Pb 1 − x Cd x Ti O 3 (0.0⩽x⩽0.08) compounds in the tetragonal phase were prepared by the solid state reaction. Neutron powder diffraction study revealed that Pb1−xCdxTiO3 exhibits an unusual structural property. Although the tetragonality (c∕a) is enhanced by Cd substitution for Pb, the cation displacement of spontaneous polarization unexpectedly decreases, which is associated with the reduced Curie temperature. The increasing of the LO-TO splitting in Pb1−xCdxTiO3 shows an anomalous behavior in comparison with other previously studied PbTiO3-based systems. It was interestingly found that a similarity exists in the behavior of the solubility dependence of the LO-TO splitting and the negative thermal expansion (NTE) in the PbTiO3-based systems, which suggests that Pb–O hybridization plays an important role in NTE mechanism of PbTiO3.