Effects of heat treatment on electrical and electromechanical properties of hydrothermally synthesized epitaxial (K_0.51Na_0.49) NbO₃ films

Effects of heat treatment on the electrical and electromechanical properties of hydrothermally synthesized epitaxial (K_0.51Na _0.49)NbO₃ films were investigated. The film composition and crystal structure did not markedly change with heat treatment from 240 to 600°C in O₂ atmosphere. However, the leakage current density drastically decreased from the order of 10¹ to 10^%5A/ cm² at 50kV/cm after heat treatment at 240 °C. The relative dielectric constant, remanent polarization, and transverse piezoelectric constant increased with increasing heat treatment temperature from 300 to 600°C (from 330 to 750 in ε_r, from 5.4 to 14 μC/cm ² in remanent polarization, and from 41 to 56pm/V in transverse piezoelectric response). H₂O desorption of 12ppm was detected in epitaxial (K_0.51Na_0.49)NbO₃ films by thermal desorption spectroscopy measurement. Such H₂O desorption can be related to the improvement of the electrical and electromechanical properties of the hydrothermally synthesized epitaxial (K_0.51Na _0.49)NbO₃ films.