Structural and electrical studies on Bi₂VO_5.5/Bi₄Ti₃O₁₂ multilayer thin films

Abstract

The textured multilayer (ML) thin films of bismuth layered ferroelectric (FE) compounds, Bi₂VO_5.5 (BVO) and Bi₄Ti₃O₁₂ (BTO) with different individual layer thicknesses were fabricated via pulsed laser deposition technique on Pt(111)/TiO₂/SiO₂/Si substrates. X-ray diffraction studies confirmed that BVO and BTO retained their respective crystal structures in these multilayer (ML) thin films. The atomic force microscopy and scanning electron microscopy studies showed smooth and dense microstructures. The polarization hysteresis (P-E) studies on a representative (BVBT30) ML thin film at 300 K confirmed the remnant polarization (2P _r ) and coercive field (E _c ) to be ~20 µ C/cm² and 250 kV/cm, respectively. The value of P r obtained was greater than that of the single layer thin film of BVO (P _r ~5.6 µ C/cm²). The room temperature dielectric constant (ε r') and the loss (D) for BVBT30 ML measured at 100 kHz were 170 and 0.01, respectively. The frequency and temperature dependent dielectric constant, impedance, modulus and ac conductivity of these ML thin films were studied as a function of frequency (100 Hz-1 MHz) in the 25-300 ° C temperature range. Two distinct electrical responses were observed in these films, which were attributed to the grain effects at low temperatures and grain boundary effects at higher temperatures. The frequency dependent electrical conductivity was fitted well with the double power law which evidenced two different types of contributions to the conductivity; the low frequency conductivity being due to the short range translational hopping and the high frequency conductivity was due to the localized or reorientational hopping.