Dielectric studies of barium bismuth titanate as a material for application in temperature sensors

Ceramic nanocrystalline samples with composition Ba_1?3aBi_2aTiO₃ were synthesized by sol–gel method, for different values of parameter a (for a = 0.0165, 0.033, 0.050). In order to determine whether barium bismuth titanate is suitable for application in temperature sensors, dielectric properties measurements were conducted on the prepared samples, as a function of both temperature (from room temperature up to 190 °C) and frequency (from 50 kHz to 1 MHz). Real and imaginary parts of dielectric constant were determined using an Impedance Analyzer HP-4194A. Depending on parameter a two different behavior were determined: (1) classical ferroelectric behavior, for the sample with low a value and (2) relaxor behavior for the samples with higher a values. Thus, a typical characteristic of relaxor ferroelectrics with a broad and dispersive dielectric maximum was observed for the samples Ba_0.85Bi_0.1TiO₃ and Ba_0.90Bi_0.066TiO₃. Temperature dependence (for real part of dielectric constant ε_r′) is almost linear, for lower temperatures than peak value (slope +1.3 1/ °C), and higher than this value (slope ?1 1/ °C). The feature of linearity is very important from practical aspects of application of this material in wireless temperature sensors. The temperature coefficient of dielectric constant for the sample with the best linearity (Ba_0.95Bi_0.033TiO₃ at 1 MHz) was found to vary from positive one +3.72 × 10^?3 1/ °C to negative value ?2.85 × 10^?3 1/ °C, in the temperature range 25–190 °C.