Yu. N. Pal’yanov

High-pressure?high-temperature treatment of natural diamonds

The results are reported of high-pressure–high-temperature (HPHT) treatment experiments on natural diamonds of different origins and with different impurity contents. The diamonds are annealed in a temperature range up to 2000oC at stabilizing pressures up to 7 GPa. The evolution is studied of different defects in the diamond crystal lattice. The influence of substitutional nitrogen atoms, plastic deformation and the combination of these is discussed. Diamonds are characterized at room and liquid nitrogen temperature using UV–visible spectrophotometry, Fourier transform infrared spectrophotometry and photoluminescence spectrometry. The economic implications of diamond HPHT treatments are discussed.

Fast relaxation intensity versus silica glass density: existence of sharp peculiarity

Low-frequency Raman spectra of densified silica glasses, annealed at different temperatures and possessing various densities, are studied. The dependence of the fast relaxation intensity versus the density can be described by linear laws below and above the density 2.26 g cm−3, but the slope of the linear law below the critical density is ten times higher than the slope of the linear law above 2.26 g cm−3. The sharp peculiarity is interpreted as a consequence of an inhomogeneous glassy structure with local ordering similar to tridimite or β-cristobalite. The dependence of the silica sample density on annealing temperature is discussed in view of the temperature dependence of the liquid silica density. A hypothesis is proposed that the true dependence of the liquid silica density is a linear function of temperature.

Suppression of fast relaxation and the Raman coupling coefficient in densified silica

Low-frequency Raman spectra of normal and pressure-densified silica are investigated. Strong suppression of fast relaxation intensity is found in densified silica in comparison with the normal type, the dependence of the fast relaxation intensity versus the density changing its behaviour near the density of the low-density crystalline SiO2 polymorphs. The light–vibration coupling coefficients extracted from the comparison of Raman spectra and the vibrational density of states are different for densified and normal silica. In the case of the most densified sample, the position of the boson peak maximum marks the transition from the square frequency behaviour of the coupling coefficient to the linear one.

The transformation features of impurity defects in natural diamonds of various habits under high P–T conditions

The results of the investigations of the transformation of impurity defects in natural diamonds of various habits at the stage of high-temperature annealing at P = 6 GPa and T = 2200°C are presented. The studies conducted allowed us to ascertain that the transformations of Aand B-defects in diamonds of octahedral and cubic habits follow general regularities. This fact shows that most of the diamonds of cubic habit with low degree of aggregation of nitrogen centers were not really annealed over a long-term interval. Unlike octahedral diamonds, those of cubic habit are characterized by a pronounced increase in the peak of H-containing defects (3107 cm–1) after annealing.

EPR of new phosphorus-containing centers in synthetic diamonds

The effect is studied of electron and X-ray irradiation on phosphorous centers in synthetic diamonds grown in the P-C medium by the Bars technology. After exposure to X-ray irradiation, a new paramagnetic phosphorus-containing center NP6, in addition to the phosphorous centers NP4 and NP5, is observed in diamonds annealed at a temperature of 2300°C and pressure of 7.5 GPa. The spectrum of NP6 is simulated to give the following parameters: A1 = 29.42 G, A2 = 23.28 G, A3 = 75.85 G, g1 = 2.00085, g2 = 2.00083, and g3 = 2.00083. The NP4-NP6 centers are assumed to be genetically related to the three nitrogenphosphorous centers NP1-NP3 and be formed as a result of the transformation of the tetrahedral environment around the phosphorous atom into an octahedral environment at an annealing temperature of 2300°C. The synthetic diamonds annealed at 2300°C were successively exposed to irradiation with electrons with energies of 3.5 MeV (5×1017 e/cm2) and annealing at temperatures of 500°C and 700°C. The EPR method is used to find that annealing of the electron-irradiated crystals at 700°C leads to the formation of a new paramagnetic center with spin S = 1 and hyperfine structure (HFS) from one phosphorus atom with the parameters: g = 2.0012, D = 19.7 G, and A(P) = 3.6 G. The center is likely to have an eightvacancy chain structure with a phosphorus atom located at the center.

Formation of Conductive Layers inside Diamond by Hydrogen Ion Implantation and Subsequent Thermal Treatment at Low or High Pressures

Abstract(111) synthetic HPTP diamond plates are irradiated by H2+ 50 keV ions in the range of the fluences of 1−13 × 1016 sm−2 and annealed in vacuum at 1 mPa (VPHT, 500–1600°C) or at high HPHT parameters (4.0–7.5 GPa, 1200–1550°C). It is shown by measuring the layer conductivity and Raman light scattering that after VPHT annealing, a buried layer of glassy carbon 10–100 nm thick with low resistance (∼1 kOhm/□) is formed, followed by HPHT with high resistance (∼1 MOhm/□) and hopping transport along defects.

Diamond monochromator-splitter with enhanced reflectivity for synchrotron radiation

AbstractIt has been shown that a damaged surface layer can enhance the reflectivity of a diamond monochromator-splitter for synchrotron radiation. The X-ray diffraction analysis with the use of asymmetric Bragg reflections allowed the determination of the layer thickness and its mosaicity dispersion equal to 3 μm and 19″, respectively. In this case, the observed integrated intensity of a quasisymmetric 422 Laue reflection (

Conditions of formation of Cr-pyrope and escolaite during mantle metasomatism: Experimental modeling

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