X-ray study of phase transitions in the system of solid solutions K2Pb4Nb10O30-Na2Pb4Nb10O30-K6W4Nb6O30

Boundaries of morphotropic phase transitions region in the system of solid solutions K₂Pb₄Nb₁₀O₃₀-Na₂Pb₄Nb₁₀O₃₀-K₆W₄Nb₆O₃₀ with the structure of the tetragonal tungsten bronze have been specified. Presence of the second morphotropic phase transition, perpendicular to the first one has been revealed. The temperature dependences of the structural parameters of some compounds have been investigated. The compounds with high values of Curie temperatures and working temperatures have been obtained.     

High-resolution infrared spectrum of the ν3 and ν2 + ν3 − ν2 bands of 14N16O2

The infrared absorption spectrum of the ν₃ band of ¹⁴NO₂ has been recorded with a resolution and a frequency accuracy much improved over the previous investigations. The K- and N-line assignments have been greatly extended and a more accurate set of spectroscopic constants derived. Several lines in the subbands with K_a ≥ 3 have been observed to be doubled by spin-rotation interaction and spin-rotation interaction constants have been obtained. Several weak series of lines in the spectrum (K_a = 0, 1, 2, and 3) have been unambiguously assigned to the “hot band” ν₂ + ν₃ ? ν₂. Lines of the K_a = 3, 4, 5, and 6 sub-bands of ν₃ have been found to be perturbed by a Coriolis interaction with the K_a = 4, 5, 6, and 7 levels of 2ν₂.     

Preparation and characterization of co-doped (Ce0.80La0.15Al0.05O1.90) and multiple-doped (Ce0.80Sm0.10Gd0.05Al0.05O1.90 and Ce0.80Gd0.10Sm0.05Al0.05O1.90) ceria

Attempts have been made to synthesize a few compositions Ce_0.80La_0.15Al_0.05O_1.90, Ce_0.80Sm_0.10Gd_0.05Al_0.05O_1.90, and Ce_0.80Gd_0.10Sm_0.05Al_0.05O_1.90 by citrate–nitrate auto-combustion method. The aim of the present investigation was to study the effect of co-doping and multiple doping on the ionic conductivity of CeO₂ for its use as solid electrolyte in intermediate temperature solid oxide fuel cells. XRD patterns showed that all the samples have fluorite-type crystal structure similar to undoped ceria. Microstructures of thermally etched samples have been studied by scanning electron microscopy. Contributions of grains σ _g and grain boundaries σ _gb to the total conductivity σ _T, have been determined using impedance analysis. Impedance measurements were made in the frequency range 1 Hz–1 MHz and temperature range 250–500 °C. Our experimental results show that multiple doping is more effective than co-doping for improving the oxide ion conductivity of ceria in the materials investigated in the present study.     

Three- and two-dimensional topological insulators in Pb2Sb2Te5, Pb2Bi2Te5, and Pb2Bi2Se5 layered compounds

The electronic structure of ternary compounds Pb₂Sb₂Te₅, Pb₂Bi₂Te₅, and Pb₂Bi₂Se₅, which have a layered structure that consists of nine-layer atomic blocks separated by van der Waals gaps, has been theoretically studied. It has been shown that all studied compounds are three-dimensional topological insulators. The possibility of the existence of a two-dimensional topological insulator has been found in ultrathin (0001) Pb₂Sb₂Te₅ and Pb₂Bi₂Te₅ films. Oscillations of the ℤ₂ topological invariant with an increase in the film thickness have been observed in the latter compound.     

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.     

High-resolution diode laser spectra of the ν4 mode of 12CF3I and 13CF3I

High-resolution spectra of the ν₄ mode of ¹²CF₃I and ¹³CF₃I have been recorded using diode laser spectroscopic techniques. The sample was cooled to 163 ± 10 K to suppress the hot bands. Natural CF₃I containing 98.9% ¹²CF₃I and 1.1% ¹³CF₃I was used for recording the spectra. About 1200 lines in the P and R branches of each isotopic molecule have been assigned and used in the least-squares fit. The pseudoparallel structure of the bands has been understood and accurate values of rotational constants have been obtained.     

Laser Stark spectroscopy of the ν4 band of CH3C15N: Fermi resonance with 3ν83

Laser Stark spectra for the ν₄ band of CH₃C¹⁵N have been measured by using CO₂ and N₂O lasers. Almost 650 resonances have been assigned to about 140 ro-vibrational transitions with J′ ≤ 34 and K ≤ 11. An anomaly of the rotational structure around K = 7 has been proved to be due to a Fermi interaction by analyzing each K subband separately. Observed data have been fitted to a model which includes ν₄-3ν₈³ Fermi coupling by the method of least squares. The standard deviation of observed from calculated frequencies is 4.6 MHz. Molecular constants derived are also listed.     

Electromodulation spectroscopy of In0.53Ga0.47As/In0.53Ga0.23Al0.24As quantum wells

In_0.53Ga_0.47As/In_0.53Ga_0.23Al_0.24As quantum wells (QWs) of various widths have been grown by molecular beam epitaxy on the InP substrate and investigated by electromodulation spectroscopy, i.e. photoreflectance (PR) and contactless electroreflectance (CER). The optical transitions related to the QW barrier and the QW ground and excited states have been clearly observed in PR and CER spectra. The experimental QW transition energies have been compared with theoretical predictions based on an effective mass formalism model. A good agreement between experimental data and theoretical calculations has been observed when the conduction band offset for the In_0.53Ga_0.47As/In_0.53Ga_0.23Al_0.24As interface equals 60%. In addition, it has been concluded that the conduction band offset for the In_0.53Ga_0.23Al_0.24As/InP interface is close to zero. The obtained results show that InGa(Al)As alloys are very promising materials in the band gap engineering for structures grown on InP substrate.     

Magnetic properties of Nd0.9Dy0.1Fe3(BO3)4

The magnetic properties of trigonal Nd_0.9Dy_0.1Fe₃(BO₃)₄ substituted compound with the competitive Nd-Fe and Dy-Fe exchange interactions have been investigated. It has been shown that in Nd_0.9Dy_0.1Fe₃(BO₃)₄ a spontaneous spin-reorientation transition from an ease-axis state to an easy-plane occurs near 8 K. Anomalies of the magnetization curves are observed in a spin-flop transition induced by the magnetic field B‖c. The calculations were performed using a molecular-field approximation and a crystal-field model for the rare-earth subsystem. Extensive experimental data on the magnetic properties of Nd_0.9Dy_0.1Fe₃(BO₃)₄ have been interpreted and good agreement between theory and experiment has been achieved using the obtained theoretical dependences.     

Emission features of Ho ion in Nb2O5, Ta2O5 and La2O3 mixed Li2O-ZrO2-SiO2 glasses

Li₂O-ZrO₂-SiO₂: Ho³⁺ glasses mixed with three interesting d-block elemental oxides, viz., Nb₂O₅, Ta₂O₅ and La₂O₃, were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The luminescence spectra of Nb₂O₅ and Ta₂O₅ mixed Li₂O-ZrO₂-SiO₂ glasses (free of Ho³⁺ ions) have also exhibited broad emission band in the blue region. This band is attributed to radiative recombination of self-trapped excitons (STEs) localized on substitutionally positioned octahedral Ta⁵⁺ and Nb⁵⁺ ions in the glass network. The Judd-Ofelt theory was successfully applied to characterize Ho³⁺ spectra of all the three glasses. From this theory various radiative properties, like transition probability A, branching ratio β_r and the radiative lifetime τ_r, for ⁵S₂ emission levels in the spectra of these glasses have been evaluated. The radiative lifetime for ⁵S₂ level of Ho³⁺ ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied the La₂O₃ mixed glass exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Ho³⁺ ions.     

Multicomponent GeSe2-CdI2-TeO2 (Bi2O3) systems: glass formation and properties

The glass-forming regions of the GeSe₂-CdI₂-TeO₂ (I), GeSe₂-CdI₂-Bi₂O₃ (II) and GeSe₂-TeO₂-Bi₂O₃ (III) systems have been determined. The obtained glassy phases have been characterized by their basic physicochemical parameters such as temperatures of glass transition, crystallization, and melting, density and microhardness. The phase T-X diagram of the GeSe₂-CdI₂ system, which is the basic joint line for systems I and II, has been specified. Three non-variant equilibria (two eutectic and one syntectic) have been observed at temperatures 350, 280 and 375 °C for compositions containing 15, 95 and 33.3 mol% GeSe₂, respectively. A new intermediate phase with probable composition of 2CdI₂·GeSe₂ has been formed.     

Vibrational spectra and force constants of symmetric tops: ν1, ν5, and 2ν5 of CF335Cl and CF337Cl

The gas phase infrared spectra of CF₃³⁵Cl and CF₃³⁷Cl have been recorded in the ν₁ region and 2ν₅ regions with a resolution of 0.09 cm^?1. Additionally the ν₅ fundamental of CF₃Cl, with natural isotopic abundance, has been reinvestigated with a resolution of approximately 0.36 cm^?1. Molecular constants have been evaluated from the observed spectra by means of polynomials and band contour simulation. The possibility of a Fermi resonance between ν₁ and 2ν₅ is discussed.     

The XPS and XAES spectra of Na0.88Mn0.56PS3

Na_0.88Mn_0.56PS₃compounds have been synthesized by starting from MnPS₃ polycrystalline powders by means of a two-step cation-exchange process at a higher intercalation time than the one used for producing the literature reported Na_0.62Mn_0.69PS₃ compounds. The obtained samples have been characterized by X-ray photoelectron spectroscopy (XPS). The resulting spectra of the so-synthesized compounds have been compared with those observed in Na_0.62Mn_0.69PS₃ in our previous paper and similar electronic properties have been noted. In particular by XPS it has been shown that greater sodium content affects neither the core-level binding energies of the host matrix elements nor the type of link between Na⁺ and (Mn_1−xPS₃)⁻.     

Pure rotational spectra of 32SF535Cl, 32SF537Cl,and 34SF535Cl up to 300 GHz

Pure rotational spectra of the three molecules ³²SF₅³⁵Cl, ³²SF₅³⁷Cl, and ³⁴SF₅³⁵Cl in their ground vibrational states have been observed up to 300 GHz (8 < J < 80). Molecular parameters have been computed with good accuracy for the three isotopic species. The “K-type” splitting characteristic of molecules belonging to the C_4v symmetry group has been clearly seen and measured.     

Optical spectroscopy of Ca3Sc2Si3O12, Ca3Y2Si3O12 and Ca3Lu2Si3O12 doped with Pr

The silicates Ca₃Sc₂Si₃O₁₂, Ca₃Y₂Si₃O₁₂ and Ca₃Lu₂Si₃O₁₂, both undoped and doped with Pr³⁺ ions, have been synthesized by solid-state reaction at high temperature. The luminescence spectroscopy and the excited state dynamics of the materials have been studied upon VUV and X-ray excitation using synchrotron radiation. All doped samples have shown efficient 5d-4f emission upon direct VUV excitation of 5d levels, but only Ca₃Sc₂Si₃O₁₂:Pr³⁺ shows luminescence upon interband VUV or X-ray excitation. The VUV excited emission spectra of Ca₃Y₂Si₃O₁₂:Pr³⁺ and Ca₃Lu₂Si₃O₁₂:Pr³⁺ show features attributed to emission from two distinct sites accommodating the Pr³⁺ dopant. The decay kinetics of the Pr³⁺ 5d-4f emission in Ca₃Sc₂Si₃O₁₂:Pr³⁺ upon VUV excitation across the band gap are characterized by decay times in the range 25-28 ns with no significant rise after the excitation pulse. They appear to be faster upon X-ray irradiation than for VUV excitation. Weak afterglow components are attributed to defect luminescence.     

Microwave fourier transform spectroscopy of pure rotational ν4 ↔ ν4 transitions and reanalysis of the ν2ν4 dyad of methane-d4

Pure rotational transitions of a spherical top in a degenerate vibrational state have been observed directly for the first time with the help of pulsed microwave Fourier transform (MWFT) spectroscopy. Twelve rotational transitions in the v₄ = 1 vibrational excited state of CD₄ have been identified. The theoretical basis for the transition moments has been developed and the line strengths of the rotational transitions have been estimated. The measured rotational transition frequencies have been included in a reanalysis of the data from a previously recorded high-resolution FTIR spectrum of the ν₂ and ν₄ bands. The v₄ = 1 state of CD₄ is strongly coupled to the v₂ = 1 state by Coriolis interaction. Thirty molecular parameters of the $\text{ν}{}_2\text{ν}{}_4$ dyad have been fitted finally from the combined microwave and infrared data. The microwave data are reproduced with a standard deviation of 42 kHz, and the infrared data with a standard deviation of 0.0002 cm^?1; in each case, this is close to the estimated experimental prescision.     

Photoelectron and electronic absorption spectra of SCl2, S2Cl2, S2Br2 and (CH3)2S2

Photoelectron and electronic absorption spectra of SCl₂, S₂Cl₂, S₂Br₂, and (CH₃)₂S₂ have been measured and analyzed. Quantum chemical calculations (CNDO/ 2 and MWH (Mulliken-Wolfsberg-Helmholtz) have been carried out and the electronic structures have been described in terms of molecular orbital theory. The variation in differential photoionization cross-section as a function of incident photon energy and results of MO computations are used to identify ionization bands and assign ground state MO configurations. Suggested ground state electronic structures coupled with computed virtual MO's are used to interpret the visible and near-ultraviolet electronic absorption spectra. The low energy excited states are described as molecular states followed by the initial members of Rydberg series. Calculated oscillator strengths for molecular transitions are in good agreement with those observed experimentally. Quantum defects, δ, for the Rydberg states have been calculated from the Rydberg equation using the adiabatic first ionization potential.     

Optical absorption and thermoluminescence properties of ZnF2-MO-TeO2 (MO=As2O3, Bi2O3 and P2O5) glasses doped with chromium ions

Optical absorption, thermoluminescence, infrared spectra and differential thermal analysis of three different tellurite glass systems viz., ZnF₂-As₂O₃-TeO₂, ZnF₂-Bi₂O₃-TeO₂ and ZnF₂-P₂O₅-TeO₂ containing 0.4% of Cr₂O₃, have been investigated. Results have been analysed in the light of different oxidation states of chromium ion and the most suitable host for lasing Cr³⁺ ions has been identified and reported.     

The infrared spectra of 12C32S, 12C34S, 13C32S,and 12C33S

Using a tunable diode laser spectrometer, the infrared absorption spectra of four isotopic species of carbon monosulfide have been observed in the positive column of a dc discharge of CS₂ and Ar. The wavenumbers of 115 vibration-rotation transitions between 1180.5 and 1266.1 cm^?1 have been measured. These lines were assigned to the 1-0, 2-1, 3-2, and 4-3 bands of ¹²C³²S, the 1-0 and 2-1 bands of ¹²C³⁴S and ¹³C³²S, and the 1-0 band of ¹²C³³S. These new data have been combined with the previous infrared and microwave results to determine Dunham coefficients (Y_ij), the Dunham potential expansion constants (a₀,a₁,a₂,a₃, and a₄), and the classical turning points by the RKR method.