The crystal structure and phase transition of $(1-x)Pb(Yb_{1/2}Ta_{1/2})O_3-xPb(Fe_{1/2}Ta_{1/2})O_3$
$(PYT_1-_xPFT_x)$ solid solutions for 0≤×≤0.25 have been studied by X-ray diffraction, dielectric constant, E-P hysteresis measurement and transmission electron microscopy (TEM). From the analysis of the superlattice structure of $PYT_{1-x}PFT_x$ solid solutions, it is found that the crystal structure of the $PYT_{1-x}PFT_x$ changes from the monoclinic to the pseudocubic as x increases beyond x=0.22 at room temperature. In the composition region (x＜0.22), the dielectric constant vs. temperature curve exhibits a sharp normal paraelectric-antiferroelectric phase transition. For x≥0.10, the dielectric dispersion at 177℃ which is the secondary phase transition point of pure PYT disappears. For x=0.22, the dielectric constant vs. temperature curve shows significantly broad and weak frequency dependence near the transition temperature. It is considered not relaxor but normal ferroelectric transition as PFT and PFN. Also in the TEM analysis, the antiferroelectric phase still exist below the secondary phase transition temperature. This means that ferroelectric and antiferroelectric phase is co-exist at room temperature for x≤0.10. In the selected area diffraction pattern(SADP), an intermediate phase which implicately exhibits incommensurate phase behavior is observed. It is thought that its origin is the local strain change due to the ionic size difference between $Yb^{3+}$ and $Fe^{3+}$.
