Natalia Solopova

Terapascal static pressure generation with ultrahigh yield strength nanodiamond

Terapascal static pressure generation is enabled in laboratory due to implementation of nanocrystralline diamond microballs. Studies of materials’ properties at high and ultrahigh pressures lead to discoveries of unique physical and chemical phenomena and a deeper understanding of matter. In high-pressure research, an achievable static pressure limit is imposed by the strength of available strong materials and design of high-pressure devices. Using a high-pressure and high-temperature technique, we synthesized optically transparent microballs of bulk nanocrystalline diamond, which were found to have an exceptional yield strength (~460 GPa at a confining pressure of ~70 GPa) due to the unique microstructure of bulk nanocrystalline diamond. We used the nanodiamond balls in a double-stage diamond anvil cell high-pressure device that allowed us to generate static pressures beyond 1 TPa, as demonstrated by synchrotron x-ray diffraction. Outstanding mechanical properties (strain-dependent elasticity, very high hardness, and unprecedented yield strength) make the nanodiamond balls a unique device for ultrahigh static pressure generation. Structurally isotropic, homogeneous, and made of a low-Z material, they are promising in the field of x-ray optical applications.

High-pressure spectroscopic study of siderite (FeCO3) with a focus on spin crossover

Abstract Fe-bearing carbonates have been proposed as possible candidate host minerals for carbon inside the Earth’s interior and hence their spectroscopic properties can provide constraints on the deep carbon cycle. Here we investigate high-pressure spin crossover in synthetic FeCO3 (siderite) using a combination of Mössbauer, Raman, and X-ray absorption near edge structure spectroscopy in diamond-anvil cells. These techniques sensitive to the short-range atomic environment show that at room temperature and under quasi-hydrostatic conditions, spin crossover in siderite takes place over a broad pressure range, between 40 and 47 GPa, in contrast to previous X-ray diffraction data that described the transition as a sharp volume collapse at approximately 43 GPa. Based on these observations we consider electron spin pairing in siderite to be a dynamic process, where Fe atoms can be either high spin or low spin in the crossover region. Mode Grüneisen parameters extracted from Raman spectra collected at pressures below and above spin crossover show a drastic change in stiffness of the Fe-O octahedra after the transition, where they become more compact and hence less compressible. Mössbauer experiments performed on siderite single crystals as well as powder samples demonstrate the effect of differential stress on the local structure of siderite Fe atoms in a diamond-anvil cell. Differences in quadrupole splitting values between powder and single crystals show that local distortions of the Fe site in powder samples cause spin crossover to start at higher pressure and broaden the spin crossover pressure range.

Raman spectroscopy of glassy carbon up to 60 GPa

In the present work in experiments in a diamond anvil cell at room temperature we studied the behavior of glassy carbon under high pressure up to 60 GPa by means of in situ Raman spectroscopy. Raman bands typical for glassy carbon were clearly observed in the entire pressure interval. We did not see any noticeable changes in the type of chemical bonding in glassy carbon up to the highest pressure reached. The yield strength of the material under confining pressure was found to be maximum of about 7 GPa, inconsiderably higher than that measured at ambient pressure (1.4 GPa on literature data).

The system MgCO3–FeCO3–CaCO3–Na2CO3 at 12–23 GPa: Phase relations and significance for the genesis of ultradeep diamonds

Physical–chemical experimental studies at 12–23 GPa of phase relationships within four-members carbonate system MgCO3–FeCO3–CaCO3–Na2CO3 and its marginal system MgCO3–FeCO3–Na2CO3 were carried out. The systems are quite representative for a set of carbonate phases from inclusions in diamonds within transitional zone and lower mantle. PT-phase diagrams of multicomponent carbonate systems are suggested. PT parameters of boundaries of their eutectic melting (solidus), complete melting (liquids) are established. These boundaries define area of partial melting. Carbonate melts are stable, completely mixable, and effective solvents of elemental carbon thus defining the possibility of ultra-deep diamonds generation.

Kinetic peculiarities of diamond crystallization in K-Na-Mg-Ca-Carbonate-Carbon melt-solution

The kinetic peculiarities of diamond crystallization in multicomponent K-Na-Mg-Ca-carbonate-carbon system have been studied in conditions of diamond stability at 1500–1800°C and 7.5–8.5 GPa. It has been established that the diamond phase nucleation density at a fixed temperature of 1600°C decreases from 1.3 × 105 nuclei/mm3 at 8.5 GPa to 3.7 × 103 nuclei/mm3 at 7.5 GPa. The fluorescence spectra of obtained diamond crystals contain peaks at 504 nm (H3-defect), 575 nm (NV-center), and 638 nm (NV-defect), caused by the presence of nitrogen impurity. In the cathodoluminescence spectra, an A-band with the maximum at 470 nm is present. The obtained data make it possible to assign the synthesized diamonds in the carbonate-carbon system to the mixed Ia + Ib type.