Simple Binary Compounds Research Articles

Correlation between the refractive index and the energy gap of simple and complex binary compounds—II

In the first paper of the series the authors gave a correlation between the high-frequency dielectric constant (ϵ ∞) and the average energy gap ( E p) for simple and complex binary compounds, but the proposed relation included a third variable, R (the interatomic separation). In the present communication, a pure correlation between ϵ ∞ and E p is established without any other variables. The two characteristic constants appearing in the formulation are shown to have non-flexible values. The validity of the correlation is established by using the available values of ϵ ∞ and E p in different families. The two constants in the proposed correlation are identified as a family characteristic and an ion characteristic, respectively.

Correlation between the refractive index and the energy gap of simple and complex binary compounds

A simple relation between the high-frequency refractive index and the corresponding energy gap, established by Gopal, has been critically examined. It has been shown that the validity of such a relation is highly questionable. Through a close analysis of this relation, its shortcomings are eliminated and a generalized single parameter correlation is proposed which is valid for a large number of binary A N B 8− N type solids and also for the complex A 2B, AB 2, A 3B and A 3B 2 semiconductors.

ChemInform Abstract: OPTICAL ELECTRONEGATIVITY, χ*, OF TRANSITION METAL IONS IN SIMPLE COMPOUNDS

The difference between simple binary compounds and complexes is discussed in the context of charge-transfer (electron-transfer) absorption spectroscopy and correlations involving the optical electronegativities χ* and χopt. Using existing data, mainly for binary chlorides and bromides, values of χ* are obtained for Cr3+, Mn2+, Fe2+, Co2+, and Ni2+, and applied to binary sulphides and doped zinc sulphide crystals.

Plasmon approach to the average energy gap of Mg, Ca and Sr compounds

The average energy gap of magnesium, calcium and strontium compounds has been calculated by using the plasma oscillation theory of solids. The calculated values are in fair agreement with the observed values and the values calculated by different workers. Our calculations are not restricted to simple binary and ternary compounds, but can also be sucessfully applied to all types of compounds.

Optical electronegativity, χ*, of transition-metal ions in simple compounds

The difference between simple binary compounds and complexes is discussed in the context of charge-transfer (electron-transfer) absorption spectroscopy and correlations involving the optical electronegativities χ* and χopt. Using existing data, mainly for binary chlorides and bromides, values of χ* are obtained for Cr3+, Mn2+, Fe2+, Co2+, and Ni2+, and applied to binary sulphides and doped zinc sulphide crystals.

Electronegativity and a model hamiltonian for chemical applications

A study is made of the connection between a one-electron model hamiltonian of the Anderson—Hubbard type and the electronegativity, both for free atoms and for simple binary compounds. Non-linear terms in the valence electron occupation number must be included in the hamiltonian in addition to the usual linear tenn. It is found that interatomic interactions occurring in the compound increase the non-linearity substantially over that for the separated atomic constituents. This approach improves the physical understanding of the connection between the clectronegativities of the cation and the anion and (1) the Fermi energies (work functions) of solid compounds and (2) charge transfer in heteronuclear molecules. Charge transfer is specifically discussed for donor-acceptor organic solids and for strongly polar molecules with mutual cation-anion polarization effects included.

Valence band photoemission spectroscopy of a ternary layered semiconductor: ZnIn 2S 4

UV photoemission spectroscopy (UPS) experiments have been carried out on the layer compound ZnIn 2S 4 employing several different photon energies in the range h ̵ ω = 9.5−21.2 eV . The energy distribution curves (EDC's) exhibit four valence band density of states structures besides the Zn 3 d peak. These five peaks appear 0.90 eV, 1.6 eV, 4.3 eV, 5.8 eV and 8.7 eV respectively below the top of the valence band, E v . The atomic orbital character of the shallowest peak A appears different from that of the three deeper valence band peaks B, C and D and this is discussed in terms of the more or less pronounced ionic character of the intralayer chemical bonds. These results demonstrate that an overall understanding of the electronic states in complex structures can be achieved by an approach based on photoemission experiments and chemical bonding considerations which has been widely used in the past to study simple binary layer compounds.

Quantum-defect theory of heats of formation and structural transition energies of liquid and solid simple metal alloys and compounds

The tables of $l$-dependent ion-core radii ($l=0,1,2$) derived from free-ion quantum defects and previously presented by Simons and Bloch are extended to include halogens and the group-$\mathrm{I}\ensuremath{-}B$ metals (Cu, Ag, and Au). From these radii hybridized bond-orbital coordinates with $\ensuremath{\sigma}$ and $\ensuremath{\pi}$ character are formed. The dual bond-orbital coordinates are used to discuss the structures, uniaxial distortions, and melting points of more than 100 simple binary compounds belonging either to the octet family ${A}^{N}{B}^{P\ensuremath{-}N}$ with $P=8$ or to the suboctet family $2\ensuremath{\le}P\ensuremath{\le}6$. Two conclusions emerge: the quantum bond-orbital $\ensuremath{\sigma}$ and $\ensuremath{\pi}$ dual coordinates describe the physical properties of these materials much more accurately than traditional classical coordinates such as size and electronegativity, and the dual quantum coordinates are equally accurate for octet and suboctet compounds. The success of the quantum coordinates implies that bond charges with $\ensuremath{\sigma}$ and $\ensuremath{\pi}$ components make important contributions to the structural energies of these materials. The dual coordinate cellular scheme developed by Miedema and co-workers to describe the sign of the heat of formation of liquid and solid metal alloys is examined within the context of orbital, $l$-dependent ion-core radii. We show that Miedema's original coordinate set is unphysical, but that his inductively revised coordinates which are derived from more than 500 binary phase diagrams are remarkably accurate. Apparent irregularities in the revised coordinates are shown by comparison with the orbital shell model to be correct and the consequence of core shell structure.

Structural Stability of Suboctet Simple Binary Compounds

Structural Stability of Suboctet Simple Binary Compounds

Electronegativity as a unifying concept in the determination of Fermi energies and photoelectric thresholds

The method proposed by Nethercot for the determination of the Fermi energies and photoelectric thresholds of simple binary compounds has been successfully applied to some AB 2 compounds and metals.

Prediction of Fermi Energies and Photoelectric Thresholds Based on Electronegativity Concepts

A simple formula involving the geometric mean of the electronegativities of the two components is proposed for the determination of the Fermi energies and hence the photoelectric thresholds of simple binary compounds, and is found to be surprisingly accurate for all presently available data. A theoretical basis for the use of the "postulate of the geometric mean" is also given.

Covalent and ionic crystal radii and Phillips ionicity

Correlating bond length, crystal structure and Phillips ionicity in simple binary compounds with covalent crystal radii shows that most oxides and some fluorides have to be regarded as covalent compounds with respect to their crystal radii. “Anomalous covalent” octahedral radii of oxygen and fluorine should be interpreted as ionic radii.

Esca. results versus other physical and chemical data

X-ray photoemission spectra yield quantities of very direct interest in physics and chemistry. In this paper the relations of these spectra to other data and concepts are discussed. Both initial-state and final-state properties may be studied: the former are treated first. Charge distributions in molecules alter the effective (Coulomb plus exchange) potential experienced by core electrons in molecular ground states, there by shifting their binding energies. The shifts can be calculated by abinitio methods or more directly by using potential models based on intermediate-level molecular-orbital theories such as INDO. One version, the ground-state potential model (GPM) yields good predictions of core-level shifts among atoms in similar environments. Alternatively, the measured shifts may be used to derive charges on individual atoms in molecules. It is more difficult to derive charges in solids in this way, but a characteristic splitting in the more tightly-bound valence bands yields a direct measure of ionicity in simple binary compounds of the zinc-blende and rocksalt structures. Atomic orbital composition of molecular orbitals can be deduced from photoemission spectra. In solids such as diamond and graphite comparison of photoemission spectra with x-ray emission spectra yields the atomic-orbital composition of the valence bands. Turning to final-state properties, the spectra are dominated by relaxation effects. Again a simple approach—the relaxation potential model (RPM)—predicts core-level shifts well for cases in which the atomic environments are varied substantially. Among ammonia and the methylamines, for example, the N(ls) shifts are predicted correctly by RPM, while GPM reverses the order. For paramagnetic molecules RPM predicts electron charge transfer toward the positive hole but usually spin transfer away, in agreement with experiment. Extra-atomic relaxation in metals, a many-body effect, is manifest both as a contribution to the binding energy and as line-shape asymmetry. Delocalized valence electrons also show relaxation shifts that can be understood as polari zation of the electron gas toward the “Coulomb hole”. Auger lines show larger relaxation shifts. Comparison of core-level or Auger shifts in nonmetallic solids separately is questionable because there is no reference level, but intercomparison of the two is meaningful. Finally, core-level binding-energy trends in series of simple alcohols, etc., agree quantitatively with proton affinities and core-level shifts in other functional groups. This suggests extending the concept of Lewis basicity to include lone pairs of core electrons. Thus, core-level shifts measure the chemical reactivity—a quantity of great chemical importance that depends on both initial- and final-state properties—rather directly. Rela xation energies are shown to be the dominant cause of trends in the lowest ionization potentials of simple alcohols and amines.

Lindemann fusion criterion and characteristic temperature of cubic crystals

The Lindemann fusion criteria of cubic crystals of simple substances and binary inorganic compounds, and the energy for an atom to overcome the potential barrier during diffusion are examined.

Lattice self-potentials and madelung constants for some compounds

The computerised potential and electrostatic energy calculations described in Part 1 can be used as the first step in more sophisticated calculations, four types of which are described. (i) The results obtained by calculating the actual crystal field in a sodium vacancy in NaCl are compared to the results of the familiar approximation for that situation. (ii) CaF2 and β-alumina are used as examples of compounds in which there is remarkable similarity between some of the interstitial and some of the lattice sites. A complete calculation of all the self-potentials and the Madelung constant of β-alumina is included. (iii) In a discussion of p- and n-type semiconduction in simple binary compounds, self-potentials are used to show that many structures have a built-in preference for a deviation from stoichiometry, although other factors (not considered in this paper) can obscure this preference. (iv) The concept of a solid-state energy storage using compounds with two different cations in non-interacting sublattices is explored, using the mineral quenselite (PbMnO2(OH)), as an example. The computer program is used to evaluate this mineral with respect to its energy density.

Role of Crystal Structure in Diffusion. I. Diffusion Paths in Closest-Packed Crystals

A consideration of the crystal structures of simple binary compounds shows that they can be represented by closest packings of the larger anions in which two kinds of interstices are available for occupation by the metal atoms. In hexagonal closest packings, the octahedral voids form continuous chains by sharing opposite faces while the tetrahedral voids form isolated pairs. In cubic closest packings, each kind of void shares faces only with unlike voids. The specific diffusion paths available in these compounds depend, therefore, on the manner in which the voids are occupied. Continuous diffusion paths comprised of normally unoccupied voids exist in ZnO and α-ZnS type structures so that voidal diffusion can take place without requiring defect formation. Similarly, voidal diffusion can occur in BiO3, CrCl3, and CdI2 type structures. Conversely, all possible continuous diffusion paths are blocked by metal atoms in the NiAs, NaCl, and antifluorite-type structures so that vacancy or interstitialcy mechanisms are necessary to account for diffusion.