Synthesis Of High-pressure Phases Research Articles

Kawai-type multianvil ultrahigh-pressure technology.

Since the large-volume press with a double-stage multianvil system was created by the late Professor Naoto Kawai, this apparatus (Kawai-type multianvil apparatus or KMA) has been developed for higher-pressure generation, in situ X-ray and neutron observations, deformation experiments, measurements of physical properties, synthesis of high-pressure phases, etc., utilizing its large sample volume and capacity in stable and homogeneous high temperature generation compared to those of competitive diamond anvil cells. These advancements in KMA technology have been made primarily by Japanese scientists and engineers, which yielded a wealth of new experimental data on phase transitions, melting relations, and physical characteristics of minerals and rocks, leading to significant constraints on the structures, chemical compositions, and dynamics of the deep Earth. KMA technology has also been used for synthesis of novel functional materials such as nano-polycrystalline diamond and transparent nano-ceramics, opening a new research field of ultrahigh-pressure materials science.

Scale-Free Modeling of Coupled Evolution of Discrete Dislocation Bands and Multivariant Martensitic Microstructure.

A scale-free model for the coupled evolution of discrete dislocation bands and multivariant martensitic microstructure is developed. In contrast to previous phase field models, which are limited to nanoscale specimens, this model allows for treating the nucleation and evolution of martensite at evolving dislocation pileups, twin tips, and shear bands in a sample of an arbitrary size. The model is applied for finite element simulations of plastic strain-induced phase transformations (PTs) in a polycrystalline sample under compression and shear. The solution explains the one to two orders of magnitude reduction in PT pressure by plastic shear, the existence of incompletely transformed stationary state, and optimal shear strain for the strain-induced synthesis of high pressure phases.

Halide based shock-wave treatment of fluid-rich natural phases

For the synthesis of high pressure phases from natural minerals and the shock wave treatment of fluid bearing phases a halide based method was developed. The experiments were performed in the pressure range between 25 and 162 GPa with a success rate for the new method of 100% for the new method. Based on the Impedance Corrected Sample Recovery Capsule under avoiding the adiabatic decompression a direct comparison between different loading paths and sample holder geometries is possible. The recovered samples show neither indications of melting in the case of kaolinite and very limited degassing in the case of carbonates. The recovery of amorphous water bearing Al-Si-phases with Aluminum in four-, five- and six-fold coordination was possible. The samples were analyzed with scanning electron microscopy, x-ray diffraction, nuclear-magnetic-resonance- and infra-red-spectroscopy and the results were directly compared.

Strain-induced phase transformations under high pressure and large shear in a rotational diamond anvil cell: Simulation of loading, unloading, and reloading

Coupled plastic flow and strain-induced phase transformations (PTs) under high pressure and large plastic shear in a micron scale sample under loading, unloading, and reloading in a rotational diamond anvil cell (RDAC) are studied in detail, utilizing finite element approach. A plastic strain-controlled, pressure-dependent kinetic equation, which describes strain-induced PTs, is used. The effects of four main material parameters in this equation on PTs and plastic flow in RDAC in three-dimensional formulation are systematically analyzed. Multiple experimental phenomena are reproduced and interpreted, including pressure self-multiplication/demultiplication effects, small ‘steps’ on pressure distribution in the two-phase region, simultaneous occurrences of direct and reverse PTs, oscillatory distribution of pressure for weaker high-pressure phase, and a thin layer of high-pressure phase on a contact surface. During unloading, unexpected intensive plastic flow and reverse PT are revealed, which change the interpretation of experimental results. The effect of unloading and reloading paths on PTs is examined. Two types of pressure variations are revealed, which are qualitatively consistent within experimental observations for ZnSe and KCl. Obtained results lead to ways of controlling PTs by varying compression-torsion paths and can be utilized for the search of new high pressure phases, ways to reduce pressure for the synthesis of high pressure phases, and to retain them at ambient pressure.

Synthesis of high-pressure phases of silica by laser-induced optical breakdown

We report on synthesis of compressed silica phase formed inside a α-quartz host crystal using powerful shock-wave and thermal transients generated via local optical breakdown induced by low-energy, tightly focused femtosecond laser pulses. Structural characterization of irradiated areas by the X-ray diffraction technique reveals signatures of a new high-pressure phase of silica, which is theoretically expected to form at a pressure of 120 GPa.

Structural phase transitions in highly compressed substance and the synthesis of high-pressure phases

Structural phase transitions in highly compressed substance and the synthesis of high-pressure phases

Femtosecond Laser Synthesis of High-Pressure Phases of Si

The high pressure simple hexagonal structure of silicon, which has not been synthesized, is quenched using femtosecond laser-driven shock wave. Any high-pressure phases of silicon do not remain after the pressure release in the case of the hydrostatic and conventional shock compression methods. We found the existence of the simple hexagonal structure after the intense femtosecond laser irradiation to silicon by analyzing the crystalline structures using a synchrotron grazing-incidence XRD method. Femtosecond laser-driven shock wave is a useful tool for the synthesis of non-equilibrium high-pressure phases.

Role of Constituent Configuration on Shock-Induced Reactions in a Ni+Al Powder Mixture

AbstractUltra-fast reactions initiated within or immediately behind the shock front in powder mixtures are of importance in the synthesis of high-pressure phases and next-generation energetic materials. Reactions in nickel and aluminum powder mixtures and the establishment of a reaction threshold have been the source of many studies over the last 20 years. Prior work has suggested that the criterion for reaction is most probably mechanochemical in nature, in which shock loading environment plays a larger role than absolute shock energy input. The mechanisms responsible for intimate mixing of fresh reactants are however still unclear. In this work we are investigating the role of particle size and morphology on the loading, mixing, and their subsequent shock-induced reaction behavior, by performing shock-compressibility experiments on equi-volumetric mixtures of nickel and aluminum powders, with variations in nickel particle size (micron and nano-scale) and shape (spherical and flake). Determination of shock states is accomplished through time-resolved in situ PVDF gauge measurements of input shock stress and shock propagation speed obtained from transit time through the thickness of powder mixture. The reaction product shock-compressibility state is also being calculated based on constant pressure approximations to allow correlation with measured states for inference of the occurrence of shock-induced chemical reactions. The results of this study suggest that powder configuration in the nickel-aluminum system can be modified to encourage or discourage reaction.

Phase transformations of disordered structures of graphite-like boron nitride under high-temperature shock compression

The pattern of phase transformations in boron nitride under high-temperature shock compression has been studied using a previously proposed method for high-temperature shock-wave synthesis of high-pressure phases followed by rapid quenching. Fine powders of turbostratic and partially ordered graphite-like BN were used as initial structures. Shock compression was carried out in ring devices at a pressure of 30 GPa and a temperature above 2500 K. A mixture of dense phases (wurtzitic and sphaleritic) was found to form from the graphite-like structures under those conditions; the total yield of those phases and the relative amount of the sphaleritic modification are considerably higher when turbostratic BN is the starting material. Both of the dense phases formed have a nanocrystalline grainstructure. The wurtzitic phase does not transform into the sphaleritic phase under those conditions, which points to cubic BN forming directly from the graphite-like structures.