Ionic conductivity and structural properties of MnO-doped Bi4V2O11 system

Bi₄V₂O₁₁ exists in three phases viz. α, β, and γ. High temperature γ-phase can be stabilized to room temperature owing to its higher conductivity by the partial substitution of metallic cations for vanadium in Bi₄V₂O₁₁. Phase transitions from α → β and β → γ are composition and temperature-dependent. Mn²⁺-doped compounds Bi₄V_2−x Mn _x O_{11− δ} (0 ≤ x ≤ 0.4) have been synthesized by solid state reaction technique and investigated by X-ray diffraction and ionic conductivity measurement. High ionic conducting γ-phase is stabilized for x ≥ 0.2. The ionic conductivity of the series of Bi₄V_2−x Mn _x O_{11− δ} samples has been measured by using ac impedance spectroscopy technique. The conductivity data do show departure from its simple Arrhenius behavior for all of the compositions. The highest conductivity observed for x = 0.2 sample can be attributed to lower activation energy.     

Nonlinear transport in {\sf \beta}-Na 0.33V 2O 5

Transport properties of the charge ordering compound β-Na_0.33V₂O₅ are studied in the temperature range from 30 K to 300 K using current driven DC conductivity experiments. It is found that below the metal-insulator transition temperature ( ) this material shows a nonlinear charge density modulation behavior. The observed conductivity is discussed in terms of a classical domain model for charge density modulation transport.     

Search for new oxide-ion conducting materials in the ceria family of oxides

We have adopted a modified combustion route, namely, a mixed fuel process (MFP) to prepare a novel series of nano-crystalline single- and multiple-doped ceria compositions with controlled powder characteristics, large surface area, finer particle size, high sinterability, and high oxide ion conductivity at intermediate temperatures (500–700 °C). Using the mixed fuel process, we have prepared nano-particles of single- and multiple-doped ceria powders with dopants such as Ca, Gd, and Sm and a suitable combination of the same. In the pursuit for identifying new oxide-ion-conducting materials in this family of oxides, we have pursued the idea of co-doping effect on the single doped compositions with proper introduction of a second dopant. Effect of these dopants on the thermal decomposition and physico–chemical characteristics of the precursor and the powders prepared thereby were studied in detail. Finally, the effects of multiple co-doping on the microstructural and electrical properties were compared to understand the origin of the effect of dopant characteristics on the oxide ion conductivity of Ce_1−x M _x O₂ solid solutions. Our experimental results established unequivocally that co-doping is very effective in identifying new materials with remarkably high ionic conductivity with substantial reduction in the cost for technological applications. Among the studied compositions, the maximum conductivity with minimum activation energy was observed for the triply co-doped CCGS composition (; E _a = 0.56 eV), which is much higher compared to the conductivity exhibited by most of the reported co-doped ceria compositions. In conclusion, an effective way to improve the oxide ion conductivity of ceria-based oxides by proper choice of dopants and co-doping is achieved.     

Activation energy and conductivity of glasses in the P2O5–V2O5–Li2O system

The conductivity of glasses in the 50\textP_\text2 \textO_\text5 - x\textV_\text2 \textO_\text5 - ( 50 - x )\textLi_\text2 \textO50{\text{P}}_{\text{2}} {\text{O}}_{\text{5}} - x{\text{V}}_{\text{2}} {\text{O}}_{\text{5}} - \left( {50 - x} \right){\text{Li}}_{\text{2}} {\text{O}} system was studied as a function of temperature and composition. For all compositions, the conductivity variation as a function of temperature followed an Arrhenius type relationship. Isothermal variation of conductivity as a function of composition showed a minimum for a molar ratio x near 20. Probable mechanisms for decrease of conductivity with decrease of vanadium oxide concentration were explained. The minimum in room temperature was attributed to increase of V⁴⁺/V⁵⁺ with decrease of vanadium oxide in specific concentrations of vanadium oxide. Activation energy increased with decrease of V₂O₅ content. This behavior was attributed to increase of average spacing between vanadium ions.     

Role of Fe,Mn, and Zn ions as dopants on the electrical conductivity behavior of sodium phosphate glass

Sodium phosphate glass undoped and doped with different concentrations of chlorides of iron, manganese, and zinc were prepared by melt quenching. The synthesized glasses were characterized by elemental analysis, X-ray diffraction, infrared (IR) spectroscopy, differential scanning calorimetry, and electrical conductivity studies. The undoped sodium phosphate glass (Na₂O–P₂O₅) has low electrical conductivity σ compared to all doped glasses except for 10% FeCl₃-doped samples for which σ is found to be the lowest, and the trend is

Preparation of sol-gel method P2O5-Al2O3-SiO2 glasses and their characterization

Nanostructures P₂O₅-Al₂O₃-SiO₂ glasses were prepared by sol-gel method. The glasses were characterized by XRD, FTIR and TG/DTA methods. The average pore size of the glass was less than 3 nm as measured by N₂ adsorption — desorption method. The thermal stability was measured as a function of decomposition temperature and weight loss calculations. Proton conductivities of all samples increased with an increase in relative humidity (40–90 %), indicating that continuous paths suitable for proton conduction were developed when glasses heat treated at 300 °C due to the adsorption of water. The temperature dependence of the conductivity for all compositions increases with increasing temperature in the range 30–90 °C with relative humidity 70 %. The overall conductivity was in the range 10⁻⁴–10⁻³ S/cm for compositions.     

Critical Hardy–Lieb–Thirring Inequalities for Fourth-Order Operators in Low Dimensions

This paper considers Hardy–Lieb–Thirring inequalities for higher order differential operators. A result for general fourth-order operators on the half-line is developed, and the trace inequality

Electrical properties of a new Ag+ ion conducting glassy system: x[0.75AgI:0.25AgCl] : (1−x)[Ag2O : P2O5]

A new fast Ag⁺ ion conducting glassy system: x[0.75AgI:0.25AgCl]: (1−x)[Ag₂O: P₂O₅], where 0.1 ≤ x ≤ 1 in molar weight fraction, has been synthesized by melt-quench technique using a high-speed twin roller-quencher. An alternate host salt: ‘quenched [0.75AgI: 0.25AgCl] mixed system/ solid solution’, has been used in place of the traditional host AgI. The compositional dependence conductivity studies on the glassy systems: x[0.75AgI:0.25AgCl]: (1−x)[Ag₂O: P₂O₅] as well as xAgI: (1−x)[Ag₂O: P₂O₅] prepared identically, indicated that the composition at x=0.75 exhibited the highest room temperature conductivity. The composition: 0.75[0.75AgI: 0.25AgCl]: 0.25[Ag₂O: P₂O₅] has been referred to as optimum conducting composition (OCC). The study also revealed that the new/ alternate host yielded better electrolyte system. The activation energy (E_a), involved in the thermally activated conductivity process has been computed from ‘log σ − 1/T’ Arrhenius plot. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

A sharp decrease of resistivity in La0.7Ca0.3Mn0.96Cu0.04O3: Evidence for Cu-assisted coherent tunneling of spin Polarons

Nearly a 50% decrease of the resistivity ρ(T, x) is observed upon just 4% Cu doping at the Mn site of La_2/3Ca_1/3Mn_1−x Cu_xO₃. When the observed phenomenon is attributed to a decrease of the spin-polaron energy E _σ(x) below T _C (x), all of the data are found to be well fitted by the nonthermal coherent tunneling expression , assuming that the magnetization in the ferromagnetic state is given by the expression . The best fits through all the data points suggest and E _σ(x)≃E _σ(0)(1−x)⁴ for the explicit x dependence of the Cu-induced modifications of the Mn-spin-dominated zero-temperature spontaneous magnetization, residual paramagnetic contribution, and spin-polaron tunneling energy, respectively, with E _σ(0)=0.12 eV. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 812–815 (10 June 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Electrical characterization of highly Titania doped YSZ

The defect fluorite region of the ternary system ZrO₂-Y₂O₃-TiO₂ encompasses compositions which offer both, good electronic and oxygen ion conductivity which enable good catalytic activity for the direct oxidation of methane in a solid oxide fuel cell (SOFC). The electrical properties of compositions Y_xTi_yZr_1−(x+y)O_2−x/2 (with x=0.15, 0.2, 0.25 and y=0.15, 0.18) were characterised in order to find the composition with highest ionic and electronic conductivity. High titanium dopant concentrations (Y) of 15 and 18 atom%, near the solubility limit of Ti⁴⁺ in the fluorite structure, have been introduced to achieve a high electronic conductivity at low oxygen partial pressure. The yttrium content x has been varied between 15 and 25 atom% to find the fluorite composition with the highest ionic conductivity for each titanium level. In the pO₂-range from 0.21 to 10⁻¹³ atm the conductivity is predominantly ionic and constant over that range. The maximum ionic conductivity is 0.01 Scm⁻¹ for the compositions, which contain 15 atom% yttrium. Substantial electronic conductivity is introduced into the system at low oxygen pressures below 10⁻¹³ atm via reduction of Ti⁴⁺ ions to Ti³⁺. The maximum electronic conductivity of 0.2 Scm⁻¹ at 930 °C has been measured for a sample with 18 atom% titanium. The slope of all log(σ) vs. log(pO₂) plots follows a pO ₂ ^−1/4 -dependence. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Al,F-doped new perovskite lithium fast ion conductor Li3x La2/3−x□1/3−2x Ti1−y Al y O3−y F y (x=0.11)

Al, F-doped new perovskite lithium ion conductors (x=0.11) have been prepared by solid state reaction. It is found that a pure perovskite-structured phase with space group of P4mm(99) exits in the composition range of 0<y≤0.10. The sample with y=0.02 possesses the highest ionic conductivity of 1.06×10⁻³ S/cm at room temperature, and its decomposing voltage is 2.3 V. The factors affecting the conductivity of this system are discussed.     

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.     

Synthesis and electrical characterisation of different doped magnesium titanates

The synthesis and characterization are reported for the cubic spinel titanate Mg_(2−x)Ni_xTiO₄ (x≤0.25) and Mg_(2−x)Mn_xTiO₄ (x≤1). Single phase samples were observed for Mg_(2−x)Ni_xTiO₄ and with x≤0.4 for Mg_(2−x)Mn_xTiO₄. AC measurements were carried out on four different compositions (x=0.01, 0.03, 0.04 and 0.15) in the Mg_(2−x)Ni_xTiO₄ series and for Mg_1.9Mn_0.1TiO₄. For all these compounds, increasing conductivity with temperature and Arrhenius conductivity dependence are observed, the activation energy is around 0.28 eV for the Ni compounds and is 0.184 eV for Mg_1.9Mn_0.1TiO₄. The DC conductivity was recorded over a range of oxygen partial pressures (10⁻¹⁹ to 1 atm) at 930 °C. The Mg_(2−x)Ni_xTiO₄ compounds show a n-type behaviour whereas the Mg_(2−x)Mn_xTiO₄ show a p-type behaviour at high p(O₂) and n-type at low p(O₂). The stability under reduced conditions was checked and discussed for the different synthesized compounds. Paper presented at the 5th Euroconference onSolid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Synthesis and conductivities of the apatite-type systems, La9.33+xSi6−yMyO26+z (M=Co, Fe, Mn) and La8Mn2Si6O26

Apatite-type oxides of formula (La/Sr)_10−xSi₆O_26+y have been attracting significant interest recently, because of their high oxide ion conductivity. In this paper we report the synthesis and conductivities of phases based on doping La_9.33Si₆O₂₆ with Co, Fe, Mn on the Si site, according to the formula La_9.33+x/3Si_6−xM_xO₂₆ (M=Co, Fe, Mn). Substitution limits observed were x≤1.5 (Co), x≤1.25 (Fe), x≤0.5 (Mn). Higher Mn levels could be achieved by substituting onto the La site, with it being possible to prepare the phase La₈Mn₂Si₆O₂₆. The highest conductivities were observed for the Co doped samples, although investigations into the dependence of conductivity on p(O₂) (0.2–10⁻⁵ atm.) indicated that the conductivity was dominated by the electronic component in these cases. In contrast, the conductivities for the Fe and Mn doped samples were mainly ionic in the same p(O₂) range. Experiments into varying the oxygen content of these doped phases indicated that increasing the oxygen content above the nominally stoichiometric O₂₆ appears to increase the oxide ion conductivity. Preliminary studies of the reactivity of the electrolyte La_9.33Si₆O₂₆ with potential SOFC cathode materials (La_1−xSr_xMO₃; M=Co, Fe, Mn) suggests that reaction can occur at high temperatures leading to the incorporation of the transition metal into the apatite electrolyte. However, the fact that these doped phases exhibit high conductivities suggests that this may limit any problems caused by such a reaction at the electrolyte-electrode interface. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

κ-generalized statistics in personal income distribution

Starting from the generalized exponential function , with exp ₀(x)=exp (x), proposed in reference [G. Kaniadakis, Physica A 296, 405 (2001)], the survival function P_>(x)=exp _κ(-βx^α), where x∈R⁺, α,β>0, and , is considered in order to analyze the data on personal income distribution for Germany, Italy, and the United Kingdom. The above defined distribution is a continuous one-parameter deformation of the stretched exponential function P_> ⁰(x)=exp (-βx^α) to which reduces as κ approaches zero behaving in very different way in the x→0 and x→∞ regions. Its bulk is very close to the stretched exponential one, whereas its tail decays following the power-law P_>(x)∼(2βκ)^-1/κx^-α/κ. This makes the κ-generalized function particularly suitable to describe simultaneously the income distribution among both the richest part and the vast majority of the population, generally fitting different curves. An excellent agreement is found between our theoretical model and the observational data on personal income over their entire range.     

Ionic and electronic transport in perovskite-type La(Ga,M)O3−δ (M=Mg, Cr, Fe, Co, Ni, Nb)

Oxygen ion conduction in La_0.9Sr_0.1Ga_1−xM_xO_3−δ (M=Cr, Fe; x=0 – 0.20), LaGa_1−xM_xO_3−δ (M=Co, Ni; x=0.20 – 0.60), LaGa_1−x−yCo_xMg_yO_3−δ (x=0.35 – 0.60; y=0.10 – 0.25) and LaGa_0.85−xMg_0.15(Nb_0.33Mg_0.66)_xO_3−δ (x=0 – 0.20) is reported. At temperatures below 1200 K the ionic conductivity of La(Ga,M)O_3−δ (M=Co, Ni) increases with increasing oxygen nonstoichiometry, but is lower than for La(Ga,Mg)O_3−δ and (La,Sr)GaO_3−δ. Co-doping with Nb and Mg was found to result in decreasing ionic transport in La(Ga,Nb,Mg)O_3−δ due to blocking of oxygen sites by Nb⁵⁺. Small additions of Fe to the B-site of La_0.9Sr_0.1GaO_3−δ increase the ionic conductivity, whereas substitution of Cr for Ga has the opposite effect. Incorporation of transition metal cations into the Ga site leads to a higher p-type electronic conductivity in all studied perovskites. Paper presented at the 6th Euroconference on Solid Sate Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

An ab initio molecular dynamics study of ionic conductivity in hexagonal lithium lanthanum titanate oxide La0.5Li0.5TiO3

To date, the fastest lithium ion-conducting solid electrolytes known are the perovskite-type ABO₃ oxide, with A = Li, La and B = Ti, lithium lanthanum titanate (LLTO) Li_3x La_{( 2 \mathord}

The hyperfine and isotope structure of the Cd intercombination line – revisited

Careful analysis of the intercombination 5¹S₀–5³P₁ line of the ¹¹³Cd isotope with two hfs components and was carried out. The hyperfine splitting of this line was determined to uncertainty less than 10^-3 cm^-1 using neon-perturbed Doppler limited spectra.     

Neutralization of antiprotons at nuclei

A method is given for calculating the cross section for neutralization of for medium and heavy nuclei in terms of the optical potential, by addition of the neutralization operator . The method is reasonable for energies . Explicit forms are obtained for the differential and total cross sections for an optical potential in the form of a complex rectangular well, V(r) = V₀., in which V₀ differs; from zero within the nucleus and . The value of V_o corresponding to the observed cross section for lead is derived. The dependence of the total cross section on V₀ for copper is given.I am indebted to P. E. Nemirovskii for direction and valuable advice.     

Lithium intercalation in α′-NayV2O5 synthesized via the hydrothermal route

Vanadium bronzes Na_yV₂O₅ are synthesized via the hydrothermal route from a mixture of V₂O₅ and NaOH in the presence of a reducing agent. Fine crystalline powders made of needle-like particles are obtained that exhibit the layered structure typical of the α′-Na_yV₂O₅ phase (y≈1). Electron delocalization arises from a hopping process of unpaired electrons between V⁴⁺ and V⁵⁺. Alkaline cations are intercalated between the oxide layers and discharge curves show that up to one Li⁺ ion per vanadium can be reversibly inserted between the [V₂O₅] layers in the 3.3–0.5 V range. Chemical diffusion coefficient of Li ions in Li_xNaV₂O₅ is found to be dependent on the degree of intercalation. D⁺ varies from 1×10⁻¹⁰ up to 5×10⁻¹⁰ cm²/s for 0≤×≤2. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.