Synthesis and Luminescent Properties of Bismuth Titanates Bi1.6HoxTi2O7 – δ and Bi1.6Mg0.1HoxTi2O7 – δ

Physics of the Solid State - Pyrochlores Bi1.6HoxTi2O7 – δ and Bi1.6Mg0.1Ho xTi2O7 – δ, where x = 0, 0.01, 0.05, and 0.1, and...     

Martensitic Transformation,Magnetotransport Properties,and Magnetocaloric Effect in Ni47 – xMn42 + xIn11 Alloys (0 ≤ x ≤ 2)

Physics of the Solid State - The structure, electrical and magnetic properties of Ni47 – xMn42 + xIn11 (0 ≤ x ≤ 2) alloys upon changing the...     

Fabrication and characterization on an organic/inorganic 2 × 2 Mach–Zehnder interferometer thermo-optic switch

An organic/inorganic hybrid 2 × 2 directional coupler (DC) Mach–Zehnder interferometer (MZI) thermo-optic (TO) switch was successfully designed and fabricated using simple direct ultraviolet photolithography process. The hybrid organic/inorganic waveguide structure includes poly-methyl-methacrylate-glycidyl-methacrylate (P(MMA-GMA)), SU-8 2005 and silica as core, upper cladding and under cladding, respectively. Device optimization and simulation were performed to decrease radiation loss and leakage loss, quicken response time and cut down power consumption. Measurements of the fabricated devices at 1550 nm wavelength result in a switching power of 7.2 mW, a response time of ∼100 μs, and crosstalk of −22.8 and −26.5 dB under cross state and bar state, respectively. Besides, the driving-noise-tolerance characteristics of this device were experimentally investigated by directly imposing a generated tunable noise on the pure driving signal (4 V_pp) and the minimum extinction ratio is larger than 18 dB under a noise level of 2.5 V_pp. The effect of noise on extinction ratio was found decreased with the increase of noise frequency.     

Ab initio study of Yb on the Ge(111)–(3 × 2) and Si(111)–(3 × 2) surfaces

The surface reconstruction, 3 × 2, induced by Yb adsorption on a Ge (Si)(111) surface has been studied using first principles density-functional calculation within the generalized gradient approximation. The two different possible adsorption sites have been considered: (i) H₃ (this site is directly above a fourth-layer Ge (Si) atom) and (ii) T₄ (directly above a second-layer Ge (Si) atom). We have found that the total energies corresponding to these binding sites are nearly the same, indeed for the Yb/Ge (Si)(111)–(3 × 2) structure the T₄ model is slightly energetic by about 0.01 (0.08) eV/unitcell compared with the H₃ model. In particular for the Ge sublayer, the energy difference is small, and therefore it is possible that the T₄, H₃, or T₄H₃ (half of the adatoms occupy the T₄ adsorption site and the rest of the adatoms are located at the H₃ site) binding sites can coexist with REM/Ge(111)–(3 × 2). In contrast to the proposed model, we have not determined any buckling in the Ge = Ge double bond. The electronic band structures of the surfaces and the corresponding natures of their orbitals have also been calculated. Our results for both substrates are seen to be in agreement with the recent experimental data, especially that of the Yb/Si(111)–(3 × 2) surface.     

Tuneability of Sm(1 − x)CexFeO3 ± λ perovskites: Thermal stability and electrical conductivity

Trimetallic perovskite oxides, Sm_(1 ? x)Ce_xFeO_3 ± λ (x = 0–0.05), were prepared by thermal decomposition of amorphous citrate precursors followed by calcinations. The material properties of the substituted perovskites were characterized by X-ray diffraction (XRD), X-ray florescence spectroscopy (XRF), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The doped materials exhibited a single perovskite phase in air up to 1350 °C and have specific surface areas in the range of 2.696–8.665 m²/g. In reducing atmosphere (5%v/vH₂/N₂), the unsubstituted perovskite (x = 0) decomposed into two phases while the ceria stabilized materials (x = 0.01, x = 0.03, x = 0.05) remained in a single phase as revealed by XRD analysis. Their conductivities were measured by the four point probe method in air and in dilute hydrogen (5%v/vH₂/N₂) separately. The ceria substituted materials show increased stability versus reduction and phase separation for a wide temperature range (up to 1000 °C). Although undoped SmFeO₃ has higher conductivity under oxidizing conditions than ceria doped SmFeO₃ due its p-type nature, the situation is reversed under reducing conditions. The ceria substituted perovskites (Sm_(1 ? x)Ce_xFeO_3 ± λ, x = 0–0.05) showed higher conductivity in reducing than in oxidizing conditions, suggesting that ceria doping at the A-site has changed the SmFeO₃ from p-type to n-type semi-conducting behavior.     

Radiation stability of M1 − xPrxF2 + x (M = Ca,Sr, Ba) crystals

The radiation stability of the mixed crystals M_1 ? xR_xF_2 + x (M = Ca, Sr, Ba) depends on types of the alkaline-earth and rare-earth ions. Different to Eu- and Ce-containing systems, M_1 ? xPr_xF_2 + x solid solutions have a low radiation resistance, which may be associated with hole trapping on praseodymium ion according to the reaction Pr³⁺ → Pr⁴⁺ which is typical for praseodymium. The coloration efficiency of M_1 ? xPr_xF_2 + x crystals grows in the row Ca → Sr → Ba, which is explained satisfactorily within the model of rare-earth clusters, the structure of which is determined by the ratio of the base alkaline-earth cation to the praseodymium ion radii.     

Oxygen nonstoichiometry and defect equilibrium in La2 − xSrxNiO4 + δ

Nonstoichiometric variation of oxygen content in La_2 ? xSr_xNiO_4 + δ (x = 0, 0.1, 0.2, 0.3, 0.4) and decomposition P(O₂) were determined by means of high temperature gravimetry and coulometric titration. The measurements were carried out in the temperature range between 873 and 1173 K and the P(O₂) range between 10^? 20 and 1 bar. La_2 ? xSr_xNiO_4 + δ showed the oxygen excess and the oxygen deficient compositions depending on P(O₂), temperature, and the Sr content. The value of partial molar enthalpy of oxygen approaches zero as δ increases in the oxygen excess region, which indicate that the interstitial oxygen formation reaction is suppressed as δ increase. The relationship between δ and logP(O₂) were analyzed by two types of defect equilibrium models. One is a localized electron model, and the other is a delocalized electron model. Both models can well explain the oxygen nonstoichiometry of La_2 ? xSr_xNiO_4 + δ with a regular solution approximation.     

Atomic and nanostructures of monolayer c(2 × 2)NiN on Cu(0 0 1)

Structures of monolayer nickel nitride (NiN) on Cu(0 0 1) surface are studied by X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). Formations of Ni–N chemical bonds and NiN monolayer at the surface are confirmed by XPS on the N-adsorbed Cu(0 0 1) surfaces after Ni deposition and subsequent annealing to 670 K. A c(2 × 2) structure is always observed in the LEED patterns, which is a quite contrast to the (2 × 2)p4g structure observed usually at the N-adsorbed Ni(0 0 1) surface. Atomic images by STM indicate the mixture of Ni–N and Cu–N structures at the surface. Density of the trenches on the N-saturated surface decreases and the grid pattern on partially N-covered surfaces becomes disordered with increasing the Ni coverage. These results are attributed to the decrease of the surface compressive stress at the N-adsorbed Cu surface by mixing Ni atoms.     

Mobility of Charge Carriers in a Single Crystal and Nanoceramic of the Superionic Pb1 – xSnxF2 Conductor (x = 0.2)

Physics of the Solid State - A crystallophysical model of ion transfer in the superionic Pb1 – xSnxF2 conductor with a fluorite (CaF2) structure is proposed. The...     

A Study of the Structure and Magnetic Properties of FeRh1 – xIrx (x = 0.5–1) Alloys by First-Principles Methods

Physics of the Solid State - The structure and magnetic properties of FeRh1 – xIrx alloys (x = 0.5, 0.625, 0.75, 0.875, and 1) are investigated by first-principles methods...     

Electronic structure of CuClxBr1 − x,CuClxI1 − xand CuBrxI1 − xalloys

In this work, the electronic structure and disorder effects in copper halides alloys are studied by means of the full potential linearized augmented plane wave (FLAPW) method. The calculated bowing parameter shows that the main contribution is due to the relaxation effects, though the charge transfer remains relatively significant, while the volume deformation contribution is negligible. The total bowing is found to be small in the three studied alloys. Results agree well with experimental and available theoretical works.     

Haven Correlation Parameter for Diffusion of Fluorine in Superionic Conductors La1 – ySryF3 – y

Physics of the Solid State - The processes of electric charge transfer (conductivity) and mass transfer (diffusion) in La1 ‒ ySryF3 – y superionic...     

Preparation,surface state and band structure studies of SrTi(1 − x)Fe(x)O(3 − δ) (x = 0–1) perovskite-type nano structure by X-ray and ultraviolet photoelectron spectroscopy

In this report, SrTi_(1 ? x)Fe_(x)O_(3 ? δ) photocatalyst powder was synthesized by a high temperature solid state reaction method. The morphology, crystalline structures of obtained samples, was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscopy (TEM), respectively. The electronic properties and local structure of the perovskite STF_x (0 ≤ x ≤ 1) systems have been probed by extended X-ray absorption fine structure (EXAFS) spectroscopy. The effects of iron doping level x (x = 0–1) on the crystal structure and chemical state of the STF_x have been investigated by X-ray photoelectron spectroscopy and the valence band edges for electronic band gaps were obtained for STF_x by ultraviolet photoelectron spectroscopy (UPS). A single cubic perovskite phase of STF_x oxide was successfully obtained at 1200 °C for 24 h by the solid state reaction method. The XPS results showed that the iron present in the STF_x perovskite structure is composed of a mixture of Fe³⁺ and Fe⁴⁺ (SrTi_(1 ? x)[Fe³⁺, Fe⁴⁺]_(x)O_(3 ? δ)). When the content x of iron doping was increased, the amount of Fe³⁺ and Fe⁴⁺ increased significantly and the oxygen lattice decreased on the surface of STF_x oxide. The UPS data has confirmed that with more substitution of iron, the position of the valence band decreased.     

Elastic Constants and Related Mechanical Properties of YxIn1 – xN Ternary System

Physics of the Solid State - Using a pseudo-potential approach within the virtual crystal approximation, the elastic properties of YxIn1 – xN semiconductor ternary alloys in...     

1.55 μm silicon-based reflection-type waveguide-integrated thermo-optic 2 × 2 switch

In this work a waveguide-integrated 2 × 2 switch operating at the infrared communication wavelength of 1550 nm is proposed and theoretically discussed. The device is based on the total internal reflection (TIR) phenomenon and the thermo-optic effect (TOE) in hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si). It takes advantage of a bandgap-engineered a-Si:H layer to explore the properties of an optical interface between materials showing similar refractive indexes but different thermo-optic coefficients. In particular, thanks to modern plasma-enhanced chemical vapour deposition (PECVD) techniques, the refractive index of the amorphous film can be properly tailored to match that of c-Si at a given temperature. TIR may be therefore achieved at the interface by acting on the temperature. The device is integrated in a 4 μm-wide and 3 μm-thick single-mode rib waveguide. The substrate is a silicon-on-insulator (SOI) wafer with an oxide thickness of 500 nm. We calculated an output crosstalk always better than 24 dB and insertion losses as low as 3.5 dB.     

Spectral and Structural Characteristics of (Lu1 – xEux)2(WO4)3 Tungstates

Physics of the Solid State - The structure, luminescence, and IR absorption spectra of (Lu1 – xEux)2(WO4)3 solid solutions are studied in a wide range of europium...     

Facile synthesis and characterization of FeP x V1 − x O4 nanobelts with enhanced photocatalytic performance

Journal of Nanoparticle Research - A 3D heterogeneous TiO2/ZnO array was successfully synthesized on FTO substrate via hydrothermal process. The 3D TiO2/ZnO array exhibited enhanced light...     

H/D Isotope Effect in the Conductivity of CaZr1 – xScxO3 – α in Reducing Atmospheres

Physics of the Solid State - The ionic (proton and deuteron) conductivity of the system CaZr1 – xScxO3 – α (x = 0.03–0.20) is studied...     

Spectral and Structural Characteristics of Molybdates (Lu1 – xEux)2(MoO4)3

Physics of the Solid State - The structure, the photoluminescence, and IR absorption spectra of solid solutions (Lu1 ‒ xEux)2(MoO4)3 have been studied over a wide range of...     

Spin Fluctuations and Concentration Magnetic Transitions in Chiral Helical Ferromagnets Fe1 – xCoxSi

Physics of the Solid State - The fluctuation theory is applied to the study of concentration transformations in Fe1 – xCoxSi disordered quasi-binary chiral helical...