Far infrared reflection spectra due to lattice and free carrier in ZnxHg1−xSe

Far infrared reflection spectra of Zn_xHg_1−xSe with x = 0 to 0.4 showed characteristic of two TO-phonon modes behavior and the plasmon-LO phonon coupling in the region from 20 to 500 cm⁻¹ at 5 and 300 K. The composition dependence of TO modes on the frequency is linear for the HgSe-like mode TO₁ and constant for the ZnSe-like mode TO₂. The additional TO mode due to clustering effect is observed at 113 cm⁻¹. The plasmon-LO phonon coupled modes are explained well by our model taken into account the two-mode behavior and the contribution of interband transitions in dynamic dielectric function.     

Far infrared polarization measurements of MEM(TCNQ)2 at room temperature and 4.2 K

Polarization measurements have been made in the far infrared absorption spectra on single crystals of MEM(TCNQ)₂ at 1.5, 4.2 and 298 K. We demonstrated experimentally that the direction of polarization of phonons at 126 and 156 cm⁻¹ below spin-Peierls transition are parallel to the c-axis. Secondly, we measured the absorption spectra of MEMI powder at 1.5 and 4.2 K and found that there is no absorption in the range from 130 to 170 cm⁻¹. This indicates that there is no intramolecular vibration of MEM in this region. It supports the assignment of 156 cm⁻¹ absorption as phonon. Thirdly, comparing the FIR absorption spectra at 4.2 and 298 K with linearly polarized radiation field parallel to the c-axis, we found that the height of the strong absorption band observed around 86–180 cm⁻¹ region at 4.2 K becomes lower with the raising of temperature to 298 K. We attributed this band to the pinned CDW. The lowest edge of the CDW is 70 cm⁻¹.     

Conductivity of lithium gallium silicates

Lithium gallium silicates, Li_1−xGa_1−xSi_2+xO₆: 0.03 < x < 0.37, with a beta-spodumene structure, have a low Li⁺ ion conductivity, ca. 10⁻⁹ ω⁻¹ cm⁻¹ at 400 K rising to ca. 10⁻³ ω⁻¹ cm⁻¹ by 1000 K, that changes little with composition. The phase, LiGaSiO₄, with an alpha-eucryptite structure, exhibits mainly electronic conductivity, but at a low level, ca. 10⁻⁸ ω⁻¹ cm⁻¹ at 600 K, rising to ca. 10⁻⁵ ω⁻¹ cm⁻¹ at 1000 K.     

Raman scattering investigations on Co-doped ZnO epitaxial films: Local vibration modes and defect associated ferromagnetism

Raman scattering spectroscopy has been performed on high quality Co-doped ZnO epitaxial films, which were grown on Al₂O₃ (0001) by oxygen-plasma assisted molecular beam epitaxy. Raman measurements revealed two local vibration modes (LVMs) at 723 and 699 cm⁻¹ due to the substitution of Co²⁺ in wurtzite ZnO lattice. The LVM at 723 cm⁻¹ is found to be an elemental sensitive vibration mode for Co substitution. The LVM at 699 cm⁻¹ can be attributed to enrichment of Co²⁺ bound with oxygen vacancy, the cobalt–oxygen vacancy–cobalt complexes, in Zn_1−xCo_xO films associated with ferromagnetism. The intensity of LVM at 699 cm⁻¹, as well as saturated magnetization, enhanced after the vacuum annealing and depressed after oxygen annealing.     

Study of vibrational spectra of lanthanum sulphate nonahydrate at different temperatures in the region from 4000–50 cm−1

Infrared spectra of lanthanum sulphate nonahydrate are studied over the 4000–50 cm⁻¹ range. The bands pertaining to different internal and external modes of sulphate ion and water molecules are observed and assigned. It is shown that coordinated water molecules exist at two site symmetries C₁ and C_i, which provides confirmation of crystallographic data. Lattice water is not found in these crystals. The effect of low temperature on librational modes of coordinated water and their lattice vibrations are studied in the 550–50 cm⁻¹ region. The potential force field constants are calculated for rocking, wagging and twisting librational modes of water at 290 K, 80 K and 60 K. The higher value of the potential constant for the rocking mode from the wagging librational mode shows the in-plane bend of the hydrogen bond in lanthanum sulphate crystals.     

Low-frequency optical lattice vibrations in Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te alloys

The lattice reflection spectra of the Hg_{1 ? x} Cd _x Te (x = 0.06–0.70) alloys measured in the low-frequency range of optical vibrations (the region of the anomalous mode of Hg-Te vibrations in HgTe) at room temperature are interpreted. The low-frequency modes observed at frequencies of 98, 105, and 112 cm^?1 for all compositions of the Hg_{1 ? x} Cd _x Te alloy are assigned to the modes of Hg-Te vibrations, as was previously done for modes of Cd-Te vibrations in the quasi-molecular approximation. According to the double-well potential model for the Hg atom in the crystal lattice of the alloy, the Hg atom either can occupy the center of the anion tetrahedron or can be located in the off-center position. The fundamental strong mode of Hg-Te vibrations at a frequency of about 120 cm^?1 (at T = 300 K) corresponds to the vibrations of the off-center Hg atom, and the low-frequency vibration modes correspond to the vibrations of the Hg atom located at the center of the anion tetrahedron.     

Ionic conductivity and crystal structure for the Li3−2xCr2−xTax(PO4)3 system

The monoclinic phase (P2₁/n) was formed for 0≤x≤0.6 and the NASICON-type rhombohedral phase (R3̄c) was obtained for the region 0.8≤x≤1.2 in the Li_3−2xCr_2−xTa_x(PO₄)₃ system. The activation energy for Li⁺ migration was ca. 0.45 eV for the monoclinic structure and ca. 0.36 eV for the rhombohedral structure. The maximum conductivity of 8.4×10⁻⁶ S cm⁻¹ at 298 K was obtained for x=0.8 of the Li_3−2xCr_2−xTa_x(PO₄)₃ system. The conductivity of LiCrTa(PO₄)₃ was enhanced about three to five times by the addition of the lithium salt due to the improvement of the sinterablity. The maximum conductivity was 2.4×10⁻⁵ S cm⁻¹ at 298 K for LiCrTa(PO₄)₃–0.2Li₃BO₃.     

Low frequency phonon spectra of mixed crystal CdxHg1−xTe

Far infrared absorption spectra for the mixed crystal Cd_xHg_1?xTe with x=0.18 to 0.45 in the wavenumber region of 10 to 400cm^?1 and temperature region of 4.5 to 300K are reported. A low frequency absorption band has been found between 20 and 50 cm^?1 for all the samples which have been measured in addition to the two-phonon bands in both sides of the reststrahlen absorption bands of the material. By comparison with the phonon densities of states estimated from the phonon frequencies of CdTe, we have attributed this band to TA band modes induced by the disorder and “impurity” effects.     

Type III - Type I transition and strain-effect in Hg1−xCdxTeCdTe and Hg1−xZnxTeCdTe superlattices

In this paper, the results of Hg_1−xZn_xTeCdTe strained layer superlattices grown by MBE are reported, and compared to Hg_1−xCd_xTeCdTe superlattices. Both Type III and Type I Hg_1−xZn_xTeCdTe superlattices with different strain have been grown on CdTe(111)B/GaAs(100) and CdTe(100)/GaAs(100) substrates and characterized by electron, X-ray diffraction, infrared transmission and Hall measurements. The values of hole mobility between 5×10³ up to 2×10⁴cm²v⁻¹s⁻¹ at T = 23K along (111)B growth orientation and up to 4.9×10⁴cm²v⁻¹s⁻¹ at T = 5K along (100) growth orientation are obtained for Type III superlattices whereas in Type I superlattices, the hole mobility is between 200–300cm²v⁻¹s⁻¹. This drastic change in the hole mobility between Type III and Type I superlattices along with the role of the strain are discussed in this paper.     

Absorption of CO laser radiation by NO

Absorption of CO i.r. laser radiation by NO has been studied over the temperature range 300°–4000°K using a grating-tunable CO laser in conjunction with a room-temperature absorption cell and a shock tube. The CO laser line with strongest absorption at elevated temperatures was determined to be the V = 7 → 6, J = 12 → 13 line at 1935.4817 cm^-1, which is nearly coincident with the ²Π_{$\text{3}\text{2}$}V = 0 → 1, J = 37/2 → 39/2 transition in NO. The absorption cell measurements (300°K) were used to infer the position of the NO absorption line (a Λ-doublet at 1935.492 and 1935.497 cm^-1) as well as collision-broadening parameters in pure NO and NO dilute in foreign gases: 2γ° (collision-broadened full width at half maximum in cm^-1 atm^-1 at 300°K) = 0.110, NO-NO; 0.072, NO in Ar; 0.069, NO in Kr; 0.109, NO in N₂. Calculations of the NO absorption coefficient at 1935.4817 cm^-1 are presented for a range of conditions applicable to current studies in combustion and NO_x kinetics. Shock tube measurements (630°–4000°K) supporting these calculations are also reported.     

Raman spectroscopy of smithsonite

Raman spectroscopy at both 298 and 77 K has been used to study a series of selected natural smithsonites from different origins. An intense sharp band at 1092 cm⁻¹ is assigned to the CO₃²⁻ symmetric stretching vibration. Impurities of hydrozincite are identified by a band around 1060 cm⁻¹. An additional band at 1088 cm⁻¹ which is observed in the 298 K spectra but not in the 77 K spectra is attributed to a CO₃²⁻ hot band. Raman spectra of smithsonite show a single band in the 1405–1409 cm⁻¹ range assigned to the ν₃ (CO₃)²⁻ antisymmetric stretching mode. The observation of additional bands for the ν₃^g modes for some smithsonites is significant in that it shows distortion of the ZnO₆ octahedron. No ν₂ bending modes are observed for smithsonite. A single band at 730 cm⁻¹ is assigned to the ν₄ in phase bending mode. Multiple bands be attributed to the structural distortion are observed for the carbonate ν₄ in phase bending modes in the Raman spectrum of hydrozincite with bands at 733, 707 and 636 cm⁻¹. An intense band at 304 cm⁻¹ is attributed to the ZnO symmetric stretching vibration. Copyright © 2007 John Wiley & Sons, Ltd.     

Molecular and atomic adsorption states of oxygen on Cu(111) at 100–300 K

Adsorption states of oxygen on Cu(111) at 100–300 K were investigated by means of HREELS. Two molecular species were characterized by different OO stretching frequencies (v(OO)) at 610 cm⁻¹ and 820–870 cm⁻¹, which are assigned to the peroxo-like species (O²⁻₂) adsorbed in a bridged form and the one in a bidentate form bound on an atop site, respectively. The bridged peroxo species is preferred at the low coverage and the atop peroxo species becomes dominant at the higher coverage. In addition to the peaks due to the molecular oxygen, a peak assigned to v(CuO) of atomic oxygen was observed at 370 cm⁻¹ at the high coverage. The frequency of this mode was higher than the frequency reported for Cu(111) exposed to oxygen above 300 K, indicating that the adsorption state of atomic oxygen formed at 100 K is different from that above 300 K. The v(OO) modes became faint after annealing to 170 K because of O₂ dissociation. The v(CuO) mode of the atomic oxygen formed at 100 K remained up to 230 K and disappeared after annealing to 300 K. No desorption of O₂ was detected on annealing to 300 K. It was also found that vibrational spectra for adsorbed NH₃ are influenced by the adsorption states of atomic oxygen on Cu(111).     

Electronic and vibrational absorption spectra in falcondoite

Optical absorption spectrum of Ni²⁺ ion in Falcondoite, a new mineral has been studied at 300 K. From the nature and positions of the observed bands a succesful interpretation of all the bands could be made assuming octahedral symmetry for the Ni²⁺ ion in the crystal. The bands at 9255, 15 380 and 27 390cm⁻¹ are assigned to ³T_2g(F), ³T_1g and ³T_1g(P) and the other band at 24385 cm⁻¹ assigned to ¹T_2g(D). The crystal field and the Racah parameters are evaluated to be Dq = 925 cm⁻¹, B = 1000 cm⁻¹ and C = 4095 cm⁻¹. NIR and IR spectra of the sample are also studied. The fundamental vibrational modes of H₂O are identified in the IR spectrum. The bands observed in the NIR spectrum are due to overtones and combination tones of water molecule.     

CW and pulsed Pb1–xSnxSe diode laser spectroscopy of 14NH3 and 15NH3 molecules

The absorption spectra of ¹⁴NH₃ and ¹⁵NH₃ molecules from 930 cm^-1 to 1220 cm^-1 have been obtained with CW and pulsed Pb_1–xSn_xSe diode lasers. The laser emission frequency has been tuned by varying crystal composition, diode temperature, hydrostatic pressure, or injection current. The registration of the absorption spectra with CW PbSe laser continuously tuned by varying hydrostatic pressure has been accomplished. The possibility of gas isotope abundancies measurements by diode lasers is considered.     

Vibrational properties of one- and two-mode behaviour in spinel type mixed systems Zn1−xCdxCr2S4

The infrared reflectivity spectra of spinel type mixed crystals Zn_1−xCd_xCr₂S₄ have been measured from 40 to 900 cm⁻¹. Four or five bands were observed at both end members in the region of intermediate composition. The three bands in higher energy show one-mode behaviour and the other two bands show two-mode behaviour. The concentration dependences of these mode frequencies are interpreted by a model proposed already, in which the 2 basic units and the 6 force constants are contained. By comparing the force constants associated with the Zn-site in several spinels, it is suggested that the two-mode behaviour arises from the large difference in the force constants between the two end members. The E_g (260 cm⁻¹) and T_2g (160 cm⁻¹) Raman modes for ZnCr₂S₄ were also observed and used for the determination of the force constants.     

Raman spectra of apatites: La10−x Si6−y (Al,Fe)y O26±δ

Raman spectra of eight polycrystalline apatites of the general formula La_10−xSi_6−yM′_yO_{26 ± δ} with M′ = Al or Fe were obtained at 300 K. Raman spectra of La₁₀Si₄Fe₂O₂₆ and La_9.83Si_4.5Al_1.5O₂₆ were investigated in the range 80–1000 K and 80–623 K, respectively. Tentative assignments of bands to stretching and bending modes of SiO₄ tetrahedra and to M'O vibrations are proposed. Except for the two new bands, which appear around 700 cm⁻¹ when Al is replaced by Fe, only some band broadenings and relative intensity changes are observed as a function of the rate of O5 or La vacancies. Most of the bands soften and broaden continuously when raising the temperature. This is an indication that the Al‐ and Fe‐substituted apatites do not undergo any structural change up to 1000 K. Above 1000 K, the broad and weak shoulder observed at 850 cm⁻¹ for La₁₀Si₄Fe₂O₂₆ is replaced by a strong band at 868 cm⁻¹, suggesting that SiO₄ tetrahedra undergo a structural modification. All compounds show the same residual band broadening at 80 K. This suggests that there is a small rate of static disorder preferentially related to the solubility of Al and Fe in the Si sublattice rather than to other defects. Moreover, the observation of FeO modes indicates that the dynamics of the solid solution obeys the so‐called two‐mode behavior. The occurrence of FeO stretching vibrations 150 cm⁻¹ lower than for those of SiO suggests that the coordination number of iron could be larger than 4, particularly for the Fe⁴⁺ species. Copyright © 2006 John Wiley & Sons, Ltd.     

Pressure-Broadened Linewidth Measurements in the ν2Band of the CH3Radical

Pressure broadening coefficients for an infrared transition of the methyl radical have been measured for the first time. CH₃radicals, generated by pyrolyzing di-tert-butyl peroxide in a flow of either N₂or Ar, were probed using a tunable diode laser and a multipass absorption cell. The Lorentz half-width of theQ(6,6) line of the ν₂band of CH₃at 607.024 cm⁻¹was measured as a function of pressure at 295 K. The broadening coefficients (HWHM) areb(Ar) = 0.0310 ± 0.0012 cm⁻¹atm⁻¹andb(N₂) = 0.0390 ± 0.0020 cm⁻¹atm⁻¹. These coefficients are lower than those for CH₄–Ar, N₂broadening. This may be due to a lower polarizability or smaller effective hard collision diameter for CH₃relative to CH₄.     

Photoinduced infrared activity in trans(CH)x: Inter[retation in terms of a lattice dynamical model

A lattice dynamical calculation for the photoinduced infrared vibrational modes is reported. By using the perturbed Green function method we have been able to compute the new frequencies and the integrated intensities of the photoinduced infrared modes at ω_1H⋍500 cm⁻¹, ω_2H⋍1260 cm⁻¹ and ω_3H⋍1370 cm⁻¹ in trans(CH)_x and at ω_1D⋍400 cm⁻¹ and ω_2D⋍1045 cm⁻¹ in trans(CD)_x. Most of the features of the photoinduced infrared spectra can be explained in terms of long conjugation length segment properties. Only the higher frequency tail of the band shape peaked at ω_1H and ω_1D can be related to the pertubbation determined by a photogenerated charge trapped in short segments. The calculated frequencies and integrated intensities are in good agreement with the experimental results.     

Optic-mode coupling in ferroelectric gadolinium molybdate

Separate measurements of the A₁(TO) and A₁(LO) Raman spectra of ferroelectric gadolinium molybdate at 80°K and above have elucidated the origin of the anomalous temperature dependence of the two lowest frequency lines in the A₁(TO) spectrum. The observed behavior is postulated to be the result of coupling among modes at 44.5, 51.5, and 83 cm^?1 (at 80°K). The 44.5 and 83 cm^?1 modes become the degenerate, soft zone-boundary modes of the paraelectric phase while the 51.5 cm^?1 mode changes to B₂ symmetry. The two lowest frequency lines are the same as those observed previously in i.r. absorption.     

ESR study of vanadyl ion in tripotassium citrate

ESR spectra of VO²⁺ doped tripotassium citrate are recorded at room temperature. The observed spectra are fitted to a spin Hamiltonian of orthorhombic symmetry with g_x = 2.001 ± 0.001, g_y = 1.997 ± 0.001, g_z = 1.945 ± 0.001, A_x = (49.0 ± 1) × 10⁻⁴ cm⁻¹, A_y = (66.8 ± 1) × 10⁻⁴ cm⁻¹ and A_z = (168.4 ± 1) × 10⁻⁴ cm⁻¹. The covalency and Fermi contact terms are evaluated and compared with those of other lattices.