High pressure Raman spectroscopy of stoichiometric ferroelectric potassium lithium niobate

Abstract

Abstract Ferroelectric Potassium Lithium Niobate (KLN) has a diffusive ferroelectric (FE) to paraelectric (PE) phase transition at 400-550°C depending on the content of lithium in the composition. In a crystal of stoichiometric and low lithium composition with Tc = 540°C, we have observed at least one high-pressure phase transition by Raman spectroscopy in a diamond-anvil cell. The phase transition was diffusive but first order in nature. At ambient temperature, the high pressure phase transition from tetragonal to orthorhombic symmetry was determined to occur at 53 ± 3 kbar. We observed mode softening for the low frequency modes as well as the internal and external niobate modes. A peak at ∼200 cm−1 showed a marked intensity increase near the phase transition. We have calculated the mode Gruneisen parameters of 14 out of 20 Raman active A1(z) modes polarized parallel to the ferroelectric axis.