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We evaluate in this work the effect of Gd substitution on the dc activation energy, Edc, and ionic conductivity of the pyrochlore-type gadolinium zirconate, P-Gd2Zr2O7. Several compositions with the general formulae Gd2−yLnyZr2O7 (Ln =E r 3+ ,Y

We report on the influence of structural disorder on the oxide-ion conductivity of Dy2(Ti1� yZry)2O7 (y = 0.55 and 0.90). A significant disorder is induced by mechanical milling synthesis of the samples, and, depending on the Zr/Ti, a partial and progressive structural ordering can be achieved by subsequent annealing at temperatures between 800 and 1500 C. Ionic conductivity is relatively high for both compositions (up to 10 � 4 S/cm at 900 K), and the activation energies for dc conductivity (in the range 1.02–1.32 eV) are found to be larger in samples with more structural disorder. This result is quantitatively explained, by using Ngai’s coupling model, in terms of the enhancement of interactions between mobile oxygen vacancies in a more disordered structure. 2007 Elsevier B.V. All rights reserved.

Iron oxychloride has been lithiated by the reaction with n -butyllithium and thereafter exposed to air. Lithium intercalation increases several orders of magnitude of the electrical conductivity of the pristine material although the intercalate remains a semiconductor. This phase, after being exposed to atmospheric humidity becomes an ionic conductor, with a conductivity comparable to that of some molten salts, and does not show electronic conduction in the whole range of temperatures of measurement (150–300 K), a strong non-Arrhenius behaviour being observed. Impedance spectroscopy and NMR techniques, among others, have been used to follow this behaviour.

Different compositions in a solid solution of general formula Dy2(Ti1−yZry)2O7, showing high oxygen ion conductivity, have been successfully prepared at room temperature via mechanochemical synthesis. Stoichiometric mixtures of the constituent oxides were dry milled together in a planetary ball mill by using zirconia vials and balls. Chemical changes in the powder mixtures as a function of composition and milling time were followed by X-ray diffraction and revealed that, in all cases and after milling for 19 h, the powder mixtures consisted of a single phase. Electrical properties were measured on sintered pellets as a function of frequency, temperature and zirconium content, revealing an increase in conductivity of more than one order of magnitude for y ⩾ 0.4 , which, as observed in the similar Y2(Ti1−yZry)2O7, has been related with the onset of disordering of the anion sublattice. Despite increasing structural disorder with increasing Zr content, conductivity remains almost constant for y > 0.6 , reaching a maximum value of ∼5×10−3 for Dy2Zr2O7 at 900 °C.

The structure of interfaces in superconducting/ferromagnetic YBa2Cu3O7−x/La0.67Ca0.33MnO3 superlattices has been analyzed by scanning transmission electron microscopy and high spatial resolution electron energy loss spectroscopy. Individual layers are flat over long lateral distances. The interfaces are coherent, free of defects, exhibiting no roughness, and are located at the BaO plane of the superconductor. Concerning chemical disorder, EELS measurements show the absence of measurable chemical interdiffusion within experimental error bars.

The reaction of iron oxychloride with n-butyl-lithium has been re-examined, important changes being found in the structure and properties of the lithiated compounds as compared to the pristine material. Lithium intercalation by these means increases several orders of magnitude the electrical conductivity of FeOCl although the intercalate remains semiconductor. From the structural and microstructural point of view the lithiation results in complex changes, including inter alia staging, superstructures, etc., and it seems to be quite an heterogeneous process.

We report on the effects of light ion (He + ) irradiation on the superconducting properties of epitaxial YBa 2 Cu 3 O 7− δ thin films. Films were grown by a pure oxygen dc sputtering system operated at high pressure (3.4 mbar). Irradiation at 80 keV and doses ranging between 10 14 and 10 15 cm −2 shows a systematic degradation of the superconducting transition temperature. We have studied the effects of annealing on the recovery of the superconducting properties of films irradiated at different fluences. Two sets of irradiated samples were evaluated, fully oxidized and deoxygenated samples. Irradiated fresh samples do not show significant recovery upon room temperature annealing for times as long as 6 months. Irradiated deoxygenated samples, however, show an up to 10 K increase in the critical temperature after 2 months room temperature annealing. The different behavior is discussed in terms of the two effects caused by irradiation: oxygen displacements from the CuO chains into stable interstitial positions along the a -axis, and oxygen disorder in the deoxygenated samples.

The solid solution La2/3−xLi3xTiO3 (0.03

Complex admittance measurements have been performed on α-NaFeO 2 and on the product Na 0.9 FeO 2 obtained by sodium extraction, both being polycrystalline powders. The electrical conductivity in both samples is proposed to be due to sodium ions hopping between octahedral positions through the adjacent, empty, tetrahedral ones characteristic of a rock-salt structural framework. The parent material shows an activation energy in the dc conductivity of 0.31 eV between 306 and 498 K. Removal of sodium, in spite of creating octahedral vacancies, results in lower conductivity values, and a higher activation energy of 0.58 eV in a similar temperature range.

In this paper, we present results of current–voltage and admittance spectroscopy measurements on n + p junctions made by Si implantation into Zn doped In .53 Ga .47 As. The I–V characteristics show that the main conduction mechanisms at forward bias is recombination in the space-charge zone, whereas a thermally-activated tunneling dominates the reverse characteristics at low bias and trap-assisted tunneling at medium and high bias. The use of Kramers–Kronig transforms on the admittance spectroscopy data allow us to detect a deep level at 0.36 eV, probably ascribed to thermally activated Zn acceptor dopants in p-In .53 Ga .47 As.

An analysis of electrical conductivity relaxation and nuclear magnetic resonance spin-lattice relaxation has been conducted to study the dynamics of the ionic diffusion process in the crystalline ionic conductor Li 0.5 La 0.5 TiO 3 . Dc conductivity shows a non-Arrhenius temperature dependence, similar to the one recently reported for some ionic conducting glasses. Taking into account this non-Arrhenius dependence for the relaxation times, spin-lattice and conductivity relaxations are compared in the same frequency and temperature ranges. A single “stretched exponential” relaxation function of the form f ( t )=exp(−( t / τ ) β ), with β =0.4, can be used to describe both relaxation processes in which correlation times differ in the preexponential factor.

Lanthanum–lithium–sodium double chromates Li1−xNaxLa(CrO4)2 were prepared and analysed by means of admittance spectroscopy. Their a.c. conductivity parameters are correlated with structural details of high and low temperature forms of pure lanthanum–lithium double chromates. Lithium compounds show the lowest conductivity values and the highest activation energy for ion motion, while the sample Li0.5Na0.5La(CrO4)2 exhibits the highest conductivity 10−5 S cm−1 and the lowest activation energy 0.58 eV.

An in situ analysis of an r.f. discharge is carried out. The relationship between the discharge parameters, composition and growth rate of the deposited thin films and the glow discharge optical spectroscopy signal is presented. Three semiconducting single-phase chalcopyrite targets of Cu(Ga, In)Se2 were sputtered in an Ar atmosphere. The composition of the discharge was measured and it correlated with the composition of the deposited thin films. To be able to extend the determination of the film properties to different discharge conditions we have studied the variation in the optical emission with the Ar pressure and the r.f. power. The behaviour of the optical emission intensities as a function of both the Ar pressure and discharge power is explained in terms of the variation in the electron energy distrobution function.

Epitaxial YBa2Cu3O7 (YBCO) thin films doped with 5–20 wt % Ag have been grown “in situ” at high oxygen pressure by a dc sputtering technique on (001) SrTiO3 substrates. Critical current densities, Jc, were measured in 5 wt % Ag-doped YBCO films in magnetic fields up to 6 T, and were found to be greater than the values obtained for undoped samples. Current-voltage (I–V) characteristics were used to investigate the vortex phase transition, in magnetic field of 6 T applied parallel to the c-axis. The ϱ-j curves scale according to the 3D vortex-glass (VG) model with values of the critical exponents similar to those found for undoped YBCO samples (ν=1.4 and z=4.87).