Electronic properties of ion-implanted yttria-stabilized zirconia

Ion implantation of iron and titanium has been applied to modify the surface properties of polycrystalline yttria-stabilized zirconia ((ZrO2)0.87(YO1.5)0.13 (YSZ)) discs in an attempt to prepare surfaces with a mixed conductivity and by this an enhanced surface oxygen exchange kinetics. Surface-sensitive spectroscopic techniques were applied to investigate the implanted layers as a function of different pretreatments such as oxidation, reduction and annealing. Depth profiles were recorded by Rutherford Backscattering Spectroscopy (RBS) and X-ray Photoelectron Spectroscopy (XPS) in combination with sputtering. Ion Scattering Spectroscopy (ISS) and XPS were used to investigate the surface composition and valency of implanted ions. Electronic properties like the band gap, the work function and the energy difference between the Fermi level and valence band edge (EF-EV) were obtained from Ultraviolet Photoelectron Spectroscopy (UPS) and Electron Energy Loss Spectroscopy (EELS). Overlayers of Fe2O3 or TiO2 are formed during oxidation of as-implanted samples. The Fe- and Ti-oxides could be reduced in hydrogen to the oxidation states Fe2+, Fe0 or Ti3+. Annealing of the samples leads to decreased surface concentrations of the implanted ions due to in-diffusion. At the surface of the annealed iron-implanted samples, Fe2+ and metallic Fe could be generated after further reduction whereas at the surface of the annealed Ti-implanted samples only Ti4+ was detectable.\u

Measurement of ionic conductivity in mixed conducting compounds using solid electrolyte microcontacts

Ion conducting (=electron blocking) microelectrodes were used to measure the oxygen ion conductivity in mixed conducting oxides as a function of the thermodynamic activity of oxygen. The reported data concern mixed conducting perovskites of the composition La0.8E0.2CoO3 with E=Mg, Ca, Sr. The microelectrodes were made of yttrium-stabilized zirconia (radius 10–100 μm). Practical conditions and limitations of the microelectrode technique are described, e.g. the influence of the shape of the microelectrode, the microstructure of the interface and the pretreatment of the sample surface as well as further details for the measurement. Here, steady-state current–voltage curves were analyzed according to the Hebb–Wagner theory. The oxygen ion conductivity was calculated from these curves. The primary advantage of the microelectrode technique as compared to conventional planar contacts is the small effective diffusion length of about 10–100 μm due to the small electrode diameter and the radial geometry. Therefore, the time constants for approaching the steady state are two to four orders of magnitude lower as compared to a conventional thin sample with 1-mm thickness (=diffusion length)

SANS Investigation and Conductivity of Pure and Salt-Containing Poly(bismethoxy-phosphazene)

Poly(bismethoxyphosphazene) (PBMP) was synthesized, giving polymer melts with T-g = -70.9 degrees C. The chain dynamics of melts and DMF solutions of poly(bismethoxyphosphazene) (PBMP) was investigated by Small-Angle Neutron Scattering (SANS). The radius of gyration R-g was found as 144.7 +/- 0.2 angstrom, and the average MW from SANS was 95000 Da. DMF revealed to be a good solvent for this polymer. From the scattering intensity of polymer solutions for high q-data, the slope was -1.647 in almost exact agreement with the expected excluded volume exponent by Flory which is (5)/(3) affirming the good solvent property of DMF. GPC measurements of THF solutions were evaluated based on a universal calibration of polystyrene standards resulting in a rather similar value of 1.05 x 10(5) Da. Another series of SANS experiments was done with solutions of LiSO3CF3 (LiTf) in the title polymer. They also showed low T-g values down to -50 degrees C at 15 wt %. The SANS results (5 and 10 mol % LiTf as referred to the monomer units) showed almost no effect of the dissolved salt on the melt conformation of the polyphosphazene (almost random coil), and thus revealed a rather small interaction between salt and polymer. We also measured the ionic conductivity of salt-in-polymer systems with concentrations from 5 to 20 wt % LiTf. The room-temperature conductivity was 1.7 x 10(-5) S/cm at 20 wt % LiTf and is thus rather high. The low interaction between salt and polymeric solvent,is in agreement with the predominance of neutral ion pairs which is often observed in such polymer electrolytes

Impact of delithiated Li0FePO4 on the decomposition of LiPF6-based electrolyte studied by accelerating rate calorimetry

Accelerating rate calorimetry (ARC) was used to investigate the impact of delithiated Li0FePO4 on the decomposition of LiPF6-based electrolyte. We used 1 M LiPF6 in a solvent mixture composed of dimethyl carbonate and ethylene carbonate ( 1:1 w/w). Commercially available LiFePO4-based 18650 lithium-ion cells were completely charged up to a cut-off voltage of 4.2 V and afterwards disassembled in an argon filled glove box. The whole sample preparation for an ARC experiment was carried out under argon atmosphere to prevent atmospheric influences. Beside the self heating rate, we also analysed the pressure rise during an experiment to evaluate the influence of delithiated Li0FePO4 on the electrolyte decomposition, which is primarily initiated by the conducting salt LiPF6. The results show both in the self heating rate and the pressure development an inhibiting effect of delithiated Li0FePO4 on the electrolyte decomposition. This effect is independent of the state of charge (SOC) and seems to be typical for (delithiated) Li0FePO4 in contrast to a commercial [Ni0.33Co0.33Mn0.33]O2/LiCoO2 blend. Besides that, we investigated the thermal behaviour of the bare Li0FePO4 and in presence of salt-free solvent. X-ray diffraction after measurements of delithiated Li0FePO4 in presence of electrolyte or salt-free solvent showed a new crystalline phase

Correlations of ion motion and chain motion in salt-in-polysiloxane-g- oligoether electrolytes

The transport properties of salt and chains in a salt-in-polymer electrolyte consisting of polysiloxane-g-oligoether with different concentrations of lithium triflate, LiSO 3CF 3, are investigated. Temperature-dependent impedance spectroscopy, viscosity, and multinuclear self-diffusion NMR characterize the mobility of the chains and the different salt species, i.e., ion pairs or single ions. Comparison of different transport parameters allows conclusions about the motions of different species and correlations between them. For example, comparing diffusion coefficients and conductivities via the Nernst-Einstein equation, the fraction of undissociated ion pairs is concluded to be larger than 90%. Macroscopic and microscopic viscosities describe chain and small species motions, respectively. Distinct differences are observed between the temperature-dependence of the transport parameters of ion pairs, which is of Arrhenius-type, and that of the transport of chains or single ions, which deviates from Arrhenius, indicating a strong correlation with the chain dynamics for the latter. Most interestingly, the comparison of conductivity and fluidity data shows that their temperature dependence can be fully superimposed to a master curve in an Arrhenius plot, if shifted by a small value ?(1/T) along the inverse temperature axis. This novel master curve scaling is a proof of the strong correlation of matrix and charge carrier dynamics. It is observed here for the first time in a macromolecular system, with the shift value ?(1/T) as a quantity describing the correlation. © 2012 American Chemical Society

Composites of Ce0.8Gd0.2O1.9 and Gd0.7Ca0.3CoO3−δ as oxygen permeable membranes for exhaust gas sensors

The transport and catalytic properties of mixed conducting composites prepared from Gd0.7Ca0.3CoO3-δ (GCC) and Ce0.8Gd0.2O1.9 (CGO) were determined. In total, three compositions with 43, 60 and 75 vol.% CGO have been prepared. The composites have potential applications as oxygen permeable membrane in an amperometric sensor for NOx detection in exhaust gases.\ud \ud At all compositions, three different phases were found in the annealed composite as a result of solid state reactions during annealing. The gadolinium content of the CGO phase was increased. The GCC was transformed into a phase with K2NiF4-structure and an additional CoO phase appeared.\ud \ud Electron conductivities were determined in the range 100 to 750°C. The oxygen ion conductivities were measured by a microelectrode technique between 650 and 750°C. Permeation measurements were carried out between 850 and 1000°C. Effective ionic conductivities were calculated from the permeation results. The latter agreed well with the microelectrode data extrapolated to higher temperatures. The composition dependence of the conductivities was explainable by a statistical percolation model.\ud \ud The investigated composites exhibit good oxygen ion conductivities. Typical ionic conductivity values for a composite with 75 vol.% CGO increased from 4x10-4 (Ω cm)-1 at 650°C to 4.2x10-2(Ω cm)-1 at 1000°C.\ud \ud The heterogeneous catalysis of surface gas reactions was tested by exposing powdered samples to various gaseous mixtures with O2, N2, CO, CO2, H2O, SO2 and propene at temperatures up to 800°C. No conversion of NO to oxygen and nitrogen as well as no extensive formation of N2O was detected. It is concluded that the composite membranes are suitable for the intended applications.\ud \u

Neutron diffraction and electrochemical studies on LilrSn4

Large quantities of single phase, polycrystalline LiIrSn4 have been synthesised from the elements by melting in sealed tantalum tubes and subsequent annealing. LiIrSn4 crystallises with an ordered version of the PdGa5 structure: I4/mcm, a = 655.62(8), c = 1128.6(2) pm. The lithium atoms were clearly localised from a neutron powder diffraction study: R-p = 0.147 and R-F = 0.058. Time-dependent electrochemical polarisation techniques, i.e. coulometric titration, chronopotentiometry, chronoamperometry and cyclic voltammetry were used to study the kinetics of lithium ion diffusion in this stannide. The range of homogeneity (Li1+Delta delta IrSn4, -0.091 <= delta <= + 0.012) without any structural change in the host structure and the chemical diffusion coefficient (similar to 10(-7)-10(-9) cm(2)/s) point out that LiIrSn4 is a first example of a large class of intermetallic compounds with lithium and electron mobility. Optimised materials from these ternary lithium alloys may be potential electrode material for rechargeable lithium batteries. (C) 2005 Elsevier Inc. All rights reserved