Diffuse phase transitions, electrical conduction, and low temperature dielectric properties of sol-gel derived ferroelectric barium titanate thin films

Ferroelectric thin films of barium titanate were fabricated by sol-gel technique on platinum substrates. The processing temperature was 700°C. The films obtained with a thickness of 1.5 μm were dense, transparent, and showed ferroelectricity. Scanning electron microscopy and x-ray diffraction were used for studying the surface morphology and crystallographic structure of the film. Films in the metal-ferroelectric-metal configuration (MFM) were used for the electrical measurements. Dielectric constant and loss tangent were found to be 430 and 0.015, respectively, at 10 kHz under ambient conditions. The ∈′(T) curve shows broad peak centered around 120°C as in the case of diffuse phase transition. The ac conductivity is proportional to ω^0.9 in the low frequency region and ω^1.8 in the high frequency region. The dc conductivity versus temperature curve showed a change in the slope around 125°C, corresponding to the phase transition. To study the low temperature phase transitions, dielectric parameters on the films were measured to a temperature down to about 10 K. Remanent polarization (P_r) and coercive field (E_c) obtained from the hysteresis loop at room temperature are ∼2.0 μC/cm² and ∼27 kV/cm, respectively. Capacitance-voltage studies performed on the MFM structures showed butterfly loop at 135°C.