Effect of (Na,K)-Excess Precursor Solutions on Alkoxy-Derived (Na,K)NbO3 Powders and Thin Films

Lead-free (Na 0.5 K 0.5 )NbO 3 (NKN) powders and thin films were fabricated from stoichiometric (Na/K=50/50), 4 mol % excess (52/52, 53/51, and 55/49), and 10 mol % excess (55/55, 56/54, 58/52, and 60/50) precursor solutions by the sol–gel process. The NKN55/55 powder heat-treated at 800 °C showed an orthorhombic phase and rectangular grains whose size was estimated to be about 300 nm. With increasing Na/K ratio, grain size increased to about 1 µm and the cubic–tetragonal ( T c ) phase transition peak emerged at 392 °C in a differential thermal analysis (DTA) curve. On the other hand, single-phase NKN thin films were fabricated at 600 °C from the (Na,K)-excess precursor solutions (58/52 and 60/50). In particular, the NKN58/52 thin film showed a low leakage current density (10 -7 A/cm 2 at 40 kV/cm), and the maximum polarization P max and dielectric constant ε r at 1 kHz were 9.1 µC/cm 2 and 725, respectively.