Effect of Substrate Orientation on Energy Storage in NaNbO3-Based Thin Films

Substrate orientation offers a route to tailoring the dielectric and energy-storage properties of lead-free oxide thin films. In this work, 1.0 mol.% Mn-doped 0.96NaNbO3–0.04CaZrO3 (NNCZ–Mn) thin films were fabricated via a sol–gel method on (100)-, (110)-, and (111)-oriented Nb-doped SrTiO3 substrates and exhibited corresponding preferential out-of-plane orientations. The (111) film combined higher permittivity and lower leakage current with a larger recoverable polarization, yielding the best energy-storage performance among the three orientations. It achieved a recoverable energy density of approximately 23 J/cm3 with an efficiency of 65% at an electric field of 666.67 kV/cm and reached approximately 35 J/cm3 at 970 kV/cm with an efficiency of 48%. Its recoverable energy density also exhibited moderate thermal stability over 23–160 °C, good frequency stability over 400–2000 Hz, and good fatigue resistance after 106 cycles. This study demonstrates the potential of substrate orientation control for improving solution-processed NaNbO3-based thin-film capacitors.