Dielectric, Ferroelectric, Pyroelectric, and Piezoelectric Properties of La‐Modified Lead‐Free Sodium–Potassium Bismuth Titanate Thick Films

La 2 O 3 ‐doped sodium–potassium bismuth titanate (Na 0.82 K 0.18 ) 0.5 Bi 0.5 TiO 3 (NKBT) lead‐free thick films have been prepared on Pt‐electroded alumina substrates using a combination of screen printing and subsequent infiltration of the corresponding composite sol. Their densification, microstructure, dielectric, ferroelectric, pyroelectric, and piezoelectric properties were investigated with variation of the La 2 O 3 content. The resulting 40 μm‐thick NKBT films doped with 1.0 mol% La 2 O 3 show minimum leakage current density of 1.56 × 10 −9 A/cm 2 at an applied field of 100 kV/cm, remanent polarization of 21.6 μC/cm 2 , and coercive field of 58 kV/cm. The high pyroelectric coefficient of 2.0 × 10 −4 C·(m 2 ·°C) −1 , the calculated detectivity figure of merit as high as 0.81 × 10 −5 Pa −0.5 , and the value of remanent d 33eff of 108 pm/V at room temperature (20°C) were observed in 1.0 mol% La 2 O 3 ‐doped NKBT thick films, which can be comparable with that of the commonly used lead‐based materials. The enhancement of the pyroelectric and piezoelectric performances is attributed to the reduction of lattice tetragonality, uniform microstructure, and improved densification in La‐modified NKBT thick films.