Evidence of phase heterogeneity in sol–gel Na0.5K0.5NbO3 system

Na0.5K0.5NbO3 thin films have been synthesised via a sol–gel route using commercially available ethoxides of sodium, potassium and niobium. X-ray diffraction confirmed that film crystallisation occurred at ≥600 °C, but extra peaks indicated the presence of secondary phase(s). The thin films displayed non-ferroelectric polarisation hysteresis loops. Evidence of phase heterogeneity was found from detailed analyses of the thermochemistry of the NKN precursor gels which showed multiple heating DTA exotherms for crystallisation around 480–550 °C. Additionally, heating DTA endotherms and cooling exotherms for NKN gels around 800–850 °C confirm the presence of a second phase.