Effective ionic charges and chemical bonding in GaSe and GaTe from chemical shifts of X-ray K absorption discontinuities

Chemical shifts in the X-ray K absorption edges of gallium and selenium in some of their binary compounds have been studied using a bent crystal X-ray spectrograph. The shifts are found to be governed by the effective charges on the absorbing ions, which have been calculated using Suchet's theory. For the compounds GaSe and GaTe, however, the effective ionic charges cannot be calculated for want of data on the divalent radius of gallium. The plot of the chemical shift, δE, against the theoretically calculated effective ionic charge, q, has been used to determine the charges on the ions in these two compounds. The effective charges, thus determined, provide information about the chemical bonding in the compounds.     

Chemical shifts of the copper and cobalt K absorption discontinuities in some ternary compounds

The present paper reports the chemical shifts of the K X-ray absorption discontinuities of copper and cobalt in ternary compounds. Relationships between the chemical shifts ΔE of the discontinuities and the various bond parameters (C, E_g, and f_i) calculated from Levine's theory have been established. It is found that distinctly separate curves can be drawn for different valencies (Cu¹⁺ and Cu²⁺, Co²⁺ and Co³⁺) of the absorbing ions. Making use of Levine's method for calculating bond charges, the effective charges q on the absorbing ions have been evaluated. The dependence of ΔE on q has been confirmed.     

Crystal radii of ions in alkaline earth chalcogenides

The crystal radii of ions in alkaline earth chalcogenides have been calculated from the effective nuclear charges of isoelectronic ions. The ionic radii thus calculated are found to follow the polarizability—radius cubed relation, according to which the ratio of the electronic polarizability of an ion to the cube of its radius in the free state is nearly equal to that in the crystalline state. The interionic separations in alkaline earth chalcogenides and also AB₂ and A₂B type crystals obtained from the ionic radii reported in the present paper agree closely with the experimental values.     

Determination of bond lengths in some compounds of rhenium from the x-ray LIII absorption discontinuity

The shapes and the fine structure of the x-ray L_III absorption discontinuity of rhenium have been studied in seven octahedral (K₂ReCl₆, K₂ReBr₆, (pyH)₂ReCl₆, (dipyH)₂ReCl₆, Re(dipy)Cl₄, K₃ReO₂(CN)₄ and ReO₃) and three tetrahedral (KReO₄, NH₄ReO₄ and NaReO₄) compounds. The bond lengths in these compounds have been determined by applying Levy’s theory to the data on the fine structure associated with the edge beyond the molecular orbital region.     

ESCA Studies on Silicon Compounds Using an Internal Standard for Calibration

X-ray photoelectron spectra (ESCA) for some silicon compounds have been measured. As an internal standard the Cls binding energy of the carbon atoms of incorporated phenyl groups have been used. The actual value of this binding energy was determined from a previously found relation between E_b Cls and the infrared absorption intensity (A_CH) of the C-H stretching vibrations of the phenyl group.

In this way a correlation between the binding energy of the silicon atom (Si2p) and its effective charge (q_Si) could be set up: E_b = 1.53 q + 100.6. The charges were quoted from quantum chemical calculations in literature or derived from a previously reported relation between the infrared absorption intensity (A_CH) and total charge of the phenyl group in compounds of the type C₆H₅X.     

An ESCA investigation of some dithiooxalato complexes

A series of dithiooxalato complex ions have been investigated as their tetraphenyl-phosphonium and potassium salts. Core-electron binding energies (E_b) of S, C, and O were determined, as well as those of the metals. From the first-mentioned data, effective charge values (q) were estimated for the atoms of the ligands. For this purpose linear relations (E_b = k · q + E_bO) were used that had been previously derived within a scheme using C ls (phenyl) as the internal standard. From the data thus obtained the effective charge on the metal atoms could be estimated. The data is used to test if analogous linear relations also hold for the heavy elements; for example, we have found E_b(Pt) = 3.17 · q_pt + 71.1 eV.     

On the core electron binding energy of carbon and the effective charge of the carbon atom

From Mulliken population data based on ab initio calculations of a series of substituted aromatic compounds and from well-calibrated XPS data (core electron binding energies, E_b) an empirical relation between E_b(C1s) and the charge on the carbon atoms, q_c, has been found: E_b(C1s = 6.42q_c + 4.52q²_c + 285.8 (eV). It is also found that XPS data for other carbon-containing species, notably the cyanide ion, can be described by this relation.     

Extrapolation from positive to negative energy of the Woods-Saxon parametrization of the n-208Pb mean field

The real part V(r); E) of the nucleon-nucleus mean field is assumed to have a Woods-Saxon shape, and accordingly to be fully specified by three quantities: the potential depth U_v(E), radius R_V(E) and diffuseness a_v(E). At a given nucleon energy E these parameters can be determined from three different radial moments [r^q]_v = (4π/A) ∝V(r; E)r^q dr. This is useful because a dispersion relation approach has recently been developed for extrapolating [r^q]_V(E) from positive to negative energy, using as inputs the radial moments of the real and imaginary parts of empirical optical-model potentials V(r; E) + iW(r; E). In the present work, the values of U_v(E), R_v(E) and a_v(E) are calculated in the case of neutrons in ²⁰⁸Pb in the energy domain −20 < E < 40 MeV from the values of [r^q]_V(E) for q = 0.8, 2 and 4. It is found that both U_V(E) and R_v(E) have a characteristic energy dependence. The energy dependence of the diffuseness a_a(E) is less reliably predicted by the method. The radius R_V(E) increases when E decreases from 40 to 5 MeV. This behaviour is in agreement with empirical evidence. In the energy domain −10 MeV < E < 0, R_V(E) is predicted to decrease with decreasing energy. The energy dependence of the root mean square radius is similar to that of R_V(E). The potential depth U_v slightly increases when E decreases from 40 to 15 MeV and slightly decreases between 10 and 5 MeV; it is consequently approximately constant in the energy domain 5 < E < 20 MeV, in keeping with empirical evidence. The depth U_v increases linearly with decreasing E in the domain −10 MeV < E < 0. These features are shown to persist when one modifies the detailed input of the calculation, namely the empirical values of [r^q]_v(E) for E > 0 and the parametrization [r_q]_w(E) of the energy dependence of the radial moments of the imaginary part of the empirical optical-model potentials. In the energy domain −10 MeV < E < 0, the calculated V(r; E) yields good agreement with the experimental single-particle energies; the model thus accurately predicts the shell-model potential (E < 0) from the extrapolation of the optical-model potential (E > 0). In the dispersion relation approach, the real part V(r; E) is the sum of a Hartree-Fock type contribution V_HF(r; E) and of a dispersive contribution ΔV(r; E). The latter is due to the excitation of the ²⁰⁸Pb core. The dispersion relation approach enables the calculation of the radial moment [r^q]_ΔV(E) from the parametrization [r^q]_w(E): several schematic models are considered which yield algebraic expressions for [r^q]_ΔV(E). The radial moments [r^q]_HF(E) are approximated by linear functions of E. When in addition, it is assumed that V_HF(r; E) has a Woods-Saxon radial shape, the energy dependence of its potential parameters (U_HF, R_HF, a_HF) can be calculated. Furthermore, the values of ΔV(r; E) can then be derived. It turns out that ΔV(r; E) is peaked at the nuclear surface near the Fermi energy and acquires a Woods-Saxon type shape when the energy increases, in keeping with previous qualitative estimates. It is responsible for the peculiar energy dependence of R_V(E) in the vicinity of the Fermi energy.     

Chemical shift of the Ga and As Kα1,2 and Kβ1,3 X-ray emission lines

By means of a double crystal spectrometer and a computer the chemical shifts of the Ga Kα_1,2, As Kα_1,2 and Kβ_1,3 lines were determined with high accuracy. An interpretation of the results obtained with a free ion model and a calculation according to the Hartree method shows agreement of the values calculated for the effective atomic charges with those based on chemical experience, and also the presence of a charge transfer from the A atom to the B atom in A^IIIB^V compounds. The existence of binding charges is one of the reasons for the fact that |q_A| ≠ |q_B|. The interpretation of the Kβ_1,3 and Lα shifts shows the limitations of the free ion model.     

Correlation of x-ray chemical shift and bond parameters calculated from levine's theory

The Cu K absorption edge shift in the systems CuCl, CuBr, CuI, CuO, CuS, CuSe, Cu₂O, CuFeS₂ and CuCl₂ · 2H₂O has been studied using a Cauchois-type bent crystal X-ray spectrograph. The bond parameters ionic gap C^μ and average bond gap E^μ_gb calculated from Levine's theory have been correlated with the chemical shift ΔE. The correlation is found to be linear and further it has been observed that distinct separate curves between ΔE and the bond parameters C^μ and E^μ_gb can be drawn for Cu⁺¹ and Cu⁺² ions. The curves have been used to determine bond parameters for the system CuCl₂ · 2H₂O.     

Combustion synthesized MgAl2O4:Cr phosphors—An EPR and optical study

Magnesium aluminate (MgAl₂O₄) doped with trivalent chromium (Cr³⁺) was synthesized by the combustion method. The prepared sample was characterized by X-ray powder diffraction, Brunauer-Emmet-Teller (BET) adsorption isotherms and diffuse-reflectance UV-vis spectroscopy techniques. Electron paramagnetic resonance (EPR) and photoluminescence (PL) studies have been performed at room temperature and at 110 K. The EPR spectrum exhibit resonance signals at g=5.37, 4.53, 3.82, 2.26 and 1.96 characteristic of Cr³⁺ ions. The luminescence of Cr³⁺-activated MgAl₂O₄ exhibits a red emission peak around 686 nm from the synthesized phosphor particles upon 551 nm excitation. The luminescence is assigned to a transition from the upper ²E_g→⁴A_2g ground state of Cr³⁺ ions. By correlating EPR and optical data the crystal field splitting parameter (D_q), Racah inter-electronic repulsion parameter (B) and the bonding parameters have been evaluated and discussed. The bonding parameters suggests that the ionic nature of Cr³⁺ ions with the ligands and the Cr³⁺ ions are in distorted octrahedral environment.     

Study of chemical shift in Ll and Lƞ X‐ray emission lines in different chemical forms of 48Cd and 50Sn compounds using WDXRF technique

Chemical shift in Ll and L? X‐ray emission lines of ₄₈Cd and ₅₀Sn elements in various chemical compounds was determined with high resolution wavelength dispersive X‐ray fluorescence (WDXRF) spectrometer. The positive and negative shifts were measured in ₄₈Cd compounds viz, CdS, CdB₄O₇, CdCl₂, Cd₃(PO₄)₂, CdCO₃, CdI₂ and CdO with reference to pure Cd foil and ₅₀Sn compounds viz, Sn(CrO₄)₂, SnO, SnO₂, SnCl₂, SnF₂, SnF₄ with reference to pure Sn foil. The measured energy shifts in Ll X‐ray emission lines range from ?0.47 to 1.82 eV and L? emission lines range from ?2.67 to 1 eV for both compounds. The effective charges (q, q ^/ , q ^// , and q ^/// ) were calculated from four models (Pauling method, Suchet method, Levine method and Batsonav method) and found to be linear dependence with chemical shift. The measured chemical shifts were correlated with effective charge, number of ligands and electronegativity of the central metal atom in the given compounds.     

Effective ionic charges in CdGa2Se4 and CdGa2S4

Available experimental data (Raman and Infrared) on the optic phonon spectra in defect chalcopyrite crystals CdGa₂Se₄ and CdGa₂S₄ are used to determine the dynamical ionic effective charges. The results are compared with those found in other ternary compounds as spinels and chalcopyrites. An emperical correlation between the normalized Szigeti charges and the optical dielectric constant is discussed.     

Effect of rare earth substitutions on some physical properties of Mn-Zn ferrite studied by positron annihilation lifetime spectroscopy

Mn-Zn ferrite substituted with rare earth ions have been investigated by means of positron annihilation lifetime spectroscopy (PALS). The variations of lifetime parameters τ_av, I₂, and κ with ionic radius of rare earth ions, grain size and electrical resistivity for all samples have been studied. The intergranular pores increase with increasing the ionic radius of rare earth ions and grain size of the samples.     

An X-ray photoelectron spectroscopy study of volatile tin compounds

Core-level X-ray photoelectron spectra of fifteen compounds of tin have been measured in the gas phase. The compounds include various organo and halo compounds as well as tin(IV) nitrate and Sn{N[Si(CH₃)₃]₂}₂. The tin binding energies span a range of 4.4 eV and are well correlated by the “transition-state” point-charge potential model equation using atomic charges calculated by the CHELEQ electro-negativity equalization method. As expected, the empirically determined parameter k for tin is smaller than the k values obtained in previous work for carbon, silicon, and germanium. For Sn(NO₃)₄, and Sn{N[Si(CH₃)₃]₂}₂, the bonding can be described as a weighted average of several resonance structures. In these cases the binding energy data were used in conjunction with the CHELEQ method to determine the resonance structure weightings.     

The anion and cation effects in the magnetic anisotropy of rare-earth compounds: Charge screening by conduction electrons

The formation of magnetic anisotropy (MA) in rare-earth compounds with transition metals has been analyzed. The screening of the charges creating the crystal field by conduction electrons has been shown to play an important role. The calculations took into account the Friedel charge-density oscillations. The model used for RCo₅ is the point-charge crystal field including nonuniform screening by conduction electrons with an anisotropic Fermi surface. The mechanisms of strong MA due to light-element impurities (hydrogen and nitrogen) are considered. The effective charge of an impurity can heavily depend on its ionic radius and the characteristics of the Fermi surface (in particular, on the Fermi momentum k _F ) of the screening electrons. The screening of the cation and anion charge in hydrides and nitrides based on the R₂Fe₁₇ and RFe₁₁Ti intermetallic compounds is discussed.     

ELECTRONIC STRUCTURE OF THE T*-TYPE SUPERCONDUCTORS (Bi0.5Sr1.5)(Y, Ce)2Cu2Oy STUDIED BY PHOTOELECTRON SPECTROSCOPY

The electronic structure of T^*-type compounds (Bi_0.5Sr_1.5)(Y_2-xCe_x)Cu₂O_y has been studied by X-ray photoelectron spectroscopy. From analysis of the results, it was found that cation deficiency in Ce⁴⁺ introduced holes to conduction planes in the T^* phase as in the p-type infinite layer compounds. Some Cu ions in the sample without cation-deficiency contained two-oxygen coordination, which resulted in the incompleteness of the CuO₂ sheets. Bi ions in the T^* phase cuprates take exact valence of 3_{+, Pb ions cannot replace them due to the too large an ionic radius of Pb²⁺/Pb⁴⁺.}     

Topological and thermodynamic investigations of ternary mixtures containing cyclic ether: Excess molar enthalpies

Excess molar enthalpies, H_ijk^E, of 1,3-dioxolane or 1,4-dioxane (i) + aniline (j) + benzene or toluene (k) ternary mixtures have been measured as a function of composition at 308.15 K. The H_ijk^E data have been fitted to Redlich-Kister equation to determine ternary adjustable parameters along with their standard deviations. It has been observed that H_ijk^E values predicted by Graph theory compare well with their corresponding experimental values. The observed data have been analyzed in terms of (i) Graph theory (which involves the topology of a molecule); (ii) Prigogine-Flory-Patterson; and (iii) Sanchez and Lacombe theories.     

Bond-stretching and bond-bending force constant of binary tetrahedral (AB and AB) semiconductors

In this Letter we present the two expressions relating the bond-stretching force constant (α in N/m) and bond-bending force constant (β in N/m) for the A^IIIB^V and A^IIB^VI semiconductors with the product of ionic charges (Z₁Z₂) and nearest neighbor distance d (Å). Interatomic force constants of these compounds exhibit a linear relationship when plotted on a log-log scale against the nearest neighbor distance d (Å), but fall on different straight lines according to the ionic charge product of the compounds. A fairly good agreement has been found between the observed and calculated values of the α and β for binary tetrahedral semiconductors.     

Studies on the opto-electronic properties of III–V and II–VI group semiconductors from optical electronegativities

New empirical relations have been proposed to evaluate bond energies (E_s) in compound semiconductors, first from the knowledge of optical electronegativities of the constituent ions and secondly from the energy gap values. The validity of the two relations has been tested in the case of certain III–V and II–VI group semiconductors by comparing the calculated values of E_s, with those in the literature. From the computed values of E_s, refractive indices have been calculated. The Penn gap (E_p), Fermi energy (E_F) and S_o-parameter for these semiconductors have also been determined. The estimated values of these parameters are utilized to evaluate the electronic polarizabilities (α). The computed values of a compare excellently with the standard data.