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We have obtained the metastable phase of the thermoelectric alloy Bi0.4Sb1.6Te3 with electron type conductivity for the first time using the method of quenching under pressure after treatment at P=4.0 GPa and T=400–850 °C. We have consequently performed comparative studies with the similar phase of Sb2Te3. The polycrystalline X-ray diffraction patterns of these phases are similar to the known monoclinic structure α-As2Te3 (C2/m) with less monoclinic distortion, β ≈ 92°. We have measured the electrical resistivity and the Hall coefficient in the temperature range of T=77−450 K and we have evaluated the Hall mobility and density of charge carriers. The negative Hall coefficient indicates the dominant electron type of carriers at temperatures up to 380 K in the metastable phase of Sb2Te3 and up to 440 K in the metastable state of Bi0.4Sb1.6Te3. Above these temperatures, the p-type conductivity proper to the initial phases dominates.

Powder X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and molecular dynamics have been employed to investigate structural transformations in hexagonal and cubic modifications of fullerite C60 after the action of high pressure (4 GPa) within the temperature range 20–1450°C. It has been found that fullerene molecules polymerize to afford polymer structures only in the case of face-centered cubic samples. Under the effect of high pressure and temperature, fullerite C60 with a hexagonal close-packed structure is initially transformed into the cubic modification and, then, forms polymerized structures, which, during an increase in the treatment temperature, become less stable and ordered than the same polymerized structures obtained directly from cubic fullerite C60. X-ray photoelectron spectroscopy measurements suggest deformation of the cages of fullerene molecules in the polymerized structures.

Solid fullerenes C60 and C70 have been treated at high pressure of 15 GPa and high temperatures of 520 - 1820 K for a time of exposure of 60 s and a quenching rate of 300 K s−1 using a toroid-type apparatus. X-ray diffraction and Raman spectra confirm the realization of 3D-polymerized phases in these solids at 15 GPa. The pressure/temperature maps of synthesis of metastable carbon phases on the basis of C60 and C70 have thus been extended to 15 GPa. The longitudinal and shear sound wave velocities were measured by acoustic microscopy techniques. A maximum sound wave velocity of (21±1)×105 m s−1 was observed in the sample synthesized from C60 at T = 1170 K. The elastic constants were calculated using experimental data. The acoustic microscopy images of experimental samples have been investigated.

Superhard superconducting samples with a critical temperature of TC = 10.5 - 12.6 K were obtained by high-pressure / high-temperature sintering of synthetic diamond powders coated with a niobium film and in 50% - 50% composition with superhard C60 fullerene. Superhard superconductors with TC = 9.3 K were obtained when diamond and molybdenum powders were sintered at a pressure of 7.7 GPa and a temperature of 2173 K. Superconducting samples with TC = 36.1 - 37.5 K have been obtained in the systems diamond-MgB2 and cubic boron nitride-MgB2.

The Raman spectra of single-wall carbon semiconducting nanotubes of the HiPCO type were investigated upon excitation at 1.06 µm at pressures up to 3 GPa. A method of purification of the initial material from iron is proposed and the diffraction patterns of purified nanotubes are considered. The diameters and chiralities of the nanotubes manifesting themselves in the spectra are determined. Pressure dependences of the frequencies are obtained and the Gruneisen parameters and their relationship with interatomic interactions in nanotubes are discussed.

Crystalline and disordered 3D-polymeric C60 and C70 with different lattice parameters and with densities in the range of 2.2÷3.25 g cm−1 were obtained by high-pressure-high-temperature treatment at P=11.5÷15 GPa, T=670÷1800 K. Their d.c. electrical conductivity was investigated at temperatures 30÷350 K. The variable range hopping mechanism dominates in all samples up to room temperature. A temperature activated conductivity via delocalized states was observed at T>160÷260 K in crystalline C60 samples and in some samples with disordered structure. The evaluated band gap value is Eg=0.28÷0.54 eV for different crystalline structures and 0.06÷0.25 eV for disordered ones.

The fullerites C60 and C70 have been treated at high pressure, 15 GPa, and high temperatures 300–1820 K, using the toroid apparatus. The value of 15 GPa has been fixed by the abrupt change of electroresistivity of ZnS. X-ray diffraction and Raman spectra confirm the realization of 3D-polymerized phases in these fullerites at 15 GPa. The formation of superhard phases with high elastic properties is begun at temperature 100 K lower than that it was at 13 GPa. The (P, T) maps of C70 and C60 are extended to 15 GPa.

Rhombohedral C60 polymer was subjected to high-pressure-high-temperature treatment at P =13 GPa, T =620-1620 K. After quenching, crystalline and disordered structures with densities in the range of 2.1-2.9 g cm-1 were obtained. The structures of the samples have been investigated by powder X-ray diffraction and Raman scattering. DSC analysis showed a transformation of the polymeric structure into monomeric on annealing in the range 400-640 K. The temperature dependence of the electrical resistance of samples with disordered structure was measured in the range 2.5-300K. For different samples, the conductivity was proportional to T1/2, T3/2, T4 and exp(-1/T1/4).

X-ray diffraction patterns, Raman spectra, and the hardness of C70 fullerite subjected to a high pressure with shear are investigated. It is shown that these conditions favor the phase transformation of molecular fullerite into the hard amorphous phase. The hardness of a specimen removed from a diamond anvil cell loaded up to 26 GPa under shear deformation applied is found to be equal to 30 GPa.

C60 and C70 fullerenes polymerized under pressures between 9.5 and 13 GPa and temperatures between 670 and 1850 K were investigated by differential scanning calorimetry (DSC) in the range 240–640 K ...

We report the results of the study of the polycrystalline powder of the diamond–lonsdaleite system by X-ray diffractometry, transmission electron microscopy and UV Raman spectroscopy. The measured data of structural parameters are in good agreement with ab initio calculations. We show that the Raman spectrum is proportional to the phonon density of states of the diamond–lonsdaleite system.

Polymeric structures on the basis of La@C 82 endofullerene were synthesized and investigated for the first time. Bulk samples of about 10 mg weight were obtained by static high-pressure-high-temperature treatment at 9.5 GPa and 520; 720 K. The structure of quenched samples was studied by powder X-ray diffraction and transmission electron microscopy. Several new crystalline structures were found and attributed to the formation of dimers, 2D- and 3D-polymeric structures. Magnetic susceptibility of synthesized samples was investigated in the temperature range 5-300 K.

Some scenarios of the (3D) polymerized fullerene structure formation are proposed. The atomic positions of two such C 60 orthorhombic phases have been calculated by the energy optimization of the 3D polymerized C 60 cluster geometry and have been refined by the profile analysis of experimental X-ray diffraction patterns. The pattern simulations show good agreement ( R wP -factor∼10%) with diffraction patterns of superhard samples prepared at 12–13 GPa pressures and 820 K temperature.

High-pressure studies on fullerenes have previously shown the existence of one- and two-dimensional (2D) polymerized C 60 structures. Synchrotron radiation measurements, performed on C 60 samples quenched from 13 gigapascals and 820 kelvin, yield unambiguous proof for the existence of a three-dimensional (3D) polymerized C 60 derivative. Moreover, unusual ellipsoidal Debye-Scherrer diffraction patterns are observed, which shows that the giant anisotropic deformation induced by the nonhydrostatic compression is retained in the quenched samples. The multiple bonding possibilities of the highly symmetrical C 60 allow the retention (down to ambient pressure) of the deformation, a phenomenon reported previously only under high pressure.

For the first time investigations of structure and physical properties of C70 after treatment at 4 ≤ P ≤ 12.5 GPa and 300 ≤ T ≤ 1770 K were carried out by X-ray, Raman and infrared spectroscopy. The results are plotted in a (P, T) diagram. The new superhard 3D-polymerized tetragonal phase has been found at P ≥ 9.5 GPa. The superhard disordered state of samples produced from C70 at 12.5 GPa with a hardness close to that of (100)-face diamond has also been found.

The elastic properties of C60 fullerite samples synthesized under pressure P=13.0 GPa at high temperatures were investigated using acoustic microscopy. The velocities of longitudinal (c L=17–26 km/s) and transverse (c T=7.2–9.6 km/s) elastic waves in the samples were measured. It was established that the longitudinal sound velocity of ultrahard fullerites is higher than that of any other known solid. The bulk modulus of these ultrahard samples is higher than that of diamond and reaches a value greater than 1 TPa. The high bulk modulus, the relatively large shear moduli, and the substantial Poisson ratio indicate that the structure of the ultrahard fullerites is fundamentally different from that of diamond.

X-ray diffraction, hardness, conductivity, Raman and infrared studies of solid C 60 subjected simultaneously to high pressure at 8 GPa and temperatures up to 1820 K have been carried out. A hard disordered state is formed at temperatures higher than 920 K and a cross-linked layered structure is proposed for this state. Crystalline phases obtained at T 60 cages and formation of an amorphous structure. The 3-D polymerization of solid C 60 at high-pressure–high-temperature treatment is discussed.

Data from recent experimental studies of C60 under high pressures are collected and analyzed, concentrating on the polymerized states where covalent intermolecular bonds have been formed through treatment of molecular C60 at high pressures and temperatures at or above room temperature. We give an overview of the observed phase transformations and the structures of metastable polymeric phases, both crystalline and disordered, as analyzed under ambient conditions, and we present and discuss a pressure-temperature diagram showing which synthesis conditions result in which final phases in the pressure range up to 20 GPa (200 kbar) and at temperatures up to 2300 K. The physical properties of the various phases are discussed whenever enough data are available. The pressure-temperature stability limits for C60 and the conditions for the transformation of C60 into graphite, diamond and chaoite-type carbon are derived.

Superhard and ultrahard phases of C60 were synthesized by quenching at high pressures up to 13 GPa and high temperatures in the 300–2100 K range. The structures of the samples are discussed on the basis of X-ray and Raman spectra and electron microscopy data. The following physical properties of hard samples were studied: specific gravity; specific heat in the range 400–600 K; sound velocities; elastic moduli; electrical properties; resistance to uniaxial stress; stability against oxidation. These properties are different from those of diamond and other carbon forms. The hardness of ultrahard fullerites exceeds the hardness of diamond.

in the pressure range \rangeunit{8}{13}{GPa} and the temperature range \rangeunit{600}{2100}{K} were studied. These properties are the specific gravity, specific heat in the range \rangeunit{400}{600}{K} , sound velocities, elastic moduli, electrical properties, resistance to uniaxial stress and stability against oxidation. These properties are different from those of diamond and other carbon forms. The hardness of ultrahard fullerites exceed the hardness of diamond. The structures of the samples are described on the basis of X-ray data.

New data concerning the solid C60 phase transformations in the pressure-temperature range P = 6.5–13 GPa, T = 300–2100 K and nonhydrostatic conditions are presented and plotted in the P-T coordinates. The structure of superhard and ultrahard carbon phases obtained with these conditions is investigated by X-ray powder diffractometry and Raman scattering. New crystal structures of distorted bcc type and transient to diamond states are revealed in the synthesized samples. Fragments of different lengths of polymerized fullerene cages are found from resonance Raman spectra of the samples obtained at P = 13 GPa and T < 1200 K.

Investigations of X-ray diffraction patterns, Raman spectra, hardness and other physical properties were carried out for fullerite after a heat treatment up to 1830 K at 9.5 and 13 GPa nonhydrostatic pressure of bulk samples. Both superhard and ultrahard forms of carbon have been obtained from C60 at 620–1830 K. The hardness of the materials exceeded that of diamond. The X-ray and Raman measurements have shown that both crystal structures and fullerene molecules were retained in superhard and ultrahard states, but a gradual increase of disorder occurred and a random network of linked molecules at high temperatures was formed.

An “in situ” X-ray diffraction study of the GeTe under shear deformation and nonhydrostatic pressure conditions has been performed. By applying the shear deformation, two phase transitions with structure changes from NaCl to GeS and further to CsCl types were first detected at 19.2 and 38 GPa respectively. The X-ray powder diffraction data and unit-cell parameters of both pressure-induced phases of GeTe are given. The shear-deformation dependence of the GeTe transition pressures is found.

Phase transitions were found with use of an in situX-ray anvil-type of apparatus with a boron annulus at pressures up to 12 GPa. The disordering of vacancies in the In sub-structure, or α→βtransition, was found in In2Te3at p > 1.9 GPa. The next transformation from the β-form into the Bi2Te3type of structure was observed in both sesquitellurides at 2.0 GPa and 5.0 GPa for In2TGe3and Ga2Te3respectively. The In2Te3metastable phase of the Bi2Te3resulted from heating up to 200° C at p > 4.0 GPa, and it remained in a normal condition on release of the pressure. The X-ray powder diffraction data of pressure-induced phases, volume changes and bulk modulus of both sesquitellurides are given. The compressibility anisotropy of the layer pressure-induced phase was observed. The mechanism of the crystal structure transformation from the face-centered cubic structure into the Bi2Te3type is proposed to be due to the displacement of atoms from the space diagonal of the cube [111] into [112]-cubic direction and the rhombohedral distortion of the angle between these directions.

Superhard superconducting samples with a critical temperature of T C = 10.5-12.6 K were obtained by high-pressure / high-temperature sintering of synthetic diamond powders coated with a niobium film and in 50% - 50% composition with superhard C 60 fullerene. Superhard superconductors with T C = 9.3 K were obtained when diamond and molybdenum powders were sintered at a pressure of 7.7 GPa and a temperature of 2173 K. Superconducting samples with T C = 36.1-37.5 K have been obtained in the systems diamond-MgB 2 and cubic boron nitride-MgB 2 .

New data on the synthesis conditions, structure and physical properties of the superhard and ultrahard samples created from solid C60 by static high-pressure high-temperature treatment in the range of 9. 5-13 GPa ; 600 -2100 K are represented. Measured velocities of the compressional sound waves in the ultrahard fullerites exceed the highest values for diamond. Bulk elastic modulus for the hardest fullerite samples more than twice exceeds that of diamond. Ultrahard fullerite tip is applied for measurements of hardness of diamond and fullerites. Maximum hardness of fullerite is measured to be 310±40 GPa.

High-pressure high-temperature polymerization of C70 fullerite obtained at first time. New crystal structures of rhombohedrally distorted fcc type and bct type are found for the samples quenched after treatment at p = 6. 5-12. 5 GPa and T = 500-900 K. In the temperature range of 900-1720 K a disordered cross-linked layered structures are found. Samples with bct type crystal structure and with disordered structure have hardness in the range of 30-90 GPa and their density varies in the range of 2. 1-2. 8 GPa. These data are compared with the data for materials obtained from C60 fullerite under the same conditions.

Electrical resistivity of crystalline and disordered fullerite samples obtained by static high-pressure-high-temperature treatment of C60 and C70 at P = 12.5 GPa and T = 820-1500 K was investigated in the temperature range of 2.4-300 K. Room-temperature activation energy of charge carriers was found to be in the range 40-200 meV. T3/2 and T4 dependencies of conductivity versus temperature were revealed both in crystalline and disordered structures. Photoluminescence spectra of C60 samples treated at P = 13 GPa, T = 770-1470 K show 50 nm short-wavelength shift of characteristic 750 nm PL band.

Annealing of 2D- and 3D-polymeric C[sub60] fullerene obtained under pressures of 9.5 and 12.5 GPa and temperatures of 670 and 770 K has been investigated by DSC in the range 240–640 K. An endotherm ...

We present synchrotron X-ray diffraction measurements performed on C60 samples quenched from 13 GPa and 820 K. The analysis of all the reciprocal space of a quenched sample shows that it consists of a 3-D arrangement of polymerised fullerene molecules. Moreover, it is shown that the intensity distribution in reciprocal space occurs in ellipsoidal surfaces instead of the normal spherical surfaces characteristic of a powder sample. This implies that the applied anisotropic stress is imprinted in the quenched transformed samples.

Velocities of the longitudinal and shear sound waves are measured in ultrahard fullerites created by static high-pressure-high-temperature treatment under P=13 GPa and T=1670–1870 K. The highest value of 26.0 km/s for the longitudinal waves is measured, that is about 40% more than in diamond. Bulk modulus of different ultrahard fullerites covers the range of about 600–1700 GPa. The highest hardness is about 30×103 kg/mm3. We ascribe these unique properties to formation of 20–30 atoms clusters by the walls of adjacent molecules under process of 3D-cross-linking. Most distinctly these clusters declare themselves in the cubic structure with the lattice parameter about 6 A and 32 atoms per unit cell.