Metallic xenon. Polarizability. Equation of state

It is shown that some of the physical properties of inert gas (IG) condensates (polarizability, compressibility, metallization under pressure, equation of state) may be well described taking into account the first excited state of atoms only. The Herzfeld criterion of metallization well corresponds to the Mott transition criterion and to the percolation threshold. For metallic xenon concentration of the molecular type excitations corresponds to the Bose condensation temperature $T_C\sim 4000K$. The BCS formula gives $T_c\sim 5000K$. If phonons are changed by fluctuations of interatomic interaction energy. A simple relations between the parameters of atoms at metallization has been found.Comment: 2 pages, RevTe

The Two-Component Model and Metallization of Van der Waals Crystals

The paper discusses a model of Van der Waals crystals in which band-gap structures do not form. An effect of strong and chaotic electron-electron repulsion, which was excluded from consideration in the traditional approach, is taken into account. A condensate exists as a result of a dynamic equilibrium among atoms acted upon by constant Van der Waals forces and periodically forming and disappearing covalent bonding. One part of atoms is, on the average, in the ground, and the other, in excited state, to form diatomic virtual molecules. Treated in terms of this pseudoclassical model, the interatomic distances, binding energies, volumes, and pressures at which metallization, for instance, of inert gases and hydrogen, sets in is described by simple relations involving only two spectroscopic parameters of atoms (molecules). Applying pressure to a VdW crystals transfers it from the insulator first to a Bose superconductor, and after that, to a Fermi metal. An empirical relation $T_c \sim N^{2/3}$ between the superconductivity transition temperature $T_c$ and the particles concentration $N$ in chalcogens under pressure is considered as an example of such situation.Comment: 3 pages, RevTeX

Metallic sulphur. "Electronic" mechanism of superconductivity?

It is shown that the rapid increase of the superconducting transition temperature $T_c$ of sulphur with increasing pressure above 93 GPa does not contradict with some hypothetical ``electronic'' mechanism of superconductivity with participation of the electron interaction energy fluctuations. Such ``electronic'' mechanism is supposed to be intrinsic property of the molecular condensates and corresponds to very high $T_c$. The low $T_c$ of sulphur (10 -17)K is likely connected with the magnetic properties of the sulphur atoms and molecules. The equation of state for sulphur is obtained. The molar volume of sulphur at metallization is 10 cm}$^3${/mol. The principal difference between the ''physical'' and the ''chemical'' type bonds are discussed. Under some pressure one bond type is changed by another and}${T}_c${may have an extremum (transition from the Bose condensation to the BCS superconductivity).Comment: RevTeX, 7 pages, no figure

Bose-Einstein Condensation Picture of Superconductivity in High Temperature Superconductors (Dilute Metals)

Structures and parameters of some high and low temperature superconductors (HTSC, LTSC) are considered basing on the alternative estimate of the O2- ion radius magnitude (0.5-0.6) A. Phase transitions into the superconducting state are considered as the Bose-Einstein condensation (BEC). The super HTSC with Tc = 371 K (YBa2Cu3Se7) and TC ~ 400K (Ag2(Ag3Pb2H2O6)) and LTSC with Tc~0.3K (SrNbxTi(1-x)O3) are shown to be of the BEC type. Instability of the structure of the first one results from higher magnitude of the Se2- ion radius in comparison with the O2- radius. The second one forms quasi one-dimensional structures and is rather inpractical. The electron density and the effective mass are estimated for some stoichiometric and non-stoichiometric (nano-composite) high temperature superconductors, which have some peculiar features. Large effective masses can indicate existance of polarons (bipolarons) in such systems. Some new superconductors MgxWO3.Comment: 5 pages, 5 figure

Dilute Metals: Superconductivity, Critical Currents, Magnetic Properties

Properties of oxides are interpreted as a result of existence of the virtual sublattices formed by the atomic quantum states. An infinite cluster with the superconductivity of the Bose-Einstein condensate kind can be formed in the ground state sublattice at certain oxigen atoms concentration in the effectively diluted system of metal atoms (above the percolation threshold). Then the electron pairs concentration n/2 can be much less than the metal atoms concentration N in the oxide. The similar situation takes place in metals with superconductivity of the BCS type. Above the percolation threshold the superconductivity Tc may be limited by the magnetic properties of the oxigen 2p4quantum state sublattice. Data on the critical current density allow us to estimate the electronic pair density n/2 and to obtain an information concerning the superconductivity nature.Comment: 3 pages,1 figure

Metallic Xenon. Conductivity or Superconductivity?

It is demonstrated that the point of view that metallization of xenon as a result of a band - gap closure has some discrepancies with experimental result. A superconductivity transition as an alternative possibility is examined. At such supposition critical temperature of superconductivity transition T is about 5000 K. A mechanism of inert gas condensation by virtual excitations of molecular type is discussed.Comment: 11 pages, LaTeX, epsf, 5 EPS figure

"Artificial" superconductors. Superconducting phases in the MgxWO3 nanocomposite (x = 0.037; 0.125 - Tcx = 140; 280 K)

Superconductivity of some compounds may be explained as resulting from Bose-Einstein condensation (BEC) of atomic electron pairs of divalent atoms or electron pairs of diatomic molecules made up of univalent atoms. "Artificial" superconductors of such types can be tailored using nonstoichiometric ompounds. Synthesis of "natural" stoichiometric superconductors is a much more complicated problem. In these cases, we have two methods of obtaining dilute metals in a state intermediate between the metal and the insulator.Comment: 3 pages, 3 figure

Molecular Crystals and High-Temperature Superconductivity

A simple model of the molecular crystal of $N$ atoms as a statistical mixture in real space of $NX$ atoms in excited and $N(1-X)$ atoms in well localized ground state is considered. The phase coherence of the atomic wave functions is suppose to be absent. A bond energy of crystal is supposed to be a result of the pair interaction of $NX$ excited atoms. These molecular type pair excitations do not interact one with another before the metallization, and do not contribute to the pressure. Nevertheless, the pressure of such kind of crystals is determined by the interatomic distances, and by the binding energy of pairs. The possibility of the insulator-superconductor transition of such a ``gas'' of $NX/2$ pairs, ``dissolved'' among $N(1-X)$ atoms in ground state is discussed. This kind of transition is supposed to occur in the oxigen $O_2$, in the sulphur $S$, and, possibly, in the xenon $Xe$ crystals under pressure. The same kind of transition is likely to take place in HTSC materials, metal-ammonia and hydrogen-palladium solutions under normal conditions, due to similarity of some of their properties with the corresponding ones of molecular crystals.Comment: RevTeX, 2 eps figures, submitted to Phys. Rev. Let

Superconductivity of the two-component non-stoichiometric compounds with incommensurate sublattices

There exists a class of non-stoichiometric materials (berthollides) that can be considered as constituted by two sublattices, which have specific physicochemical properties. These properties can be essentially modified by even rather weak interaction between these components. One of them can be regarded as a rigid matrix, while another one as a filling in the form of isolated atoms, molecules or clusters. Structures containing voids of the diameter up to D ~ (1 - 2)nm in diameter in the stoichiometric sublattice belong to this class of compounds. These voids are filled by the second component (of diameter d_{0}), which can be compressed or stretched because of the sublattice parameters misfit. A stretched matter (D - d_{0} = h > 0) can exist in a unique intermediate state between the metal and the dielectric; this state cannot be implemented by another way. The period doubling occurs and a weak modulation of the metal lattice constant leads to forming not only the energy gap, but the bound electronic states of the molecular type with two paired electrons as well. Validity of this model with the Peierls-type lattice instability for explanation of the well known experimental data on superconducting transition temperature (T_{c}) in such systems (fullerides, perovskite-type compounds like Na-WO_{3}, high temperature superconductors) is considered in this work. The transition temperature T_{c} of fullerides is proportional to h/D; for the tungsten-bronzes with Na, Rb, or Cs, T_{c} > 0 for h > 0, and T_{c} ~ 0 for h < 0.Comment: 3 pages, RevTeX

Superconductors with Superconducting Transition Temperatures Tc = 91K (1999), 120K (1994), 340K (2000), and 371K (1995): Experimental Errors or a Technological Puzzle? Two-Component Nonstoichiometric Compounds and the Insulator--Superconductor--Metal Transition

One of the reasons for the lack of understanding of both the mechanisms underlying the HTSC phenomenon and of the instability of materials with Tc > 300 K may be the widely accepted but wrong ideas about the types of chemical bonding in a substance and the radii of the atoms and ions. A revision of these concepts started in the beginning of the XX century in connection with the investigation of non-stoichiometric compounds (the berthollides) but did not reach a critical level until recently. Most of the HTSC materials, however, are actually non-stoichiometric nanocomposites, whose components "dilute" or "stretch" one another. Each component resides in an "intermediate" state, which still remains poorly studied. For instance, in a system of particles having two paired electrons each, the unbroken electron pairs may start tunneling at a certain "medium" concentration with the system becoming a Bose superconductor (the state between the insulator and the metal with BCS superconductivity). For univalent atoms (Na,Ag), however, such possibility realizes neither in intermediate nor in the final state. Univalent metals are not superconductors. In the berthollides, however, a possible Jahn-Teller-Peierls-type instability may give rise to formation of diatomic molecules (Na2, Ag2)with electron pairs, and superconductivity can set in. It is possibly such systems that were obtained by chance in experiments with univalent components and reported to have Tc of up to 371 K. Structures of a number of HTSC materials are considered