Electrical and thermophysical properties of mechanochemically obtained lanthanide hafnates

This contribution presents the synthesis and thermophysical characterization of seven lanthanide hafnates Ln₂Hf₂O₇ (Ln=Sm³⁺, Eu³⁺, Gd³⁺, Dy³⁺, Y³⁺, Ho³⁺, Yb³⁺); the title samples were prepared at room temperature by mechanically milling stoichiometric mixtures of the corresponding elemental oxides. Irrespective of the lanthanide ion involved, milling promotes the formation of highly disordered fluoritelike materials. Postmilling thermal treatments facilitate the formation of the fluorite ordered derivative, the pyrochlore structure, but only for the larger lanthanides (Sm³⁺, Eu³⁺, Gd³⁺). Impedance spectroscopy measurements revealed that these materials show a moderate‐to‐good oxygen ion conductivity at high temperatures; furthermore, those adopting the pyrochlore structure give higher σ_dc and lower E_dc than their fluorite analogues (σ_dc at 750°C>10^?3 S·cm^?1 vs <5·10^?4 S·cm^?1, respectively). The same trend also holds for the thermal resistivity at high temperatures; the highest thermal resistivity and thus, lowest κ was obtained for Eu₂Hf₂O₇ (κ~1.3·W·m^?1·K^?1 at 800°C). Therefore, Ln₂Hf₂O₇ phases might be attractive component materials for electrochemical devices and thermal insulating coatings.     

Struktur und elektrische Leitfähigkeit von polymeren organischen Halbleitern

In this review article we want to give information about low molecular and polymer organic semiconductors, which were recently synthesized in our institute. Specific electric conductivities up to σ_298°K = 9.0 · 10^?5Ω^?1 · cm^?1 and thermic activation energies of E = 0.30 eV of polyenearylenes, respectively -heteroarylenes were measured. Polyazomethines have a maximum σ_298°K = 3.3 · 10^?9Ω^?1 · cm^?1 and E = 0.35 eV. Polymers with indophenine units have conductivities up to σ_298°K = 1.1 · 10^?4Ω^?1 · cm^?1 and E = 0.39 eV. A maximum of σ_298°K = 5.0 · 10^?2Ω^?1 · cm^?1 and E = 0.05 eV was found for bis-(1.2-dicyanoethylenedithiolo)-metal salts. Polymers with a phthalocyanine- or hemiporphyrazine-like structure achieve a conductivity of σ_298°K = 2.3 · 10^?2Ω^?1 · cm^?1 and E = 0.15eV. Coordination polymers of dimercaptomaleic acid, respectively their monoamide show a maximum of σ_298°K = 3.2 · l0^?lΩ^?l · cm^?1 and E = 0.20 ev. Polymers with σ_298°K ≤1.5 · 10^?5 Ω^?l · cm^?l and E ≥ 0.5 eV were obtained by the polymerization of succinonitrile. All the investigated substances show an electronic conductivity. The existence of an ionic conductivity could, in all cases, be excluded by using direct current measurements over a long period of time.     

X-ray crystal structure of the dye 2-bromo-4-cyano-4′-N,N-diethylaminoazobenzene

The crystal structure of 2-bromo-4-cyano-4′-N,N-diethylaminoazobenzene has been determined from X-ray diffraction data: C₁₇H₁₇N₄Br, mol. wt = 357·1. Triclinic, Pī (No. 2), α = 13·162(5) Å, b = 7·516(3) Å, c = 8·496(4) Å, α = 101·63(4)°, β = 95·79(4)°, γ = 91·49(4)°, V = 818·10 ų, Z = 2, D_c = 1·45 g cm^?3, F(000) = 378, λ(Mo_Kz) = 0·7107 Å, μ(Mo_Kα) = 26·70 cm^?1. The structure was solved by direct methods and refined by full-matrix least-squares to R = 0·053 for 2081 independent reflexions. The molecule possesses an essentially planar azobenzene skeleton. The effects of substituents on the geometry of the azo group are discussed. Significant molecular parameters are: NN, 1·264(6) Å; ₁BrC, 1·904(5) Å; mean NC, 1·410(7) Å; NNC, 115·7(2)° and 113·0(2)°; NCC (cis relative to NN), 125·4(3)° and 123·1(2)°; CC(Br)C, 123·0(2)°.     

X-ray crystal structure of the dye 2-cyano-4-bromo-4′-N,N-diethylaminoazobenzene

The crystal structure and molecular conformation of 2-cyano-4-bromo-4′-N,N-diethylaminoazobenzene (C₁₇H₁₇N₄Br, mol. wt. = 357·2 a.m.u) has been determined from X-ray diffraction data; triclinic, P$\text{1}$ (No. 2), a = 10·132(11) Å, b = 12·216(16) Å, c = 6·966(11) Å, α = 104·21(9)°, β = 92·67(12)°, γ = 97·22(7)°, V = 826·5(9) ų, Z = 2, D_c = 1·436 g cm^?3, F(000) = 378, λ(MoKα) = 0·71069 Å, μ(MoKα) = 26·0 cm^?1. The structure was solved by the multiple solution direct method and refined by full-matrix least-squares to R = 0·059 for 1538 independent observed reflections. The azobenzene skeleton is planar to within 0·06 Å. Most significant bonding data are: NN, 1·290(8) Å; BrC, 1·866(6) Å; mean CN (azo) 1·380(8) Å; NNC, 113·6(4) and 115·3(4)°; NCC (cis relative to NN) 125·9(4)° and 126·7(4)°; NCC (trans) 116·8°(5)° and 116·1(4)°.     

Electrical properties of diphenyldiacetylene annealed under elevated pressure

A unique class of conjugated compounds composed of the derivative of condensed polycyclic aromatic compound with the phenyl group and diphenyldiacetylene oligomer was synthesized by annealing of diphenyldiacetylene under elevated pressure. The effect of annealing pressure on the conductivity of the compounds was studied. The total conductivity of the compound decreased with a decrease of frequency, approaching a constant value (dc conductivity: C_dc). The dc conductivity of the compound increased from below 10^?15 to 10 S cm^?1 with increasing annealing pressure. The dc conductivity of the oligomer was below 10^?15 S cm^?1 and that of the derivative increased from 10^?8 to 10 S cm^?1 with decreasing H/C (H/C:0.45–0.04). The conduction of the conjugated compound was electronic. The temperature coefficient of those dc conductivities was positive, with an approximately linear relation between In (C_dcT^0.5) and (1/T)^0.25, where T is the temperature. The ac conductivities C_ac were proportional to temperature and frequency f and had the following equation C_ac = Tf^S, S = 0.67–0.75. These results showed that the conduction mechanism can be explained by the hopping in a manifold of states at the Fermi level. © 1994 John Wiley & Sons, Inc.     

Structure of the dye 2,6-dichloro-4′-N,N-diethylaminoazobenzene

The structure of 2,6-dichloro-4′-N,N-diethylaminoazobenzene has been determined from X-ray diffractometer data: C₁₆H₁₇Cl₂N₃, MW = 322·2, monoclinic, P2₁/n, a = 11·160 (2), b = 12·066 (2), c = 13·633 (3) Å, β = 116·46 (2)°, V = 1643·5 ų, Z = 4, D_c = 1·30 g cm^?3, F(000) = 672, λ(MoKα) = 0·71069 Å, μ(MoKα) = 3·94 cm^?1. The structure was solved by direct methods and refined to R = 0·073 for 1495 independent reflexions. The molecule is non-planar with a dihedral angle of 87·8° between the phenyl rings. The effects of substituents on the aromatic ring geometry are discussed. Significant molecular parameters are: NN, 1·164 (9) Å; mean ClC, 1·741 (6) Å; mean CN(azo), 1·487 (9) Å; NNC, 112·4 (2)° and 109·1 (2)°; NCC (cis relative to NN), 125·5 (3)° and 122·4 (2)°; NCC (trans relative to NN) 114·0 (3)° and 119·5 (3)°; mean CC(Cl)C, 122·3 (3)°.     

Study of hyperbranched poly(glycidol) sulfate electrolyte

Hyperbranched poly(glycidol) alkali sulfate (SHPG‐M) was prepared based on hyperbranched poly(glycidol). Polyurethane–hyperbranched poly(glycidol) (PU–SHPG‐M) sulfate electrolyte is a kind of single ionic or cationic conducting polymer electrolyte. Such a single ionic polymer electrolyte can obviously reduce the polarization and has little decay of direct current (DC) conductivity. SHPG‐M was characterized by Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), atomic force microscopy (AFM) and impedance analysis. The optimum conductivity is ～3 × 10^?6 S·cm^?1, with 30–40% SHPG‐M in the polymer electrolyte at room temperature. The species of cation greatly effects the ionic conductivity of the polymer electrolyte; that is, σ_SHPG‐Li > σ_SHPG‐Na > σ_SHPG‐K, with same SHPG‐M content in the polymer electrolyte. The ionic conductivity increases with an increase of temperature, and the dependence of ionic conductivity on temperature fits the Arrhenius equation well. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1185–1190, 2003     

Electrochemical characterization of BaCe0·7Zr0·1Y0·16Zn0·04O3-δ electrolyte synthesized by combustion spray pyrolysis

BaCe_0·7Zr_0·1Y_0·16Zn_0·04O_3-δ perovskite has been investigated due to its potential as an electrolyte in industrial steam electrolysis applications. The lowest area specific resistance (ASR) is achieved as 4.0 Ω cm² at 711 °C under 3% wet Ar atmosphere. The conductivity is calculated as 2.93 × 10^?2 S cm^?1 and kept stable for a ~70 h testing period. ASR increased at lower temperature (511 °C) under the same atmosphere and a new impedance arc (with 4.5 Ω cm² ASR and 2 × 10^?8 F equivalent capacitance) is formed, indicating second phase formation. No second phase formation is observed at the same temperature under dry 5% H₂ in Ar. The second phase formation/degradation of the electrolyte is attributed to Ba(OH)₂ and CeO₂ formations around 500 °C under wet atmospheres. At elevated temperatures, ~700 °C, BaCe_0·7Zr_0·1Y_0·16Zn_0·04O_3-δ exhibits both excellent protonic conductivity and stability which makes it a great candidate for both industrial fuel cells and steam electrolysers.     

Fabrication and characterization of a solid polymeric electrolyte of PAN‐TiO2‐LiClO4

The ionic conductivity of PAN‐TiO₂‐LiClO₄ as a function of TiO₂ concentration and temperature has been reported. The electrolyte samples were prepared by solution casting technique. Their conductivity was measured using the impedance spectroscopy technique. The highest room temperature conductivity of 1.8 × 10^?4 S cm^?1 was obtained at 7.5 wt % of TiO₂ filler. It was observed that the relationship between temperature and conductivity were linear, fitting well in Arrhenius and not in Vogel‐Tamman‐Fulcher equation. The pre‐exponential factor, σ₀ and E_a are 1.8 × 10^?4 S cm^?1 and 0.15 eV, respectively. The conductivity data have been supported by differential scanning calorimeter (DSC) analysis. DSC analysis showed that there was a significant change in glass transition temperature (T_g) with the filler concentration. The SEM micrograph revealed that the TiO₂ particles are dispersed in the electrolyte, thus enhancing its conductivity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and performance study of cordierite/mullite composite ceramics for solar thermal energy storage

The employment of solar energy in recent years has reached a remarkable edge. It has become even more popular as the cost of fossil fuel continues to rise. Energy storage system improves an adjustability and marketability of solar thermal and allowing it to produce electricity in demand. This study attempted to prepare cordierite/mullite composite ceramics used as solar thermal storage material from calcined bauxite, talcum, soda feldspar, potassium feldspar, quartz, and mullite. The thermal physical performances were evaluated and characterized by XRD, SEM, EPMA, and EDS. It was found that the optimum sintering temperature was 1280°C for preparing, and the corresponding water adsorption was 11.25%, apparent porosity was 23.59%, bulk density was 2.10 mg·cm^?3, bending strength was 88.52 MPa. The residual bending strength of specimen sintered at 1280°C after thermal shock of 30 times decreased to be 57 MPa that was 36% lower than that before. The thermal conductivity of samples sintered at 1280°C was tested to be 2.20 W·(m·K)^?1 (26°C), and after wrapped a PCM (phase change materials) of K₂SO₄, the thermal storage density was 933 kJ·kg^?1 with the temperature difference (ΔT) ranged in 0‐800°C. The prepared cordierite/mullite composite ceramic was proved to be a promising material for solar thermal energy storage.     

Studies of the development of fibrillar structure in nylon 6

Very thin films of poly(vinyl alcohol) could be prepared by utilizing the adsorption of polymer molecules at air/water interface from the aqueous solutions of the poly(vinyl alcohol) derived from vinyl trifluoroacetate. The films prepared by the bubble method were thinner than those obtained by the frame method. The minimum thickness of the former films was 260 Å and that of the latter was 1800 Å. These very thin films resisted water at temperatures below 55°C. The maximum Young's modulus of the drawn/annealed films prepared from these samples was 30 GPa. The permeability of water, J_w/δP, was 2–6 × 10^?3 cm · s^?1 atm^?1 (0–55°C) for the untreated film (thickness: 1800 Å) prepared by the frame method and 0.8–2.2 × 10^?2cm · s^?1 · atm^?1 (5–55°C) for the untreated film (360 Å) prepared by the bubble method, and depended on the thickness of film.     

Thermal and dc Conductivity Behavior of Fly Ash Filled Polyaniline Composites

In this paper temperature dependence of dc conductivity (σ_dc) of emeraldine base form of polyaniline (PANI) and fly ash filled PANI are presented. Samples were prepared by in situ polymerization of aniline using ammonium persulphate as an oxidant and hydrochloric acid as dopant. Fly ash filled PANI composites were prepared by adding 3 gms of fly ash. Thermal characteristics of samples were measured using differential scanning calorimetry. The dc conductivity (σ_dc) of fly ash filled PANI was found to be on the order of 1.63 × 10^?11 s/cm at room temperature, which was lower than that of pure PANI. The activation energies calculated from σ_dc for PANI and the PANI 3 fly ash system were 1.35 and 1.16 eV, respectively. It was found that addition of fly ash to PANI drastically decreased the enthalpy from 2259.2 to 196.6 mJ. the endothermic peak due to the glass transition temperature shifted from 99.8 to 94.6°C. This was attributed to the change in the morphology of the composites on adding fly ash, as observed in the scanning electron micrographs.     

Faradaic rectification study of the metal/metal ion reactions

The kinetic parameters for Ag⁺/Ag and Cu²⁺/Cu reactions at the equilibrium potential and in the absence of dc polarisation have been obtained using the faradaic rectification method at audio frequencies. The values of transfer coefficients, ion exchange current densities and apparent rate constants, obtained for the two reactions at 27°C using 1·0mM of each of the Ag⁺ and Cu²⁺ in 1·0M KNO₃, are respectively 0·22; 7·3mA/cm²; 3·6·10^?3 cm/s and 0·45; 10·7 mA/cm²; 1·1×10^?4cm/s. These data are comparable to those reported in the literature. For obtaining reliable and reproducible results for the studies with metal/metal ion reactions suitable experimental conditions have been described.     

Synthesis and applications of composite cathode based on Sm0.5Sr0.5Co3−δ for solid oxide fuel cell

Cobaltite based perovskites, such as Sm_0.5Sr_0.5Co_3?δ (SSC), are attractive solid oxide fuel cell (SOFC) cathodes due to their high electrochemical activity and electrical conductivity. To obtain higher fuel cell performance with smaller particles, nano-sized SSC powders were synthesized by a complex method with/without carbon black, HB170. However, during synthesis, carbon black reacted with Sr, and unfortunately formed SrCO₃. To obtain pure perovskite SSC, a calcination temperature of 900 °C is needed. At 680 °C, an SOFC with SSC (calcined at 700 °C and synthesized without HB170) exhibited a higher fuel cell performance, of 0.68W·cm^?2, than that with SSCHB (calcined at 900 °C and synthesized with HB170), of 0.58W·cm^?2. Adding GDC for composite cathode is more effective in SSCHB porous cathodes than in SSC porous cathodes. At 680 °C, the composite cathode of SSCHB6-GDC4 exhibited the highest maximum power density of 0.72W·cm^?2 which results from the combined effects of lowered charge transfer polarization and mass transfer polarization. To obtain higher fuel cell performance, optimum composition and processes are necessary.     

Microstructure-property relationships in composites of 8YSZ ceramics and in situ graphitized nanocellulose

Ceramic matrix composites (CMC) of 8 mol.% yttria-stabilized zirconia (8YSZ) mixed with natural fiber nanocellulose (0.75, 1, 2 wt%) were prepared by spark plasma sintering (SPS). Nanocellulose markedly improved the densification of the 8YSZ ceramic matrix and induced significant grain size refinement. It was demonstrated that in situ graphitization of nanocellulose during the SPS processing resulted in 6 nm thin turbostratic graphite layers homogeneously covering the 8YSZ ceramic grains. The dielectric properties were analyzed by electrical impedance spectroscopy suggesting a low percolation threshold near or below ≈ 1.6 vol% graphite, above which mixed ionic-electronic conduction dominates. The CMCs are stable under reducing conditions (5%H₂/Ar atmosphere) at least until 800 °C with a high conductivity of σ_dc = 0.17 S?cm^?1 even at 900 °C (8YSZ-2%CNF). These features make the 8YSZ-nanocellulose CMCs promising candidates for application in medium- to high-temperature electrochemical devices.     

Effect of reaction kinetics of polymer electrolyte on the ion‐conductive behavior for poly(oligo oxyethylene methacrylate)–LiTFSI mixtures

The effect of the reaction kinetics on the ionic conductivity for a comblike‐type polyether (MEO) electrolyte with lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) was characterized by DSC, complex impedance measurements, and ¹H pulse NMR spectroscopy. The ionic conductivity of these electrolytes was affected by the reaction condition of the methacrylate monomer and revealed by the glass transition temperature (T_g), spin–spin relaxation time (T₂), steric effects of the terminal groups, and the number of charge carriers indicated by the VTF kinetic parameter. In this system, the electrolytes prepared by the reaction heating rate of 10°C/min of MEO–H and 15°C/min of MEO–CH₃ showed maximum ionic conductivity, σ_i, two to three times higher in magnitude than that of the σ_i of the others at room temperature. As experimental results, the reaction kinetic rate affected the degree of conversion, the ionic conductivity, and the relaxation behaviors of polyether electrolytes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2149–2156, 2003     

Phase development in ZnO varistors

Based on a typical ZnO varistor composition (97·0 mol.-% ZnO, 1·0 mol.-% Bi₂O₃, 1·0 mol.-% Sb₂O₃, 0·5 mol.-% MnO and 0·5 mol.-% Co₃O₄), phase development of the ZnO varistor during sintering has been investigated using in situ high temperature X-ray diffraction up to 900°C, and conventional ambient X-ray diffraction for samples sintered at 900°C to 1250°C. The results indicate that α-Bi₂O₃ can be detected until 700°C; the pyrochlore phase can be detected in the samples heat treated at 700°C and up to 1250°C; the spinel phase is present at and >900°C. However, the main phases in the varistor are established by 950°C. By this temperature, the essential microstructure features are formed, and the varistors exhibit non-linear electrical properties, with a non-linear coefficient α of 35 and breakdown field of 8000 V cm^?1. With increasing sintering temperature, both the α value and breakdown field decrease.     

The specific volume of poly(4-methylpentene-1) as a function of temperature (30°–320°C) and pressure (0–2000 kg/cm2)

The dependence of the specific volume of a commercial sample of poly(4-methylpentene-1) (Mitsui TPX, RT-20, abbr. PMP) on temperature (30°–320°C) and pressure (0–2000 kg/cm²) has been determined. Results are reported in tabular form and as approximate fits, making use of the Tait equation. The data show that the crystalline melting transition of this type of PMP is completed at 235°C under zero pressure and gives indication of a glass transition temperature T_g at about 20°C at p = 0. Its approximate pressure dependence is given by dT_g/dp ≈ 0.015°C kg^?1 cm². The zero pressure results on the melting and glass transitions are in agreement with DTA results. The p-v-T data, quenching experiments, and a determination of the crystalline unit cell (tetragonal, a = b = 18.70 Å, c = 13.54 Å) confirm earlier work indicating that the room-temperature crystalline specific volume of PMP is greater than the amorphous specific volume. This unusual density behavior persists to a temperature of 50–60°C at p = 0 and to temperatures as high as 230–240°C under a pressure of 2000 kg/cm².     

Preparation and characterization of novel hybrid thermoplastic poly(ether urethane)/poly(vinylidene fluoride) elastomers,and their application as solid polymer electrolytes

A comb‐like polyether, poly(3‐2‐[2‐(2‐methoxyethoxy)ethoxy]ethoxymethyl‐3′‐methyloxetane) (PMEOX), was reacted with hexamethylene diisocyanate and extended with butanediol in a one‐pot procedure to give novel thermoplastic elastomeric poly(ether urethane)s (TPEUs). The corresponding hybrid solid polymer electrolytes were fabricated through doping a mixture of TPEU and poly(vinylidene fluoride) with three kinds of lithium salts, LiClO₄, LiBF₄ and lithium trifluoromethanesulfonimide (LiTFSI), and were characterized using differential scanning calorimetry, thermogravimetric analysis and Fourier transform infrared spectroscopy. The ionic conductivity of the resulting polymer electrolytes was then assessed by means of AC impedance measurements, which reached 2.1 × 10^?4 S cm^?1 at 30 °C and 1.7 × 10^?3 S cm^?1 at 80 °C when LiTFSI was added at a ratio of O:Li = 20. These values can be further increased to 3.5 × 10^?4 S cm^?1 at 30 °C and 2.2 × 10^?3 S cm^?1 at 80 °C by introducing nanosized SiO₂ particles into the polymer electrolytes. Copyright © 2006 Society of Chemical Industry     

Pore model parameters of cation-exchange membranes

Parameters of the equivalent pore model of different membranes (NAFION-125, MRF-26, and the polyethylene-polystyrenesulphonic acid membranes (PE/PSSA)) were estimated from measurements of water hydraulic permeabilities. The pore radius calculations were performed according to the modified Ferry-Elford equation r_θ = r_FEθ, where r_FE is the radius calculated from the Ferry-Elford relation and Å the tortuosity factor. The PE/PSSA membranes, expanded in hot water, were similar to the MRF-26 membranes in their equivalent pore model parameters (radius 20 – 24 Å, and specific permeation rate 5.09 and 4.30.10^?16 cm², respectively). The NAFION-125 membrane exhibits the smallest pore radius (14 Å) and specific permeation rate (0.841·10^?16 cm²).