Complex Impedance Method Research Articles

High ionic conductivity of Mg–Al layered double hydroxides at intermediate temperature (100–200 °C) under saturated humidity condition (100% RH)

Ionic conduction properties of layered double hydroxides (LDHs), [Mg (1 − x) Al ( x) (OH) 2](CO 3) x/2 · nH 2O (═CO 3-type) and [Mg (1 − x) Al ( x) (OH) 2](OH) x · nH 2O (═OH-type), have been investigated in the temperature range of 25–200 °C under saturated water vapor pressure (100% RH). Conductivity was measured by the complex impedance method using pressed pellet samples. The conductivity of an OH-type sample ( x = 0.25) is as high as 4 × 10 − 3 S cm − 1 already at room temperature. On heating, it increases as slowly (the activation energy E a ∼ 55 meV) as those of liquid electrolyte solutions, suggesting that ions are transported via exchange of protons between OH − and H 2O species in the interlayer space of the LDH (a kind of the Grotthus mechanism). The conductivity at 200 °C reaches 3 × 10 − 2 S cm − 1 . Although the conductivity of the CO 3-type counterpart is considerably low (∼ 10 − 6 S cm − 1 ) at room temperature, it increases with increasing temperature with showing a jump by about four orders of magnitude around 80 °C, after which the compound is turned into an almost the same liquid-like conductor as the OH-type sample; the conductivity jump is probably due to the interlayer reaction CO 3 2− + H 2O = 2OH − + CO 2 (g). Thus those Mg–Al LDH materials show the potential application as solid electrolyte materials for intermediate temperature fuel cells, not only because they have high conductivity but also they should not suffer from the degradation by CO 2 which is a serious problem for conventional anion exchange membranes.

Ink‐Jet Printing: A Versatile Method for Multilayer Solid Oxide Fuel Cells Fabrication

The potential of ink‐jet printing for fabrication of components for solid oxide fuel cells has been explored. An anode interlayer, consisting of a composite of NiO and yttria‐stabilized zirconia (YSZ), and an electrolyte layer, YSZ (8 mol%), were ink‐jet printed on a tape cast anode support, 55 wt% NiO–45 wt% YSZ (8 mol%). Scanning electron microscopy of the printed layers sintered at 1400°C revealed a dense electrolyte layer measuring 10–12 μm in thickness. Single cells using these printed layers and strontium‐doped lanthanum manganate (LSM, La0.8Sr0.2MnO3)‐based pasted cathodes were assessed by DC polarization and AC complex impedance methods. The cells exhibited a stable open circuit voltage of 1.1 V around 800°C, in a hydrogen atmosphere. A maximum power density of 500 m·(W·cm)−2 was achieved at 850°C for a typical cell with the electrolyte and anode interlayer cosintered at 1400°C. A composite cathode interlayer, LSM–YSZ, and a cathode current collection layer, LSM, were also ink‐jet printed and incorporated in single cells. However, cells with all components ink‐jet printed showed decreased performance. This pointed to critical issues in the composite cathode microstructure, which is controlled by the composite ink design/formulation and printing parameters that need to be addressed.

Preparation of YSZ solid electrolyte by slip casting and its properties

Fully stabilized YSZ solid electrolyte was prepared by slip casting. The density was measured according to the Archimedes principle and the linear shrinkage was calculated from measuring the sizes of samples before and after sintering. XRD analysis was conducted to verify the phase structure of both the starting YSZ powder and the prepared YSZ electrolyte. The microstructure of fracture surface and the electrical properties of the samples sintered at different temperatures were investigated via SEM and a complex impedance method, respectively. By comparison of the properties and features among the samples, a slip casting method was established to be a simple way to manufacture high-quality YSZ electrolyte at the sintering temperature of 1550°C for 3 h, which provides a new approach for YSZ electrolyte with complex shapes and mass production.

The effect of dispersed SrTiO 3 particles on the ionic conduction of (La,Li)Ti 2O 6

Ionic conductivity of La 4/3 − y Li 3yTi 2O 6 (LLTO), where y value is 0.21, dispersed by various amount of strontium titanate (SrTiO 3) was measured by complex impedance method, and powder X-ray diffraction (XRD) measurements and scanning electron microscope (SEM) observations were carried out. With increasing SrTiO 3 concentration, the conductivity decreased. At 34 mol%, the Bragg peaks at 11, 26 and 35° in LLTO disappeared in XRD patterns and small non-angulated crystals were shown in SEM. The behavior of ionic conductivity was discussed by using the effective medium approximation (EMA) theory.

Structure electronic and ionic conductivity study versus Ca content in Ca 10− xSr x(PO 4) 6F 2 apatites

Substitution effect on the crystallographic structure in Ca 10− x Sr x (PO 4) 6F 2 solid solution are studied by X-ray diffraction patterns and Rietveld refinements. Full potential electronic structure calculations based on LCAO (linear combination atomic orbital) are also performed using the obtained crystallographic parameters. DOS modification and the charge transfer are estimated versus the calcium content. According to the complex impedance method, ionic conductivity changes are explained.

Study of ionic conductivity, dielectric characteristics and capacitance measurement of γ-irradiated conducting polymeric electrolytes

High conductivity and high specific capacitance of certain kinds of ion-conducting solid polymer electrolytes has been the subject of intensive study in recent years. These materials play an important role in understanding the polymer characteristics and its technological applications with tremendous impact on several aspects of our life. Extensive studies have been undertaken to investigate ion transport behavior and the effect of γ-irradiation on polymer materials. In this communication, an attempt has been made to study the electrical and dielectric properties including capacitance measurement for pure PVA and PVA-H3PO4 complexed electrolytes under γ-radiation. Various parameters such as conductivity, dielectric constant, dielectric loss, loss tangent and capacitance values have been determined using complex impedance method over the temperature range 303–383 K and frequency domain 10 kHz–1 MHz for different molar ratios of complexed materials. Particular attention and emphasis have been given to the conducting polymers in the capacitance performance of the polymeric system.

Pressure and compositional dependence of electric conductivity in the (Mg 1 − xFe x) 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.

Synthesis of single crystal (Mg 1−xFe x) 1−δO ( x=0.001–1.00) solid-solution and electrical conduction mechanism at high temperature and pressure

The (Mg,Fe) 1− δ O rock salt-type solid solution is believed to be one of the major constituents in the Earth's lower mantle. The rock salt-type (Mg 1− x Fe x ) 1− δ O ( x=0.001–0.43) single crystals (∼8 mm in diameter) were made by a melt-growth method using high temperature graphite heater (up to 3300 K) in the Ar atmosphere and by a FZ method in the CO 2–H 2 atmosphere ( pH 2/ pCO 2=0.1). Electrical conductivity measurements were carried out as functions of temperature and frequency by a the complex impedance method under pressure (5 GPa and ∼1800 K, and, 0.1 MPa and ∼1400 K). The ratio of Fe 3+/(Fe 2++Fe 3+) in the solid solution decreases with MgO contents under the same oxygen fugacity. Our experimental results show a change in charge transport mechanism in the (Mg 1− x Fe x ) 1− δ O 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. Chemical composition and homogeneity of specimen rather than pressure greatly influence the electric conductivity. The activation energy for the (Mg 0.99Fe 0.01) 1− δ O solid solution is 2.4 eV corresponding with a migration enthalpy of O ions vacancies. It is proposed that possible dominant electrical conduction mechanism in ferropericlase under the lower mantle conditions, at least in the higher temperature region, is a super ionic conduction.

High-pressure sintered yttria stabilized zirconia ceramics

Fast densification of 8YSZ ceramics under a high pressure of 4.5 GPa was carried out at different temperatures (800, 1000, 1450 °C), by which a high relative density above 92% could be obtained. FT-Raman spectra indicate that the 8YSZ underwent a phase transition from partially tetragonal to partially cubic phase as temperatures increase from 1000 to 1450 °C when sintering under high pressure. The electrical properties of the samples under different high-pressure sintering conditions were measured by complex impedance method. The total conductivity of 0.92 × 10−2 S cm−1 at 800 °C has been obtained for 8YSZ under high pressure at 1450 °C, which is about 200 °C lower than that of the samples prepared by conventional pressureless sintering.

Intermediate-temperature composite proton electrolyte CsH 5(PO 4) 2/SiO 2: Transport properties versus oxide characteristic

Composite solid electrolytes (1 − x)CsH 5(PO 4) 2/ xSiO 2 ( x = 0–0.75) based on silica with different specific surface areas have been studied by the complex impedance, DSC, and X-ray diffraction methods. The proton conductivity of composites is shown to depend on the silica's specific surface area: the higher the specific surface area the stronger influence on the transport properties of composites. The maximal composite conductivity was 2.3 mS∙cm − 1 at T = 140 °C, which exceeded the conductivity of pure CsH 5(PO 4) 2 by more than one order of magnitude. The drastic changes in the transport properties of composites are governed by the salt dispersion and/or amorphisation, which are confirmed by the changes in thermodynamic parameters. An H 2/air fuel cell based on CsH 5(PO 4) 2/SiO 2 demonstrates a maximum power density of 8 mW/cm 2 at U = 0.3 V and a current density up to 80 mA/cm 2 at a short circuit.

Lithium conductivity and lithium diffusion in NASICON-type Li1+xTi2–xAlx(PO4)3 (x= 0; 0.3) prepared by mechanical activation

LiTi2(PO4)3 (LTP) and Li1.3Al0.3Ti1.7(PO4)3 (LATP) (S. g. R-3c) have been prepared using conventional ceramic and mechanical activation (MA) methods. It has been shown that preliminary mechanical activation of initial mixtures leads to different nature and amount of dielectric admixtures in the final product after heat treatment at 800–1000 °C as compared with ceramic method. Transport properties of as prepared materials have been studied by lithium ionic conductivity at d.c. and a.c. (complex impedance method), and 7Li NMR spin-lattice relaxation rate T1–1 measurements. Lithium ionic conductivity of mechanochemically prepared LTP and LATP was characterized by significant reduction of grain boundary resistance, especially for LTP, while the bulk conductivity and Li ion diffusion does not noticeably change. The activation energy of bulk conductivity and Li ion diffusion, i.e. short-range motion, appeared to be almost the same for all samples and was equal to ~0.20 eV. On contrary, the activation energy of d.c.-conductivity, i.e. long-range Li ion motion decreases from ~0.6 eV for ceramic samples to ~0.4 eV for samples prepared via mechanochemical route. It was proposed that MA leads to formation of nano-particulate high-conductive grain boundaries both in LTP and LATP.

Mechanosynthesis, Radiation-Thermal Modification and Characterization of Nanostructured Scandia Stabilized Zirconia Ceramics

AbstractSSZ-based ceramics were obtained by sintering of nanopowders derived at room temperature by mechanochemical synthesis from refined technical grade ZrO2 nano-precursors. RT-treatment by 2.5 MeV electrons up to 1563 K was used for the modification of ceramics. Powders and ceramics were characterized by XRD, Raman, SEM and EDS, TEM, SIMS techniques. The phase composition of Zr0.89Sc0.1Ce0.01O1.95 ceramics was very close to cubic structure but better fitting of XRD patterns was obtained for rhombohedral lattice. Conductivity of solid electrolytes for IT SOFC was studied by complex impedance method. To stabilize cubic structure and increase conductivity at operation temperature of To ∼ 1000 K, the composition of SSZ solid electrolyte was optimized by addition of yttria and sintering aids. The interaction of admixtures with minor dopants leading to intergrain phase was revealed. During fast sintering, ceramics keep a memory about inhomogeneous disordered solid solutions in a form of nanostructuring. Conductivity data indicate nanostructuring of ceramics too: activation energies of bulk and grain boundary conductivities are close (Eb ∼ 0.9 eV, Egb ∼ 1.05 eV). Annealing of ceramics at high temperatures increases conductivity at To and promotes grain growth.

Lithium superionic conduction in lithium borohydride accompanied by structural transition

The electrical conductivity of lithium borohydride (LiBH4) measured by the ac complex impedance method jumped by three orders of magnitude due to structural transition from orthorhombic to hexagonal at approximately 390K. The hexagonal phase exhibited a high electrical conductivity of the order of 10−3Scm−1. Furthermore, the conductivity calculated from the Nernst-Einstein equation using the correlation time obtained from Li7 nuclear magnetic resonance was in good agreement with the measured electrical conductivity. It was concluded that the electrical conductivity in the hexagonal phase is due to the Li superionic conduction.

Influence of cationic vacancies on the ionic conductivity of oxyapatites

Oxyapatites are very promising materials in terms of ionic conductivity. They can be considered as a potential electrolyte for fuel cells as SOFC. Substituted silicated rare earth oxyapatites with formula La 9.33+ z/3− x Me x □ 0.67− z/3 (SiO 4) 6O 2+ z/2− x/2 ( z < x < z + 4) have been prepared by solid-state reaction at high temperature. Two series have been synthesized: a first one is oxygen stoichiometric with formula La 9.33−2 x/3 Me x □ 0.67− x/3 (SiO 4) 6O 2, and a second one is anion deficient with formula La 9.17−2 x/3 Me x □ 0.83− x/3 (SiO 4) 6O 1.75□ 0.25. In both cases, cationic vacancies are similarly controlled and vary from 0.67 to 0 per unit cell: the aim is to study the influence of cationic vacancies on the ionic conductivity with two distinct oxygen stoichiometries. Cell parameters of the high-purity oxyapatites have been refined in order to check the strontium incorporation. Discontinuous evolution of the a parameter underlined the strong electrostatic interactions between the defects of the most highly substituted samples. Electrical properties of the samples have also been studied by the complex impedance method between 280 and 620 °C. The evolution of conductivity and activation energy with the cationic vacancies content gives information on the conductivity mechanism, highlighting the importance of the global stoichiometry of the material.

Influence of porosity on the electrical properties of La 9.33(SiO 4) 6O 2 oxyapatite

Oxyapatites are very promising materials in terms of ionic conductivity. They can be considered as a potential electrolyte for fuel cells as SOFC. The influence of porosity on the electrical properties of La 9.33(SiO 4) 6O 2 oxyapatite is reported here. Hot pressed pellets with various densification ratios have been characterized by the complex impedance method. The high frequency response associated with the bulk contribution is much more affected by the porosity than the grain boundaries contribution: as a consequence, the electrical behaviour of the samples has been considered in assimilating the porous ceramics to composite materials made of apatite with various amounts of air inclusions. Thus, the porosity dependence of conductivity, activation energy and permittivity are reported here. A percolation threshold has been highlighted for porosity values greater than 30%, involving great lowering of the electrical performances.

Influence of anionic vacancies on the ionic conductivity of silicated rare earth apatites

Oxyapatites are very promising materials in terms of ionic conductivity. They can be considered as a potential electrolyte for Solid Oxide Fuel Cells (SOFC). Doped silicated rare earth apatites with formula La 9.33− x Ca x (SiO 4) 6O 2− x/2 (0 ≤ x ≤ 1) have been prepared by solid state reaction at high temperature in order to determine the influence of anionic vacancies on the electrical properties of the material. The incorporation of calcium in the structure has been checked by characterizations of the powders (X-ray diffraction, helium pycnometry). The cell parameters of the hexagonal apatite were refined. Samples were sintered at 1550 °C. Electrical properties of each composition have been studied between 280 and 620 °C by the complex impedance method. The evolution of the bulk conductivity and of the activation energy with the substituting ratio gives information on the conductivity mechanism in these materials. An improvement of ionic conductivity about one order of magnitude has been observed for low calcium substitution ratios.

Mesoporous hydroxyapatites prepared in ethanol–water media: Structure and surface properties

Porous calcium hydroxyapatite Ca 10(PO 4) 6(OH) 2 (HAp) has been prepared from calcium hydroxide and NH 4H 2PO 4 solutions in alcohol–water media at various temperatures. The resulting powders have been characterized using X-ray diffraction, FT-IR spectroscopy, TG/TD analyses, nitrogen porosimetry, dynamic light scattering, complex impedance method and scanning electron microscopy. The temperature of the reaction and the use of ethanol as the solvent significantly alter the HAp morphology and particle size. The as-precipitated materials are mainly amorphous but they can become highly crystalline after heat-treatment at 800 °C, while still retaining high specific surface area. A correlation between structural and surface properties has been established.

Crystallographic studies of sugar binding by factor H domains 6–8

Crystals of Na3Nb4As3O19 were synthesized by a solid-state reaction. It crystallizes in the orthorhombic system, space group C2221 with a = 13.014(2) Å, b = 24.170(3) Å and c = 5.0880(9) Å. The structure can be described as a three-dimensional anionic framework containing two kinds of tunnels parallel to [0 0 1] direction where Na+ cations are located. The ionic conductivity was measured, on pellets of polycrystalline powders, between 573 and 893 K in the frequency range 0.01–13000 kHz through the complex impedance method. A correlation between electrical and structural properties was also discussed.

Fabrication of Li 2O–B 2O 3–P 2O 5 solid electrolyte by flame-assisted ultrasonic spray hydrolysis for thin film battery

Li 2O–B 2O 3–P 2O 5 glass soot was fabricated from aqueous precursor solution of a CH 3CO 2Li·2H 2O and BCl 3, POCl 3 by the flame-assisted ultrasonic spray hydrolysis. The aqueous precursor solution of the lithium acetates was first atomized with an ultrasonic vibrator (1.7 MHz). B 2O 3 and P 2O 5 were formed from BCl 3 and POCl 3 by oxy-hydrogen flame. Their properties were investigated by SEM, XRD, TGA–DSC and impedance analyzer. The formed particles in glass soot had spherical shape and the size of approximately 50–100 nm. XRD analysis revealed that the amorphous phase and crystalline phases were mixed in glass soot and the crystalline phases were B(OH) 3 and B 2O 3. The crystalline B(OH) 3 and B 2O 3 found in glass soot completely disappeared by heat treatment. Conductivity was measured by complex impedance method using impedance analyzer and the conductivity was 10 −8 S/cm.

Physico- and electrochemistry of composite electrolytes based on PEODME–LiTFSI with TiO 2

The effect of fumed TiO 2 fillers (pure and modified by H 2SO 4) on ionic conductivity of composite electrolytes based on poly(ethylene oxide) dimethyl ether (PEODME) oligomer ( M w = 500) doped with lithium bis-(trifluoromethanesulfonyl)imide LiN(CF 3SO 2) 2 (LiTFSI) are studied by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR) and complex impedance methods. The electrochemical stability of the electrolytes in the potential range of 4 V versus Li electrode has been confirmed by voltammetric measurements. Li electrode reactions have been followed by means of impedance spectroscopy. The growth in time of the resistance of the interfacial (Li electrode–polymer electrolyte) layers was inhibited upon the addition of fillers.