The crystal structure and the phase transition behavior of La-substituted $0.88PbYb_{1/2}Nb_{1/2}O_3[PYN]$-$0.12PbTiO_3[PT]$ ceramics have been investigated by X-ray diffraction, transmission electron microscopy, and dielectric constant measurements. Ceramic 0.88PYN-0.12PT was reported to undergo ferroelectric-paraelectric diffuse phase transition which depends on the applied frequency. The crystal structure of room temperature phase may will be determined considered to be pseudocubic and the presence of ${111}_cubic$ superlattice reflections indicates the ordered arrangement of B-site cations. In this study, the effect of substitution of Pb-site by La atoms has been investigated on the crystal structure and phase transition behaviors. With the increasing La contents, the phase transition becomes relatively sharp, and the transition temperature increased. X-ray and selected area electron diffraction results show that for 0.02≤x≤0.08 (x: content of $LaYbO_3$ in mole%) the room temperature crystal structure is found to be orthorhombic and a superstructure due to the antiparallel displacement of the Pb atoms still remain. Comparing to the previous results of antiferroelectric PYN, we suggest that the La substitution evokes enhancement of antiferroelectricity in the 0.88PYN-0.12PT ceramics.
