Vanishing of the Phase Transitions in Ferroelectric Hexagonal BaTiO_3 at High Pressure

概要

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The dielectric constant ε_c along the c-axis of hexagonal BaTiO_3 has been measured from 5 K to 300 K as a function of hydrostatic pressure p up to 4 GPa. The hexagonal to orthorhombic transition point T_0 (222 K at 10^5 Pa) decreases at a rate of 34 K/GPa and vanishes at pressures above p_c=3.4 GPa; the T_0 vs p curve is well represented by an equation of T_0=a(p_c-p)^<1/2> over the whole pressure range. While, the ferroelectric phase transition point T_c (77 K at 10^5 Pa) initially increases and then decreases only slightly with increasing pressure ; interestingly, the dielectric anomaly at T_c disappears at pressures above 1 GPa. Another lattice instability like a quantum paraelectricity seems to exist at low temperatures. Some discussions are presented for the mechanism of the phase transitions.
社団法人日本物理学会の論文
1994-04-15