Order-disorder character of PbTiO₃

We report the displacive and order-disorder characters of PbTiO₃ analyzed using a classical atomic model which was developed under the inverse relation between the bond length and the bond valence. The ferroelectric phase changes to the paraelectric phase around 700K, and the histograms of Ti-O and Pb-O bond lengths have three peaks which become a single peak above the phase transition temperature. The order-disorder character of this material was clearly shown by analyzing the ion displacement magnitudes.