Perovskite phase formation in the relaxor ferroelectric system Pb(Fe1/2Nb1/2)O3-Pb(Zn1/3Nb2/3)O3 - BaTiO3 : their dielectric and thermal expansion studies

Abstract

In the binary system of PFN-PZN, prepared by different methods, the samples prepared by the B-site oxides mixing route showed high dielectric constant (K_max and K_loss), but also marginally high dielectric loss compared to those prepared by the straight calcination and Columbite routes. PFN-rich compositions in this system showed very good dielectric properties. As the PZN concentration was increased, especially above 60%, the dielectric constant decreased sharply. The temperature of dielectric maximum, T_max, increased almost linearly with the PZN content. Compositions containing more than 40 mole % of PZN showed frequency dispersion of T_max.

The compositions of the ternary system PFN-PZN-BT showed higher dielectric constant compared to their binary counterparts. Addition of BT decreased T_max in the PFN-PZN system, making it possible to "tune" the T_max to a desired temperature. The addition of 10-15 mole % of BT to PFN, PZN, and 0.5PFN-0.5PZN compositions brought down T_max to around room temperature. Thus, these compositions possessed very high dielectric constants in the order of 8000-16000 and low dielectric loss of ~0.04 - 0.004 at room temperature. In the (PFN?-PZN?)??-BT? system, the values of dT_max/dy for x = 0, 0.5, and 1 are 9.6, 8.11, and 6.95 K/mole % of BT, respectively. PFN-BT compositions showed frequency dispersion of T_max (?T_max), though these materials do not exhibit ?T_max individually. A composite approach of mixing two compositions having different T_max's and firing them at appropriate temperatures to broaden the Curie range was successfully employed. These materials had very low temperature coefficient of capacitance (TCC), which is very useful for capacitor applications. The composite fired at 1243 K has a TCC of +1% and -10% in X5, Y5, and Z5 temperature ranges.