  Pb-free ferroelectric thin films are gaining attention due to their
applicability in memory, sensor, actuator, and microelectromechanical system.
In this work, Na$_{0.4}$K$_{0.1}$Bi$_{0.5}$TiO$_3$ (NKBT0.1) ferroelectric thin
films were deposited on Pt(111)/Ti/SiO$_2$/Si substrates using the pulsed laser
deposition technique at various substrate temperatures (600-750 $^\circ$C). The
comprehensive structural, microstructural, and ferroelectric properties
characterizations depicted that the grain size, dielectric constant, and
remnant polarization increased with higher deposition temperatures. The
influence of higher substrate temperatures on the control of (100)-preferential
orientations was observed, indicating the importance of deposition conditions.
Significantly, films deposited at 700 deg C exhibited reduced dielectric loss
of 0.08 (at 1kHz), high dielectric constant of 673, and remnant polarization of
17 microC/cm2 at room temperature. At this deposition temperature, a maximum
effective piezoelectric coefficient of 76 pm/V was availed. Based on the
structural analysis, dielectric properties, and ferroelectric behavior, the
optimal deposition temperature for the NKBT0.1 thin films was 700 $^\circ$C.
This study contributes to the understanding of the influence of substrate
temperature on the structural and ferroelectric properties of Pb-free NKBT0.1
thin films, providing insights for the development of high-performance
ferroelectric devices.
