Ferroelectricity versus Antiferroelectricity in the Solid Solutions of PbZrO3and PbTiO3

The phase diagram of the solid solutions of PbZrO 3 –PbTiO 3 system has been established by investigating dielectric, dilatometric, calorimetric and structural properties. In Pb(Zr97–Ti 3 )O 3 four kinds of polymorphic modification have been found, that is, successively, the antiferroelectric, the other antiferroelectric, the ferroelectric and the paraelectric phases. By making use of the phase diagram and of the forced transition which causes a phase change from antiferroelectric phase to ferroelectric one owing to an influence of intense electric field, the free energies of these four states have been compared with one another as functions of temperature and the concentration of the solid solution. It is found that the antiferroelectric phase near the Curie point 230°C in pure PbZrO 3 is more stable than the ferroelectric one by only about 4 cal/mole; and with increasing concentration of PbTiO 3 the free energy of the ferroelectric phase decreases gradually at an initial rate of 0.5 cal. /mole/atomic percent. At the same time the two antiferroelectric phases lose their stability at the rates 5.8 cal./mole/atomic percent and 2.3 cal./mole/atomic percent respectively. The atomic arrangement in the ferroelectric Pb(Zr58–Ti42)O 3 has been examined. The sample of this concentration has the rhombohedral structure C 3 v 5 – R 3 m : The displacement of Pb atom relative to Zr or Ti atom is about 0.14 KX along the 111 direction.