Pressure-Dependent Raman Scattering Spectrum of Piezoelectric (Li,Na,K)NbO3 Lead-Free Ceramics

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High-pressure Raman scattering experiments have been carried out for (Na0.5K0.5)NbO3 and Lix(Na0.5K0.5)1-xNbO3 (abbreviated as LNKN-100$x$) ceramics using a diamond-anvil cell (DAC) in the backscattering geometry. Appreciable spectral changes occurred between 2.04 and 3.41 GPa in (Na0.5K0.5)NbO3 ceramics, which was a sign of the orthorhombic (O) to tetragonal (T) phase transition. The Raman modes of T-phase LNKN-6 and LNKN-7 were less affected by increasing pressure, indicating them to be particularly stable against hydrostatic pressure. In LNKN-5.5, however, a pressure-induced phase transition from a polymorphic O–T phase mixture to a single O phase, similar to the case of LNKN-3, was observed at around 2.84 GPa, since the hydrostatic compression might favor the dense O phase rather than the T phase. Accompanying this result, it was newly found that a further important role of Li substitution in LNKN ceramics is the introduction of tensile stress in the crystal structure.
2010-09-25