Thermodynamic nature of phase transitions in Pb(ZrxTi1-x)O-3 ceramics near the morphotropic phase boundary .1. Structural studies

The room-temperature structures of Pb(ZrxTi1-x)O-3 ceramics are shown to be tetragonal for x less than or equal to 0.52 and rhombohedral for x greater than or equal to 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 greater than or equal to 0.525 confirms that the MPB consists of a two-phase region and that it is tilted towards the Zr-rich end.