Dielectric properties of EuF2

Dielectric constant (?) and loss (tan δ) of EuF₂ have been measured for the first time as a function of frequency in the temperature range from liquid nitrogen to 300°C. The data has been used to obtain the values of conductivity (σ). The conductivity values are frequency independent in the high temperature region and yield 1.05 eV for the activation energy for conduction.     

New Li+ ion conductors in the system Li4SiO4−Li3AsO4

In the system Li₄SiO₄-Li₃AsO₄, Li₄SiO₄ forms a short range of solid solutions containing up to 14 to 20% Li₃AsO ₄, depending on temperature, and γ-Li₃AsO₄ forms a more extensive range of solid solutions containing up to ≈55% Li₄SiO₄. The Li₄SiO₄-Li₃AsO₄ phase diagram has been determined and is of binary eutectic character. The ac conductivity of polycrystalline samples was measured over the range 0 to at least 300°C for nine different compositions. The two solid solution series have much higher conductivity than the pure end-members; maximum conductivity was observed in the γ-Li₃AsO₄ solid solutions containing ≈40 to 55% Li₄SiO₄, with values of $\text{≈2×10}{}^{\mathrm{?6}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$ at 20°C rising to ≈0.02 Ω^?1 cm^?1 at 300°C. These values are comparable to those found in the system Li₄SiO₄-Li₃PO₄. The variation with composition of the Arrhenius prefactor and activation energy has been interpreted in terms of the mechanisms of conduction. Li₃AsO₄ is a poor conductor essentially because the number of mobile Li⁺ ions is very small. This number, and hence the conductivity, increases dramatically on forming solid solutions with Li₄SiO₄, by the creation of interstitial Li⁺ ions. At ≈40 to 55% Li₄SiO₄, the number of mobile Li⁺ ions appears to be optimised. An explanation for the change in activation energy of conduction at ≈290°C in Li₄SiO₄ and at higher temperatures in Li₄SiO₄ solid solutions is given in terms of order-disorder of the Li⁺ ions.     

Electron concentration and mobility in In2O3

The electron concentration and mobility in polycrystalline In₂O₃ have been measured as a function of temperature and partial oxygen pressure, in the temperature range from 25 to 700°C. These experimental data are critically compared with literature data. A conduction model is proposed. Theoretical values of the electron concentration as a function of the partial oxygen pressure are reported for temperatures from 700 to 1400°C. An estimate is given for the minimum room temperature “intrinsic” electron concentration in In₂O₃ after a high temperature annealing experiment. It is also shown that interpretations of conductivity values for porous material in terms of carrier concentration only, can be very misguiding.     

D.C. electrical conductivity in LiNH4SO4

The d.c. electrical conductivity of pure, doped and quenched samples of LiNH₄SO₄ is measured between liquid nitrogen temperature and 290°C. A-type conductivity anomalies are observed at 10°C and at 186.5°C along the ferroelectric axis. The mechanisms of electrical conduction in the various phases and at the transition points are discussed.     

High temperature phase transition in NH4H2PO4

NH₄H₂PO₄ (ADP) has been investigated by infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis and d.c. conductivity in the temperature range of 25–180° C. Sharp reversible changes were observed in the region from 400 to 500 cm^?1 of the infrared spectra in the temperature range of 138–174° C. Similar and supportive data were obtained with DSC, TGA and DC conductivity measurements. The results clearly suggest a high temperature phase transition for ADP before its melting point.     

Effect of Sn-doping at Mo-site on the conductivity of La2Mo2O9 series of compounds

Taking oxygen ion conductor La₂Mo₂O₉, as a base compound, a series of Sn-doped La₂Mo_2−x Sn _x O_9−δ, x = 0, 0.01, 0.02, 0.03, 0.05, 0.1, 0.15, 0.2 specimens were prepared and characterized by XRD for phase and crystal structure determination and ac impedance spectroscopy for ac and dc conductivity measurement. We have found that there is slight improvement in overall conductivity of the specimen with x = 0.03 at 800°C compared to the undoped compound at the same temperature. The value of conductivity when extrapolated to 800°C is found to be 0.055 S cm-1 for the specimen with x = 0.03, whereas conductivity of undoped specimen at the same temperature is found to be 0.033 Scm⁻¹.     

Electrical conductivity of the solid system AgI-Sb2S3

Electrical conductivity of the solid system AgI-Sb₂S₃ and its dependence on composition within the temperature range from room temperature to 280°C was investigated. The temperature of phase transition β→α AgI divides the conductivity region into low-temperature and high-temperature parts. Within the high-temperature region the conductivity increases monotonously with an increase in mole fraction of AgI, while within the low-temperature one its maximum appears at Agl mole fraction of 0.6. This composition is glassy and was investigated in detail with regard to the conductivity and the double layer capacitance. The electric conductivity course was explained in the light of structure investigations.     

Ionic transport in the lithium nitride bromides,Li6NBr3 and Li1 3N4Br

The ionic and electronic conductivities of the lithium nitride bromides Li₆NBr₃ and Li_{1 3}N₄Br have been studied in the temperature range from 50 to 220°C and 120 to 450°C, respectively. Both compounds are practically pure lithium ion conductors with negligible electronic contribution. Li₆NBr₃ has an ionic conductivity Ω of 2 × 10^-6Ω^-1cm^-1 at 100°C and an activation enthalpy for σT of 0.46 eV. Li_{1 3}N₄Br shows a phase transition at about 230°C. The activation enthalpy for σT is 0.73 eV below and 0.47 eV above this temperature. The conductivities at 150 and 300°C were found to be 3.5 × 10^-6 Ω^-1cm^-1 and 1.4 × 10^-3Ω^-1cm^-1, respectively. The crystal structure is hexagonal at room temperature with $\text{a = 7.415 (1)}\text{A}\text{?}$ and $\text{c = 3.865 (1)}\text{A}\text{?}$.     

Electrical conductivity of Na2SO4(I)

The electrical conductivity of the solid phase Na₂SO₄(I) has been measured between the melting point at 884°C and the first order phase transition at about 240°C. The measurements have been performed using complex impedance measurements on pellet samples as well as on U-cells. The electrical conductivity is strongly dependent on sample at low temperatures and the activation energy ranges from 0.5 eV to 1.7 eV over the measured temperature range.     

Low temperature electrical conductivity,dielectric constant,and phase transitions in (NH4)2SO4 and (ND4)2SO4

Careful axiswise measurements of d.c. conductivity and dielectric constants of (NH₄)₂SO₄ from 50 to - 196°C establish two distinct phase transitions, instead of one, at temperatures -49.5 and -58°C which remain unchanged in (ND₄)₂SO₄. Explanation based on successive distortions of non-equivalent (NH₄)⁺ is offered. Low temperature transport process in the crystal also is discussed.     

Hot stage X-ray diffractometer studies on Ag2PbI4 and Ag4PbI6

Mixtures of AgI and PbI₂ cooled from the melt result in the peritectic formation of a fast ion conducting phase centred about Ag₄PbI₆, which is face centred cubic with a = 6.33(5)A; this phase exhibits high electrical conductivity. On cooling to about 125°C, dissociation occurs to γAgI and PbI₂, accompanied by the transient formation of another phase, centred about Ag₂PbI₄. A modified form of the T-x section of the equilibrium phase diagram at AgI concentrations greater than 60 mole % and below 300°C is proposed.     

Low-temperature performance of thin solid electrolyte cell based on MoO3-doped Bi2O3

Improvement of low-temperature performance of oxygen sensor was studied by preparing a thin film of 15 μm thickness. Melt-quenched Bi₂O₃ film doped with 16 mol% MoO₃ was used as an electrolyte after HF treatment. Impedance measurements were carried out in the frequency range DC-100 KHz. Resistance of electrolyte in the form of thin film (110ω) was negligibly small compared with the overall resistance of the cell (287 Kω) at 350°C. Oxygen/air concentration cell was constructed and the cell performance was measured at 350 and 300°C. Transference number close to unity and rapid response were observed at 350°C, however the cell showed a long response time of about 3 min at 300°C.     

Ionic and electronic conduction of oxygen ion conductors in the Bi2O3−Y2O3 system

The ionic conduction of sintered samples of Bi₂O₃?Y₂O₃ containing 20–30 mol% Y₂O₃ has been investigated by means of ac conductivity experiments and EMF measurement of an oxygen concentration cell using the specimen tablet as electrolyte. Ac conductivity was measured at a frequency of 10 kHz under oxygen partial pressures ranging from 1 to 10^-21 atm. The results show that these materials possess high ionic conduction. The conductivities for samples containing 22.5–30 mol% Y₂O₃ are many times higher than those of stabilized zirconia-based solid electrolyte at corresponding temperatures. The ratio of E_meas./E_calc. of an oxygen concentration cell Pt∣O₂(air)∣Bi₂O₃?Y₂O₃∣O₂(pure oxygen)∣Pt is close to 1 which shows that the materials containing 22.5 to 30 mol% Y₂O₃ are nearly pure ionic conductors. The p-type conductivity is negligible at higher P_O2 values. The n-type conduction for a sample containing 27.5 mol% Y₂O₃ was investigated using the Coulomb titration technique in which the following cell was used: Pt Rh∣O₂(air)∣Bi₂O₃?Y₂O₃∣[O]_sn∣W.log P_é=-767000/T+665. P_é is equal to 2.6×10^-61 atm at 800°C. The n-type conductivity is also very small. Thus these materials are good oxygen ionic conductors.     

Lithium aluminum nitride,Li3AlN2 as a lithium solid electrolyte

Single phase of Li₃AlN₂ was prepared from the mixture of Li₃N/AlN = 1.2 to 1.5 in molar ratio at 700°C and at 900°C. It crystalizes in the cubic system derived from antifluorite-type structure having the lattice parameter $\text{a = 9.470}\text{A}\text{?}$. It is a pure ionic conductor having conductivity of 5 × 10^?8ω^?1cm^?1 at room temperature and an activation energy of 52 kJ/ mol. Its decomposition voltage was 0.85 V at 104°C. The TiS₂/Li₃AlN₂/Li cell could be discharged at a constant current of 45 μA/cm² at 104°C.     

Effect of deuteration on the electrical conductivity,dielectric constant and phase transitions in LiNH4SO4

Measurements of dc conductivity and dielectric constant show that deuteration causes an upward shift of the high temperature phase transition point from 186.5 to 191°C and a downward shift of the low temperature transition point from 10 to -1.5°C in LiNH₄SO₄. Mechanisms of phase transitions and of electrical transport in the crystal are discussed.     

Mn3O4包覆对LiNi0.5Mn1.5O4正极材料界面电化学性能的提高

本文采用化学湿磨法,首次将金属氧化物Mn₃O₄包覆于LiNi_0.5Mn_1.5O₄颗粒表面,使得电极材料的电子电导率从1.53×10^-7 S/cm 提高到3.15×10^-5 S/cm. 电化学测试结果表明Mn₃O₄包覆大大提高LiNi_0.5Mn_1.5O₄正极材料的倍率性能和高温循环稳定性. 最佳包覆样品为2.6wt% Mn₃O₄包覆的LiNi_0.5Mn_1.5O₄,在10 C倍率下具有108 mAh/g的高放电容并且在55 °C下100次循环后仍有78%的容量保持率,远大于未包覆样品67%的容量保持率.     

Na+ ion conductivity and crystallographic cell characterization in the Hf-nasicon system Na1+xHf2SixP3−xO12

We have measured the effect of varying the mobile ion concentration on the sodium ion conductivity in the Hf-Nasicon system, Na_1+xHf₂Si_xP_3-xO₁₂, for 1.4 ? x ? 2.8. The conductivity is greatest for Na_3.2Hf₂Si_2.2 P_0.8O₁₂: σ_25°C = 2.3 × 10^?3 (ω cm)^?1, and σ_250°C = 1.7 × 10^?1 (ω cm)^?1. These values are approximately 50% greater and worse, respectively, than the values reported for the best Zr-Nasicon. We have characterized the variation of lattice parameters with composition and found the behavior to be similar to that of Zr-Nasicon. A small distortion from rhombohedral to monoclinic symmetry occurs for compositions 1.8 ? x ? 2.2.     

Ionic conductivity in Na4ZrSi3O10

A new compound, Na₄ZrSi₃O₁₀, belonging to the ternary system Na₂O-SiO₂-ZrO₂ is presented. Based on X-ray powder methods, it is assigned monoclinic symmetry with the probable group C 2/c. The ionic conductivity was found to be 4 x 10^-3Ω^-1cm^-1 at 300°C and the activation energy for ionic motion is 42 kJ/mol.     

Anomalous acid proton self-diffusion in N(CH3)4HSO4 — A candidate for proton superionic conductivity

The appearance of a “liquid-like” proton T₂ component above 100°C and the relatively high value of the proton self-diffusion coefficient D = (5–8) × 10^-7cm²sec^-1 between 175°C and 200°C demonstrate the onset of a super-ionic state in N(CH₃)₄HSO₄. The ratio between the “liquid” and “solid” like components shows that acid protons are responsible for the high ionic conductivity.     

Preparation and characterization of co-doped (Ce0.80La0.15Al0.05O1.90) and multiple-doped (Ce0.80Sm0.10Gd0.05Al0.05O1.90 and Ce0.80Gd0.10Sm0.05Al0.05O1.90) ceria

Attempts have been made to synthesize a few compositions Ce_0.80La_0.15Al_0.05O_1.90, Ce_0.80Sm_0.10Gd_0.05Al_0.05O_1.90, and Ce_0.80Gd_0.10Sm_0.05Al_0.05O_1.90 by citrate–nitrate auto-combustion method. The aim of the present investigation was to study the effect of co-doping and multiple doping on the ionic conductivity of CeO₂ for its use as solid electrolyte in intermediate temperature solid oxide fuel cells. XRD patterns showed that all the samples have fluorite-type crystal structure similar to undoped ceria. Microstructures of thermally etched samples have been studied by scanning electron microscopy. Contributions of grains σ _g and grain boundaries σ _gb to the total conductivity σ _T, have been determined using impedance analysis. Impedance measurements were made in the frequency range 1 Hz–1 MHz and temperature range 250–500 °C. Our experimental results show that multiple doping is more effective than co-doping for improving the oxide ion conductivity of ceria in the materials investigated in the present study.