Structural, morphological and electrical properties of graphene oxides obtained by Hummers, Tour and modified methods: a comparative study

The aim of this paper is the comparison of structural, morphological and electrical properties of thermally extended graphite synthesized by chemical oxidation of graphite with sulfur of nitric acids at all other same conditions. Thermal treatments of graphite intercalation compounds were performed at a temperature of 600°C on the air for 10 min but additional annealing in temperature range of 100-600oC for 1 hour was done. The obtained materials were characterized by XRD, Raman spectroscopy and impedance spectroscopy. The evolution of structural ordering of thermally extended graphite samples at increasing of annealing temperature was traced. It was determined that the additional annealing allows to control the electrical conductivity and structural disordering degree of extended graphite samples that is useful for preparation of efficient current collectors for electrochemical capacitors.

Long-range ordering and local structural disordering of BiAgSe2 and BiAgSeTe thermoelectric

Thermoelectric materials are promising for energy harvesting using waste heat. The thermal management of the thermoelectric materials are attracting scientific and technological interests. The narrow bandgap semiconductor BiAgSe2 are good...

О ширине запрещенной зоны AgSbSe-=SUB=-2-=/SUB=-

Spectral ellipsometric studies of AgSbSe2 have been carried out, and the spectra of optical constants and permittivity have been determined in the photon energy range of 0.07-6.5 eV. To describe the obtained spectra, the Tauc-Laurents, modified Forouhi-Bloomer and Cody-Laurents models were used. It was found that the Cody-Laurents model better describes the sub-edge region of the spectrum of optical constants. It is shown that the spatial structural disordering of AgSbSe2 crystals has a significant effect on the optical properties, the shape of the absorption edge, and the structure of the band gap. Based on the analysis of the obtained spectra and using various methods, the band gap of AgSbSe2, Еg = 0.32 eV, was determined.

Формирование Ферми-дуг при T<< T-=SUB=-c-=/SUB=- в окрестности d-волновых узлов структурно неоднородных ВТСП YBa-=SUB=-2-=/SUB=-Cu-=SUB=-3-=/SUB=-O-=SUB=-6.92-=/SUB=-

The effect of structural inhomogeneity on the superconducting gap near d-wave for optimally doped high-Tc superconductors YBa2Cu3O6.92 sites is considered. For this purpose, the heat capacity was investigated in the temperature range T = 2-10 K and in magnetic fields H = 0-9 T for a series of fine-crystalline samples with different degrees of controlled structural disordering. The information on the features of superconducting gap near d-wave sites in structurally disordered samples is obtained. It is shown that the d-wave sites inherent in an ideal crystal structure under the influence of structural disorder are modified with the formation of small Fermi arcs in the vicinity of nodal points at T << Tc, not covered by a superconducting gap. In this case, the gap itself remains at T ≤ Tc in other directions of the Brillouin zone and coexists with the Fermi arcs. This transformation is accompanied by an increase in the steepness of the nodal slope, a decrease of the Volovik effect, and the generation of a linear term γ (0) T of the metallic type in the temperature dependence of heat capacity, which should not be present in superconductors with an ideal crystal structure and the nature of which has not yet been established.

Design and perspective of amorphous metal nanoparticles from laser synthesis and processing

Amorphous metal nanoparticles (A-NPs) have aroused great interest in their structural disordering nature and combined downsizing strategies (e.g. nanoscaling), both of which are beneficial for highly strengthened properties comparing to...

Structural and electrophysical properties of thermally expanded graphite prepared by chemical methods: comparative analysis

The aim of this paper is the comparison of structural, morphological and electrical properties of thermally extended graphite synthesized by chemical oxidation of graphite with sulfur of nitric acids at all other same conditions. Thermal treatments of graphite intercalation compounds were performed at a temperature of 600°C on the air for 10 min but additional annealing in temperature range of 100-600oC for 1 hour was done. The obtained materials were characterized by XRD, Raman spectroscopy and impedance spectroscopy. The evolution of structural ordering of thermally extended graphite samples at increasing of annealing temperature was traced. It was determined that the additional annealing allows to control the electrical conductivity and structural disordering degree of extended graphite samples that is useful for preparation of efficient current collectors for electrochemical capacitors.

Stimulated Raman Scattering in Yttrium, Gadolinium, and Calcium Orthovanadate Crystals with Single and Combined Frequency Shifts under Synchronous Picosecond Pumping for Sub-Picosecond or Multi-Wavelength Generation around 1.2 µm

Comparative investigation of stimulated Raman scattering (SRS) characteristics in the YVO4, GdVO4, and Ca3(VO4)2 orthovanadate crystals at both low and high frequency anionic group vibrations is presented. It was found that GdVO4 is the most perspective for SRS generation on both the ν1 stretching and ν2 bending modes of internal anionic group vibrations with the strongest SRS pulse shortening under synchronous picosecond pumping. It is as a result of GdVO4‘s widest linewidth (17cm−1) of the homogeneously broadened scheelite-type component of the bending ν2 Raman line that led to the strongest SRS pulse shortening down to the dephasing time of the widest (scheelite-type) Raman mode at the secondary intracavity short-shifted SRS conversion. It allowed us to achieve SRS pulses with sub-picosecond duration under tens-of-picoseconds pumping due to the strongest 42-fold pulse shortening. Using the Ca3(VO4)2 crystal with essentially wider Raman lines (~50cm−1) did not allow us to generate SRS pulses shorter than 1 ps. It can be explained by inhomogeneous broadening of the Raman lines in Ca3(VO4)2 because of its structural disordering. Using the measured SRS pulse duration, the homogeneous broadening of the inhomogeneously broadened bending Raman line of Ca3(VO4)2 was estimated to be ~9cm−1. Among the orthovanadate crystals, the YVO4 crystal with the highest Raman gain and with homogeneously broadened Raman lines allowed us to realize the most efficient SRS lasing and SRS pulse shortening truly down to inverse half-width of the bending Raman line.

Predicting short-range order and correlated phenomena in disordered crystalline materials

Disordered crystalline materials are used in a wide variety of energy-related technologies. Recent results from neutron total scattering experiments have shown that the atomic arrangements of many disordered crystalline materials are not random nor are they represented by the long-range structure observed from diffraction experiments. Despite the importance of disordered materials and the impact of disorder on the expression of physical properties, the underlying fundamental atomic-scale rules of disordering are not currently well understood. Here, we report that heterogeneous disordering (and associated structural distortions) can be understood by the straightforward application of Pauling’s rules (1929). This insight, corroborated by first principles calculations, can be used to predict the short-range, atomic-scale changes that result from structural disordering induced by extreme conditions associated with energy-related applications, such as high temperature, high pressure, and intense radiation fields.