Dielectric behavior of lead iron tantalate -: lead titanate ceramics

Dielectric properties of complex perovskite Pb(Fe1/2Ta1/2)O-3 (PFT) and its solid solutions with normal ferroelectric PbTiO3 (PT) were studied. The addition of 5 - 25 mol % of PbTiO3 was used to shift upwards the temperature of the ferroelectric-paraelectric transition of pure PFT. Dielectric permittivity and dissipation factor of the ceramics were determined in the temperature range from -55 to 550 degrees C at frequencies 10 Hz - 1 MHz. Dc resistivities of the samples were measured in the temperature range 20 - 500 degrees C. The PFT-based ceramics sintered at 1050 degrees C showed a relatively high dielectric permittivity (3000 - 5700 at Curie temperature) and a high resistivity (10(11) - 10(13) Omega cm at 20 degrees C). Two broad maxima in the dielectric permittivity versus temperature plots were observed at a given frequency. The location of the first one, corresponding to the ferroelectric - paraelectric transition, changed from -30 degrees C for pure PFT to 80 degrees C for 0.75PFT-0.25PT ceramics. The second maximum, related to dielectric relaxation, occurred at higher temperatures in the range 200 - 500 degrees C and was strongly dependent on frequency and the content of dopants.