Insertion of 3d- and 4f-Elements into Silver Iodide

The interaction of manganese and some 4f-metals (M) with silver iodide is studied. The samples are obtained by sputtering M onto the surface of polycrystalline AgI films (0.2 m, 300 K) in a vacuum. Optical absorption in the samples is interpreted as the insertion of M ions into AgI with the formation of dopants AgI:M. A new phase with an optical bandgap of 3.7 eV emerges in the samples with elevated concentrations of La, Ce, Pr, Nd, Sm, or Dy (n _M/n _Ag 0.1). X-ray diffraction patterns for such samples with Sm correspond to structures with large interfacial distances, for example, 0.99, 0.87, 0.76, and 0.67 nm. In air, AgI forms in the samples with a new phase; this process is hindered by the sputtered protective coatings. According to optical absorption data, X-ray diffraction, and local microanalysis the Mn insertion into AgI is followed by the formation of a new phase (2Ag:Mn:4I), which may belong with solid electrolytes Ag₂MI₄, where nonmagnetic M are known (Zn, Cd, Sn, Hg, Pb).     

Experimental confirmation of neoclassical Compton scattering theory

Incoherent X-ray scattering spectra of diamond and silicon crystals recorded on the BESSY-2 electron storage ring have been analyzed. All spectral features are described well in terms of the neoclassical scattering theory without consideration for the hypotheses accepted in quantum electrodynamics. It is noted that the accepted tabular data on the intensity ratio between the Compton and Rayleigh spectral components may significantly differ from the experimental values. It is concluded that the development of the general theory (considering coherent scattering, incoherent scattering, and Bragg diffraction) must be continued.     

Interface design in nanosystems of Advanced Superionic Conductors

First attempt of practical realization of new interface engineering approach “from advanced materials to advanced devices” for nanosystems of Advanced Superionic Conductors (ASICs), based on AgI (CuI) compounds is presented. Crystallochemical method of symmetry perfect ASIC//electrode interface searching is developed. Some new theoretical results of ASIC//indifferent electrode conjugated commensurate heteropairs with coherent interfaces and preliminary experimental results of the creation of thin-film supercapacitor — prototype based on the lattice matched heterojunction — are given. Future perspectives of the ASIC//electrode interface design suited for micro(nano)electronics and microsystem technology (MST) are discussed. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14–18, 2004.     

Nanoionics of advanced superionic conductors

New scientific direction — nanoionics of advanced superionic conductors (ASICs) was proposed. Nanosystems of solid state ionics were divided onto two classes differing by an opposite influence of crystal structure defects on the ionic conductivity σ_i (energy activationE): I) nanosystems on the base compounds with initial small σ_i (large values ofE); and II) nanosystems of ASICs (nano-ASICs) withE ≈0.1 eV. The fundamental challenge of nanoionics as the conservation of fast ion transport (FIT) in nano-ASICs on the level of bulk crystal was first recognized and for the providing of FIT in nano-ASICs the conception of structure-ordered (coherent) ASIC//indifferent electrode (IE) heteroboundaries was proposed. Nano-ASIC characteristic parameterP=d/λ _Q (d is the thickness of ASIC layer with the defect crystal structure at the heteroboundary, and λ _Q is the screening length of charge for mobile ions of the bulk of ASIC) was introduced. The criterion for a conservation of FIT in nano-ASIC isP≈1. It was shown that at the equilibrium conditions the contact potentialsV at the ASIC//IE coherent heterojunctions in nano-ASICs areV«k _BT/e. Interface engineering approach “from advanced materials to advanced devices” was proposed as fundamentals for the development of applied nanoionics. The possibility for creation on the base of ASIC//IE coherent heterojunctions of the efficient energy and power devices (sensors and supercapacitors with specific capacity ≈10^?4 F/cm² and maximal frequencies 10⁹–10⁰ Hz,) suited for micro(nano)electronics, microsystem technology and 5 Gbit DRAM was pointed out.     

Influence of samarium on optical absorption in thin films of the solid electrolyte RbAg4I5

The fundamental optical absorption of films of the solid electrolyte RbAg₄I₅ electrolyte films decreases (by approximately 25%) after vacuum evaporation of Sm films onto them, and a broad strong-absorption band with a maximum at 2.4 eV appears within the bad gap. The films bleach after 5–10 days in dry air. The observed phenomena are attributed to a high concentration (∼3×10²⁰ cm⁻³) of point defects, including F-centers, in nonstoichiometric RbAg₄I₅:Sm, and also to the oxidation of Sm. In colored films the ionic conductivity is σ⋍0.9σ ₀, and in bleached films it is close to the initial value σ ₀. Fiz. Tverd. Tela (St. Petersburg) 39, 1544–1547 (September 1997)     

UV absorption of RbAg4I5-RE (Sm, Yb) thin-film systems

UV spectra of samples prepared by vacuum deposition of Sm and Yb thin films on 100–200-nm thick films of the RbAg₄I₅ solid electrolyte (SE) at 300–350 K contain strong absorption bands peaking at about 4.3 and 5.0 eV. After deposition of ～5 nm of Sm, the ionic conductivity σ of the samples decreases from σ ₀ to ≈0.9 σ ₀, and the SE lattice parameter, from 11.24 to ≈11.15 Å, with the x-ray reflection halfwidth increasing from 0.5 to 0.8°. Further growth of Sm concentration in the samples changes the x-ray diffraction pattern, the absorption at 4.3 and 5.0 eV increases, a new absorption edge forms at 3.8 eV, and σ decreases down to ～10^?2 σ ₀. It is conjectured that the strong UV absorption bands in heavily defected silver halides of the RbAg₄I₅-Sm(Yb) system is genetically related to the 4d ¹⁰→4d ⁹5s electronic transitions in free Ag⁺ ions.     

UV absorption of thin-film RbAg4I5-RE (Sm, Yb) systems

UV-spectra of samples obtained by vacuum deposition of RE (Sm, Yb) thin films onto films of the solid electrolyte RbAg₄I₅ (300 – 350 K, thickness 100 – 200 nm) exhibit bands of strong absorption with maxima at 4.3 and 5.0 eV. After the deposition of Sm (≈ 5 nm), the ionic conductivity σ of the samples decreases to ≈ 0.9 σ₀ and the lattice parameter from 11.24 to 11.15 Å. The halfwidth of X-ray reflections increases from 0.5 to 0.8⁰. Further increase of the concentration of Sm in the samples changes the X-ray diffraction pattern. Under such conditions, the absorption in the regions of 4.3 and 5.0 eV further increases; a new single edge of absorption at 3.8 eV appears and σ declines to ≈10^?2 σ₀. It is supposed that a genetic relation exists between the UV-bands of strong absorption in the highly defective silver-halides of the RbAg₄I₅-RE system and the electronic transitions 4d¹⁰ ?4d⁹ 5s in free Ag⁺ ions.     

Method of uniform effective field in structure-dynamic approach of nanoionics

In the structure-dynamic approach of nanoionics, the method of a uniform effective field \( {F}_{\mathrm{eff}}^{j,k} \) of a crystallographic planeX ^j has been substantiated for solid electrolyte nanostructures. The \( {F}_{\mathrm{eff}}^{j,k} \)is defined as an approximation of a non-uniform field \( {F}_{\mathrm{dis}}^j \)of X ^j with a discrete- random distribution of excess point charges. The parameters of \( {F}_{\mathrm{eff}}^{j,k} \)are calculated by correction of the uniform Gauss field \( {F}_{\mathrm{G}}^j \) of X ^j . The change in an average frequency of ionic jumps X ^k ?→?X ^k?+?1 between adjacent planes of nanostructure is determined by the sum of field additives to the barrier heights η _k , _k?+?1, and for \( {F}_{\mathrm{G}}^j \) and \( {F}_{\mathrm{dis}}^j \), these sums are the same decimal order of magnitude. For nanostructures with length ~4 nm, the application of \( {F}_{\mathrm{G}}^j \) (as \( {F}_{\mathrm{eff}}^{j,k} \)) gives the accuracy ~20 % in calculations of ion transport characteristics. The computer explorations of the “universal” dynamic response (Reσ ^??∝?ω ⁿ ) show an approximately the same power n < ≈1 for\( {F}_{\mathrm{G}}^j \) and \( {F}_{\mathrm{eff}}^{j,k} \).     

A step towards nanoionics

The interaction of finely focused 20–100 keV electron beam at 10–1000 A/cm² current densities with 30–150 nm films of the RbAg₄I₅-family solid electrolytes has been studied. The results obtained show that it is possible to form arrays of electrochemical devices with single elements ≈ 10 nm in size in the films. Arrays of 100×100 nm structures consisting of a solid electrolyte film on C-, Au-and Ag-thin supports are demonstrated.