Crystal structure and orthorhombic–tetragonal phase transition of nanoscale (Li0.06Na0.47K0.47)NbO3

Lead-free nano (Li0.06Na0.47K0.47)NbO3 powders, with pure perovskite structure and various grain sizes between about 30 and 60 nm, have been successfully synthesized by a novel sol–gel method, in which Nb2O5 was used as the Nb source. The refining XRD and Raman spectra were used in combination with TEM to investigate the evolution of lattice structure and phase transformation behavior as a function of grain size. The results demonstrated that the growth process of grains has been divided into two stages, and the distortion of unit cell apparently decreases with decreasing grain size. At around 35 nm, the phase structure of (Li0.06Na0.47K0.47)NbO3 changed from orthorhombic to tetragonal. This phenomenon is related to a grain size-induced structural phase transition. For the well accepted wisdom that niobates get super piezoelectric properties in orthorhombic–tetragonal transition region, our results suggested a critical size for the application of (Li0.06Na0.47K0.47)NbO3 in nano piezoelectric devices.