Sodium-potassium niobate nanorods with various crystal structures and their application to nanogenerator

(Na1-xKx)NbO3 (NKN) nanorods with an orthorhombic (OR) structure, a rhombohedral (RH) structure, or a polymorphic phase (PP) structure, which contains both OR and RH structures, are prepared. The presence of RH and PP NKN nanorods is explained by the existence of OH- defects at the O2- sites of the NKN nanorods. The PP NKN nanorods grown on a Nb5+-doped SrTiO3 substrate show the largest piezoelectric strain constant of 175pm/V because they have more directions for dipole rotation than OR and RH NKN nanorods. Piezoelectric nanogenerators (NGs) are synthesized using composites consisting of NKN nanorods with various structures and polydimethylsiloxane. The largest open-circuit output voltage is 35V, and the short-circuit current is 5.0A, which are obtained using the NG containing 0.7g of PP NKN nanorods. Moreover, this NG shows a maximum output power of 16.5W for an external load of 10.0M Omega.