Ferroelectricity and Antiferroelectricity in Ceramic PbZrO3Containing Ba or Sr

Phase transitions in solid solutions (Pb—Ba)Zr${\mathrm{O}}_3$ and (Pb—Sr)Zr${\mathrm{O}}_3$ have been studied by dielectric, dilatometric, and calorimetric measurements. It is shown that when the Ba concentration in (Pb—Ba)Zr${\mathrm{O}}_3$ compositions exceeds a threshold value of about 5 percent, a ferroelectric intermediate phase begins to appear between the paraelectric and antiferroelectric phases of pure PbZr${\mathrm{O}}_3$. The temperature range of this intermediate phase increases with the Ba concentration. Though no intermediate phase can be observed in compositions which contain Ba ions with less than this threshold concentration, a forced transition from the antiferroelectric phase to a ferroelectric phase can be caused by the application of a strong electric field at temperatures just below the Curie point. In the (Pb—Sr)Zr${\mathrm{O}}_3$ system we can also observe an intermediate phase, but this phase proves to be another antiferroelectric phase and not a ferroelectric one. It is concluded, from these situations, that the antiferroelectric phase in pure PbZr${\mathrm{O}}_3$ must be very peculiar, the free energy of this phase being closely adjacent to those of a ferroelectric phase as well as another antiferroelectric phase.