The role of As2O3 on the stability and some physical properties of PbO-Sb2O3 glasses

PbO-Sb₂O₃ glasses added with different concentrations of As₂O₃ (10-55 mol%) were prepared to understand their IR spectra, elastic properties (Young's modulus E, Shear modulus G, microhardness H), optical absorption and dielectric properties (constant ε, loss tan δ, ac conductivity σ_ac over a moderately wide range of frequency and temperature and breakdown strength in air medium at room temperature). Results have indicated that the structure of the PbO-Sb₂O₃-As₂O₃ glass is more rigid when the concentration of As₂O₃ is around 40 mol%.     

ESR in X-irradiated As2O3 glass

X-irradiation of glassy As₂O₃ at 77K or 300K produces an unusually large density (～5×10¹⁸ cm^-3) of paramagnetic centers which are stable at 300K. The average spin-Hamiltonian parameters (g = 1.998, g_⊥ = 1.984, A₆ = 243G, A_⊥ = 114G) indicate that these centers are analogous to those previously observed in As₂Se₃ and As₂S₃ glasses and that they consist of unpaired electrons localized on a non-bonding 4p orbital of an As atom. Unlike the results obtained for As₂Se₃ and As₂S₃, the concommitant holes in As₂O₃ are trapped on Fe²⁺ impurity sites which become Fe³⁺ and not on non-bonding oxygen p orbitals. The radiation induced ESR is also accompanied by a stable optical absorption tail which lies within the band gap and increases exponentially with energy. This absorption can be partially bleached with the application of sub-band-gap light.     

Kinetics of photo-induced edge shift in optical transmission of amorphous As2S3 film

Photo-induced edge-shift affect in As₂S₃ film has been studies for different intensities of incident light. This process depends only on the total energy E of light. A simple experimental relationship between shift of edge Δλ and E

$\text{1 ?}\text{Δλ(E)}\text{Δλ(∞)}\text{=}\text{exp}\text{(-K·E)}$

has been obtained, which coincides with a theretical prediction deduced from a model based on a first-order reaction.     

X-ray photoelectron spectroscopy of Co3O4, Fe3O4, Mn3O4, and related compounds

The metal 2p region spectra of the mixed valence spinels, Co₃O₄, Fe₃O₄, Mn₃O₄, and related compounds were studied. The satellite splittings of Co 2p_{$\text{3}\text{2}$} for the octahedrally coordinated cobaltous ions are 6.2 eV and those for the tetrahedrally coordinated ones are about 5.3 eV. The Co 2p spectrum for Co₃O₄ is considered to be the sum of spectra of magnetic cobaltous ions and low-spin cobaltic ions. In the cases of Fe₃O₄ and Mn₃O₄, the oxidation states were not clearly distinguished because both the divalent and trivalent ions of iron and manganese are high-spin.     

Glass formation in the As2Se3-As2Te3-Sb2Te3 system

Chalcogenide glasses from the As₂Se₃-As₂Te₃-Sb₂Te₃ system were synthesized for the first time. The glass-forming region was determined by X-ray diffraction and electron microscopic analyses.The basic physicochemical parameters such as density (d), microhardness (HV) and temperatures of phase transformations (glass transition T_g, crystallization T_cr and melting T_m) were measured. Compactness and some thermomechanical characteristics such as volume (V_h) and formation energy (E_h) of micro-voids in the glassy network as well as the elasticity module (E) were calculated. The glass-forming ability was evaluated according to Hruby's criteria (K_G). The correlation between composition and properties of the (As₂Se₃)_x(As₂Te₃)_y(Sb₂Te₃)_z glasses was established and comprehensively discussed.     

Kβ2 X-ray emission bands of Ga and As and their compounds

Ga and As Kβ₂ emission bands of the compounds under study consist of a more or less pronounced Kβ₂ main band, a short-wavelength side band which according to calculations by the ‘sudden approximation’ method may be essentially assigned to a KM_IV,V → M_IV,VN_II,III satellite, and long-wavelength 3d → 1s bands. Compounds such as Ga₂(SO₄)₃, Ga(NO₃)₃, Ga₂O₃, NaH₂AsO₄, K₃AsO₄, and As₂O₃ also show long-wavelength side-maxima at a distance of about 12 and 15 eV, respectively, from the main band, which are due to electron transitions from bands or levels with a preponderant 0 2s character.The Kβ₂ main band of A^IIIB^V compounds is less pronounced owing to the widths of the K levels and to instrumental distortions. The distance between the maxima of the state density of the upper valence bands can be recognized only by a shoulder or asymmetry of the band at the long-wavelength side. By calculation of the Ga and As Kβ₂ bands in GaAs with a pseudopotential kp band structure method, and allowing for the influence of both the transition probability and instrumental distortion excellent agreement with experiment is obtained.     

Electronic structure analysis of Mn- and Fe-codoped In2O3 by photoemission yield measurements

The valence band electronic structures of Mn- and/or Fe-doped In₂O₃, i.e., In₂O₃:Mn, In₂O₃:Fe, and In₂O₃:(Mn, Fe), are investigated by photoemission yield measurements. Significant changes are observed in the threshold energy of photoemission, depending on the doped magnetic ions, which indicates that an additional occupied band appears above the top of the valence band of In₂O₃ owing to doping with Mn and/or Fe ions. It is confirmed that the order of the threshold energies of photoemission, E_PET, is E_PET(In₂O₃:Mn)<E_PET(In₂O₃:(Mn, Fe))<E_PET(In₂O₃:Fe)<E_PET(In₂O₃). To gain a better understanding of these results, first-principles molecular orbital calculations are also carried out, which successfully explain the observed changes in the photoemission threshold energies.     

Two-dimensional spin ordering in YFe2O4

A neutron diffraction study was performed on a single crystal of a new compound YFe₂O₄ below its Néel point. In a slightly oxygen deficient crystal, the elastic magnetic scattering takes the form of Bragg line along the c axis at $\text{(}\text{n}\text{3}\text{,}\text{n}\text{3}\text{, l) (n ≠ 3m)}$ in the hexagonal lattice. This fact indicates the two-dimensional long range order of a commensurate sinusoidal spin structure.     

Photoluminescence decay affected by variable range hopping in band tail in amorphous As2S3

Photoluminescence decay was observed with various excitation energies and at various temperatures in amorphous As₂S₃. The decay at high temperature or with the high excitation energy had the $\text{t}{}^{\mathrm{<mtext>-3</mtext><mtext>2</mtext>}}$ long time behavior. This decay is concluded to arise from the combination of the tunneling recombination and the variable range hopping of carriers in the band tail.     

Magnetic and structural studies of Cr2O5 and Cr3O8

The infrared spectra, indexed X-ray powder diffraction patterns, magnetic susceptibilities between 80 and 300 K, and electron paramagnetic resonance spectra at 80 and 300 K are reported for Cr₂O₅ and Cr₃O₈. The results indicate that both oxides are Cr³⁺/Cr⁶⁺ mixed-valence compounds which contain CrO₆ octahedra and CrO₄ tetrahedra in different ratios. The valence formula for Cr₂O₅ is Cr³⁺₂Cr⁶⁺₄O₁₅ and that of Cr₃O₈ is Cr³⁺₂Cr⁶⁺₇O₂₄. The X-ray powder data for Cr₂O₅ and Cr₃O₈ could be indexed on the basis of a monoclinic unit cell $\text{(a = 12.01(2), b = 8.52(1), c = 9.39(1)}\text{A}\text{?}\text{β = 92.0(1)°)}$ and an orthorhombic unit cell $\text{(a = 12.01(7), b = 36.60(7) and c = 3.82(1)}\text{A}\text{?}\text{)}$, respectively.     

Low binding energy satellites in the 3d X-ray photoelectron spectra of rare earths (R) in RMn2Si2 and RGa2

The 3_d core-level X-ray photoelectron spectra of rare earths (R) in RMn₂Si₂ (R = Pr, Nd, Sm, Gd) and RGa₂ (R = Pr, Nd, Sm) have been recorded. A structure has been detected on the low binding energy side of each of the 3d_{$\text{5}\text{2}$} and 3d_{$\text{3}\text{2}$} photoemission peaks. The structure identified as a shake-down satellite shows no chemical shift. The energy separation of the satellite has been measured with respect to the main 3d_{$\text{5}\text{2}$} peak. The present results have been examined in the light of recent experimental and theoretical reports.     

Lattice parameters variation with temperature of Ti2O3 and (Ti0.98V0.02)2O3 from single crystal X-ray data

The lattice parameters of Ti₂O₃ and (Ti_0.98V_0.02)₂O₃ have been measured as a function of temperature (24–670°C for Ti₂O₃ and 24–440°C for V-doped Ti₂O₃) from single crystal X-ray data. The high temperatures were attained by blowing hot argon directly on the crystal mounted on an automatic Philips diffractometer. This experimental set-up gives standard deviations which are at least 10 times better than those of the previous measurements and allows to keep Ti₂O₃ as such well above the transition. The variations of a, c, $\text{c}\text{a}$ (hexagonal axes) for pure Ti₂O₃ are in agreement with the previous results. On the contrary we did not observe any transition in the unit cell volume. The V-doping seems to attenuate the transition which is visible only on the a vs T curve     

Proprietes optiques et structure electronique de MnAu2

The optical spectrum of the helical antiferromagnetic compound MnAu₂(t_N = 90°C) has been measured, using a scanning ellipsometric method, in UHV, between 0.47 and 5.7 eV, at temperatures ranging from 88 to 700 K. Below 0.6 eV the experimental data can be fitted to a Drude-like intraband model. The maximum of the interband absorption occurs at 5.1 eV, while the onset of interband absorption may be placed at 0?.4eV as is suggested by the rapid rise of $\text{ε}{}_2\text{(ω)}\text{λ}$. below 0.5 eV. In the absence of theoretical work, the analysis of the optical spectrum leads to a preliminary rough model of the electronic structure; the proposed local density of d states is represented. The 5.1eV peak is attributed to d → E_F transitions (parabolic edge at 2.7 eV similar to Au), originating in the lower part of the band, associated mainly with Au sites. To account for the moment $\text{(}\text{3.6μ}{}_{\mathrm{S}}\text{at Mn}\text{)}$, the upper d band (mainly Mn sites) is split: the d↑ band is below E_F (interband edge at 0.4eV), while the d↓ band contains 1.4 electrons. ESCA measurements tend to confirm this model. An important unusual fact is the sharp anomaly of /~ε(ω) in the infrared, around T_N; attempts to correlate this with magnetic (s-d) interactions have been initiated.     

Hole mobility in evaporated layers of As2S3.CdI2

The hole drift mobility in As₂S₃.CdI₂ has been determined using Spear's method. The room-temperature value is 10^?4$\text{cm}{}^2\text{Vs}$, the activation energy 0.2 eV. The hole yield appears to be controlled by geminate recombination.     

Electrical conductivity of the system Y2O3CeO2

The electrical conductivity of the system Y₂O₃CeO₂ was measured in the temperature range 500–1100°C and P_o2 range 10^–7?10^?1 atm. Possible defect models were suggested on the basis of conductivity data, which were investigated as a function of temperature and of P_o2. The observed activation energies were 0.40 eV and 1.79 eV in the low- and high-temperature regions, respectively. The observed conductivity dependences on P_o2 were in the temperature range 500–750°C and at temperatures from 750–1100°C. It is suggested that the system Y₂O₃CeO₂ shows a mixed ionic plus hole conduction due to an O^″_i defect and an electronic hole conduction due to a V^'''_Y defect in the low- and high-temperature regions, respectively.     

Kerr-effect and dielectric tensor elements of magnetite (Fe3O4) between 0.5 and 4.3 eV

The complex polar Kerr effect (rotation and ellipticity) of magnetite single crystals has been measured at room temperature between 0.5 and 4.3 eV. From the magneto-optical data and the optical constants, the off-diagonal elements (?_xy) of the dielectric tensor has been derived. Three well separated magneto-optical transitions have been indentified. At about 0.75 eV one strong magneto-optical structure with a diamagnetic line shape is assigned to a $\text{3d}{}^6\text{→3d}{}^5\text{(}{}^6\text{A}{}_{\mathrm{1g}}\text{) 4s}$ transition from Fe²⁺ in octahedral sites. Two other structures with paramagnetic line shapes near 1.85 and 2.90 eV are assigned to the orbital promotion processes $\text{3d}{}^6\text{(Fe}{}^{\mathrm{2+}}{}_{\mathrm{oct}}\text{)→3d}{}^5\text{(}{}^4\text{T}{}_{\mathrm{1g}}\text{) 4s}$ and $\text{3d}{}^5\text{(Fe}{}^{\mathrm{3+}}{}_{\mathrm{tet}}\text{)→3d}{}^4\text{(}{}^5\text{T}{}_2\text{) 4s}$, respectively, which take into account Fe 3d^n?1 final state effects.     

Optical mode softening in the incommensurate phase of Sr2Nb2O7

In the incommensurate phase below about 220°C of Sr₂Nb₂O₇, the soft mode, of which frequency decreases toward 215°C has been found by the Raman scattering measurements in the $\text{b(cc)}\text{b}$ scattering geometry. The level repulsion and the intensity transfer between the soft mode and another low frequency mode are clearly observed. The uncoupled soft mode frequency ω_s has been found to be expressed as ω_s =A(T_tr?T)^β, where β= 0.38 ± 0.02. Pressure dependence of the soft mode has also been measured up to 24kbar. No remarkable pressure dependence has been observed.     

Photoelectron spectra of As4S3, P4S3, P4Se3 and As4O6

The He(I) UV photoelectron spectra of As₄S₃, P₄S₃, P₄Se₃ and As₄O₆ are reported in this paper. The spectra of As₄S₃ and the isostructural molecules P₄S₃ and P₄Se₃ comprise seven broad but clearly defined peaks, whilst the spectrum of As₄O₆ consists of six peaks and two shoulders. By comparing the spectra with one another and with the photoelectron spectra of other arsenic and phosphorus compounds, the character and symmetry species of the highest-energy occupied molecular orbitals of the molecules have been assigned.     

Energies of the n2S12 and n2D32,52 states of Cs

Using the technique of Doppler-free two-photon spectroscopy the energies of the n²S_{$\text{1}\text{2}$} (12 ? n ? 35) and n²D_{$\text{3}\text{2}$,$\text{5}\text{2}$} (11 ? n ? 48) states of CsI have been measured with a thermionic detector. The absorption spectrum of molecular iodine was used as a reference giving us a total estimated accuracy of about 2 × 10^-7. Taking also into account the energies of the 7–11 ²S_{$\text{1}\text{2}$} and 5 and 6 ²D_{$\text{3}\text{2}$,$\text{5}\text{2}$} states measured by other authors and using an extended Ritz-formula we found the ionization limit to be E_i = 31406.468 ± 0.006 cm^-1.     

Structure,vibrational study and conductivity of the trihydrated uranyl bis(dihydrogenophosphate): UO2(H2PO4)2·3H2O

The X-ray structure (293 K) of UO₂(H₂PO₄)₂·3H₂O has been refined (R = 0.062): M_r = 518g, space group: P2₁/c (Z = 4); $\text{a = 10.816(1)}\text{A}\text{?}$, $\text{b = 13.896(2)}\text{A}\text{?}$, $\text{c = 7.481(1)}\text{A}\text{?}$, β = 105.65(1)^°, $\text{V = 1082.7(2)}\text{A}\text{?}{}^3$; D_c = 3.17 Mg m^?3. The structure consists of infinite chains along the (101) axis with U atoms bridged by two H₂PO₄ groups. The U atom is surrounded by a pentagonal bipyramid of oxygen atoms, one of them being an equatorial water molecule. The cohesion between the chains is ensured by hydrogen bonds involving the two last water molecules. An assignment of IR and Raman bands with isotopic substitution spectra is proposed. A phase transition at 128 K was made evident by DSC and spectroscopy. The room-temperature phase is characterized by a high disorder of the OH bond orientation while in the low-temperature phase H₂O and POH species appear well oriented. The conductivity seems to occur by proton transfer and protonic-species rotation at the POH-water molecular interface between the chains. ac conductivity has been determined by means of the complex-impedance method ($\text{σ}{}_{\mathrm{<mtext>RT</mtext>}}\text{～ (3?12) × 10}{}^{\mathrm{?5}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$; E ～ 0.20 eV).