Dielectric/piezoelectric properties and temperature dependence of domain structure evolution in lead free single crystal

(K0.5Na0.5)NbO3 (KNN) single crystals were grown using a high temperature flux method. The dielectric permittivity was measured as a function of temperature for [001]-oriented KNN single crystals. The ferroelectric phase transition temperatures, including the rhombohedral–orthorhombic T R − O , orthorhombic–tetragonal T O − T and tetragonal–cubic T C were found to be located at −149  ∘C, 205 ∘C and 393 ∘C, respectively. The domain structure evolution with an increasing temperature in [001]-oriented KNN single crystal was observed using polarized light microscopy (PLM), where three distinguished changes of the domain structures were found to occur at −150  ∘C, 213 ∘C and 400 ∘C, corresponding to the three phase transition temperatures.