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For LiKSO4, the transition temperatures TI–II from the room-temperature phase I to the intermediate phase II, and TII–III from phase II to the low-temperature phase III increase with pressure p as d T I–II d p ≈ 8.3° C/kbar and d T II–III d p ≈ 21.7° C/kbar . Phase II vanishes at the triple point (4.3 kbar, 14.0°C).

The dielectric measurement of the layered antiferroelectrics Cu(HCOO)2·4H2O was carried out over a range from −45°C to 0°C under uniaxial stresses parallel or perpendicular to the layers. The results of stress dependences of the dielectric constant, the transition and the characteristic temperatures are discussed on the basis of the phenomenological theory and the dimer model.

Effects of hydrostatic pressure on the phase transition points of ferroelectric NH 4 LiSO 4 were studied by dielectric measurements at 1 kHz over a temperature range of 0∼210°C and a pressure range up to 2 kbar. The observed pressure coefficients of I–II and II–III phase transition temperatures (186.5°C and 10°C at 1 atm, respectively) were 9.8 deg/kbar and -3.3 deg/kbar, respectively.

The dielectric properties of cholesteryl 2, 2, 3, 3-tetrafluoropropionate were measured under hydrostatic pressures of up to 5 kbar. The reciprocal permittivity ε -1 was found to vary almost linearly with temperature T in the normal phase I under a pressure p, and the peak value of ε at the I-II (normal-incommensurate) phase transition temperature T I-II increased with increasing p in the low-pressure region below 3 kbar and tended to saturate in the high-pressure region above 3 kbar. The slope of T I-II against p was 6°C/kbar in the low-pressure region and decreased in the high-pressure region. The dielectric relaxation curves in phase II shifted towards higher temperatures with p, while the relaxation frequency decreased with p at constant temperature. The relaxation curves converged at the II-III (incommensurate-incommensurate) phase transition temperature T II-III with decreasing frequency under pressure. The pressure dependence of activation parameters such as the enthalpy, entropy and volume was also estimated. The slope of T II-III against p was 1.6°C/kbar in the low-pressure region and increased in the high-pressure region. The region of phase II was found to be extended in the low-pressure region and narrowed in the high-pressure region by the application of pressure.

The pressure (0–6 kbar), temperature (-200∼-70°C) and dc bias field (0–9×105V/m) dependence of the dielectric properties (permittivity, spontaneous polarization, coercive field and phase transition temperatures) of trissarcosine calcium chloride (TSCC) were measured. The effect of pressure on the dielectric properties was remarkable. A remarkable decrease in the permittivity occurred at a pressure of about 5 kbar, where the ferroelectric state terminates. The new phase III appeared when pressure was applied and became more stable with increasing pressure. Judging from the dc bias field and temperature dependence of the permittivity and the non-occurrence of hysteresis loops and other considerations, the pressure-induced phase III is believed to be antiferroelectric. The dielectric properties associated with the paraelectric-ferroelectric transition in TSCC are also successfully interpreted in terms of a phenomenological theory.

Anomalous dielectric behaviors in 3M2CPOOB with extremely large spontaneous polarization P s and in 2MBNCBC indicating the reversal of the sign of the P s have been studied under hydrostatic pressure up to 2 kbar. The slope of the pressure-temperature phase diagram was comparable to that of DOBAMBC and other smectic liquid crystals, suggesting that the ferroelectricity is not influenced strongly. Anomalies in both compounds were not influenced by the application of pressures of less than 2 kbar.