Résumé
The results obtained by high pressure neutron powder diffraction and single-crystal x-ray diffraction for the P4mm–Pm $\bar{3}$ m phase transition in the prototype ferroelectric perovskite lead titanate are shown. Neutron diffraction is found to be strongly sensitive to the dipolar moment in the PbTiO3 unit cell due to the gradual reduction of the displacement of the Ti and O atoms from centrosymmetric positions in the cubic perovskite structure which exhibits anti-phase scattering of Pb, Ti and O atoms. From applying both techniques, the anomalously high Debye–Waller factor for the lead atoms confirms the disordered character of the cubic phase. High pressure single crystal x-ray diffraction also perfectly describes the ferroelectric–paraelectric transition and will be the technique of choice to solve higher pressure structures for PbTiO3.