Showing papers on "Lattice energy published in 1971"

Higher order multipole three-body van der Waals interactions and stability of rare gas solids

Abstract: Long range van der Waals interactions to higher orders of both multipole and perturbation expansions are examined. In particular the dipole- dipole-dipole, dipole-dipole-quadrupole, dipole-quadrupole-quadrupole, quadrupole-quadrupole-quadrupole and dipole-dipole-octupole three body terms to third order perturbation, and the dipole-dipole-dipole- dipole term to fourth order perturbations are considered. Apart from the dipole-dipole-octupole term the contributions of these factors to the lattice energy of crystalline Ne, A, Kr and Xe are evaluated. The relative stability of the FCC and HCP structures is examined but does not appear to be firmly established by these terms. However, the results indicate that if the octupole polarizabilities of the rare gas atoms prove to be large then there would be a distinct preference for the FCC structure with respect to the dipole-dipole-octupole contribution.

A Model for the Prediction of Lattice Parameters of Solid Solutions

Abstract: A new model is presented which makes it possible to predict the lattice parameters of metallic solid solutions as a function of composition. This method is based on the hypothesis that the measured lattice parameter of a solid solution alloy is the average of all the interatomic spacings within a selected region of the lattice.

Spectroscopic Study of the Phase Transition in Crystalline Adamantane

Abstract: The infrared spectrum of crystalline adamantane (tricyclo‐3,3,1,1‐decane, C10H16) has been studied at temperatures below and above the first‐order phase transition at 208°K and as a function of temperature through the transition. Splittings of the vibrational transitions and appearance of gas‐phase‐forbidden transitions below 208°K are in agreement with theoretical predictions. A hysteresis is observed in the spectroscopic characteristics over a range of a few degrees around the heat‐capacity peak occurring at the transition temperature. Calculations of lattice energy, frequency splittings, and barriers to molecular rotation have been carried out using central force functions between nonbonded atoms derived from physical properties of a number of crystals. The splittings, heat of sublimation, transition energy, and crystal structural parameters are in semiquantitative agreement with experiment. The vapor pressure of adamantane in the temperature range 312–366°K has been measured, and the heat of sublimati...

Phase Transitions in the Quinol Clathrate Compounds. II. The Quinol Methanol Clathrate Compound

Abstract: Low temperature heat capacities of the nonstoichiometric clathrate compounds with methanol were measured on four specimens of different occupation fractions. Heat capacity anomalies were found at 65.7. 61.0, 54.4 and 44.4 K, corresponding to the occupation fractions 0.974, 0.897, 0.837 and 0.728, respectively. Magnitude of the entropy change of transition is consistent with the view that the transition is due to randomization of direction of the methanol molecules along the c-axis. Single crystal dielectric data support this interpretation. Variation of the transition temperature with the occupation fraction was compared with data on analogous systems. The lattice energy calculation showed that the dipole interaction between methanol molecules corresponds to 27 or 67 K of temperature depending on the component of the moment taken into account.

Lattice Energies, Charge Distributions and Thermochemical Data for Salts containing Complex Ions

Abstract: This article reports recent developments in the calculation of the lattice energies of ionic salts containing complex ions. It is now possible not only to derive values of lattice energies and thermochemical data for the ions but also to obtain the distribution of charge on the complexion.

The dissociation energy of F- and the stability of alkali perfluorides

Abstract: Multiconfiguration valence bond calculations using accurate AO bases have been carried out for F2 and F2 -. A dissociation energy of at least 1·06 eV is predicted for the F2 - ion. Lattice energy calculations together with this value lead to an approximate value of ΔG = -16 kcal mole-1 for the reaction The true value may be much closer to zero.

On the Vapor Pressure of Solid Argon

Abstract: The vapor pressure of solid argon was measured by a precision apparatus with a standard error of ±0.023 Torr in the temperature range from 75.0 to 83.8 K, and that of liquid argon to the same precision from 83.8 to 85.2 K. The data were used to determine the coefficients A and B of the two parameter vapor pressure equation, log10 p = A + (B/T), and to locate the triple point of argon by an extrapolation method. The results are in good agreement with those of other workers. The static lattice energy E0 of the solid and geometrical mean frequency ωg of the vibrational spectrum, corrected for the presence of lattice vacancies, gas imperfection, and finite crystal volume, were also determined from the data. When determined over successive small temperature intervals, E0 is found to increase as the temperature increases, as expected. The magnitude of E0 agrees with the value obtained from a lattice-sum calculation on the basis of a Lennard–Jones (6–12) potential to within ±0.17%.

Electronically Induced Crystallographic Transition

Abstract: In this paper a model is presented which exhibits a so-called electronically induced crystallographic transition. The model consists of two interpenetrating one-dimensional identical lattices of attractive $\ensuremath{\delta}$ potentials. Shifting one sublattice with respect to the other defines a distortion, where the nondistorted system is assumed to have a periodicity which is half the periodicity of such a sublattice. The model is closely related to one discussed by Adler and Brooks. It is shown by a computer calculation that the competition between the lattice and electronic energies results in a second-order phase transition. The narrow band limit is discussed in terms of a two- and four-level scheme. It appears that only a second-order phase transition can occur, unless the repulsive term in the lattice energy is too weak. In that case the two sublattices will coincide at zero temperature, which is an unphysical situation.

Contribution of the lattice energy to the stability of aliovalent iron species formed after57Co decay in CoX2 (X = F, Cl, Br, Oh)

Abstract: Mossbauer emission spectra of 57Co in β-Co(OH)2 and CoBr2 are reported. The proportion of ferric ions stabilized after 57Co electron capture increases with increasing lattice energy along the series of cobaltous compounds; a thermodynamical model is suggested to explain the stability of aliovalent ions after 57Co EC in cobalt compounds with simple ligands. Les spectres Mossbauer d'emission de 57Co dans β-Co(OH)2 et CoBr2 ont ete etudies. Dans une serie de composes cobalteux, la proportion d'ions ferriques stabilises apres capture electronique du cobalt 57 croǐt avec l'energie du reseau. On propose un modele thermodynamique pour expliquer la stabilite des ions aliovalents apres CE de 57Co dans les composes a ligandes simples.

A Molecular Theory of the Thermal Transitions of Polymers. II.

Abstract: A molecular theory is developed in order to elucidate the nature of melting and glass transition of polymers. Rotational oscillations of chain units around chain axis are considered. It is assumed that the units of trans linkage have a sinusoidal interchain potential field in a hexagonal lattice but for gauche the potential field has not such sinusoidal form. The lattice energy is calculated by summing up the Lennard-Jones type pair interactions between units. A critical temperature for the transition between uniform and non-uniform rotational orientations of units is obtained for crystalline or glassy state on the basis of molecular field approximation. Melting temperature ( T m ) and glass temperature ( T g ) can be predicted from it and the empirically known correlation between T m and T g is well explained. The results are in good agreement with the experimental data on polyethylene.

Debye temperature variations in alkali-halide single crystals as a function of their chemical compositions

Abstract: The Debye temperature ­D for 18 alkali-halide single crystals is calculated using the elastic constants for temperature between 4.2 °K and 300 °K. The results are analyzed. We have characterized the various compounds in terms of the crystal lattice energy U and the ratio of cation-to-anion mass M/m. Graphs of the functions ­d = f(M/m) and ­(D) = f(U) are presented, together with a plot of the surfaces of the function ­d = f(T, M/m). It is found that the Debye temperature for the solid Solution KCl-KBr, in various concentrations, fits the curves of the function ­D = f(M/m) rather well when these curves are constructed from data for the pure single crystals.

CHAPTER FIVE – Lattice Faults

Abstract: Publisher Summary This chapter focuses on lattice faults. Lattice energy being a measure of inter-atomic forces, is a crucial one and one which can be estimated readily for ionic structures; for these depend simply on electrostatic forces between a regularly placed set of positive and negative charges. The chapter further focuses on thermal energy and specific heat. Thermal energy is attributed primarily to vibrations of a lattice and theory, notably the Debye theory, is mainly concerned with predicting its vibrational modes. The first basic fault is the dislocation. A fault that can maintain a row of atoms in such a metastable lattice position is the dislocation, postulated notably by Taylor and Orowan. There are three basic types of dislocation: (1) Positive Edge-Type, (2) Negative Edge-Type, and (3) Screw Dislocation. The second basic fault is the point fault. Solid diffusion too must be fault-dependent but dependent on a second basic fault: the point fault. Boundary faults, with dislocations and point-fault, make up the three principal kinds of lattice fault.