Size-Dependent Thermal Stability and Optical Properties of Ultra-Small Nanodiamonds Synthesized under High Pressure.

Diamond properties down to the quantum-size region are still poorly understood. High-pressure high-temperature (HPHT) synthesis from chloroadamantane molecules allows precise control of nanodiamond size. Thermal stability and optical properties of nanodiamonds with sizes spanning range from <1 to 8 nm are investigated.

Extended Defects in Graphene and Their Contribution to the Excess Specific Heat at High Temperatures.

The recent experiments on fast (microsecond) pulse heating of graphite suggest the existence of sharp maximum (6500 K at 1-2 GPa) on its melting curve. To check the validity of these findings, we propose to investigate the accumulation of extended in-plane defects in graphene. Such defects would contribute to thermodynamic properties of graphene and impose the upper limit on its melting temperature.

Secondary Relaxation in Supercooled Liquid Propylene Glycol under Ultrahigh Pressures Revealed by Dielectric Spectroscopy Measurements.

1,2-Propanediol (propylene glycol) is a well-known glassformer, which easily vitrifies under wide range of cooling rates. An interesting feature of propylene glycol is that, similar to glycerol, it retains one-mode primary relaxation (slow α process) under a wide range of external P- T conditions. It was demonstrated that the emergence of secondary (β) relaxation requires the application of very high pressures P > 4.

Structural and Dielectric Relaxations in Vitreous and Liquid State of Monohydroxy Alcohol at High Pressure.

2-Ethyl-1-hexanol monoalcohol is a well-known molecular glassformer, which for a long time attracts attention of researchers. As in all other monohydroxy alcohols, its dielectric relaxation reveals two distinct relaxation processes attributed to the structural relaxation and another more intense process, which gives rise to a low-frequency Debye-like relaxation. In this monoalcohol, the frequency separation between these two processes reaches an extremely high value of 3 orders of magnitude, which makes this substance a rather convenient object for studies of mechanisms (supposedly common to all monoalcohols) leading to vitrification of this type of liquids.

Structure and topology of three-dimensional hydrocarbon polymers.

A new family of three-dimensional hydrocarbon polymers which are more energetically favorable than benzene is proposed. Although structurally these polymers are closely related to well known diamond and lonsdaleite carbon structures, using topological arguments we demonstrate that they have no known structural analogs. Topological considerations also give some indication of possible methods of synthesis.

Diamond monohydride: the most stable three-dimensional hydrocarbon.

Most of the hydrocarbons are either molecular structures or linear polymeric chains. Discovery of graphene and manufacturing of its monohydride - graphane have incited interest in the search for three-dimensional hydrocarbon polymers. However, up to now all hypothetical hydrocarbon lattices significantly have lost in terms of energy to stacked graphane sheets and solid benzene.

Fluctuation-dissipation theorem and the dielectric response in supercooled liquids.

We consider the correlation between static conductivity and dynamic dielectric relaxation in a number of polar organic liquids. Experimental evidence suggests that in the simple cases the linear dependence between characteristic frequency of relaxation process and the value of static susceptibility is observed. However, this proportionality can be broken due to the appearance of additional relaxation processes (secondary or high-frequency ones) so it can be confused with the "fractional" variant of Debye-Stokes-Einstein relation.

Crystallization and vitrification of ethanol at high pressures.

We present the high pressure (up to 3 GPa) dielectric spectroscopy study of ethanol in supercooled liquid and solid states. It was found that ethanol can be obtained in the glassy form by relatively slow cooling in the pressure range below 1.5 GPa.

Magnetoresistance of the high-pressure ferromagnetic phases (GaSb)2M (M=Cr,Mn).

For the first time magnetoresistance of the ferromagnetic high-pressure phases (GaSb)2M (M=Cr,Mn) has been measured in a wide range of temperature and magnetic field. It was found that the magnetic field dependencies of resistivity of both systems contain several contributions, including relatively smaller s-d exchange (Yosida-type) components in low fields and a quadratic positive term (PMR) in the low temperature region. The magnitude of the predominated negative term (NMR), which can be attributed to the quantum corrections effects, demonstrates a peak in the vicinity of Curie temperature.

Phase transformations in methanol at high pressure measured by dielectric spectroscopy technique.

The dielectric response in methanol measured in wide pressure and temperature ranges (P < 6.0 GPa; 100 K < T < 360 K) reveals a series of anomalies which can be interpreted as a transformation between several solid phases of methanol including a hitherto unknown high-pressure low-temperature phase with the stability range P > 1.2 GPa and T < 270 K.

Dielectric spectroscopy and ultrasonic study of propylene carbonate under ultra-high pressures.

We present the high pressure dielectric spectroscopy (up to 4.2 GPa) and ultrasonic study (up to 1.7 GPa) of liquid and glassy propylene carbonate (PC).

Electrotransport and magnetic properties of Cr-GaSb phases synthesized under high pressure.

The electrotransport and magnetic properties of new phases in the Cr-GaSb system were studied. The samples were prepared by high-pressure (P=6-8 GPa), high-temperature treatment and identified by x-ray diffraction and scanning electron microscopy. One of the CrGa(2)Sb(2) phases with an orthorhombic structure Iba2 has a combination of ferromagnetic and semiconductor properties and is potentially promising for spintronic applications.

Glassy dynamics under superhigh pressure.

Nearly all glass-forming liquids feature, along with the structural alpha-relaxation process, a faster secondary process (beta relaxation), whose nature belongs to the great mysteries of glass physics. However, for some of these liquids, no well-pronounced secondary relaxation is observed. A prominent example is the archetypical glass-forming liquid glycerol.

AsS melt under pressure: one substance, three liquids.

An in situ high-temperature--high-pressure study of liquid chalcogenide AsS by x-ray diffraction, resistivity measurements, and quenching from melt is presented. The obtained data provide direct evidence for the existence in the melt under compression of two transformations: one is from a moderate-viscosity molecular liquid to a high-viscosity nonmetallic polymerized liquid at P approximately 1.6-2.