Antiferroelectric lead zirconate, a material for energy storage

Abstract

Lead zirconate (PbZrO₃) is an antiferroelectric material melting at about 12507deg;C and having the Curie temperature of 230°C.¹ The free energy of the antiferroelectric orthorhombic phase is very close to that of a ferroelectric rhombohedra1 especially near the Curie point.¹ An evidence of the existence of a stable ferro-electric phase over a temperature range of a few degree has been reported.² Some impurities e.g. Ba, Ti help to stabilize the ferroelectric phase,³ others, e.g. Ca, Sr, tend to supress it.² Also it is reported that on the application of strong electric field to the material in the antiferroelectric state and when this field is increased beyond some threshold value the ferroelectric phase becomes energetically favourable and gives rise to antiferroelectric (AFE) to ferroelectric (FE) transition. Jaffe⁴ has reported that this leads to high energy storage for DC field, because of the large increase in polarization that accompanies the transition. Field of 60 kV/cm has induced AFE-FE transition at 200°C. The breakdown in ceramic generally propagates along grain boundaries. It was thought likely that dielectric strength could be enhanced by the use of a small amount of inorganic binder. This procedure of adding glass to ceramic dielectric has become popular in recent years as a of reducing sintering temperature and modifying electrical property.⁵ Such materials showed promise for energy storage applications. Energy storage capabilities were determined experimentally by simple electrical circuit theory. The net effect of the glass addition on dielectric properties is that the peak value of permittivity decreases, whereas temperature range over which F.E. phase is stable increases. Although the permittivity decreases, dielectric strength enhances due to the glass bonding, leading to the substantial rise in the stored electrical energy (½ CV²). The sample is subjected to the electric field up to about 5 kV/cm. From dependence of energy density on field strength, it can be predicted that the attained energy density is approximately =7 × Joule/cm³, corresponding to the trical field of 40 kV/cm. This value of energy density is lower than that reported by Bum6 by two orders. The quantitative effect of the glass addition on dielectric properties and energy storage capacity also depend upon the nature and the position of the glass used for bonding.