Pure-phase (K, Na)NbO3 (KNN) powders with orthorhombic symmetry were successfully synthesized by solvothermal method using isopropanol as solvent, without the addition of water. The as-prepared powders were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry to show the variation of phase, morphology, size distribution and chemical composition under different synthetic conditions, such as fill factors (FF) of the solvothermal system and alkalinity of the starting solution. Compared with the traditional hydrothermal method and the so-called solvothermal method (water aided in fact), small grains with well crystallinity were obtained using 100% isopropanol as reaction medium. The results indicate that both fill factor and alkalinity have significant effects on the phase structure and size distribution of the as-obtained KNN powders. Pure orthorhombic perovskite-structured KNN powders with a grain size of 100 nm were synthesized at the following condition: reaction time, 16 h; reaction temperature, 240 °C; fill factor, 70%; and alkalinity, 1 M. Small grains (~100 nm) tend to form mesocrystals (~10 µm) with tetrakaidecahedron structures, and the possible formation mechanism was proposed. The solvothermal method without the addition of water is a promising alternative to synthesize pure and refined powders under mild reaction conditions.

The citrate complexing sol–gel process to fabricate lead-free (K,[Formula: see text]Na)NbO3 ferroelectric thin films was studied. Soluble niobium source of niobium–citric acid (Nb–CA) solution was utilized as a raw material to synthesize (K,[Formula: see text]Na)NbO3 thin films, by pyrolyzing at 450–550[Formula: see text]C and annealing at 650[Formula: see text]C. The film pyrolyzed at 450[Formula: see text]C shows poor crystallization with porous morphology, whereas the film pyrolyzed at 550[Formula: see text]C appear to be well-crystallized and denser, and the ferroelectricity was also proved by the [Formula: see text]–[Formula: see text] hysteresis loop measurement.

Lead-free (K, Na)NbO 3 (KNN) ferroelectric films were fabricated on Ti substrates by sol-gel non-alkoxide process. Nb 2 O 5 was used to prepare the soluble niobium source by citrate method. KNN thin films with perovskite phase were obtained by pyrolyzing at 500°C and annealing at 700°C. The influence of A-site ion excess on the phase, microstructure and electric properties of the films was investigated. X-ray diffraction and energy-dispersive spectroscopy (EDS) data indicate that the volatilization of K was severer than Na during the thermal treatment, and K excess is assisted to get pure perovskite phase. Meanwhile, the P-E loops and the dielectric curves manifest that K excess plays a role to improve the ferroelectric performance, while Na excess contributes to good dielectric property.