Synthesis of homogeneous (Na1−xKx)NbO3 nanorods using hydrothermal and post-heat treatment processes

To synthesize (Na1−xKx)NbO3 nanorods, the Nb2O5-added (1 − y)NaOH–yKOH specimens with 0.0 ⩽ y ⩽ 0.9 were heated at 160 °C and subsequently annealed at 500 °C. Homogeneous Na-rich (Na1−xKx)NbO3 nanorods were only synthesized for the specimen with y = 0.15. However, NaNbO3 nanorods were formed for specimens with y < 0.15, and K-rich (Na1−xKx)NbO3 nanoplates were obtained for specimens with y > 0.2. The (Na8xK8−8x)Nb6O19⋅nH2O transient phase was formed in the specimen with y = 0.15 heated at 160 °C for 8.0–12.0 h, and this phase transformed into the Na-rich (Na1−xKx)NbO3 nanorods after annealing at 500 °C. Therefore, the formation of a homogeneous (Na8xK8−8x)Nb6O19⋅nH2O phase at a low temperature is very important for the synthesis of the (Na1−xKx)NbO3 nanorods. The (Na8xK8−8x)Nb6O19⋅nH2O phase was considerably influenced by the heating temperature, and the processing time. The Na-rich (Na1−xKx)NbO3 nanorods have rectangular shape with various sizes, and the growth direction of these nanorods is [0 0 1].

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► NKN nanorods have been produced using hydrothermal method for the first time. ► The growth direction of the NKN nanorod is [0 0 1]. ► (Na8xK8−8x)Nb6O19nH2O produced at 160 °C and transformed into NKN nanorods at 500 °C. ► The NKN nanorods can be used for the piezoelectric energy harvester.