Investigation On Physical Properties Of Hydric Molecular System Under High Pressure And High Temperature Conditions

High pressure investigation on physical properties of hydric molecular system plays an important role both on fundamental research and fundamental application research of condensed matter. Under high pressures several molecular solids undergo some changes, such as structural transition, molecular dissociation, and insulator-metal transition and so on. The knowledge of their action under pressure is evry useful for understanding the important progress in condense materials, such as the force between atoms or molecules, it's also useful for realizing the practicality area of physical models, finding out new rule, and presenting theoretical base for practicality application. Investigation on the force between molecule and equation of state of some small molecular systems may accelerate the development of earth and planet science, provide lots of theoretical base for understanding its internal composition and evolvement rule.Both of NH3 and H2O belong to typical Hydric Molecule and they occupy a large content in the nature, because of the existence hydrogen bonding there are many structural transation. For hundards of years, people engaged in explore the high pressure and high temperature properties. On the one hand, liquid water and ammonia under high temperature and high pressure were used in hydrothermal syntheses studies and economic manufacture, on the other hand, there are abundant water and ammonia which exist at these extreme conditions, for example the Uranus and Neptune, buried between a rocky core and a gaseous atmosphere, their interiors are mostly composed of a thick intermediate layer of"hot ices", predominantly water, hydrocarbons and ammonia. Many observable properties of these planets, such as gravitational moments, and partially also their atmospheric composition, are thought to be determined by the physical and chemical properties of matter within this layer. At the same time the molecular dissociation under high pressure were found in water and ammonia system. on account of above reasons, NH3 and H2O are ideal system for investigating the microcosmic mechanism of dissociation and the source of macrocosmic properties.The main content in this thesis includes room temperature high pressure investigation, electricial heating high temperature and high pressure investigation and laser heating high temperature and high pressure investigation. In the course of preparing this thesis, we established electricial heating Brillouin scattering system, laser heating platelet geometry Brillouin scattering system, and cage type confocal Raman scattering system; we also introduced some novel experiment method, such as in situ increasing pressure under high pressure and sample encapsulation technique. Some interested topic, including liquid-liquid phase transition, isostructural transition and superionic state under extreme conditions were analyze in detail.It was found that water possess of many special physical and chemical properties because of the existence of hydrogen bonding, in the solid state, each H atom in one molecule participate in forming hydrogen bonding, and a tetrahedron framework can be found among the H2O molecule. When the ice change to liquid water state, some of hydrogen bonding was destroyed the tetrahedron skeleton of ice became breakdown, however, within a short range there were still lots of hydrogen bonding in the liquid and they also present as a tetrahedron configuration, and the configuration of hydrogen bonding can be changed when the temperature and pressure was changed, this structural transition from liquid to liquid has attracted more attention in recent years. We investigated the Brillouin spectra of water at high temperatures and high pressures with the electricial heating Brillouin scattering system, the pressure dependence of acoustic velocity, elastic constant along several isotherms were obtained, a subtly cusp can be found in the elastic constant evolutions and it was regarded as the phase transition boundary from low density water to high density water. The Phase diagram of water was developed. The pressure dependences of refractive index were obtained using both platelet and back scattering geometry Brillouin spectra, the isothermal equation of state was presented. Using laser heated high temperature and high pressure Brillouin scattering system cmbined with the molecular dynamic simulation analysis, we investigated the structural transitions of H2O from solid to superionic and liquid state at different pressure and temperatures, it was found that increasing the trmperature at 20GPa and 30GPa H2O transit from solid to liquid, the superinic state can't be observed, however, at 45GPa and 2000K the superinic state can be observed, in this state oxygen atoms vibrate around body centered cubic lattice positions while the protons jump among equivalent sies along the O-O separations.To understand the isostructural transition in the ammonia system under pressures, we studied the high pressure structural property of ammonia by in situ high pressure synchronization X ray diffraction, high pressure Raman scattering and Brillouin scattering technique. The result of synchronization X ray diffraction found that at around 10GPa the pressure evolution of interplanar spacings show a turn point, around which the slope changed obviously, the c/a-axis ratio initially slowly increase up to 10GPa and then start to decrease at a higher rate. We may understand this as a change in the electrical structure of the sample. The Brillouin scattering results present the change of shear elastic constant, a crossover can be found in the pressure evlution of C12 and C13 at about 10GPa, which may be caused by the lattice distortion. Compared with foregoing results we can also found changes at around 10GPa from the Raman spectra both in intra- and inter-band. The property of N-H bond changed and then the mode of vibration was changed. In order to find out whether the symmetric H-bonded state exists, we investigated the Raman spectra of ammonia up to 62GPa, unlike the result of M. Gauthier no change was found at 60GPa, however, the antisymmetric bending mode was detected at room temperature for the first time, and a turn point was at about 29GPa was observed, we may suppose a structural change in ammonia.To study the structure and physical properties of ammonia at high temperature and high pressures, search the superionic boundary and understand the dissociate process in molecule, we performed electrical heated Brillouin scattering measurements and laser heated Raman and Brillouin scattering measurements. The pressure evolutions of velocity, refractive index at different isotherms were obtained, and finally the equation of state of liquid ammonia was presented, no density or structural change was found in the range of our study. The laser heated Raman spectra of ammnia at 18GPa and 62GPa were obtained, combined with the molecular dynamic simulation analysis it can be found that, the ammonia system appears as the fluids at 18GPa and 1800K conditions, at this time the intermolecular modes disappear because of the crystal structure breakage, on the other hand, the jumps of proton between neighboring molecules induced the intensity of intramolecular modes became weak and disappear. Comparatively at 62GPa and 2160K conditions, the system was in the superionic phase, at this time, the proton also jumps between the moleculars, while the N atom vibrate around the crystal lattice positions.