Particle size effect on the crystal structure symmetry of K0.5Na0.5NbO3

Pure sodium potassium niobates with K0.5Na0.5NbO3 composition were prepared in powderous form with various particle sizes (75 nm–10 μm) through microemulsion mediated synthesis and subsequent annealing. An interesting change of particle shape and a mixture of fine and coarse particles were observed at a critical diameter of 200 nm. A combined study by X-ray powder diffraction (XRPD) and Raman spectroscopy demonstrated a phase transformation induced by particle size. Fine particles (<200 nm) have a triclinic structure whereas coarse particles (>200 nm) have a monoclinic structure at room temperature. Possible space groups describing both these modifications were suggested.