Features of electrical conductivity in an incommensurate phase of graphite intercalation compound C10HNO3

Electrical conductivity and conduction-electron spin resonance (CESR) have been studied in stage-2 acceptor α-graphite-nitric acid intercalation compound C₁₀HNO₃. It is found that the electrical conductivity σ_c along the c axis in the structurally incommensurate phase of this compound is temperature independent, whereas the electrical conductivity σ_a along carbon layers exhibits “metallic” temperature behavior. Analysis of the temperature dependences of σ_c, σ_a, and the CESR linewidth demonstrates that, in the incommensurate phase of the graphite intercalation compound, the electrical conductivity along the c axis is realized through a nonband mechanism—the transfer of free charge carriers along thin high-conductivity channels shunting the carbon layers adjacent to the intercalate.     

Thermoelectric properties of a dilute graphite donor intercalation compound

Data on the in-plane thermal conductivity and thermoelectric power of a stage-5 potassium donor graphite intercalation compound are reported in the temperature range 3 < T < 300 K. In the lowest temperature range the electronic contribution dominates the thermal conductivity, while at higher temperature there is a dominant lattice contribution, which is much smaller than pristine graphite. The thermopower is negative in the whole temperature range.     

Thin graphite overlayers: Graphene and alkali metal intercalation

Using LEED and angle resolved photoemission for characterisation we have prepared graphite overlayers with down to monolayer thickness by heating SiC crystals and monitored alkali metal intercalation for the multilayer films. The valence band structure of the monolayer is similar to that calculated for graphene though downshifted by around 0.8 eV and with a small gap at the zone corner. The shift suggests that the transport properties, which are of much present interest, are similar to that of a biased graphene sample. Upon alkali metal deposition the 3D character of the π states is lost and the resulting band structure becomes graphene like. A comparison with data obtained for ex situ prepared intercalation compounds indicates that the graphite film has converted to the stage 1 compounds C₈K or C₈Rb. Advantages with the present preparation method is that the graphite film can be recovered by desorbing small amounts of alkali metal and that the progress of compound formation can be monitored. The energy shifts measured after different deposits indicate that saturation is reached in three steps. Our interpretation is that in the first the alkali atoms are dispersed while the final steps are characterized by the formation of first one and then a second (2 × 2) ordered alkali metal layer adjacent to the uppermost carbon layer.     

Electrical conductivity of NaCl ¦ graphite interface

It was observed that a steady d. c. current flows through the cell graphite ¦NaCl¦ graphite even at voltages very small compared to the decomposition potential difference. The activation enthalpy of the small signal conductance (1·20±0·05) eV differs from the enthalpy of the bulk conductivity. The interface conductance is neither in simple relation to the conductivity of the crystal, nor to the partial conductivities of anions and cations. The nonlinearity of the cell and the independence of interface conductance from some properties of the bulk can be explained by the finite rate of electrochemical reactions, ensuring the charge transfer across the interfaces.     

ESR study of second stage nickel chloride graphite intercalation compound

The temperature dependences of g-factor and linewidth of C_11,3NiCl_2,13 single crystals have been measured from 10 to 400 K. The data indicate that nickel ions in graphite behave at low temperatures like Ising ions, with a phase transition occurring at about 30 K.     

Magnetic phases in transition metal chloride intercalation compounds of graphite

Magnetic susceptibility measurements on graphite-FeCl₃ (stage 2), graphite-CoCl₂ (stages 2 and 3), and graphite-NiCl₂ (stages 3 and 5) intercalation compounds are reported, showing anomalies associated with magnetic transitions. The effect of magnetic fields on the transition suggests that the magnetic phases in all these systems are similar and independent of the separation of the planes of magnetic ions. The results for all samples for stage ≥ 2 imply two magnetic phase transitions closely separated in temperature.     

Electrical conductivity of molten mixtures of potassium and sodium fluorides with calcium fluoride

The electrical conductivity of molten mixtures of calcium fluoride with sodium and potassium fluorides was investigated by impedance spectroscopy. The calcium fluoride additions to alkali metal fluoride melts decrease their electrical conductivity. Small additions of potassium and sodium fluorides to CaF₂ do not change its conductivity essentially.     

Electrical conductivity of metal powders under pressure

A model for calculating the electrical conductivity of a compressed powder mass consisting of oxide-coated metal particles has been derived. A theoretical tool previously developed by the authors, the so-called ‘equivalent simple cubic system’, was used in the model deduction. This tool is based on relating the actual powder system to an equivalent one consisting of deforming spheres packed in a simple cubic lattice, which is much easier to examine. The proposed model relates the effective electrical conductivity of the powder mass under compression to its level of porosity. Other physically measurable parameters in the model are the conductivities of the metal and oxide constituting the powder particles, their radii, the mean thickness of the oxide layer and the tap porosity of the powder. Two additional parameters controlling the effect of the descaling of the particle oxide layer were empirically introduced. The proposed model was experimentally verified by measurements of the electrical conductivity of aluminium, bronze, iron, nickel and titanium powders under pressure. The consistency between theoretical predictions and experimental results was reasonably good in all cases.     

Anisotropy of chemical bond in CdSb compound

Mooser's and Pearson's assumption as to the type of bonds in CdSb is confirmed by determining the cleavage, the anisotropy of the linear expansion and to a certain extent also the anisotropy of the amplitude of the thermal vibrations.     

Electric quadrupole nuclear orientation of182Ta as graphite intercalation compound TaCl5

Nuclear orientation of¹⁸²Ta achieved by electric quadrupole interaction in TaCl₅ molecules intercalated in oriented graphite crystals has been observed. Assuming the electric field gradient V_zz along the c-axis and proper intercalation yields V_zz=+0.32 (4)×10¹⁸V/cm². Other possibilities and sources of reduction of the nuclear orientation effect are considered.     

The first synthesis of a graphite bis(oxalato)borate intercalation compound

A new graphite intercalation compound containing the bis(oxalato)borate anion, B[OC(O)C(O)O]₂⁻, is prepared for the first time by chemical oxidation of graphite with fluorine gas in the presence of a solution containing the intercalate anion in anhydrous hydrofluoric acid. The products of stage 1-3 compounds are characterized by powder X-ray diffraction, thermogravimetric analysis, and elemental analyses. X-ray diffraction data indicate a standing-up orientation for the borate anion, with long axis perpendicular to the graphene sheets. Elemental analyses provide x and δ for the nominal composition of C_xB[OC(O)C(O)O]₂·δF, where the chelate borate and fluoride are co-intercalates, and indicate a low borate, and high fluoride, intercalate content as compared to anion packing in other graphite intercalation compounds.     

Electrical conductivity of a non-uniformly deformed metal crystal with alloying elements

The effect is considered of non-uniform deformations satisfying the condition |u ||u |, where is the free path length of an electron in the undeformed crystal and, u is the deformation tensor, on the electrical conductivity of a metal crystal with alloying elements. Account is taken of the local change of the dispersion law for conductivity electrons and also of the dependence on the coordinates of the alloying element of the electron scattering cross-section on the alloying element in the non-uniformly deformed crystal. An explicit expression is obtained for the tensor of the effective conductivity, first introduced by Herring and connecting the average volume density of the electrical current with the average electrical field in the crystal. The local electron scattering cross-section on the charged alloying elements is evaluated on the Thomas-Fermi model taking into account the local change of the constant shielding. Account is also taken of the possibility of redistribution of the alloying elements in the field of the deformations. The dependence is found and discussed of the conductivity on the sign of the constant, introduced in the continuous approximation, of the interaction of the alloying element with the deformation field. By way of illustration of the results obtained the simple case of unidimensional deformation is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 70–75, February, 1973.The writers express their gratitude to Yu. V. Kornyushin for useful discussion of this work.     

Thermal properties of graphite intercalation compounds with acids

This work is devoted to systematic thermal analysis of first to fifth stages of binary graphite intercalation compounds (GIC) with HNO₃ and ternary GICs with HNO₃–R (R=CH₃COOH, H₃PO₄) by simultaneous TG–DSC thermoanalyses (Netzsch). Thermolysis of GIC leads to the full deintercalation of acid and significant expansion of samples. The thermal properties of co-intercalated GICs-HNO₃-R and the thermal expanding coefficient of GIC depend on the nature of the intercalate. The endopeak at 110–150 °C corresponds to the loss of nitric acid was observed in DSC- curve of binary second to fifth stages of GICs with HNO₃. A wide endopeak which is characterized by the increasing of decomposition temperature in comparison with GIC-HNO₃ was observed in DSC—curve of ternary GIC with HNO₃–CH₃COOH. Thus, acetic acid stabilizes the graphite nitrate matrix. Two endoeffects due to the deintercalation of HNO₃ (110–180 °C) and H₃PO₄ (450–800 °C) were observed in the DSC-curves of co-intercalated GICs with HNO₃–H₃PO₄ of second and third stages. The value of decomposition heat (ΔH) and weight loss decrease with the increasing of the stage number of GICs. The values of ΔH are equal to 0.40–14.8 kJ/g-at C.     

Reactions of chlorine and related molecules with graphite intercalation compounds

K-graphite intercalation compounds (GICs), metal chloride-GICs and reduced products of CuCl₂-GICs were allowed to react with chlorine. Decomposition of K-GICs took place through the reaction with chlorine. The extent of the decomposition was found to be dependent not on the gas pressure of the chlorine but on the stage number of the starting GIC. Metal chloride-GICs were unreactive with chlorine, whereas chlorine could react with copper particles generated in the interlayer of graphite through the reduction of CuCl₂-GICs. The reaction products were CuCl and CuCl₂; the former exists as crystals in the interlayer, and the latter can form CuCl₂-GICs. Also reported on are reactions of GICs with chlorobenzene, benzoyl bromide and iodine monochloride.     

High-pressure synthesis of a novel form of endohedral Li diamond from Li graphite intercalation compound

A novel form of hexagonal diamond containing Li atoms in the open rooms surrounded by sp³-bonded carbon atoms was successfully synthesized from a Li graphite intercalation compound under high pressure, as had been predicted by theoretical studies. High-pressure experiments with LiC₆ were performed in the pressure range from 0.1 MPa to 43 GPa using a diamond-anvil cell. In situ X-ray diffractometry and optical microscopy revealed that LiC₆ was transformed to a hexagonal-diamond form without losing Li atoms. The c-axis of the hexagonal-diamond form was considerably longer than that of the hexagonal diamond transformed from pure graphite, which was consistent with the predicted structure of the endohedral Li diamond. The observed high-pressure form exhibited a golden metallic gloss, which was also consistent with the calculated metallic band structure.