Electrical conductivity of YSZ film grown by pulsed laser deposition

Yttria-stabilized zirconia (YSZ) thin films, 0.6–1.5 μm, were deposited on Pt and sapphire substrates by a pulsed laser deposition (PLD) method. Their structural and transport properties have been studied by means of X-ray diffraction and electrical conductivity measurements. The in-plane and the perpendicular-to-plane conductivities (hereafter, “across-plane” conductivity) of thin films were measured and compared to that of bulk sample. X-ray diffraction and electron microscopy results showed that the films on Pt and sapphire were polycrystalline cubic with a columnar structure. Both the across-plane and the in-plane conductivities of YSZ thin film were close to that of bulk specimens. Thus no conductivity enhancement was found for the present nano-crystalline YSZ films (grain or column size, 60∼100 nm).     

Electrical conductivity in a conductor 5 atoms thick

A single crystal 5 atoms thick comes close to the approximation of a quasi-two-dimensional system. Still, it retains some characteristics of the bulk material as revealed by the virtual absence of any contact effects as long as the contacts consist of thicker areas of the same crystal. Electrical conductivity and electron mobility are strongly influenced by adsorption on the surface. The onset of an additional conduction process at high current density and low temperature is reported.     

Electrical conductivity and optical properties of ZnO nanostructured thin film

The electrical conductivity, structural and optical properties of ZnO nanostructured semiconductor thin film prepared by sol-gel spin coating method have been investigated. The X-ray diffraction result indicates that the ZnO film has the polycrystalline nature with average grain size of 28 nm. The optical transmittance spectrum indicates the average transmittance higher than 90% in visible region. The optical band gap, Urbach energy and optical constants (refractive index, extinction coefficient, real and imaginary parts of the dielectric constant) of the film were determined. The electrical conductivity of the film dependence of temperature was measured to identify the dominant conductivity mechanism. The conductivity mechanism of the film is the thermally activated band conduction. The electrical conductivity and optical results revealed that the ZnO film is an n-type nanostructured semiconductor with a direct band gap of about 3.30 eV at room temperature.     

Mechanisms of conductivity ceiling in YSZ

The conductivity ceiling phenomena of O²⁻ ions in stabilized zirconia are studied in terms of the path probability method and Monte Carlo simulation. It is shown that there exist two kinds of possible mechanisms. One of them is due to an order–disorder transition of O²⁻ ions, which is caused by the repulsive interaction between O²⁻ ions, and the other is owing to a percolation transition of dopant cations network. It is proposed that the YSZ case originates in the percolation transition.     

Microstructure and conductivity of alumina-fiber-doped YSZ membranes

Alumina-fiber-doped YSZ membranes were fabricated by tape casting and pressureless sintering. With a milling time of 4 h and a slurry viscosity of ≈ 600 mPa·s (at a shear rate of 350 s⁻¹), the fibers could be dispersed homogeneously in the slurry with an average aspect ratio of ≈ 20. With 1.5 vol% Al₂O₃ fibers, the relative density of the alumina-fiber-doped YSZ membranes reached a maximum of 93%, and then decreased gradually with higher fiber addition. For the 6 vol% alumina-fiber-doped YSZ membranes, the density decreased by 7.1%, accounting to 85.1% of the theoretical value. However, the density of the 6 vol% Al₂O₃/YSZ composites (fabricated by tape lamination) was 93.4%, which has benefited from the isostatic pressing of green compacts at a pressure of 300 MPa. Obvious fiber pull-out was observed in the fracture section of the alumina-fiber-doped green tapes while not in the cross-section of the sintered membranes. With the addition of alumina fibers, the ionic conductivity of the sintered membranes decreased much more than the ROM (Rule of Mixtures) theoretical calculation, which may be attributed to impurities in fibers and pores accompanied with fiber addition.     

Electrical characterization of highly Titania doped YSZ

The defect fluorite region of the ternary system ZrO₂-Y₂O₃-TiO₂ encompasses compositions which offer both, good electronic and oxygen ion conductivity which enable good catalytic activity for the direct oxidation of methane in a solid oxide fuel cell (SOFC). The electrical properties of compositions Y_xTi_yZr_1−(x+y)O_2−x/2 (with x=0.15, 0.2, 0.25 and y=0.15, 0.18) were characterised in order to find the composition with highest ionic and electronic conductivity. High titanium dopant concentrations (Y) of 15 and 18 atom%, near the solubility limit of Ti⁴⁺ in the fluorite structure, have been introduced to achieve a high electronic conductivity at low oxygen partial pressure. The yttrium content x has been varied between 15 and 25 atom% to find the fluorite composition with the highest ionic conductivity for each titanium level. In the pO₂-range from 0.21 to 10⁻¹³ atm the conductivity is predominantly ionic and constant over that range. The maximum ionic conductivity is 0.01 Scm⁻¹ for the compositions, which contain 15 atom% yttrium. Substantial electronic conductivity is introduced into the system at low oxygen pressures below 10⁻¹³ atm via reduction of Ti⁴⁺ ions to Ti³⁺. The maximum electronic conductivity of 0.2 Scm⁻¹ at 930 °C has been measured for a sample with 18 atom% titanium. The slope of all log(σ) vs. log(pO₂) plots follows a pO ₂ ^−1/4 -dependence. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Ionic and electronic conductivity of nitrogen-doped YSZ single crystals

The ionic and electronic charge transport was studied for single crystals of 9.5 mol% yttria-stabilized zirconia with additional nitrogen doping (YSZ:N) of up to 7.5 at.% (referred to the anion sublattice and formula unit Zr_0.83Y_0.17O_1.91) as a function of temperature and nitrogen content. The total conductivity being almost equivalent to the oxygen ion conductivity has been measured by AC impedance spectroscopy under vacuum conditions in order to prevent re-oxidation and loss of nitrogen. The electronic conductivity has been determined by Hebb–Wagner polarization using ion-blocking Pt microelectrodes in N₂ atmosphere. The ionic conductivity of YSZ:N decreases in the presence of nitrogen at intermediate temperatures up to 1000 °C. The mean activation energy of ionic conduction strongly increases with increasing nitrogen content, from 1.0 eV for nitrogen-free YSZ up to 1.9 eV for YSZ containing 7.3 at.% N. Compared to nitrogen-free YSZ, the electronic conductivity first decreases at nitrogen contents of 2.17 and 5.80 at.%, but then increases again for a sample with 7.53 at.%. At temperatures of 850 °C and above, the presence of the N^3? dopant fixes the electrode potential and thus the oxygen partial pressure at the Pt electrode to very low values. This corresponds to a pinning of the Fermi level at a relatively high energy in the upper half of the band gap. At 7.53 at.% N and 950 °C, the oxygen partial pressure in YSZ:N corresponds to p_O2 = 3 × 10^? 18 bar. At temperatures above 850 °C, even in the presence of a very small oxygen concentration in the surrounding gas phase, the nitrogen ion dopant becomes highly mobile and thus diffuses to the surface where it is oxidized to gaseous N₂. The results are discussed in terms of the ionic and electronic defect structures and the defect mobilities in YSZ:N.     

Electrical conductivity of BaTi4O9 film prepared by laser chemical vapor deposition method

A BaTi₄O₉ film was prepared on a Pt/Ti/SiO₂/Si substrate by a laser chemical vapor deposition method and was investigated by impedance spectroscopy over ranges of temperature (300–1073 K) and frequency (10²–10⁷ Hz). Plots between real and imaginary parts of the impedance (Z′ and Z′′) suggest the presence of two relaxation regimes, which were attributed to grain and grain boundary responses. The conduction of both grains and grain boundaries obeys the Arrhenius format with activation energies of respectively 1.45 and 1.24 eV. The close activation energies indicate that the conduction in BaTi₄O₉ film is mainly by oxygen vacancies.     

Electrical conductivity of SmS polycrystals

The electrical conductivity of SmS polycrystals has been studied in the temperature range 300?C870 K. It has been shown that, at 300 K ?? T ?? 700 K, the concentration of conduction electrons is determined by electron transfer from impurity donor levels, and at T > 700 K, by that from the samarium 4f levels.     

Electrical conductivity of inhomogeneous superconductors

The excess electrical conductivity of an inhomogeneous superconducting film is calculated using a Random-Ginzburg-Landau model. Treating the quartic interaction within a self-consistent Hartree-approximation the excess conductivity of a random superconductor is found, for T ? T_c, to be enhanced compared to that of a homogeneous film.     

NiO+YSZ anode substrate for screen-printing fabrication of YSZ electrolyte film in solid oxide fuel cell

Anode substrate has a great effect on screen-printing fabrication of yttria-stabilized zirconia (YSZ) electrolyte film and cell performance. In this work, NiO+YSZ anode substrate was prepared by a conventional ceramic sintering method, on which dense YSZ electrolyte film was successfully fabricated by screen-printing method. Microstructure of the anode substrate and cell performance were investigated. The optimal amount of addition of starch to the anode substrate was 20 wt%. The optimal temperature for pre-sintering of NiO powder was 800 °C. A single cell with the NiO powder pre-sintered at 800 °C exhibited the highest power density of 0.95 W cm⁻² at 700 °C.     

Electrical degradation of porous and dense LSM/YSZ interface

Electrochemical cells formed by the interface between dense and porous lanthanum strontium manganate (LSM) and yttria stabilized zirconia (YSZ) were submitted to annealing temperatures varying from 1373 K to 1673 K for 200 h and studied by Impedance Spectroscopy (IS) in order to investigate how the high annealing temperature can modify the contact between LSM/YSZ and to which extension these changes influence the electrical behavior of dense and porous LSM electrodes before and after the formation of insulating phases. Up to 1473 K the annealing process did not lead to substantial electrical behavior modifications at the LSM/YSZ interfaces for both porous and dense electrodes. IS measurements show two capacitive semicircles, the best fitting of impedance data brings to an equivalent circuit constituted by a serial combination of the electrolyte resistance and two parallel combinations of a resistance and a constant phase element, CPE. The higher frequency semicircles, HF, were attributed to the diffusion of oxide ions from the interface LSM/YSZ to the oxide ion vacancies located at the electrolyte surface. The semicircle at lower frequency, LF, will be ascribed to the oxygen species adsorption and diffusion in the LSM. At 1473 K the only changes recorded are related with the sinterization process of the porous electrodes. Over of 1473 K, the resistance contributions increased largely, especially for porous electrodes, and one additional semicircle was observed. This semicircle was associated to the oxygen diffusion process at the new insulating phases formed from YSZ and LSM solid state reactions. Porous and dense electrodes exhibited different rates for the degradation process. The porous electrode degraded faster than the dense one, probably because of the morphological effects as grain growth and their coalescence during annealing at higher temperatures.     

Electrical conductivity of Sb-doped BaTiO3

Electrical conductivity of undoped and Sb-doped BaTiO₃ are measured under P_O2 between 2×10^-14 and 10⁵ Pa in the temperature range 1123–1273 K. Both powers of the oxygen pressure dependence and activation energies of electrical conductivity are determined. It has been concluded that the mechanism of Sb incorporation into BaTiO₃ depends on composition. At lower concentrations (below 0.15 mo1% Sb₂O₅) Sb incorporates into both Ba and Ti sublattices froming donor centers. Above this concentration Sb incorporates preferentially into Ti sites forming acceptor centers.     

Electrical conductivity of PbTe thin films

PbTe thin films were prepared by vacuum technique with different thicknesses ranging from 550 to 3000 Å. The electrical resistivity as a function of the film thickness and mobility was measured. The dependence of log (resistivity) and log (current) was studied as a function of the universal temperature. The activation energies were estimated before and after the break. The transition of conductivity from n-type to p-type is attributable to the increase in the number of migrating lead vacancies. An increase of the applied voltages on the thin films caused the shift of breaking temperature to higher temperatures. This shift is attributed to the creation of Pb vacancies which retard the break.