Effect of Ni(II) substitution on phase stabilization electrical properties of BICo(III)VOX.20 oxide-ion conductor

The BICO_0.20–xNI_xVOX solid electrolyte was synthesized by the standard solid-state reaction. The effect of Ni(II) substitution for Co(III) on phase stabilization and oxide-ion performance has been investigated in the compositional range 0?≤?x?≤?0.20 using X-ray powder diffraction, differential thermal analysis and AC impedance spectroscopy. The highly conductive γ′-phase was effectively stabilized at room temperature for compositions with x?≥?0.13 whose thermal stability increases with Ni content. The complex plane plots of impedance were typically represented at temperatures below 380?°C, suggesting a major contribution of polycrystalline grains to the overall electrical conductivity. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. Interestingly, the maximum ionic conductivity at lower temperatures (~2.56?×?10^?4?S^?cm^?1 at 300?°C) was observed for the composition with x?=?0.13. The variation of low-temperature conductivity with Ni content was accompanied with a general drop in the corresponding values of ΔE_LT. However, the local minimum high-temperature conductivity, σ₆₀₀?°C?~?2.26?×?10^?2?S^?cm^?1 for x?=?0.10, coupled with a local maximum value of ΔE_HT?~?0.48?eV was attributed to an increased defect trapping effect correlated with the V(V)?→?V(IV) reduction at elevated temperatures.     

Thermal conductivity at the amorphous-nanocrystalline phase transition in beech wood biocarbon

High-porosity samples of beech wood biocarbon (BE-C) were prepared by pyrolysis at carbonization temperatures T _carb = 650, 1300, and 1600°C, and their resistivity ρ and thermal conductivity κ were studied in the 5–300 and 80–300 K temperature intervals. The experimental results obtained were evaluated by invoking X-ray diffraction data and information on the temperature dependences ρ(T) and κ(T) for BE-C samples prepared at T _carb = 800, 1000, and 2400°C, which were collected by the authors earlier. An analysis of the κ(T _carb) behavior led to the conclusion that the samples under study undergo an amorphous-nanocrystalline phase transition in the interval 800°C < T _carb < 1000°C. Evaluation of the electronic component of the thermal conductivity revealed that the Lorentz number of the sample prepared at T _carb = 2400°C exceeds by far the classical Sommerfeld value, which is characteristic of metals and highly degenerate semiconductors.     

Study on electrical conductivity and phase transition in singly doped BIPBVOX (Bi2V1−xPbxO5.5−x/2) solid electrolyte

Samples of bismuth lead vanadium oxide (BIPBVOX) (Bi₂V_1–xPb_xO_5.5–x/2) singly substituted system in the composition range 0.05 ≤ x ≤ 0.20 were prepared by sol–gel synthesis route. Structural investigations were carried out by using a combination of differential thermal analysis (DTA) and powder X-ray diffraction (PXRD) technique. Energy dispersive X-ray spectroscopy analysis (EDXA) of doped samples was carried out to predict the sample purity and doping concentration. Transitions, α?β, β?γ and γ′?γ were detected by XRD, DTA and variation in the Arrhenius plots of conductivity. The ionic conductivity was measured by AC impedance spectroscopy. The solid solutions with composition x ≤ 0.07 undergo α?β phase transition, at 329 °C and β?γ phase transition at 419 °C. The highly conducting γ′-phase was effectively stabilized at room temperature for compositions with x ≥ 0.17 whose thermal stability increases with Pb content. At 300 °C, the highest value of conductivity 6.234 × 10^?5 S cm^?1 was obtained for composition x = 0.15 and at 600 °C the highest value of conductivity 0.65 S cm^?1 is observed for x = 0.17. AC impedance plots reveal that the conductivity is mainly due to the grain contribution to oxide ion conductivity.     

Electron mobility of Sr1-xLaxTiO3 ceramics between 600 °C and 1300 °C

1-x La_xO₃ ceramics (0.003<x<0.40) were measured between 600 °C and 1300 °C. The density of electrons in the conduction band was determined from Hall and thermopower measurements. A chemical approach (Ti³⁺-titration) confirmed these results. The electron mobility was calculated by combining charge carrier density and conductivity data. The temperature dependence of the mobility obeys a power law. Its exponent varies from -1.5 for slightly doped samples (x=0.003) to -2.74 for lanthanum-rich samples (x=0.4) indicating a phonon scattering controlled transport behavior. The mobility data obtained from slightly doped ceramic samples agree very well with Hall mobilities found in undoped SrTiO₃ single crystals. Received: 22 January 1997/Accepted: 1 April 1997     

Study on structural, thermal, sintering and conductivity of Cu-Co doubly substituted Bi4V2O11

Doubly substitution of vanadium by Cu and Co in the limit of 10% in Bi₄V₂O₁₁, has led to the formation of the Bi₄V_1.8Cu_0.2−xCo_xO_10.7 solid solution. X-ray diffraction shows that all the compositions present a tetragonal symmetry. The thermal analysis has revealed that the polymorph γ' phase, which is formed by a partial ordering of oxygen ions in the γ high temperature form, is stabilized at room temperature. The influence of sintering temperature on the microstructure of the samples was investigated by the scanning electron microscopy (SEM). The ceramics sintered at 820 °C for more than 3 hours present micro-craks. The evolution of the electrical conductivity with temperature and the degree of substitution has been investigated by impedance spectroscopy. The sample with x=0.1 presents the highest value of the conductivity ≈4.6×10⁻² S·cm⁻¹ at 600 °C.     

Effect of lithium ion content on the lithium ion conductivity of the garnet-like structure Li<Subscript>5+x</Subscript>BaLa<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>11.5+0.5x</Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0–2)

We report systematic studies on the transport properties by varying the lithium oxide content of the garnet-based solid electrolyte Li_5+xBaLa₂Ta₂O_11.5+0.5x (x=0, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.00) for understanding the ionic conductivity dependence on the crystal lattice parameter and carrier concentration. Powder X-ray diffraction data of Li_5+xBaLa₂Ta₂O_11.5+0.5x (x=0, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.00) indicate the existence of the garnet-like structure for any of the compositions. The cubic lattice parameter was found to increase with increasing x and reaches a maximum at x=1.00, then decreases slightly with a further increase in x. Impedance measurements obtained at 50 °C indicate a maximum of the grain-boundary resistance (R_gb) contribution to the total resistance (R_b+R_gb) at x=0.0 and a considerable decrease with increase in lithium concentration. The total (bulk + grain-boundary) and bulk ionic conductivity increase with increasing lithium content and reach a maximum at x=1.00 and then decrease slightly with further increase in x. Among the investigated compounds, Li₆BaLa₂Ta₂O₁₂ exhibits the highest total (bulk + grain-boundary) and bulk ionic conductivity of 1.5×10^-4 and 1.8×10^-4 S/cm at 50 °C, respectively. The results obtained in the present investigation of the Li_5+xBaLa₂Ta₂O_11.5+0.5x (x=0–2) series clearly revealed that the lithium content plays a major role in decreasing the grain boundary resistance contribution to the total resistance and also in increasing the ionic conductivity of the garnet-like compound. PACS 66.10.Ed; 82.45.Gj; 82.47.Aa     

Hydrothermally prepared oxide-ion and Mixed Conductors based on CeO2

The structure, thermal expansion coefficients, electrical and electrochemical properties of Ce_1−xM_xO_2−δ (M=Bi, La, Pr, Eu, Tb; x=0–0.30) solid solutions, prepared hydrothermally for the first time, are surveyed. For all cation substitution a solubility limit depending on the cation size was found. The uniformly small particle size (10–50 nm) of the hydrothermally prepared materials allows sintering of the samples into highly dense ceramic pellets at 1300–1400 °C, a significantly lower temperature, compared to that at 1600–1650 °C required for samples prepared by solid state techniques. X-ray absorption near edge spectroscopy (XANES) was used for the identification of Tb³⁺/Tb⁴⁺ or Pr³⁺/Pr⁴⁺ ions. The maximum of total conductivity in all solid solutions was found for x ∼ 0.15–0.25 with electronic contribution to the total conductivity ∼ 50 % for Tb/Pr substitution and close to zero in all other cases. The conductivity becomes more ionic with decreasing Tb/Pr substitution. The thermal expansion coefficients, determined from high-temperature X-ray diffraction data, are 11.7×10⁻⁶ K⁻¹ for CeO₂ and slowly decrease for Tb and increase for all other cases with increasing substitution. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Study of phase transition of TiO<Subscript>2</Subscript>–CaO system

Electrical conductivity of TiO₂ doped with CaO has been measured at different temperatures for various molar ratios. The conductivity after initially remaining constant till about 140 °C increases with temperature due to the migration of vacancies created by doping. After attaining a maximum value at 240 °C, conductivity decreases due to the collapse of fluorite framework. A second rise in conductivity at high temperature beyond 400 °C indicates the phase transition of TiO₂, from anatase to rutile, which is confirmed by the differential scanning calorimetry results. X-ray powder diffraction, impedance measurements, and Fourier transform infrared spectral studies were also carried out for confirming the doping effect and phase transitions in TiO₂. Doping of TiO₂ with CaO shifts the transition to lower temperatures.     

Nitrogen implantation in GaAs1−xPx (x=0.4; 0.65)

Nitrogen ions were implanted in GaAs_1−xP_x (x=0.4; 0.65) at room temperature at various doses from 5×10¹² cm⁻² to 5×10¹⁵ cm⁻² and annealed at temperatures from 600°C up to 950°C using a sputtered SiO₂ encapsulation to investigate the possibility of creating isoelectronic traps by ion implantation. Photoluminescence and channeling measurements were performed to characterize implanted layers. The effects of damage induced by optically inactive neon ion implantation on photoluminescence spectrum were also investigated. By channeling measurements it was found that damage induced by nitrogen implantation is removed by annealing at 800°C. A nitrogen induced emission intensity comparable to the intensity of band gap emission for unimplanted material was observed for implanted GaAs_0.6P_0.4 after annealing at 850°C, while an enhancement of the emission intensity by a factor of 180 as compared with an unimplanted material was observed for implanted GaAs_0.35P_0.65 after annealing at 950°C. An anomalous diffusion of nitrogen atoms was found for implanted GaAs_0.6P_0.4 after annealing at and above 900°C.     

Enhancement of conductivity in La2Mo2O9 ceramics fabricated by a novel three-stage thermal processing method

Pure and dense La₂Mo₂O₉ ceramic electrolytes with grain sizes of 1–3 μm were fabricated from nanocrystalline powders by a novel three-stage, one-cycle, pressureless thermal processing method at temperatures as low as 600 °C. Phase formation, microstructure and grain size of the samples were examined using X-ray diffraction and scanning electron microscopy. Density of the sintered samples was determined as in the range of 94–96% of the theoretical density by weight/geometric measurements. Impedance spectroscopy was used to characterize the electrical properties of the sintered samples. The conductivity of the three-stage sintered samples reaches a value of 0.018 S/cm at 600 °C and 0.05 S/cm at 700 °C, much higher than that of the samples fabricated by conventional solid-state reaction method, but similar to that of the samples sintered at 950 °C for 12 h from the same nanocrystalline powders. The high conductivity of these samples was attributed to the co-operation of the excellent performance of nanocrystalline powders and the advantages of the novel three-stage low-temperature thermal processing.     

Ionic conductivity, thermal stability and FT-IR studies on plasticized PVC / PMMA blend polymer electrolytes complexed with LiAsF6 and LiPF6

The lithium salt (x) (x=LiAsF₆, LiPF₆) was complexed with a blend of poly(vinyl chloride) (PVC) / poly(methyl methacrylate)(PMMA) and plasticized with a combination of ethylene carbonate(EC) and propylene carbonate(PC). The electrolyte films were prepared using doctor blade method and subjected to ionic conductivity measurements at nine different temperatures viz.,-30, -15, 0, 15, 30, 40, 50, 60 and 70 °C. The films were also subjected to TG - DTA and FT-IR analysis. The effect of salt on ionic conductivity is discussed. A 75:25 PMMA/PVC blend at 60 % plasticizer content has been found to possess optimal properties in terms of ionic conductivity, thermal and electrochemical stability.     

Phase stability,thermal, electrical and structural properties of (Bi2O3)1−x−y(Sm2O3)x(CeO2)y electrolytes for solid oxide fuel cells

In this study, (Bi₂O₃)_1?x?y(Sm₂O₃)_x(CeO₂)_y ternary system was synthesized by using solid-state reaction method. Structural, morphological, thermal and electrical properties of the samples were evaluated by means of X-ray diffraction (XRD), scanning electron microscopy, thermo gravimetry/differential thermal analyzer and four-probe method. The XRD measurement results indicated that the samples (x = 10–15, y = 5–10–15–20) had cubic δ-phase crystallographic structure. The phase stability of the samples was checked by the differential thermal analyzer measurements, which indicates most of the samples have stable δ-Bi₂O₃ phase. The electrical conductivity measurement results showed that the electrical conductivity increased with mol% CeO₂ molar ratio at a fixed molar ratio of Sm₂O₃. The highest electrical conductivity obtained for the (Bi₂O₃)_0.65(Sm₂O₃)_0.15(CeO₂)_0.20 system was 1.55 × 10^?2 (Ω.cm)^?1 at 600 °C. The activation energies were also calculated at low temperature range (350–650 °C) which vary from 1.1325 to 1.4460 eV and at high temperature (above 650 °C) which vary from 0.4813 to 1.1071 eV.     

Transport phenomena in superionic Na<Subscript><Emphasis Type="Italic">х</Emphasis></Subscript>Cu<Subscript>2 − <Emphasis Type="Italic">х</Emphasis></Subscript>S (<Emphasis Type="Italic">х</Emphasis> = 0.05; 0.1; 0.15; 0.2) compounds

The electronic and ionic conductivity, the electronic and ionic Seebeck coefficients, and the thermal conductivity of Na _x Cu_2 ? x S (x = 0.05, 0.1, 0.15, 0.2) compounds were measured in the temperature range of 20–450 °С. The total cationic conductivity of Na_0.2Cu_1.8S is about 2 S/cm at 400 °С (the activation energy ≈ 0.21 eV). Over the studied compounds, the composition Na_0.2Cu_1.8S has the highest electronic conductivity (500–800 S/cm) in the temperature range from 20 to 300 °С, and the highest electronic Seebeck coefficient (about 0.2 mV/K) in the same temperature range is observed for Na_0.15Cu_1.85S composition; the electronic Seebeck coefficient increases abruptly above 300 °С for all compounds. The thermal conductivity of superionic Na_0.2Cu_1.8S is low, which causes high values of the dimensionless thermoelectric figure of merit ZT from 0.4 to 1 at temperatures from 150 to 340 °С.     

MnBiAl薄膜的磁光及磁性能研究

用真空电子束蒸发制备了MnBi_xAl_0.15薄膜.当0.4≤x≤0.7时,MnBi_xAl_0.15薄膜的Kerr角与MnBi_x薄膜相比有显著增大;而当x＞0.7时,MnBi_xAl_0.15的Kerr角则比MnBi_x的要不,633nm波长测量时,MnBi_{0.5Al0.15的Kerr角为2.75°,而相对应的MnBi0.5薄膜只有1.56°.MnBi05Al0.15薄膜的室温饱和磁化强度Ms为3×10⁵A/m,比MnBi0.5薄膜的Ms(4×10⁵A/m)要小.推测当0.4≤x≤0.7时,Al可能部分占据Bi空位和部分取代Mn位,由于晶格收缩使得Mn 3d电子与Bi 6p电子的杂化概率增大,从而导致其Kerr效应增强. 关键词：}     

Employing response surface methodology and neural network to accurately model thermal conductivity of TiO2–water nanofluid using experimental data

In this research, the thermal conductivity of the H₂O–titania nanofluid is modeled versus the particle concentration and temperature via the Artificial Neural Network (ANN) and Response Surface Methodology (RSM). The experimental data include six particle concentrations and five temperatures from 30 to 70 °C. The thermal conductivity augments by the increment in nanoparticle concentration and temperature, such that the maximum thermal conductivity increment happens at the highest temperature and nanoparticle concentration (i.e., T = 70 °C and φ = 1%). It is observed that the impact of temperature on the thermal conductivity is more noticeable than the influence of particle concentration, however, the thermal conductivity demonstrates a more non-linear trend versus nanoparticle volume fraction compared with the temperature. The best structure of the neural network has 2 hidden layers with 2 and 4 neurons, respectively in the 1^st and 2^nd hidden layers. The results show that the prediction precision of the ANN correlation is better than that of the RSM correlation.     

Thermal Decomposition Behavior of a Heterocyclic Aramid Fiber

Heterocyclic aramid fibers are one of the high-performance fibers with excellent mechanical and thermal properties. In this article, the thermal decomposition behaviors of a type of the fibers were studied in nitrogen and air by pyrolysis/gas chromatography–mass spectrometry (Py/GC-MS), thermal gravimetric analysis–differential thermal analysis/Fourier transform infrared spectroscopy (TGA-DTA/FTIR), and thermal gravimetric analysis–differential thermal analysis/mass spectrometry (TGA-DTA/MS). The results showed that under nitrogen atmosphere, the thermal decomposition mainly happened between 520°C and 580°C, the temperature of the maximum weight loss rate was 550°C, and the weight remaining at 800°C was 58%. HCN, NH₃, NO₂, NO, CO₂, CO, H₂O, and some other compounds containing benzene rings were detected by the TGA-DTA/FTIR. Among these released chemicals, the intensity of the absorption peak assigned to CO₂ was the strongest. These chemicals were also identified by the TGA-DTA/MS. The Py-GC/MS analysis revealed that the number of chromatographic peaks increased with the increase of temperature. Most of the pyrolysis products were produced between 550°C and 600°C, which represented the major pyrolysis process. Moreover, the detection of benzene ring containing compound fragments reflected the process of the molecular chain scission. In air atmosphere, the thermal decomposition mainly happened between 500°C and 680°C. The maximum weight loss rate was observed at 600°C, and almost 100% weight was lost at 900°C. NH₃, NO₂, CO₂, and H₂O were detected by the TGA-DTA/MS, and the ion current intensity of CO₂ was again the strongest with a strong oxidation reaction at around 670°C. It was speculated that the thermal decomposition began with the breaking of the bonds between PPTA (poly-p-phenylene terephthalamide) blocks and heterocyclic blocks at high temperature. Then, with the increase of temperature, the chemical bonds inside the PPTA blocks and heterocyclic blocks were broken. In this process, free radicals that led to restructuring and new breakages to produce micromolecular products were introduced.     

The effect of strong electrical field on the conductivity of proton solid electrolytes NaHSO4 and KHSO4

The influence of passing of high voltage pulse discharges through proton solid electrolytes NaHSO₄ and KHSO₄ and corresponding melts on their conductivities has been investigated. We have discovered the phenomenon of high voltage activation of the investigated electrolytes which is seen by a relative increase of the conductivity. This relative conductivity increase Δσ_rel reaches 754 % (at U=2.8 kV and 181°C) and 218 % (at U=2.0 kV and 200°C) for the solid NaHSO₄ and KHSO₄, respectively. For molten NaHSO₄ and KHSO₄ Δσ_rel is considerably higher and reaches 613% (at U=1.4 kV and 207°C) and 572 % (at U=2.2 kV and 232°C), respectively. We established the “memory” effect which was seen in maintaining of the excess conductivity for a long period of time. The process of relaxation of the excess conductivity of these electrolytes has been studied. The relaxation times of the non-equilibrium charge carriers in these electrolytes varies within the range of (1.9–7.8).10⁴s.     

Gd-doped SrTi<Subscript>0.5</Subscript>Fe<Subscript>0.5</Subscript>O<Subscript>3–δ</Subscript> mixed ionic-electronic conductors: structural,thermal, and electrical properties

The effect of Sr by Gd substitution on the structural, thermomechanical, electrical, and electrochemical properties of SrTi_0.5Fe_0.5O_3–δ was investigated in the present work. The powders were synthesized by a solid-state reaction method at 1150 °C with following sintering of the ceramic samples at 1350 °C. The unit cell parameters of the sintered Sr_1–x Gd _x Ti_0.5Fe_0.5O_3–δ (x = 0–0.4) ceramics were found to decrease with a gradual increase in Gd content, and a change in the crystal symmetry from cubic to tetragonal at x ≥ 0.1 was observed. It was found that the Gd doping enhanced the stability of the ceramic samples in a reducing atmosphere and reduced the thermal expansion coefficient value. Gd doping in the amount of 5 mol% can be used for long-term stabilization of the SrTi_0.5Fe_0.5O_3–δ material’s conductivity in reducing atmospheres with no significant alteration to the transport properties and oxygen permeability.     

Effect of H<Subscript>3</Subscript>PO<Subscript>2</Subscript> on the mechanical,thermal, and electrical properties of polymers based on poly (vinyl alcohol) (PVA) and chitosan (CS)

A polymer based on poly (vinyl alcohol) (PVA) and chitosan (CS) with a weight ratio of 80:20 was prepared by solvent casting processes, and the effect of H₃PO₂ was investigated. Thermal analysis shows miscibility of the two polymer amorphous phases since a single T_g was located between those of the individual components and the melting point of the crystalline phase was depressed to 189 °C. It was found that the acid acts as a plasticizer for the PVA-CS blends and its T_g is depressed significantly to 23 °C as the acid concentration increases to 50%. Strain-stress tests also corroborate this effect. The DC conductivity of the blends follows an Arrhenius-type thermal activation behavior with activation energy of 0.1 eV in the 30–90 °C temperature range. Moreover, the conductivity increases with increasing acid content up to a maximum value of approximately 1.4 × 10^?2 S/cm for the blend with an acid concentration of 50%.     

Thermal conductivity of UC1 − xNx from 100 to 1000 °K

The thermal diffusivities of UC_{1 ? x}N_x of several compositions were measured from 100 to 1000 °K by a laser flash method. The thermal conductivity was separated into electronic and phonon components by assuming the constant Lorenz number. The phonon conductivity showed an anomalous behaviour against composition at low temperatures. The total thermal conductivity of UC_{1 ? x}N_x showed a minimum above 300 °K at an intermediate composition which moved to higher carbon content with increasing temperature. This behaviour was explained by the temperature dependence of the lattice and electronic components.