO_3$ ternary ceramic system. A morphotropic phase boundary exists in the ceramic system separating pseudo-cubic (slightly rhombohedral) and tetragonal phases. Anomalously large dielectric constants were observed for compositions lying near the morphortopic phase boundary.
The effect of dc bias on the dielectric properties and the phase transition behavior of $(1-x) [(Pb_{0.7}Ba_{0.3})(Mg_{1/3}Nb_{2/3})O_3]-xPbTiO_3$ ceramic system near the morphotropic phase boundary $(0.35 \leq x \leq 0.5)$ have been investigated. The phase transition goes through a series of character changes from a diffuse phase transition at x=0.35 to a more of less normal phase transition at x=0.5. Between the extreme compositions, the system has shown a rather anomalous phase transition behavior due to the existence of the morphotropic phase boundary centered around x=0.44, Upon exposing to a series of external biases, the averaged dielectric constant maximum temperatures of the specimens of intermediate compositions tend to oscillate with respect to the bias field. Such anomalous dielectric behavior has been ascribed to the coexistence of multiple phases in a narrow composition band whose center of gravity may be assigned as the morphotropic phase boundary.
The strains induced by high electric fields have been measured for compositions in the solid solution system (1-x)[$(Pb_{0.7}Ba_{0.3})(Mg_{1/3}Nb_{2/3})O_3]-xPbTiO_3$ using a strain gauge method. Unusual large deformations have been observed for MPB compositions. In x=0.44, the field induced strain is much less temperature-sensitive than those in other specimens.
The sintering temperature of $Pb(Mg_{1/3}Nb_{2/3})O_3$ ceramics has been lowered to below 980$^\circ$C by addition of $V_2O_5$. However, excess $V_2O_5$ addition has resulted in the unwanted formation of lead vanadates whereas the pyrochlore lead magnesium noibate content decreased. A dielectric constant maximum value, 14000, has been obtained after 1 hr sintering at 980$^\circ$C of the specimens doped with 1 mole\% $V_2O_5$ which has maximum volume fraction of the perovskite $Pb(Mg_{1/3}Nb_{2/3})O_3$. This value is only slightly smaller than that of pure $Pb(Mg_{1/3}Nb_{2/3})O_3$ ceramics sintered 1hr at 1250$^\circ$C.
