Electric-field-dependent phase volume fractions and enhanced piezoelectricity near the polymorphic phase boundary of (K_0.5Na _0.5)_1-xLi_xNbO₃ textured ceramics

The structure, ferroelectric and piezoelectric properties of 001 textured (K_0.5Na_0.5)_0.98Li_0.02NbO ₃ ceramics were investigated as a function of temperature and dc bias E. X-ray diffraction revealed an orthorhombic (O) → tetragonal (T) polymorphic phase boundary (PPB). Phase coexistence was found near the PPB over a 30 °C temperature range, where the relative phase volume fractions changed with temperature. Furthermore, increasing E applied along the 001 texture direction resulted in a notable increase in the volume fraction of the T phase at the expense of the O phase, effectively shifting the O → T boundary to lower temperature. An enhancement in the piezoelectric properties was found to accompany this increase in the T volume fraction.