Thermodynamic nature of phase transitions in Pb(Zr x Ti1−x )O3 ceramics near the morphotropic phase boundary. I. Structural studies

The room-temperature structures of Pb(Zr x Ti1−x )O3 ceramics are shown to be tetragonal for x ≤ 0·52 and rhombohedral for x ≥ 0·530 while both the rhombohedral phase (R-phase) and the tetragonal phase (T-phase) coexist at x = 0·525 corresponding to the morphotropic phase boundary (MPB). Ceramics with x = 0·530 and 0·535 undergo the following sequence of phase transitions with increasing temperature R → R + T → T → cubic (C). For x = 0·525, the sequence is R + T → T → C while, for x = 0·520, the T-phase directly transforms into C. The T-to-C-phase transitions for all the compositions is shown to be discontinuous. The phase transition sequence for x > 0·525 confirms that the MPB consists of a two-phase region and that it is tilted towards the Zr-rich end.