E.F. Hairetdinov

Composite protonic solid electrolytes in the CsHSO4-SiO2 system

Abstract Transport, thermal and structural properties of the composite solid electrolytes (1 − x )CsHSO 4 xSiO 2 (where x = 0–0.8) were investigated. The composites were prepared by mechanical mixing of components followed by heating at temperatures near CsHSO 4 melting point (483 K). The dependence of low temperature phase conductivity on x has a maximum with a value 2.5 orders of magnitude higher than that of pure CsHSO 4 and conductivity is governed by protons. Heterogeneous doping is shown to change markedly the thermodynamic parameters of the ionic component. The phase transition temperature CsHSO 4 in the composites decreases from 414 to 350 K with the increase of the content of heterogeneous additive SiO 2 from 0 to 0.7. As x raises CsHSO 4 the amorphization takes place and the relative change of ionic conductivity at phase transition diminishes, the phase transition becomes diffusive and disappears for the 0.2CsHSO 4 0.8SiO 2 composite.

Nanocomposite ionic conductors in the Li2SO4Al2O3 system

Abstract Studies are carried out of morphology, crystal structure, chemical content, thermal and transport properties of Li 2 SO 4 Al 2 O 3 composites prepared in two different ways: by thermal decomposition of the precursor Li 2 SO 4 ·2Al(OH) 3 · m H 2 O at 400°C or by using conventional mixing. It is shown that, whatever the preparation technique, if grain size of alumina in composites is small enough (of order of tens nanometers) then after prolonged heating the heterogeneous system Li 2 SO 4 Al 2 O 3 reaches the metastable thermodynamic state — a nanocomposite in which lithium sulphate is in an unusual epitaxial state. The stabilization of this state is caused by a strong interface interaction that is leading to the formation of the intermediate thin layer of lithium aluminate which “glues” Li 2 SO 4 and Al 2 O 3 phases providing the contact. The phase transition temperature of Li 2 SO 4 in composites is 100 degrees lower than in the pure salt. Ionic conductivity of Li 2 SO 4 in the composites smoothly changes at the phase transition, activation energies being 0.40±0.05 and 0.66±0.01 eV for T > 470°C and T

Composite solid electrolytes MeNO3-Al2O3 (Me = Li, Na, K)

Abstract Conductivities of nitrate composites (1 − x ) MeNO 3 - xAl 2 O 3 , where M = Li , Na and K , were investigated in comparison with conductivities of the individual salts. The composites were prepared by mechanical treatment in planetary mills followed by sintering. Conductivity isotherms exhibit maxima at x = 0.40−0.60, with the conductivity values around 10 −2 S/cm at 500 K, these are 10 3 –10 5 times higher than those of the pure salt. Temperature dependences of conductivity are not linear in Arrhenius coordinates. A possible reason for the drastic change of transport properties of nitrates in composites under study may be the stabilization of amorphous high-conducting phases of nitrates which are formed on MeNO 3 -Al 2 O 3 contacts as a result of the interface interaction between the components.

High ionic conductivity and unusual thermodynamic properties of silver iodide in AgI-Al2O3 nanocomposites

Abstract Composites (1 − x ) AgI - xAl 2 O 3 were obtained using mechanical treatment of pure AgI with highly dispersed alumina (specific area 270 m 2 /g) in planetary ball mill followed by sintering at 570–870 K. As the concentration of alumina rises, properties of the composites change: both temperature of the superionic phase transition and the heat of the transformation decreases. Average grain size of AgI diminishes with x and at x > 0.6 becomes less than 100 nm, hence, the composites may be attributed to nanocomposites. The phase transition, being very sharp in AgI, becomes diffusive for x > 0.5, the absolute values of the conductivity of both phases approaches each other. All the facts mentioned may be explained by strong interface interaction between Al 2 O 3 and AgI in the nanocomposites leading to a stabilization of a metastable high-disordered state of AgI at low temperatures. Properties of the composites are shown to be sensitive to agents adsorbed on the alumina surface. Silver iodide occurring in a metastable state within the composite may be easily transformed to stable β-AgI by treatment with water vapour. It is likely that water molecules substitute for Ag + ions weakly bonded to surface oxygen atoms of alumina, destroying the AgI-Al 2 O 3 interfaces.

Determination of the influence of the NaF rate on the charge carriers parameters in some fluoride glasses containing the NaF alkali fluoride

Abstract The bulk impedance parameters of various fluoride glasses series containing a large extent in NaF rate have been determined from an analysis of ac conductivity data measured in a wide temperature range. The charge carriers concentration in each glass studied has been evaluated using the Almond-West formalism and shown to be temperature independent. Transport properties in these materials are due to a hopping mechanism of the fraction of F − ions mobile at long range (3–5%). The variation of different conductivity parameters as a function of the NaF content has been determined. When the NaF rate increases, a conductivity decrease is observed, due mainly to a decrease of the charge carriers mobility.

Effect of nanocrystalline alumina on ionic conductivity and phase transition in CsCl

Abstract Conductivity, structure and thermodynamic parameters of CsCl in (1− x )CsCl– x Al 2 O 3 composites are investigated. As the heterogeneous dopant, highly-dispersed alumina with specific surface area 210 m 2 /g is used. Maximum conductivity 9×10 −4 S/cm at 400°C occurs at x =0.6. As x rises, conductivities of bcc and fcc phases tend to level off and at x >0.6 no conductivity drop due to the phase transition occurs. The phase transition enthalpy decreases with x and at x >0.6 no bcc–fcc phase transition is detected by DSC technique. New peaks attributed to fcc-phase with the lattice parameter a =0.694 nm are observed on X-ray powder diffractograms. At high x conductivity enhancement is likely to be due to the presence of the high-temperature fcc phase of CsCl stabilized on CsCl–Al 2 O 3 interfaces.

Hydrogen sensor based on antimonium pentoxide-phosphoric acid solid electrolyte

Abstract A solid composite electrolyte with high proton conductivity based on antimonium pentoxide with additives of phosphoric acid has been obtained. A potentiometric solid-state gas sensor using this electrolyte has been developed for detecting small amounts of hydrogen (10–2000 ppm) in gas mixtures at ambient temperature. The sensor consists of the reference electrode: Ag or Ag/(Ag + Ag2SO4), the solid composite electrolyte and H2-sensitive electrode: Pt or Pd. The electromotive force (e.m.f.) of the sensor varies logarithmically with H2 concentration for hydrogen partial pressures in the range 100–2000 ppm and depends on the oxygen partial pressure. The slope of e.m.f.-log(pH2) dependence is 170 and 200 mV for Pt and Pd, respectively, which exceeds the Nernst value, presumably due to the formation of a mixed potential. The sensor can operate at a wide range (20–95%) of a relative humidity.

Unusual transport and structural properties of mechanically treated polycrystalline silver iodide: Part I. Ionic conductivity

Abstract It is shown that the increase in conductivity of polycrystalline silver iodide due to its mechanical treatment can be attributed to the presence of metastable defects which are formed on mechanical treatment of AgI. Defects may be annealed by heating with the annealing rate depending on purity of AgI. The temperature dependence of conductivity for purified AgI has two temperature regions with different activation energies: 0.3 and 0.5–0.6 eV at 350–400 K and below 350 K, respectively, which are interpreted in terms of the extrinsic-like conductivity accompanied by the defects ‘freezing’ process at lower temperatures. As it will be reported in the following parts of the paper devoted to dielectric and structural studies of mechanically treated AgI, antiphase boundaries formed in β-γ polytypes as a result of the treatment are the most probable sources of metastable defects responsible for the conductivity enhancement observed.

Determination of charge carriers parameters of the Pb1−xBixOx2F2 solid solution

Abstract The bulk impedance parameters of polycrystalline samples of the Pb 1-x Bi x O x 2 F 2 solid solution with fluorite-type structure have been determined from an analysis of a.c. conductivity data measured in a wide temperature range. Hopping rates of mobile F - ions are extracted from frequency dependences of conductivities at different temperatures. The concentration of charge carriers in the investigated samples (0.05 ⩽ x ⩽ 0.04) has been estimated : it increases with x and its value for x = 0.40, equal to about 5–6%, is of the same order of magnitude as the maximum percentage of interstitial anions of F”-type in the Pb 1- x Bi x F 2+ x solid solution in which they play an essential role in the long-range motions. The conductivity enhancement observed with increasing x in Pb 1-x Bi x O x 2 F 2 is mainly a mobility effect.

Dielectric relaxation of free charge carriers in some fluorite-type solid solutions

Low-frequency dielectric relaxation was observed in solid solutions Ba1 − xThxF2 + x and Cd1 − xErxF2 + x of fluorite type. The relaxation can be satisfactorily described by the Havriliak-Negami formula: e∗(f) − e∞ = Δe/ {1 + [if/fr]1 − β}1 − γ. The activation energy for relaxation turned to be equal to that for DC-conductivity in the system under study. This suggests that the relaxation is closely related to the ion transport and agrees with the model of a dipole-like behavior of free charge carriers. The relaxation is of strongly non-Debye type and contributes to the high frequency conductivity in the form: σ = σDC[1 + (f/fh)α] with α = β + γ − βγ.