Processing of highly oriented (K,Na)NbO3 thin films using a tailored metal-alkoxide precursor solution

Highly oriented lead-free K0.5Na0.5NbO3 (KNN) thin films were synthesised by chemical solution deposition. The analysis of the KNN precursor solution revealed that the KNN precursor consisted of complex metal alkoxides of potassium and sodium hexaalkoxy niobates with highly symmetric Nb-O octahedra. KNN precursor films were crystallised in a perovskite phase with a (100) preferred orientation on Pt(100)/MgO(100) substrates at 650 C. The three-dimensional relationship between KNN(100) and Pt(100)/MgO(100) was confirmed by the fourfold symmetry of the pole figure. The fourfold symmetry indicated that the synthesised films were oriented in both the c and a, b directions on the Pt(100) surface. Although the insulating resistance was not sufficiently high at room temperature, the (100)-oriented KNN thin films showed potentially larger polarisation compared to the KNN thin films with no preferred orientation at low temperatures. The 2Pr and 2Ec of the oriented KNN films at -190 C were 41.0 microC/cm2 and 90 kV/cm, respectively.