Recent development of studies on phase transitions in hydrogen-bond crystals are reviewed from a theoretical point of view. These crystals have been considered to display order-disorder type behaviors in phase tansitions at atomospheric pressure. After recent high pressure studies on these crystals, transition temperatures tend to zero kelvin with increasing pressure. If disordered arrangements of radicals in their directions hold down to zero kelvin, these facts are inconsistent with the third law of thermodynamics. A possibility of a displacive type is discussed in the mechanism of phase transition in these crystals.
Temperature dependences of the dielectric constant along the ferroelectric c-axis have been measured at various pressures up to 7. 9 GPa in KH2PO4 and KD2PO4. The vanishing of the ferroelectric state has been observed at 1. 7 GPa in KH2PO4 and at 6. 3 GPa in KD2PO4. The Curie constant C of KH2PO4 is almost independent of pressure. On the other hand, that of KD2PO4 above 4 GPa decreases about three fourths of that at atmospheric pressure. The crossover of the order-disorder type to the displacive one under high pressure is discussed on the mechanism of phase transition to explain these experimental results of KD2PO4.
This article reviews recent developments in high-pressure phase studies of H2S by Raman scattering, x-ray and neutron diffractions, FT infrared absorption, and first-principles calculation. At room temperature, solid H2S shows many phase transitions under high pressures; - I - (8 GPa) -I'- (11 GPa) - IV - (30 GPa) - V - (46 GPa) - VI -. The characteristic features of each phase transition are presented and discussed by considering the behaviors of hydrogen bondings and molecular rotations.
The nature and stability of the disordered phase I and the ordered phase III of solid hydrogen bromide under pressure were investigated using the ab initio molecular dynamics method. A detailed study of the response to pressure of the orientational distribution and the orientational and vibrational dynamics in disordered phase showed that phase I can be described as a rotator phase with fluctuating hydrogen bonds up to pressures well over 10 GPa. We predict that the disorder at higher densities leads to cooperative proton-transfer dynamics. The pressure dependence of stretching modes in phase I and lattice modes in phase III was also investigated and compared well with experimental data.
Dielectric properties of hydrogen-bonded materials, 1) squaric acid with a two-dimensional network, 2) hydrogen-bonded chain systems and 3) isolated systems, are discussed. In squaric acid, we have found two types of phase change, that is, conventional order-disorder-type dielectric transition and deformation of the proton-potential from a double- to single-well type. In the case of one-dimensional system, we have found the kink-type defects due to the degeneracy of the hydrogen-bonded chain. In the isolated system, we have observed a variety of dielectric transitions, and discuss the probability of the proton-tunneling.
The cooperation of electron and proton in organic systems has a large potentiality for the creation of new molecular functions in molecular crystals. In this article, the electron-proton-cooperation in charge transfer crystals is reviewed, particularly focusing on the it spectroscopy of the phase transition in quinhydrone charge-transfer crystals under high pressures. As an example of the electron-proton cooperation at ambient pressure, the metal-insulator phase transition observed in [Pd (H2-xEDAG) (HEDAG) ]TCNQ (EDAG= ethylenediamino-glyoxime, x = ca. 0. 7) is reported.
The historical development of polymerization under high pressure has been reviewed and the possibility of an industrial application of high pressure polymerization has been discussed in our previous works on radical polymerization at high pressure. Taking recent environmental concerns into consideration and the significant advancement in the technology of high temperature and high pressure, the synthesis of fluoropolymers in supercritical carbon dioxide, especially DeSimone's process, is discussed considering the chemical kinetics at the critical point with emphasis on supercritical carbon dioxide as an excellent reaction media.
This paper describes the possibility of utilizing a synthetic diamond as a new optical element in the thirdgeneration synchrotron radiation source SPring-8. The development of the synthetic diamond allows for the branching of the low emmitance undulator source, and opens a new multi-color. At SPring-8, RIKEN Beamline I (BL45XU) is the first branched undulator beamline, which consists of two experimental stations, protein crystallography (PX) and small-angle X-ray scattering (SAXS). The branched beams are generated by a transparent diamond crystal. The PX branch of RIKEN Beamline I has been designed based on the trichromatic concept to optimize the multi-wavelength anomalous diffraction (MAD) method data collection. This concept involves three kinds of intensity data sets with three different wavelengths being taken quasisimultaneously for the single protein crystal without changing any settings on the diamond trichromator.