Crystal growth and the electronic structure of Tl3PbCl5

Total and partial densities of states of constituent atoms of two tetragonal phases of Tl₃PbCl₅ (space groups P4₁2₁2 and P4₁) have been calculated using the full potential linearized augmented plane wave (FP-LAPW) method and Korringa-Kohn-Rostoker method within coherent potential approximation (KKR-CPA). The results obtained reveal the similarity of occupations of the valence band and the conduction band in the both tetragonal phases of Tl₃PbCl₅. The FP-LAPW and KKR-CPA data indicate that the valence band of Tl₃PbCl₅ is dominated by contributions of the Cl 3p-like states, which contribute mainly to the top and the central portion of the valence band with also significant contributions throughout the whole valence-band region. Further, the bottom of the valence band of Tl₃PbCl₅ is composed mainly of the Tl 6s-like states, while the bottom of the conduction band is dominated by contributions of the empty Pb 6p-like states. The KKR-CPA results allow to assume that the width of the valence band increases somewhat while band gap, E_g, decreases when changing the crystal structure from P4₁2₁2 to P4₁. The X-ray photoelectron core-level and valence-band spectra for pristine and Ar⁺-ion-irradiated surfaces of a Tl₃PbCl₅ monocrystal grown by the Bridgman-Stockbarger method have been measured.     

Site-specific valence-band X-ray photoelectron spectra of a SrTiO3 single-crystal by X-ray standing wave technique

Site-specific valence-band X-ray photoelectron spectra of SrTiO₃ (111) were successfully obtained by using X-ray standing wave technique. Contributions of the Ti and SrO₃ derived states to the valence-band spectra were clearly separated. The spectra provided not only site-specific but also bulk-sensitive information on the SrTiO₃ crystal because of the use of a high-energy synchrotron X-ray source (hν=4750 eV) for photoelectron excitation with the large escape depth. The electronic structures calculated by the DV-Xα method using a (Sr₈Ti₂₇O₁₀₈)⁹²⁻ cluster model well reproduced the observed structures in the valence-band spectra. The partial density of states of both Ti and Sr ions in SrTiO₃ were mainly distributed over the bottom of the valence-band to produce the covalent bonding with O ions.     

First-principles FP-LAPW calculations and X-ray spectroscopy studies of the electronic structure of Zr3V3O and Zr3V3O0.6 oxides

Electronic properties of Zr₃V₃O oxide, a very promising hydrogen-storage material, were studied both from theoretical and experimental points of view employing the full potential linearized augmented plane wave (FP-LAPW) method as well as X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). Total and partial densities of states of the constituting atoms of Zr₃V₃O have been derived from the FP-LAPW calculations. These data indicate that, the O 2p-like states are the dominant contributors in the bottom of the valence band, whilst the top of the valence band and the bottom of the conduction band of Zr₃V₃O are dominated by contributions of the V2 3d-like states, with slightly smaller contributions of the V1 3d-like states as well. Significant contributions of the Zr 4d-like states throughout the whole valence-band region and near the bottom of the conduction band are also characteristic of the electronic structure of Zr₃V₃O. The XPS valence-band spectra and the XES Zr Lβ_2,15, V L_α and O K_α bands have been derived and compared on a common energy scale for Zr₃V₃O and Zr₃V₃O_0.6 oxides. This comparison of the experimental spectra was found to be in excellent agreement with the results of the FP-LAPW calculations. In addition, the XPS Zr 3d, V 2p and O 1s core-level binding energies have been measured for Zr₃V₃O and Zr₃V₃O_0.6 oxides.     

Analysis of the ν2 and ν4 infrared bands of CD4

The infrared spectrum of totally deuterated methane CD₄ has been recorded between 930 cm^?1 and 1180 cm^?1 under high resolution (0.003 cm^?1). The ν₂ and ν₄ bands of ¹²CD₄ have been reanalyzed on the basis of a complete third-order Hamiltonian including all the coupling terms linking the upper states of the two bands. A set of only 16 self-consistent parameters have been adjusted to fit more than 1650 assigned transitions reaching a maximum upper state J value of 20. The obtained standard deviation is 0.0041 cm^?1. In addition, 171 lines of the ν₄ band of ¹³CD₄ have been assigned. They have been analyzed, in the same dyad scheme, by adjusting 7 parameters of the ν₄ band together with the main ζ₂₄ Coriolis parameter. The obtained standard deviation is only 0.0012 cm^?1.     

Luminescence study of the 4f5d configuration of Nd in LiYF4, LiLuF4 and BaY2F8 crystals

Ultraviolet fluorescence of Nd³⁺ ions induced by triphotonic excitation process was studied in Nd-doped LiYF₄, LiLuF₄ and BaY₂F₈ crystals using a technique of time-resolved spectroscopy. The observed ultraviolet luminescence was due to transitions between the bottom of 4f²5d configuration and 4f³ states of Nd³⁺ ions. Narrow emission lines superposed to the broadband emissions were observed. A detailed analysis of luminescence spectrum revealed that the narrow emissions are due to parity and spin allowed radiative transitions from the Stark levels of ⁴K_11/2(5d) state created by the electrostatic interaction between the 5d electron and the two electrons of the 4f² configuration. The narrow emissions are related to the high spin state (S=3/2) which gives f-f characteristics to the f-d broadband emissions. The narrow emissions superposed to the wide emission correspond to 18%, 34% and 43% of the integrated broadband emission at 262 nm observed in LiYF₄, LiLuF₄ and BaY₂F₈ crystals, respectively. Although the 5d-4f² interaction is observed to be weaker than 5d-crystal field interaction, it is stronger enough to select only the radiative transitions from 4f²5d configuration to 4f³ states that preserves the total spin S=3/2.     

Band bending and band alignment at HfO2/HfSixOy/Si interfaces

Band bending and band alignment at HfO₂/SiO₂/Si and HfO₂/Hf/SiO₂/Si interfaces were investigated using X-ray photoelectron spectroscopy. After Hf-metal pre-deposition, a 0.55 eV band bending in Si and a 1.80 eV binding energy decrease for Hf 4f and O 1s of HfO₂ were observed. This was attributed to the introduction of negative space charges at interface by Hf pre-deposition. Band bending decrease and synchronous binding energy increases of O 1s and Hf 4f for HfO₂ were observed during initial Ar⁺ sputtering of the Hf pre-deposited sample. This was interpreted through the neutralization of negative space charges by sputtering-induced oxygen vacancies.     

The CC stretching band ν6 of allene-d4

The infrared spectrum of C₃D₄ was measured in the region of the paralled band of the CC stretching vibration ν₆ centered at ν₀ = 1920.2332 cm^?1 on a high-resolution Fourier transform spectrometer and deconvolved to a linewidth of $\text{～}\text{1}\text{2}$ of the Doppler width (～0.0023 cm^?1). The high resolution reveals the presence of strong perturbations in the K = 4 and K = 8 to 12 levels of the ν₆ upper state. For a quantitative treatment of the observed transitions, a Hamiltonian matrix including six different perturbing states was constructed and used to refine the 6 spectroscopic constants of the ν₆ state and 20 of the constants for the perturbing states. Measurement of the hot band ν₆ + ν₁₁ ? ν₁₁ whose band center is at 1916.200 cm^?1 yielded the anharmonic constant x_6,11 = ?4.033 cm^?1.     

Nature of optical properties of GdFe3(BO3)4 and GdFe2.1Ga0.9(BO3)4 crystals and other 3d5 antiferromagnets

Influence of the partial substitution of paramagnetic Fe³⁺ ions by diamagnetic Ga³⁺ ions in the trigonal crystal GdFe₃ (BO₃)₄ on its optical and magnetic properties is studied and discussed in connection with problems common for all antiferromagnets containing 3d ⁵ ions. Polarized optical absorption spectra and linear birefringence of GdFe₃ (BO₃)₄ and GdFe_2.1Ga_0.9 (BO₃)₄ single crystals have been measured in the temperature range 85–293 K. Specific heat temperature dependence (2–300 K) and structure of GdFe_2.1Ga_0.9 (BO₃)₄ crystal have been also studied. As a result of substitution of 30% Fe to Ga the Neel temperature diminishes from 38 till 16 K, the strong absorption band edge shifts on 860 cm^-1 (0.11 eV) to higher energy and the d-d transitions intensity decreases substantially larger than the Fe concentration does. Strong absorption band edge is shown to be due to Mott-Hubbard transitions. Correlation between position of the strong absorption band edge and the Neel temperature of antiferromagnets has been revealed. Properties of the doubly forbidden d-d transitions in the studied crystals and in other antiferromagnets are explained within the framework of the model of the exchange-vibronic pair absorption, which is theoretically analyzed in detail. The model permitted us to determine the connection between parameters of d-d absorption bands (intensity, width and their temperature dependences), on the one hand, and the exchange, spin-orbit and electron-lattice interactions, on the other hand.     

Extended assignment and analysis of the ν2 and ν4 infrared bands of 12CH4

Infrared spectra of the ν₂ and ν₄ bands of ¹²CH₄ have been assigned up to J′ = 20 in the ν₄ band and J′ = 17 in the ν₂ band. Assignments are presented for over 1000 transitions ranging from 1123 to 1712 cm^?1, which involve 652 upper-state energy levels of the two bands. The 652 upper-state levels have been fitted with a weighted standard deviation of 0.0026 cm^?1, almost all levels being reproduced to within their experimental error, by a Hamiltonian for the coupled upper states containing 28 refining parameters and 4 fixed parameters. Calculated relative intensities are also tabulated and discussed in relation to recent experimental intensity measurements.     

Spectral intensities in the ν3 bands of 12CH4 and 13CH4

Relative and absolute line intensities for the ν₃ bands of the ¹²C and ¹³C isotopic varieties of methane have been measured using a tunable difference-frequency laser spectrometer. From these data the integrated band strength of ¹³CH₄ is calculated to be 0.983 ± 0.007 that of ¹²CH₄, with the uncertainty representing three standard deviations. The absolute ν₃ bandstrength for ¹²CH₄ is 266.1 ± 3.0 cm^?2 atm ^?1 at 294.7 K where the errors are dominated by the pressure measurement. This band strength corresponds to an effective transition moment 〈μ₃〉 = 0.0534(3)D for ¹²CH₄ from which the ν₄ band dipole moment and the Herman-Wallis F factor can be estimated using a recent force field model for methane.     

Inelastic light scattering and photoluminescence in the mixed valence systems Eu3O4, Eu3S4 and Sm3S4

The thermally activated valence fluctuations of Eu₃S₄ and Sm₃S₄ have been studied using light scattering and photoluminescence techniques and are compared with measurements on the non-fluctuating compound Eu₃O₄, Eu₃S₄ exhibits an anomalous vibrational mode which is associated with the frequency factor of hopping, ν₂=1.3×10¹³ sec^?1. In Sm₃S₄ electronic Raman scattering is observed within the ⁷F₉ multiplet of the Sm²⁺ ion. An anomalous frequency shift of the5d-4f photoluminescence emission band in Eu₃S₄ is related to the temperature dependent fluctuation rate which passes through the reference time scale of the photoluminescence. Intra-4f photoluminescence has also been observed in Eu₃S₄ and Sm₃S₄.     

Electronic structure of TiH2

The electronic structure of TiH₂ has been studied using the augmented-plane-wave method and the LCAO interpolation. The density of states and its orbital components show that the conduction band is Ti d-like and that the valence band is largely derived from the hydrogen orbitals with small Ti 3d hybridization. The electronic charges on the hydrogen atom are ～ 1.5 as compared to 1.6–1.7 of the rare-earth metal hydrides.     

Electronic structure of non-centrosymmetric AgCd2GaS4 and AgCd2GaSe4 single crystals

X-ray photoelectron core-level and valence-band spectra for pristine and Ar⁺-ion irradiated (0 0 1) surfaces of AgCd₂GaS₄ and AgCd₂GaSe₄ single crystals grown, respectively, by the Bridgman method and the method of direct crystallization have been measured in the present work. The X-ray photoelectron spectroscopy (XPS) results reveal high chemical stability of (0 0 1) surfaces of AgCd₂GaS₄ and AgCd₂GaSe₄ single crystals. Electronic structure of AgCd₂GaS₄ has been calculated employing the full potential linearized augmented plane wave method. For the AgCd₂GaS₄ compound, the X-ray emission bands representing the energy distribution of the valence Ag d-, Cd d-, Ga p- and S p-like states were recorded and compared on a common energy scale with the XPS valence-band spectrum. The theoretical and experimental data regarding the occupation of the valence band of AgCd₂GaS₄ were found to be in excellent agreement to each other. Second harmonic generation (SHG) efficiency of AgCd₂GaS₄ by using the 320 ns CO laser at 5.5 μm has been recorded within the temperature range 80–300 K. Substantial increase of the photoinduced SHG which in turn is substantially dependent on the temperature has been detected for the AgCd₂GaS₄ compound.     

ESR study of the ferrimagnetic spinel selenide CuCr2Se4

Ferrimagnetic spinel selenide CuCr₂Se₄ has been investigated by the electron spin resonance (ESR) spectroscopy. Experimental results reveal that ESR signals originate from the localized d-shell electrons of Cr³⁺ ions. In addition, the ESR linewidth ΔH _PP increases linearly with decreasing temperature. It is suggested that the spin-orbit coupling may be one of the contributions to the broadening of ΔH _PP . Our ESR results support the model of the ferrimagnetic hybridization between localized 3d ³ electrons of Cr³⁺ with delocalized holes of Se 4p band.     

Electronic structures of MRhO2, MRh2O4, RhMO4 and Rh2MO6 on the basis of X-ray spectroscopy and ESCA data

X-ray O Kα, Rh Mγ and a series of M Lα emission spectra, ESCA spectra of the valence and inner levels, and O K and Rh M_III quantum-yield spectra for X-ray photoemission of the rhodium double oxides MRhO₂ (M = Li, Na, K), MRh₂ O₄ (M = Be, Mg, Ca, Sr, Ba, Co, Ni, Cu, Zn, Cd, Pb), RhMO₄ (M = V, Nb, Ta) and Rh₂MO₆ (M = Mo, W) have been measured and the dependence of electronic structure on the metal M analysed. For all compounds the inner part of the valence band corresponds to O 2p_σ + O 2p_π + Rh 4d states, while the outer part corresponds to Rh 4d. The valence band is separated from the conduction band by a narrow gap of width less than 1 eV. The first empty band, near the bottom of the conduction band, is formed by Rh 4d states, followed by a band due to vacant O 2p states.     

First principles study of the electron structures of CaCu3Mn4O12 and CaCu3Ti4O12

The electronic structures of CaCu₃Mn₄O₁₂ and CaCu₃Ti₄O₁₂ are investigated from HF SCF LCAO calculation. In CaCu₃Mn₄O_12, the band and the density of states show a spin asymmetric ferrimagnetic character with a small energy gap. The Mn spin is anti-aligned with the Cu spin, and the total spin moment is 9 μ_B. Our calculation correctly reproduces the observed antiferromagnetic insulating character of CaCu₃Ti₄O₁₂. The gap in the band structure, which is 2.15 eV, reasonably agrees with the experimental value 1.5 eV. The electron density populations at different planes show clearly that the electron density has symmetric character. A tilted Mn(Ti) orbital implies a typical tilted three-dimensional network of MnO₆ (TiO₆) octahedra due to doping of the Jahn–Teller ion Cu. There is no covalency between Ca, Cu and Mn(Ti) atoms. In contrast, there are stronger bonds and somewhat likely covalency between Cu and O atoms, and also between Mn(Ti) and O atoms.     

The ν2 + ν4 and 2ν2 isotropic Raman bands of 12CH4

The purely isotropic Raman spectrum of the ν₁ band, the ν₂ + ν₄ band (enhanced through interaction with ν₁), and the 2ν₂ band of ¹²CH₄ was obtained with a spectral resolution of 0.30–0.35 cm^?1 from exposures with different orientations of the linearly polarized exciting light. The ν₂ + ν₄ and 2ν₂ bands show partially resolved rotational structure. The spectra are interpreted in terms of a model which takes explicitly into account vibrational and rovibrational interactions with other vibrational states, using molecular constants determined primarily from infrared spectra. The computed contours are in excellent agreement with the experimental ones and the observed and calculated peak wavenumbers agree within one tenth of the spectral resolution limit, except for a small region near the ν₁ band. The good overall agreement represents an independent check on the overall correctness of the previously reported molecular constants. A detailed discussion is given of the contributions to the intensities of individual transitions from the three transition moment matrix elements, which in an isolated-band model are the intensity parameters of the ν₁, 2ν₄, and 2ν₂ isotropic bands, respectively.     

The high-resolution infrared spectrum of the ν11 band of allene-d4

The infrared band ν₁₁ around 300 cm^?1 of allene-d₄ has been studied at a resolution of 0.010 cm^?1. The J structure in the central Q branches of this perpendicular band was resolved and P- and R-lines were assigned to subbands with {K″} ≦ 18. A ground-state analysis resulted in B₀ = 0.232187(30) cm^?1, D₀^J = 6.3(1.0) × 10^?8cm^?1, and D₀^JK = 3.0(4) × 10^?6cm^?1. Upper-state constants including η₁₁^J and η₁₁^K were derived. Special attention was paid to the study of l-type doublings. Doublets due to q^(?)-doubling were resolved and accordingly the value q₁₁^(?) = ?0.000160(3) cm^?1 was derived. The more usual q⁽⁺⁾-doubling was also observed, and the result q₁₁⁽⁺⁾ = 0.000144(4) cm^?1 was obtained.     

Laser Stark spectroscopy of thioformaldehyde in the 10-μm region: The ν3, ν4, and the ν6 fundamentals

The ν₃, ν₄, and ν₆ bands of thioformaldehyde, H₂CS, have been studied using the technique of laser Stark spectroscopy. The H₂CS was produced by the pyrolysis of dimethyl disulfide, and the spectrum was observed using a multipass absorption cell. The band origins are ν₃, 1059.2037 cm^?1; ν₄, 990.1866 cm^?1; and ν₆, 991.0149 cm^?1. The band previously assigned as 2ν₆ has been reassigned as 2ν₂, leading to a value of the ν₂ band origin of ca. 1439 cm^?1. Rotational constants and dipole moments of the vibrational states have been determined.     

β-C3N4,β-Si3N4和β-Ge3N4的能带结构

采用基于密度泛函理论的线性丸盒轨道原子球近似(LMTO-ASA)从头计算方法,研究了β-C₃N₄,β-Si₃N₄和β-Ge₃N₄的能带结构,得到了它们的能隙分别为:4.1751,5.1788和4.0279eV。对于β-C₃N₄,由于N的部分2p电子占据了非键轨道,禁带宽度较窄;对于β-Si₃N_{4关键词：}