A monoclinic-tetragonal ferroelectric phase transition in lead-free (K0.5Na0.5)NbO3- x %LiNbO3 solid solution

A monoclinic ferroelectric phase with space group Pm has been discovered in lead-free (K0.5Na0.5)NbO3-5%LiNbO3 solid solution ceramics by high energy synchrotron x-ray powder diffraction measurements. At ambient temperature, the lattice parameters of this monoclinic structure were (am, bm, cm; β) = (4.015 Å, 3.944 Å, 3.987 Å; 90.34°). This monoclinic phase transformed to a tetragonal (P4mm) one on heating between 340 K and 360 K. The results demonstrate the presence of structurally bridging low symmetry monoclinic phase in (K0.5Na0.5)NbO3-x%LiNbO3 solid solution system: indicating a means to achieve high piezoelectricity in Pb-free systems via domain engineering.