Hydrostatic Pressure Effects on the Raman Scattering in Hexagonal Type BaTiO₃

抄録

Hydrostatic pressure effects on Raman modes in hexagonal type BaTiO₃ have been studied. Mode-Grüneisen parameters of low lying six allowed Raman modes are determined at room temperature; they are in a range 1.6∼2.8. Soft phonon modes appear below a structural phase transition temperature, T₀=220 K at 1 bar. The mode frequencies decrease with increasing pressure p; also T₀ decreases with dT₀⁄dp=−3.7 K/kbar. A quantum effect is found in the T₀ vs p relation at low temperatures and at high pressures; T₀ approaches zero as T₀∝(p_c−p)^1⁄2 where p_c∼48 kbar. The soft-mode frequency vs T curves under high pressures show non-classical behaviors with a critical index β=1/3 over a rather wide temperature range, 0.51<T⁄T₀<0.95.