Enhanced in-plane ferroelectricity in Ba[sub 0.7]Sr[sub 0.3]TiO₃ thin films grown on MgO (001) single-crystal substrate

Abstract

Highly oriented Ba[sub 0.7]Sr[sub 0.3]TiO₃ thin films were grown on MgO (001) single-crystal substrate using pulsed-laser deposition and the in-plane ferroelectric properties of the film were evaluated. X-ray diffraction characterization revealed a good crystallinity and tensile in-plane stress in the film. A well-defined ferroelectric hysteresis loop with P[sub r]=9.5 µC/cm² was observed along the (100) direction, which implied an enhanced in-plane ferroelectricity in the Ba[sub 0.7]Sr[sub 0.3]TiO₃ thin film in comparison with the Ba[sub 0.7]Sr[sub 0.3]TiO₃ ceramics. Curie temperature of the film was found to be ~88 °C, which is nearly 50 °C higher than that of the Ba[sub 0.7]Sr[sub 0.3]TiO₃ ceramics. The butterfly-shaped C-V characteristic curve also evidenced the enhanced in-plane ferroelectric property in the film, and a large dielectric tunability of 69% was found at 1 MHz under a moderate dc bias field. The observation of enhanced ferroelectricity along the in-plane direction in the highly oriented Ba[sub 0.7]Sr[sub 0.3]TiO₃ thin film was explained in terms of the increased tetragonality (a/c =1.016) induced by the lattice misfit strain.