Computations of Low-Energy Non-Icosahedral Structures of C6− 60

Abstract

Owing to the three-fold degeneracy of the LUMO in C₆₀, its hexa-anion is not subjected to Jahn-Teller distortions. In contrast to the accepted presumptions, however, computations at the MNDO, AMI, PM3, SAM1, HF/STO-3G, HF/3-21G, and HF/4-31G levels show that the completely relaxed, non-icosahedral cage of C^6? ₆₀is lower in energy. The computed energy gain varies between 60 and 150 kJ/mol and thus, it is consistently significant (the most sophisticated approach, HF/4-31G, yields 93 kJ/mol). The longest C-C bond in the relaxed structures is at most computed 0.05 Å longer compared to the 5/6 bond in the icosahedral C^6? ₆₀The symmetry of C^6? ₆₀is relaxed to D₂ A C_2v, isomer is discussed, too.     

Crystallization kinetics of bulk amorphous Se80−xSbxTe20

Crystallization kinetics of the Se_80–x Sb _x Te₂₀ (0x9) alloys have been studied using differential scanning calorimetry. The activation energies for the glass transition and that for crystallization have been determined from the heating rate dependence of the glass transition temperature and the peak crystallization temperature. The results have been analysed using the modified Kissinger's and Matusita's equations for the non-isothermal crystallization of materials. The variation of glass transition temperature with composition suggests that a small amount of Sb ( 4 at %) leads to an increase in the chain length of Se-Te, whereas further increase in Sb atomic per cent increases the number of Se-Te chains in the alloys.     

Performance of R170 mixtures as refrigerants for refrigeration at −80 °C temperature range

The refrigeration performance parameters of two binary azeotropic mixtures of R170 + R23 and R170 + R116 and a ternary azeotropic mixture of R170 + R23 + R116 were measured systematically in the low-stage loop of a two-stage cascade system. In addition, the performance of the currently used R508B refrigerant was also measured at similar conditions for comparison. A two-stage cascade refrigeration testing apparatus was designed and assembled, in which an R404A system was used as the high-temperature refrigeration stage. Thermodynamic performance parameters of the low-stage loop such as the coefficient of performance (COP), cooling capacity, and the discharge temperature of these four mixtures were measured at various condensation and evaporating temperatures. The results show that the COP of the R170 + R116 binary mixture is up to 10% higher than that of R508B. These mixtures show good potential as low-temperature stage refrigerants for applications in the ?80 °C temperature range.     

Inclusion complexes of fluorofenidone with β-cyclodextrin and hydroxypropyl-β-cyclodextrin

Background: Fluorofenidone is a novel antifibrotic drug and its aqueous solubility is low. Aim: This study was to prepare and characterize inclusion complexes of fluorofenidone (AKF-PD) with β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD). Method: The AKF-PD/cyclodextrins (CDs) inclusion complexes were prepared by coprecipitation and freeze-drying, respectively. The solubility enhancement of AKF-PD was evaluated by phase solubility method. Inclusion complexation in solid phase was studied by X-ray diffraction (XRD) and differential thermal analysis (DTA). The dissolution profiles of AKF-PD/CDs inclusion complexes were investigated and compared with those of their physical mixtures and AKF-PD alone. Results: The phase solubility diagrams of AKF-PD with β-CD and HP-β-CD were of A_L-types, and the solubility of AKF-PD could be increased by 51.5% for β-CD at 0.014 M and 794.0% for HP-β-CD at 0.254 M. The results from XRD and DTA suggested that AKF-PD could form inclusion complex with β-CD or HP-β-CD. The dissolution rate of AKF-PD from the inclusion complexes was much more rapid than AKF-PD alone. Conclusions: The formulation of AKF-PD/CDs inclusion complexes showed superior performance in improving dissolution properties of AKF-PD.     

Positional isomerism,stability, and polarizability of C20(CH2)n (n = 1–10), the cyclopropane adducts of the smallest fullerene: General formula for calculation of mean polarizability of fullerene derivatives C20XnYm and C60XnYm with fixed (n + m) number of different addends

All regioisomers of fullerene adducts C₂₀(CH₂)_n have been found and their stability and polarizability have been studied by the PBE/3ζ method. As in the case of the C₆₀ and C₇₀ adducts, mean polarizability of C₂₀(CH₂)_n quadratically depends on the number of addends and demonstrates the depression, viz. negative deviation of polarizability from the linear additive scheme. Another, linear formula is proposed for calculating mean polarizability of the C₂₀ and C₆₀ fullerene adducts with mixed functionalization C₂₀(CH₂)_nO_m and C₆₀(CH₂)_nO_m and fixed number of addends. The obtained results will be further used to work out the algorithm for counting all possible C₆₀X_n cycloadducts and searching a general formula for calculation of the C₆₀X_nY_m polarizability with variable (n + m) number of addends.     

Plastic deformation resistance of an indium-lead alloy with strain rates of 10−3–103 sec−1

Nonstandard A vs , N vs , and log vs diagrams were obtained for an indiumlead alloy using a common method together with standard vs diagrams. The strength, deformation, and energy characteristics and their variation coefficient were determined in the _pl.=10^–3–10³ sec^–1 plastic strain rate range. The influence of an increase in _pl on the plastic deformation resistance of the indium-lead alloy is revealed in a significant (up to 100%) increase in the strength and energy characteristics.Translated from Problemy Prochnosti, No. 3, pp. 53–57, March, 1990.     

Preparation and characterization of silicate nanofilms doped with europium β-diketonate complexes

Films consisting of Eu³⁺ β-diketonate complexes were deposited onto glassy substrates by means of the spin- and dip-coating techniques, using different ion/ligand ratios. Absorption spectroscopy in the infrared region revealed the typical stretching bands of the SiOSi and SiOH bonds of the inorganic matrix as well as bands relative to the CO and CH symmetric vibration of β-diketone (dibenzoylmethane). The films displayed UV-visible absorption band at 350 nm, attributed to the organic ligand. Luminescence properties were studied by photoluminescence spectroscopy. Upon ligand excitation, the emission spectra exhibited the characteristic bands of the Eu³⁺ ion corresponding to the transition from the excited state ⁵D₀ to the ground state ⁷F_J. Scanning electron microscopy confirmed the formation of a film with average thickness ranging from 80 to 100 nm. The sol-gel process and the deposition techniques resulted in the effective formation of nanofilms, which opens up perspectives for their application in photonics.     

Effect of illumination on the crystallization kinetics of amorphous Se80−xTe20Inx

The present paper reports the effect of illumination on the crystallization kinetics in amorphous Se_80–xTe₂₀In_x (0x10). The crystallization was monitored by measuring the electrical conductivity of isothermally annealed samples held at temperatures near the crystallization temperature. It is observed that the crystallization becomes faster in the presence of light as compared to a pure thermal case. There is no significant change in the activation energy under illuminated conditions as compared to the purely thermal case.     

Spin-orbit coupling of sp2 nanocarbons and magnetism of fullerene C60 in view of spin peculiarities of unrestricted Hartree–Fock solution

The paper presents the first application of unrestricted Hartree–Fock formalism to the consideration of spin-orbit coupling (SOC) of open-shell systems in general and sp² nanocarbons in particular. The SOC parameters determination is exhibited on the example of stretched ethylene. g-Factor determination addresses fullerene C₆₀ due to its peculiar “paradiamagnetic” behavior at low temperature characterized by a set of local spins with different g-factors. The approach application has allowed not only to suggest a reliable explanation of the factor variability but to supplement it by a quantitative agreement with experimental data.     

The morphology of α-Fe crystals which grow in the amorphous Fe80(C1−xBx)20 alloys

Crystallization behaviour of amorphous Fe₈₀(C_1–x B _x )₂₀ alloys, obtained by splat-cooling technique, for x values ranging from zero to unity has been investigated mainly by transmission electron microscopy. The crystalline phase which first appeared in the amorphous matrix was -Fe for all alloys studied. However, the morphology of -Fe phase changed from a spherical shape for low x values to a watch-glass shape for intermediate x values and to dendritic for large x values. The nucleation of -Fe crystals was homogeneous for low x samples while preferred nucleation on edges and surfaces was noted for samples with higher x values. The final volume fraction of -Fe phase before the appearance of the second crystalline phase increased with the increase in x.     

Can apomyoglobin form a complex with a spherical ligand? Interactions between apomyoglobin and [C60] fullerene derivative

The preparation and characterization of the stable equine skeletal muscle apomyoglobin and eee-isomer of tris-malonic acid [C60] fullerene complex is reported. For this new bio-nanomaterial preparation, a procedure of complexation-during-protein-refolding was used and the obtained compound sustained separation by gel-filtration and ion-exchange chromatography. The apomyoglobin-tris-malonic acid [C60] fullerene complex was characterized by UV-vis spectroscopy, steady state fluorescence, time-resolved fluorescence, and circular dichroism spectroscopies. Important information provided by this study, regarding the stability and properties of new material, may lead to a better understanding of the apomyoglobin protein binding characteristics, as well as to development of novel antioxidant and photodynamic therapeutic agents and components for bioelectronic devices.     

Thermochemical hole burning performance of TCNQ-based charge transfer complexes with different electrical conductivities

Thermochemical hole burning (THB) memory is an ultrahigh density data storage technique based on the scanning tunneling microscope (STM). It utilizes the STM current to induce localized thermochemical decomposition of TCNQ-based charge transfer (CT) complexes and sequentially create nanometer-sized holes as information bits. The writing reliability and hole size depend on many factors, including the properties of the storage materials and the STM tip, and the tip-sample distance and interaction. We have found here that for the high electrical conductivity CT complexes, the hole size (represented by volume) monotonically decreases with the tip displacement increasing in the direction of leaving the sample; but for low electrical conductivity samples, the hole size first increases and then decreases with the tip displacement increasing in the same direction. Subsequent experiments and analyses indicate that the surface deformation induced by the tip-sample interaction and the heat conduction of the metal tip account for such a unique phenomenon.     

Tunneling measurements of the superconductor Nd1.85C0.15CuO4−δ

We report tunneling measurements of the electron-doped superconductor Nd_1.85Ce_0.15Cu0_4–gd using break junctions. The observed finest gap structure is well expressed by the BCS density of states with the energy gap of = 6.1 meV and a very small broadening parameter, having the ratio 2/k_BT_c = 8.2 with T_c = 17.3 K. These features are similar to our tunneling results for the hole-doped cuprate superconductors. Therefore we find no essential difference in the gap structure, in spite of a common believing of the pairingsymmetry difference between them.     

Determination of PRT Hysteresis in the Temperature Range from −50 °C to 300 °C

This paper discusses the contribution of hysteresis to the measurement uncertainty of industrial platinum resistance thermometers (IPRTs). Hysteresis is one of the sources of uncertainty that has so far not been sufficiently researched and documented. The term hysteresis applies to any system that is path dependent; the output depends on the history of the input. In our case, thermal hysteresis results in different resistance values at the same temperature point, depending on whether the temperature was increasing or decreasing. The reason for such behavior is related to the construction of the thermometer (strain due to thermal expansion and contraction) and also to possible moisture inside the encapsulation. In the process of evaluation of the calibration and measurement capabilities (CMCs) of IPRTs within Working Group 8, the Consultative Committee for Thermometry (CCT WG8) concluded that the uncertainty due to hysteresis is not uniformly defined and not always added to the total uncertainty of the resistance thermometer under calibration. In order to estimate the uncertainty contribution due to the hysteresis and compare different procedures, resistance measurements were carried out on a number of IPRTs of different qualities and tolerance classes. The temperature span was between ?50 °C and 300 °C, which is the most frequent temperature range in the practical use of IPRTs. The hysteresis was then determined in different ways (change of resistance at the ice point and at the midpoint temperature according to the ASTM International Standard E644 and according to the new version of IEC Standard 60751), and a comparison of results was made.     

Design,preparation and properties of online-joints of C/SiC–C/SiC with pins

This work is aimed at providing a new joining technology for C/SiC composites and investigating the influence of drilling holes, hole distribution (including ratios of edge distance to diameter (E/D), width to diameter (W/D) and hole distance to diameter (H/D)) and the number of applied pins on the mechanical properties of C/SiC substrates and joints. The mechanical testing results show that drilling holes and hole distribution greatly affects the mechanical properties of C/SiC substrates but when adopting an optimized design principle (E/D ⩾ 3, W/D ⩾ 3 and H/D ⩾ 3) the effect could be neglected. 1D C/SiC pins with higher shearing strength (107.2 MPa) are more suitable to join the substrates. With the increase of pins (1, 2 and 4), the bearing loads of the joints increase almost linearly, and the reliability of joints is also improved in that the fracture mode changes from the interlayer damage to the substrate rupture. Besides, the joining process generates uniform and dense joining layer (composition of ZrC and SiC) and a strong bonding without obvious interface.     

Sorption of 131I− and 131IO 3 − from aqueous solution on nickel hydroxide at 20°C

Sorption of ¹³¹I^? and ¹³¹IO ₃ ^? from aqueous solution on solid Ni(OH)₂ at 20°C was studied. It was found that in sorption from aqueous solution, after 120-min contact of the liquid and solid phases at V/m = 500 ml g^?1, with an increase in the concentration of I^? and IO ₃ ^? from 10^?5 to 10^?3 M the distribution coefficients K _d decrease from 16.4 to 5.3 ml g^?1 for ¹³¹I^? and from 113.6 to 30.8 ml g^?1 for ¹³¹IO ₃ ^? . The influence of various anions (Cl^?, NO ₃ ^? , SO ₄ ^2? , and BO ₃ ^3? ) on sorption of ¹³¹I^? and ¹³¹IO ₃ ^? from aqueous solution on solid Ni(OH)₂ was studied. It was found that, with an increase in the concentration of these ions from 10^?5 to 10^?1 M, the distribution coefficients K _d of ¹³¹I^? and ¹³¹IO ₃ ^? decrease by a factor of 3–10.     

First-principles study of ZrC x N1−x alloys with electron concentration modulation

The structural and mechanical properties of the ZrC _x N_1?x alloys with electron concentration modulation were systematically investigated by using the pseudopotential plane wave method within the generalized gradient approximation. The obtained equilibrium structure parameters and mechanical properties are in good agreement with the available experimental and other theoretical results. In addition, the theoretical Vickers hardness of ZrC _x N_1?x was calculated with the empirical formula. With an increase in carbon content in this alloys the hardness increases as carbon content up to 70 % then decreases a little, which has the same hardness change trend comparing with that of TiC _x N_1?x . Also, it was found that ZrC_0.7N_0.3 alloy with a valence-electron concentration of 8.3 per unit cell possesses the greatest hardness among the whole composition range. Furthermore, the analysis of electronic properties revealed the metallic character of ZrC_0.7N_0.3 alloy. The thermodynamic stability of the designed alloy was also estimated by the calculated mixing enthalpy.