Microstructural influence on ferroelectric domain pattern and piezoelectric properties of Na0.5Bi0.5TiO3 thin films

Abstract

Sodium bismuth titanate (Na0.5Bi0.5TiO3: NBT) thin films were fabricated under various growth conditions (substrate temperature from 400 °C to 650 °C and oxygen pressures from 50 to 200 mTorr) by using pulsed laser deposition technique. The films grown at low partial pressures (< 100 mTorr) exhibited a preferred orientation along the <220> direction and at higher partial pressures (> 100 mTorr) exhibited polycrystalline nature. The microstructures were tuned from coarse faceted grains to fine spherical grains by varying the ambient pressures and the growth temperatures. The ferroelectric domain studies reveal that in case of fine spherical grains, the domain pattern was dominated by the surface morphological features and in the case of coarse faceted grain structure, domain features were independent of its morphology. Fast Fourier Transform (FFT) spectrum analysis of the domain patterns confirmed that only highly oriented films possessed periodic domain pattern and the periodicity is in the range of 140–240 nm. Further, the estimated piezocoefficient value (d33) increased from 16 to 31 pm/V with increasing the oxygen partial pressures (50–200 mTorr) and substrate temperatures (400–650 °C). The leakage current density measurements confirm that films grown at low partial pressures possess relatively larger leakage current density at room temperature.