Infrared reflectance of single crystal tetragonal GeO2

The transverse and longitudinal optical phonon frequencies of tetragonal GeO₂ have been determined by standard i.r. reflectance measurements employing classical dispersion theory to fit the experimental data. The static and high-frequency dielectric constants, as derived from the data, are also presented.     

59Co NMR study of NdCo2, GdCo2, TbCo2 and HoCo2

We have observed the ⁵⁹Co spectra of the Laves phase Co compounds with Nd, Gd, Tb and Ho. We observe a spectrum consisting of a pair of lines for Nd, Tb and Ho compounds, because the Co sites are magnetically inequivalent in the presence of dipolar or pseudodipolar fields. For the heavy rare earth compounds, the magnitude of this splitting is comparable to the dipolar splitting produced by the neighboring spins, but for Nd it is much larger. The Nd compound is also anomalous in that the average hyperfine field is only 37.2 kOe while for the 3 heavy rare earth compounds it is about 60 kOe. The magnitude of the hyperfine field is discussed in terms of a simple model relating it to the cobalt moment and the rare earth spin.     

Influence of ZrO2 in HfO2 on reflectance of HfO2/SiO2 multilayer at 248 nm prepared by electron-beam evaporation

Influence of ZrO₂ in HfO₂ on the reflectance of HfO₂/SiO₂ multilayer at 248 nm was investigated. Two kinds of HfO₂ with different ZrO₂ content were chosen as high refractive index material and the same kind of SiO₂ as low refractive index material to prepare the mirrors by electron-beam evaporation. The impurities in two kinds of HfO₂ starting coating materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum (GDMS) technology and secondary ion mass spectrometry (SIMS) equipment, respectively. It showed that between the two kinds of HfO₂, either the bulk materials or their corresponding films, the difference of ZrO₂ was much larger than that of the other impurities such as Ti and Fe. It is the Zr element that affects the property of thin films. Both in theoretical and in experimental, the mirror prepared with the HfO₂ starting material containing more Zr content has a lower reflectance. Because the extinction coefficient of zirconia is relatively high in UV region, it can be treated as one kind of absorbing defects to influence the optical property of the mirrors.     

Neutron diffraction study of magnetic ordering in PrCu2Si2, PrCu2Ge2, PrFe2Ge2 and NdFe2Ge2

A neutron diffraction study of polycrystalline PrCu₂Si₂ [1], PrCu₂Ge₂ [2], PrFe₂Ge₂ [3] and NdFe₂Ge₂ [4] intermetallics carried out at liquid helium temperature shows the presence of a collinear antiferromagnetic order below T_N = 19 ± 1 K [1], T_N = 16 ± 1 K [2], T_N = 9 ± 1 K [3] and 13 ± 1 K [4]. Magnetic moment, parallel to the c-axis is localized on RE ions only. The magnetic structure of these compounds consists of ferromagnetic layers perpendicular to the c-axis coupled antiferromagnetically with sequence +-+- for PrCu₂Si₂ and PrCu₂Ge₂ and +--+ for PrFe₂Ge₂ and NdFe₂Ge₂. The RE moments amount close to the free ion values for Fe containing compounds but are smaller in those containing Cu suggesting a fairly strong influence of crystal field.     

Neutron diffraction study of magnetic ordering in ErMn2Si2, ErMn2Ge2 and ErFe2Si2

Neutron diffraction study of polycrystalline compounds ErMn₂Si₂, ErMn₂Ge₂ and ErFe₂Si₂ was performed in the temperature range between 1.8 and 293 K. All compounds have tetragonal, ThCr₂Si₂-type crystal structure. The antiferromagnetic collinear structure of ErMn₂Si₂ and ErMn₂Ge₂ at both RT and LNT, consists of a sequence + - + - of ferromagnetic layers of Mn atoms. The magnetic moment of an Mn atom (≈2μ_B) is parallel to the c-axist. At low temperatures (LHT and lower), the ferromagnetic ordering within the Er sublattice is observed. The magnetic moment (μ_Er ≈ 9μ_B) is perpendicular to the c-axis. From the temperature dependence of the intensities of the magnetic peaks, the following values for the Curie temperatures were obtained: (10±5) K for ErMn₂Si₂ and (8.5±3) K for ErMn₂Ge₂. For ErFe₂Si₂ a collinear antiferromagnetic structure of the + - - + type was found, the magnetic unit cell consisting of the chemical one, doubled along the c-axis.     

Far ultraviolet reflectance spectra of CeF3, PrF3 and NdF3

Near-normal incidence reflectance measurements are carried out on thin films of CeF₃, PrF₃ and NdF₃ in the energy range of 6–40 eV. Tentative interpretations are given for different observed structures.     

First-principle study of native defects in CuScO2 and CuYO2

This paper studies the electronic structure and native defects in transparent conducting oxides CuScO2 and CuYO2 using the first-principle calculations. Some typical native copper-related and oxygen-related defects, such as vacancy, interstitials, and antisites in their relevant charge state are considered. The results of calculation show that, CuMO2（M = Sc, Y） is impossible to show n-type conductivity ability. It finds that copper vacancy and oxygen interstitial have relatively low formation energy and they are the relevant defects in CuScO2 and CuYO2. Copper vacancy is the most efficient acceptor, and under O-rich condition oxygen antisite also becomes important acceptor and plays an important role in p-type conductivity.     

Anisotropic optical reflectance of Hg2.91SbF6

The optical reflectivity of Hg_2.91SbF₆ single crystals was measured in the visible and near infrared regions with light polarized parallel and perpendicular to the mercury chains. The results for the parallel polarization were fitted to a dielectric model consisting of a Drude term and two Lorentzian functions describing peaks in the visible. The spectrum for the perpendicular polarization had a reflectance peak in the visible and a small, relatively constant reflectance in the infrared. The results show that Hg_2.91SbF₆ is an anisotropic metallic conductor.     

First-principle study of extrinsic defects in CuScO2 and CuYO2

Using first-principles methods, we studied the extrinsic defects doping in transparent conducting oxides CuMO₂ (MSc, Y). We chose Be, Mg, Ca, Si, Ge, Sn as extrinsic defects to substitute for M and Cu atoms. By systematically calculating the impurity formation energy and transition energy level, we find that BeCu is the most prominent extrinsic donor and CaM is the prominent extrinsic acceptor. In addition, we find that Mg atom substituting for Sc is the most prominent extrinsic acceptor in CuScO₂. Our calculation results are expected to be a guide for preparing n-type and p-type materials through extrinsic doping in CuMO₂ (MSc,Y).     

The polarized reflectance spectrum of a novel organic conductor (BEDT-TTF)2ClO4(C2H3Cl3)0.5

The polarized reflectance spectrum of a novel organic conductor, (BEDT-TTF)₂ClO₄(C₂H₃Cl₃)_0.5 was measured at room temperature over the spectral region from 340 cm^-1 to 25000 cm^-1. The reflectance spectrum provided an evidence for the anisotropic two-dimensional character of this material. The optical conductivity spectrum exhibits the existence of an optical band gap of about 0.2 eV, suggesting that this material is a semimetal rather than a metal.     

Theoretical study of stereodynamics for the N+H2/D2/T2 reactions

The effects of isotopic variants on stereodynamic properties for the title reactions have been investigated using a quasi-classical trajectory method based on the first excited state NH2（I^2A＇） potential energy surface [Li Y Q and Varandas A J C 2010 J. Phys. Chem. A 114 9644]. The forward–backward symmetry scattering of the differential cross section can be observed, which demonstrates that all these reactions follow the insertion mechanism. Three angle distribution functions P（θr）, P（φr）, and P（θr, φr） with different collision energies and target molecules H2/D2/T2 are calculated. It is shown that the product rotational angular momentum is not only aligned, but also oriented along the direction perpendicular to the scattering plane. The title reaction is mainly governed by the ＂in-plane＂ mechanism through the calculated distribution function P（θr, φr）. The observable influences on the rotational polarization of the product by the isotopic substitution of H/D/T can be demonstrated.     

Wing profile measurements of the Na-doublet lines in C2H2/O2/N2, H2/O2/N2 and H2/O2/Ar frames at 1 atm

Fluorescence-excitation (wing) profiles of the Na-D doublet lines were measured over a wavelength range extending from 0.3 to 200 Å from the line center for the red D₁ and blue D₂ wings and from 0.3 to 3 Å for the red D₂ and the blue D₁ wings, respectively. The line profiles were determined with the aid of a tunable CW dye-laser as a background source by measuring the total fluorescence intensity observed on detuning the laser wavelength. The flames were premixed, laminar, shielded flames at 1 atm, with temperatures ranging from 1860 to 2270 K; N₂ and Ar served as diluent gases. The line core and near-wing profiles (i.e. the region covering 0.3<Δλ<7 Å for the outer wings and 0.3<Δλ<3 Å for the inner ones) in all of the flames studied appeared to have the same frequency dependence, regardless of the nature and concentrations of the gases used. The blue D₂-line profile followed an unexpected (-2.2) law, while the other three profiles obeyed the theoretically expected (-2) law (the dispersion profile function). The line profile in the Δλ range between the impact and quasistatic regions was found to depend on the main perturbers involved. We found that the far blue D₂- and red D₁-wings in the Ar-diluted H₂/O₂ flame obeyed the (-$\text{5}\text{4}$) and (-$\text{3}\text{2}$) laws, respectively, as predicted by the quasi-static theory for the Lennard-Jones interaction. For the N₂-diluted C₂H₂/O₂ and H₂/O₂ flames, we did not find these wing dependences in the Δλ range investigated.     

First-principles study on the electronic structure and optical properties of T12Cd2（SO4）3 and Rb2Cd2（SO4）3

With the help of ab initio full-potential linearized augmented plane wave （FPLAPW） method, calculating the electronic structure and linear optical properties is carried out for XCd2（SO4）3 （X =Tl, Rb）. The results show that Tl2Cd2（SO4）3 （TlCdS） has a larger band gap than Rb2Cd2（SO4）3 （RbCdS） and the energy bands for RbCdS are more dispersive than those of TlCdS. From their partial densities of states （PDOS）, we have observed that the hybridization between S ionic 2p and O atomic 2p orbitals forms SO4 ionic groups. The remarkable difference between RbCdS and TlCdS is, however, the degree of hybridization between cation （Tl and Rb） and its surrounding oxygen atoms. In the view of quantum chemistry, the strong p-d hybridization indicates the existence of their cation ionic bonds （Cd-O, Rb-O, and Tl-O）. The calculations of TlCdS and RbCdS show their optical properties to be less anisotropic. Their anisotropies in the optical properties mainly occur in a low photon energy region of 5-16 eV.     

X-ray absorption spectroscopic study of mixed valence systems EuCu2Si2, YbCu2Si2 and Sm4Bi3

X-ray absorption spectroscopy technique is employed to determine the valence of the rare earth ions in EuCu₂Si₂, YbCu₂Si₂ and Sm₄Bi₃. In each case, two absorption peaks corresponding to two different valence states of respective rare earth ions have been observed. Low temperature (77 K) study of EuCu₂Si₂ indicates distinct change in the relative intensities of the absorption peaks compared to those registered at room temperature (300 K). It is inferred from the change in the relative intensities that the population of Eu²⁺ in EuCu₂Si₂ decreases at liquid nitrogen temperature compared to Eu³⁺. Conclusions drawn from these results agree well with those reported by others using different experimental techniques. In Sm₄Bi₃, Sm²⁺ and Sm³⁺ are found to occur in the ratio of 3:1.     

Polarized reflectance spectrum of β-(BEDT-TTF)2PF6

The polarized reflectance spectrum of β-(BEDT-TTF)₂PF₆ was measured over the spectral range from 720 cm^?1 to 25, 000 cm^?1 at 293 K (semiconductive phase) and at 318 K (metallic phase). The infrared band found in the conductivity spectrum, which was obtained by the Kramers-Kronig transformation of the reflectance data, is interpreted as the one associated with inter-band transition.     

Neutron diffraction study of DyCu2Ge2

The DyCu₂Ge₂ compound was studied by neutron diffraction on the Grenoble Nuclear Research Center multicounter system. The compound is isostructural to the rare earth RCu₂Ge₂ compounds with space group I4/mmm. 19 superlattice lines were observed in the 3 K pattern which are consistent with a doubling of the unit cell in the a and c directions. The moment value is 8 μ_B making an angle of 30° with a and 70° with c axis. The structure consists of ferromagnetic (1 0 1) layers with antiferromagnetic coupling between them. The Néel and Curie paramagnetic temperature of this compound is 8 K and ? 15 K respectively.     

Single crystal RuO2/Ti and RuO2/TiO2 interface: LEED, Auger and XPS study

The interactions at the evolving RuO₂/titanium interface have been studied by LEED, AES and XPS. Titanium films of up to 5 monolayers were evaporated onto well ordered and ion sputtered ruthenium dioxide crystal surfaces of (110) and (100) orientation. Stabilization of the surface oxygen content under thermal treatment in UHV (up to 600°C) with increasing titanium coverage was established. After extended (up to 4 h) annealing in O₂ at 600°C an epitaxial ordering of TiO₂ on RuO₂(110) was observed. The (1 × 1) LEED patterns from the epitaxial layer exhibit a reduced background level when compared to the RuO₂ substrate itself. These findings are correlated with the XPS data and are interpreted in connection with the disappearance of the defect RuO₂ phase in the surface layer of the RuO₂. The appearance of the (1 × 2) surface reconstruction at the RuO₂(100)/Ti interface is discussed in the context of maximum cation coordination by oxygen atoms.     

正磷酸盐晶体Ba3(PO4)2和Sr3(PO4)2高温拉曼光谱研究

测量了碱土金属正磷酸盐Ba₃(PO₄)₂和Sr₃(PO₄)₂常温及高温拉曼光谱, 对拉曼振动模式进行指认, 并分析了晶体拉曼振动光谱及晶体结构在高温下的变化. 在温度升高的过程中, 拉曼振动频率向低频移动且振动峰宽度展宽, 晶体中的P-O平均键长随温度升高而变长, 但O-P-O的键角并未发生变化. 晶体在900 ℃以下无结构相变发生. 关键词： 3(PO₄)₂和Sr₃(PO₄)₂')" href="#">Ba₃(PO₄)₂和Sr₃(PO₄)₂ 高温拉曼光谱 振动模式 高温结构     

A theoretical study of photoelectron spectra of NbO2, MoO2 and RuO2 by cluster models

DV-Xα calculations have been applied to various small clusters of rutile-family dioxides (NbO₂, MoO₂ RuO₂). It appears that by taking into consideration the potential due to the atomic charges, the density, the ionization cross sections of the energy levels, and by summing the density of states (DOS) of the two different clusters representing surface structures, computations on even small clusters provide information which compares well with the experimental XPS spectra.     

Photoemission study of the Laves-phase compounds YMn2 and Y0.97Sc0.03Mn2

A small amount of Sc substitution for Y in the antiferromagnetic metal YMn₂ results in a paramagnetic metal with a strongly enhanced electronic specific heat. We have studied the electronic structure of YMn₂ and Y_0.97Sc_0.03Mn₂ by photoemission spectroscopy. The spectra of YMn₂ taken above and below the Néel temperature did not show appreciable difference, and the spectra of YMn₂ and Y_0.97Sc_0.03Mn₂ were similar to each other. The photoemission spectra of the antiferromagnetic phase are well explained by band-structure calculation on the antiferromagnetic state while those of the paramagnetic phase are not explained by band-structure calculation on the paramagnetic state. These observations suggest that there are strong antiferromagnetic correlations in the paramagnetic phase. For the paramagnetic phase, agreement between experiment and calculation could be considerably improved by applying a model self-energy correction to the band density of states.