$BaBi4Ti4O15$ ferroelectric thin films grown by pulsed laser deposition

$BaBi4Ti4O15$ (BBiT) is an $n=4$ member of the Bi-layer-structured ferroelectric oxide family (Aurivillius phases). BBiT thin films with preferred orientations have been grown on epitaxial conducting $LaNiO3$ electrodes on (001) $SrTiO3$ by pulsed laser deposition. Cross-section electron microscopy analysis reveals that the films consist of $ct$-axis oriented regions and mixed $at$- and $ct$-axis oriented regions. The mixed $at$- and $ct$-axis oriented regions show high surface roughness due to the rectangular crystallites protruding out of the surface, whereas the $ct$-axis oriented regions show a smooth surface morphology. In the mixed $at$- and $ct$-axis oriented regions, the BBiT films exhibit saturated ferroelectric hysteresis loops with remnant polarization $Pr$ of 2 μC/cm² and coercive field $Ec$ of 60 kV/cm and no polarization fatigue up to $108$ cycles. The regions having $ct$-axis orientation with a smooth surface morphology exhibit a linear $P–E$ curve. The results show that the ferroelectric properties of a planar capacitor consisting of BBiT depend on the crystalline orientation of the film.