A broad review of recent research work on the preparation and the remarkable properties of intercalation compounds of graphite, covering a wide range of topics from the basic chemistry, physics and materials science to engineering applications.

Intercalation compounds of graphite

Two-dimensional condensed matter is realized in increasingly diverse forms that are accessible to experiment and of potential technological value. The properties of these systems are influenced by many length scales and reflect both generic physics and chemical detail. To unify their physical description is therefore a complex and important challenge. Here we investigate the distribution of experimentally estimated critical exponents, β, that characterize the evolution of the order parameter through the ordering transition. The distribution is found to be bimodal and bounded within a window ∼0.1≤β≤0.25, facts that are only in partial agreement with the established theory of critical phenomena. In particular, the bounded nature of the distribution is impossible to reconcile with the existing theory for one of the major universality classes of two-dimensional behaviour-the XY model with four-fold crystal field-which predicts a spectrum of non-universal exponents bounded only from below. Through a combination of numerical and renormalization group arguments we resolve the contradiction between theory and experiment and demonstrate how the 'universal window' for critical exponents observed in experiment arises from a competition between marginal operators.

https://iopscience.iop.org/article/10.1088/0953-8984/20/27/275233/pdf

Universal window for two-dimensional critical exponents

Modulation calorimetry and related techniques

Alkali-metal-graphite intercalation compounds (alkali-metal-GIC’s) absorb hydrogen in two ways: physisorption and chemisorption. Hydrogen uptake through the physisorption process occurs at low temperatures below about 200 K in higher stage alkali-metal-GIC’s, where hydrogen molecules are stabilized to form a two-dimensional condensed phase in the galleries of the graphite sheets. The concentration of absorbed hydrogen molecules is saturated at a rate of H2/alkali metal atom ∼2. The hydrogen physisorption shows a strong isotope effect and a swelling effect on c-axis lattice expansion. In the case of hydrogen uptake through the chemisorption process, dissociated hydrogen species are stabilized in the intercalate spaces. The activity of the chemisorption increases in the order Cs < Rb < K. The introduction of hydrogen generates a charge transfer from the host alkali metal GIC’s to the hydrogen since hydrogen has strong electron affinity. The hydrogenated potassium-GIC’s have intercalates consisting of K+-H−-K+ triple atomic layer sandwiches which are inserted between metallic graphite sheets. The inserted two-dimensional hydrogen layer is suggested to consist of H ions with a weakly metallic nature. The superconductivity of the hydrogenated potassium-GIC is also discussed in terms of the change in the electronic and lattice dynamical properties by hydrogen uptake. The hydrogen-absorption in alkali-metal-GIC’s is an interesting phenomenon in comparison with that in transition metal hydrides from the point of hydrogen storage. The hydrogen-alkali-metal-ternary GIC’s obtained from hydrogen absorption have novel electronic properties and lattice structures which provide attractive problems for GIC research. The studies of hydrogen-alkali-metal ternary GIC’s are reviewed in this article.

Hydrogen-alkali-metal-graphite ternary intercalation compounds

Two-dimensional random-bond Ising models of L × L spins are simulated extensively. In the randomness dominated critical region, the size dependences of the specific heat, C , the susceptibility, χ, and the magnetization, m , at critically are in very good agreement with the analytic predictions, C ≈ ln ln L , χ ≈ L if 7 4 , and m ≈ L −1 8 . The temperature dependences of χ and m close to the critical point can be described by power laws with the exponents of the perfect model, modified by logarithmic corrections.

The critical behaviour of the two-dimensional dilute Ising magnet

Magnetic neutron scattering from second-stage CoCl2-graphite intercalation compound

We have studied the critical behavior of the two-dimensional site-random antiferromagnet Rb 2 Co c Mg 1- c F 4 using neutron elastic and quasi-elastic scattering techniques. The variation with temperature of the intensity of the magnetic Bragg reflections shows a considerable rounding of the transition. Assuming a Gaussian distribution of transition temperature, we have determined the average Neel temperature and the degree of distribution of Neel temperature σ, and the critical exponent β in a series of compounds with c =1.0, 0.98, 0.97, 0.95, 0.89 and 0.82. The experimental data have been analysed to give the inverse correlation length and the susceptibility in the compounds with c =1.0, 0.97 and 0.89 using the determined values of and σ. The resulting values of the critical exponents β, ν, γ and η are found to coincide with the exact theoretical values for the two-dimensional Ising model within the experimental errors, and are independent of the concentration of nonmagnetic impurities.

Masatsugu Suzuki

Papers

Magnetic neutron scattering from second-stage CoCl2-graphite intercalation compound

Neutron Scattering Investigation of Static Critical Phenomena in the Two-Dimensional Antiferromagnets: Rb 2 Co c Mg 1-c F 4

Crystallographic, thermal and magnetic properties of CoCl2-graphite intercalation compound — a quasi-two-dimensional system of finite size clusters

Magnetic phase transitions in NiCl2-graphite intercalation compound

Magnetic properties of europium-graphite intercalation compound C6Eu