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 synthesized by chemical solution deposition. The analysis of the KNN precursor solution revealed that the KNN precursor consists of complex metal alkoxides of potassium and sodium hexaalkoxy niobates with highly symmetric Nb-O octahedra. KNN precursor films were crystallized in a perovskite phase with a (1 0 0) preferred orientation on Pt(1 0 0)/MgO(1 0 0) substrates at 650 °C. The three-dimensional relationship between KNN(1 0 0) and Pt(1 0 0)/MgO(1 0 0) is confirmed by the fourfold symmetry of the pole figure. The fourfold symmetry indicates that the synthesized films are oriented in both the c and a, b directions on the Pt(1 0 0) surface. Although the insulating resistance was not sufficiently high at room temperature, the (1 0 0)-oriented KNN thin films showed potentially larger polarizations 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 μC/cm2 and 90 kV/cm, respectively.