Water vapour solubility and conductivity study of the proton conductor BaCe(0.9 − x)ZrxY0.1O(3 − δ)

The perovskite BaCe_(0.9 ? x)Zr_xY_0.1O_(3 ? δ) has been prepared by solid state reaction at 1400 °C and conventional sintering at 1700 °C. Water uptake experiments performed between 400 and 600 °C, at a water vapour pressure of 0.02 atm, provide data on the concentration of protons incorporated in the sample. The direct current conductivity has been measured as a function of oxygen partial pressure, at a water vapour partial pressure of 0.015 atm. The total conductivity has been resolved into a p-type and an ionic component using a fitting procedure appropriate to the assumed defect model. An estimation of the protonic component was made by assuming a conductivity isotope effect between 1.4 and 1.8. The total conductivity, obtained using impedance spectroscopy has been measured as a function of temperature in the water and heavy water exchanged states. The activation energy has been found to be 0.56 eV to 0.59 eV in the water exchanged state with values 0.03 to 0.04 eV higher in the heavy water exchanged state. Impedance spectra measured at 200 °C showed a reduction in grain boundary resistivity with increasing cerium content. The stability of the compounds to carbon dioxide has been studied by thermogravimetry.     

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.     

Effect of Eu dopant concentration in SrCe1 − xEuxO3 − δ on ambipolar conductivity

The europium dopant concentration in strontium cerate was studied to achieve maximum hydrogen permeation. In order to determine high ambipolar conductivity, total conductivity and open circuit potential measurements were performed. Among the three different compositions of Eu-doped SrCe_1 ? xEu_xO_3 ? δ (x = 0.1, 0.15 and 0.2) studied, SrCe_0.9Eu_0.1O_3 ? δ showed highest total conductivity between 600 °C and 900 °C. However, transference number measurements showed increasing electronic conductivity with increasing dopant concentration and a stronger temperature dependence for electronic conduction. Therefore, the highest ambipolar conductivity was obtained over the compositional range from SrCe_0.85Eu_0.15O_3 ? δ to SrCe_0.8Eu_0.2O_3 ? δ depending on temperature. Finally, the hydrogen permeation flux was calculated based on the ambipolar conductivity and compared with experimental results.     

Impedance spectroscopy and piezoresponse force microscopy analysis of lead-free (1 − x) K0.5Na0.5NbO3 − xLiNbO3 ceramics

(1 ? x) K_0.5Na_0.5NbO₃ ? xLiNbO₃ (where x = 0.0, 5.0, 5.5, 6.0, and 6.5 wt.%) (KNLN) perovskite structured ferroelectric ceramics were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that single phase was formed for pure KNN while a small amount of second phase (K₆Li₄Nb₁₀O₃₀, ～3%) was present in LN doped KNN ceramics. Phase analysis indicated the change in the crystal structure from orthorhombic to tetragonal with increase in LN content. The electrical behavior of the ceramics was studied by impedance spectroscopy technique in the high temperature range. Impedance analysis was performed using an equivalent circuit model. The impedance response in pure KNN and KNLN ceramics could be deconvoluted into two contributions, associated with the bulk (grains) and the grain boundaries. Activation energies for conductivity were found to be strongly frequency dependent. The activation energy obtained from dielectric relaxation data was attributed to oxygen vacancies. From PFM we found that the composition with 6.5 wt.% LN displays stronger piezocontrast as compared to pure KNN implying an evidence of a pronounced piezoelectric coefficient.     

Pressure and compositional dependence of electric conductivity in the (Mg1 − xFex)1 − δO (x = 0.01–0.40) solid-solution

(Mg_1 ? xFe_x)_1 ? δO (x = 0.01–0.43) single crystals (~ 8 mm in diameter) were made by a melt-growth method. Electrical conductivity measurements were carried out as functions of temperature and frequency by a complex impedance method under pressure (~ 43 GPa and ~ 673 K and at 0.1 MPa and ~ 1400 K). Our experimental results show a change in charge transport mechanism in the (Mg_1 ? xFe_x)_1 ? δO solid solution at high temperature. The temperature of inflection point of the slope in Arrhenius plots depend greatly on both composition and extrinsic factors of crystals. The low-temperature conduction mechanism in (Mg_1 ? xFe_x)_1 ? δO solid solution is small polaron. Pressure effect of the electric conductivity was observed and the conductivity increased to 0.5 at log scale of S/m with increasing pressure up to 43.4 GPa. The activation energy was decreased linearly with increasing pressure. Chemical composition and homogeneity of specimen rather than pressure greatly influence the electric conductivity. The activation energy of 2.37(4) eV for the (Mg_0.99Fe_0.01)_1 ? δO solid solution might correspond to a migration enthalpy of O ions through thermally formed defects. It is proposed that a possible dominant electrical conduction mechanism in ferropericlase under the lower mantle conditions, at least in the higher temperature region, is super ionic conduction.     

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.     

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.     

Synthesis and electrical properties of nanocrystalline Ca1 − xEuxMnO3 ± δ (0.1 ≤ x ≤ 0.4) powders prepared at low temperature using citrate gel method

Nanopowders of Ca_1 − xEu_xMnO₃ (0.1 ≤ x ≤ 0.4) manganites were synthesized as a single phase using the auto gel-combustion method. The citrate method shows to be simple and appropriate to obtain single phases avoiding segregation or contamination. The Ca_1 − xEu_xMnO₃ system has been synthesized at 800 °C during 18 h, against the conventional method of mixing oxides used to obtain these materials at higher temperatures of synthesis. The formation reaction was monitored by X-ray diffraction (XRD) analysis and an infrared absorption technique (FTIR). The polycrystalline powders are characterised by nanometric particle size, ∼ 48 nm as determined from X-ray line broadening analysis using the Scherrer equation. Morphological analysis of the powders, using the scanning electron microscope (SEM), revealed that all phases are homogeneous and the europium-substituted samples exhibit a significant decrease in the grain size when compared with the undoped samples. The structure refinement by using the Rietveld method indicates that the partial calcium substitution by europium (for x ≥ 0.3) modifies the orthorhombic structure of the CaMnO₃ perovskite towards a monoclinic phase. All manganites show two active IR vibrational modes around 400 and 600 cm^− 1. The high temperature dependence of electrical resistivity (between 25 and 600 °C) allows us to conclude that all the samples exhibit a semiconductor behaviour and the europium causes a decrease in the electrical resistivity by more than one order of magnitude. The results can be well attributed to the Mn⁴⁺/Mn³⁺ ratio.     

Phase transitions and dielectric properties of (1 − x)KNbO3 − xK0.5Bi0.5TiO3 ceramics synthesized by a stirred hydrothermal process

Dielectric ceramic materials (1 − x) KNbO₃ − xK_0.5Bi_0.5TiO₃ (0 ≤ x ≤ 0.3) have been successfully synthesized via a stirred (dynamic) hydrothermal method. The microstructure, relative density and dielectric properties were studied as a function of KBT doping. The structure of the solid solutions changed from orthorhombic (x = 0; 0.05) to tetragonal (x = 0.1; x = 0.3) at room temperature. The morphotropic phase limit was obtained at x = 0.075 where we have noted the coexistence of the orthorhombic and tetragonal structures. The mean value of the measured dielectric permittivity ε_r was 700 and dielectric loss tanδ was about 0.06 at room temperature. The dielectric properties of the studied ceramics, from 80 to 450 K, depend not only on their microstructure but also on their relative density. A relaxation behavior was observed for the tanδ curves at temperature below 150 K. The activation energy (E_a) of this phenomenon increases from 0.15 to 0.34 eV with the increase of KBT amount. The conductivity σ_ac remains constant at about 10⁻⁶ S m⁻¹.     

Thermal boundary between normal conductivity and fluctuation superconductivity in YBa2Cu3O7 − δ

The absence of a linear behaviour of the dependence of the resistance() over a temperature interval 77–300 K was observed for ceramic superconductors YBa₂Cu₃O_7 − δand thick polycrystallin films of the same composition with the addition of silver. A comparative analysis of the excess conductivity for HTSC and metal samples, characterizing the deviationR(T) from a linear dependence, allows one to determine the onset temperature of fluctuation superconductivity: within 105–110 K. The analysis of fluctuation superconductivity is performed using the Aslamazov–Larkin model. A smooth transition from the one-dimensional to the two- and three-dimensional nature of superconducting fluctuations in the order parameter was observed for ceramic samples as the temperature decreased.     

Synthesis and characterization of (Pr0.75Sr0.25)1 − xCr0.5Mn0.5O3 − δ as anode for SOFCs

The complex perovskite (Pr_0.75Sr_0.25)_1 − xCr_0.5Mn_0.5O_3 − δ (PSCM) has been prepared and studied as possible anode material for high-temperature solid oxide fuel cells (SOFCs). PSCM exhibits GdFeO₃-type structure and is both physically and chemically compatible with the conventional YSZ electrolyte. The reduction of PSCM resulted in structural change from orthorhombic Pbnm to cubic Pm-3m. Selected area electron diffraction (SAED) analysis on the reduced phases indicated the presence of a √2 × √2 × 2 superlattice. The total conductivity values of ∼ 75% dense Pr_0.75Sr_0.25Cr_0.5Mn_0.5O_3 − δ at 900 °C in air and 5% H₂/Ar are 9.6 and 0.14 S cm^− 1 respectively. The conductivity of PSCM drops with decreasing Po₂ and is a p-type conductor at all studied Po₂. The average TEC of Pr_0.75Sr_0.25Cr_0.5Mn_0.5O_3 − δ is 9.3 × 10^− 6 K^− 1, in the temperature range of 100–900 °C and is close to that of YSZ electrolyte. The anode polarization resistance of PSCM in wet 5%H₂ is 1.31 Ω cm² at 910 °C and in wet CH₄ at 930 °C; the polarization resistance is 1.29 Ω cm². PSCM was unstable at 900 °C in unhumidified hydrogen. Cell performance measurements carried out using graded PSCM and La_0.8Sr_0.2MnO₃ as anode and cathode respectively yielded a maximum power density of 0.18 W cm^− 2 in wet 5%H₂/Ar at 910 °C and the corresponding current density was 0.44 A cm^− 2 at 0.4 V. The activation energy for the electrochemical cell operating in wet (3% H₂O) 5%H₂/Ar fuel is 85 kJ mol^− 1.     

Modification of B-site doping of perovskite LaxSr1 − xFe1 − y−zCoyCrzO3 − δ oxide by Mg2+ ion

Co-doping B-site of perovskite oxide La_xSr_1 ? xCo_yFe_1 ? yO_3 ? δ (LSCFO) with Cr⁶⁺ and Mg²⁺ ions has been attempted in this research for revamping chemical stability and oxygen ionic conductivity of this mixed conducting oxide. It is known that partial substitution for B-site cations of LSCFO by Cr gives rise to a significant improvement on chemical and thermal stability of the perovskite oxide. On the basis of this doped structure, introduction of an immaterial dose of Mg²⁺ ion into its B-site results in a microstructure consisting of smaller grains with higher density than its precursor. Furthermore, the resulting perovskite oxide La_0.19Sr_0.8Fe_0.69Co_0.1Cr_0.2 Mg_0.01O_3 ? δ (LSFCCMO) displays higher O^2? conductivity than the solely Cr-doped LSCFO besides the improved chemical stability against reduction in 5% CH₄/He stream at 850 °C. A detailed examination of the oxidation states of B-site transition metal ions by XPS has also been conducted as a part of structural characterizations of LSFCCMO. The assessment of relative O^2? conductivity shows that the grain boundary area plays a more important role than the bulk phase in facilitating ion transport, but with comparable boundary areas the higher densification level is favorable.     

On the superconductivity and structural properties of YBa2Cu3 − xCdxO7 − y

A series of superconducting cuprates with the nominal composition YBa₂Cu_3 − xCd_xO_7 − yand the effect of Cd substitution on Cu sites in this compound is presented. X-ray powder diffraction patterns for these cadmium cuprates with reduced diamagnetism indicate an orthorhombic unit cell like-perovskite structure for (0 ≤ x ≤ 0.15), while for higher Cd concentration, i.e.x = 1.0 the material is polyphasic. The observed superconducting transition temperature of the samples is nearly the same ([formula] K), except for (x = 1.0) whereT_cdrops to 72 K and a transition from metallic to semiconducting behavior of the normal state of the resistivity is observed. Such a decrease inT_cfor higher Cd concentration could be attributed to the presence of the green phase in this composition.     

The effects of counter cation on lithium ion conductivity: In the case of the perovskite-type titanium oxides of La2/3 − x Li3xTiO3 and LaTiO3

We performed hybrid-DFT calculations for La_2/3 ? xLi_3xTiO₃ (LLT) with lithium ion conductivity, in order to investigate the detailed lithium ion conductive mechanism from the viewpoint of molecular orbital (MO) method. It was concluded that the very ionic lithium ion in bottleneck accelerates the lithium ion conduction. The calculated MO shows no chemical bonding between lithium ion and other ions. In comparison with the perovskite-type trivalent titanium oxide of LaTiO₃, the effect of the titanium's reduction was also investigated. We showed the possibility of the high lithium conductivity in LaTiO₃.     

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...     

Reaction of tert-butyl isocyanate and tert-butyl isothiocyanate at the Ge(100) − 2 × 1 Surface

The adsorption of tert-butyl isothiocyanate and tert-butyl isocyanate at the Ge(100) ? 2 × 1 surface was probed using multiple internal reflection Fourier transform infrared (FTIR) spectroscopy X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) modeling. Results indicate that there are multiple surface products for each molecule. FTIR studies of tert-butyl isothiocyanate reveal adsorption through an S-dative bonded state, while XPS studies further suggest a reactive desorption product which leaves excess sulfur atoms at the surface. Studies of tert-butyl isocyanate indicate that the molecule dissociatively adsorbs at the surface, resulting in tert-butyl and germyl isocyanate groups, as the major pathway, in addition to forming several minor products, including a [2 + 2] cycloaddition product across the C=N bond. DFT was used to simulate vibrational spectra and map the reaction pathways, and confirms that the assigned products are energetically favorable.     

Phase Transformations and Photoluminescence Features of Gd2(1 – x)TbxEuxO3 Solid Solutions

Physics of the Solid State - Solid solutions Gd2(1 – x)TbxEuxO3 (where x = 1 and 2.5 mol %) are prepared by the sol–gel method with subsequent annealing at...     

Ferroelectric relaxor properties of (1 − x)K0.5Na0.5NbO3–xBa0.5Ca0.5TiO3 ceramics

The Ba_0.5Ca_0.5TiO₃ (BCT) composition dependent dielectric and structural properties of (1?x)K_0.5Na_0.5NbO₃–xBa_0.5Ca_0.5TiO₃ powders were investigated. Room temperature x-ray diffraction revealed the powder structure to transform from orthorhombic to cubic with increasing BCT composition. The frequency dependent dielectric constant measurements revealed a shift in the temperature of the maximum dielectric constant for at frequencies, suggesting that the system exhibits ferroelectric relaxor behavior. The system containing 15% BCT showed the closest calculated Curie–Weiss exponent to 2, which the exponent for a relaxor ferroelectric.