Raman measurements of the superionic conductor KAg4I5

Raman measurements of the superionic conductor KAg₄I₅ are reported between 77K and 296K and compared to similar data of RbAg₄I₅. The mode frequencies for the two materials are very similar and a mode at 22.7 cm^?1 abruptly and reversibly disappears at the transition temperature, T_c=137 K, as is observed in RbAg₄I₅, at 121 K.     

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.     

The electrical response of RbAg4I5/graphite inhomogeneous interfaces

The ac impedance of the cell graphite/graphite + RbAg₄I₅/graphite + RbAg₄I₅/graphite was investigated in the frequency range from 10⁻⁴ to 3 × 10⁵ Hz. A model assuming the graphite + RbAg₄I₅ mixture to represent a porous interface could explain the observed dependences in nearly the whole frequency range with the exception of the lowest frequencies. Attempts to improve the agreement presuming adsorption, discharge of charge carriers or diffusion of neutral species failed. An excellent fit could be achieved assuming a frequency dependent ac conductivity of the interface, approximately proportional to the frequency, as in the bulk of many solids with low conductivity, such as amorphous semiconductors or dielectrics.     

The splitting of the infrared vibrational spectra of RbAg4I5 in the low-temperature γ-phase

Spectra of the dynamic conductivity σ(v) of the superionic RbAg₄I₅ single crystal in the γ-phase have been measured at the frequencies 2–33 cm^?1 by means of monochromatic submillimeter spectroscopy with resolution 0.001 cm^?1. Several tens of well-resolved narrow and intensive lines were observed at liquid helium temperature. The obtained results are qualitatively discussed.     

A correction method for thermally lowered fission track ages

Abstract

Onset of electric current has been detected on illuminating the near–contact regions of RbAg₄I₅ crystals. The spectral and temperature characteristics of this current have been studied. A method is proposed for studying the spectrum of electronic states in the α-phase of the RbAg₄I₅ crystal. The dependence of the magnitude of the current and its spectral characteristics on the particular region of the RbAg₄I₅ crystal which is exposed to the light was used for the analysis of the variations in the distribution of defects along the length of the sample and the processes which occur near the electrode-(solid electrolyte) junctions.     

Mössbauer studies of microscopic disorder in solid electrolytes

We implement for the first time Mössbauer Spectroscopy (MS) to investigate short-range properties of disorder in solid electrolytes. MS in¹²⁹I and¹¹⁹Sn was carried out in RbAg₄I₅ and as impurity in Ag₂Se, respectively. Measurements were performed both in the superionic and the normal phases. It is shown that localized cation hopping is an inherent feature of the α-AgI-type solid electrolytes. In RbAg₄I₅, at temperatures far belowT _c, a small fraction of Ag is still locally mobile and atT>T _c, its concentration increases exponentially. A strong linear temperature dependence of the point-charge electric field gradient is observed and explained in terms of local hopping. With¹¹⁹Sn in Ag₂Se we observe the onset of “local melting” of the Ag surrounding the SnSe₄ cluster at 50 K below the bulk superionic phase transition. The characteristic features of MS related to microscopic studies of solid electrolytes are fully described.     

Study of the phase composition of AgI microcrystals by exciton spectroscopy and differential scanning calorimetry

Differential absorption spectra of RbAg₄I₅ have been measured in the exciton absorption region of AgI within the temperature range 27–250 °C. In the same temperature range, the temperature behavior of the heat capacity of RbAg₄I₅, Rb₂AgI₃, and KAg₄I₅ have been obtained by differential scanning calorimetry. An analysis of the results suggests that, in AgI microcrystals less than r _cr in size, the upper boundary for stability of the low-temperature β modification is higher by several tens of degrees. Fiz. Tverd. Tela (St. Petersburg) 40, 852–854 (May 1998)     

Proprietes electroniques et electrogalvaniques dutellurure d'argent β domaine d'existence

A study of the electronic and electrogalvanic properties of β silver telluride has been performed on samples whose non-stoichiometry has been determined by coulometric titration with the cell Ag/RbAg₄I₅/Ag₂Te/Pt. The data lead to the adoption of a model of Frenkel defects on the silver sublattice that are fully ionised. Their formation enthalpy is H_F′ = 0,70 eV. On the tellurium side this model is completed by the association V_AgV_Ag^x. Th homogeneity range is reported from ?10°C to 132°C: it extends essentially on the tellurium side of the stoichiometric composition.     

Ionic photoconductivity of RbAg4I5 superionic crystals

A new effect of illumination on ionic conductivity and activation energy of migration of mobile Ag⁺ cations in RbAg₄I₅ superionic crystals has been detected and studied. Reversible changes in the ionic conductivity due to illumination of superionic crystals are caused by reversible changes in the structure of electronic centers caused by elastic strain around these centers. The effect of elastic deformation on the process of ionic transport and activation energy for diffusion of mobile silver cations has been studied. Photostimulated recovery of the ionic conductivity after its change due to preliminary illumination of a RbAg₄I₅ superionic crystal with light of wavelength λ≃430 nm has been detected. This recovery of the ionic conductivity is due to excitation of centers in complexes generated by previous illumination of tested samples. Zh. éksp. Teor. Fiz. 112, 698–706 (August 1997)     

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.     

The effect of point defects on the ionic conductivity of RbAg4I5 solid electrolytes

Abstract

The effect has been studied of additive coloring on the magnitude of ion conductivity of RbAg₄I₅ crystals. It has been found that slight changes of silver stoichiometry of 10^?3 at.% can lead to considerable variations of the ionic conductivity Δ[sgrave]_i/[sgrave]_i ? 0.1. The dependence has been observed of the magnitude of ion conductivity on the ratio between the integral intensities of the main bands in the photoluminescence spectrum of the γ-phase of RbAg₄I₅ which associated with the luminescence centres containing vacancies and interstitials of silver cations.     

Light induced phenomena in superionic crystals

The phenomena of the reversible transformation of concentration and a structure of luminescence centers and of the concentration of mobile silver ions in local irradiated region of RbAg₄I₅ superionic crystals are studied. A new effect of illumination on ionic conductivity and activation energy of migration of mobile Ag⁺ cations in RbAg₄I₅ superionic crystals are observed. Reversible changes in the ionic conductivity due to illumination of superionic crystals are caused by reversible change in the structure of electronic centers caused by elastic strain around these centers. The effect of elastic deformation on the process of ionic transport and activation energy for diffusion of mobile silver cations are studied. Photostimulated recovery of the ionic conductivity after its change due to preliminary illumination of a RbAg₄I₅ superionic crystal with light of wavelength λ=430 nm are detected. This recovery of the ionic conductivity is due to excitation of centers in complexes generated by previous illumination of tested samples.     

Evidence for an order-disorder transformation in the solid electrolyte RbAg4I5

Specific heat and optical birefringence measurements made on RbAg₄I₅ are found to yield Ising-like critical exponents at the 208 K phase transition. A model involving indirect coupling of Ag⁺ sites through distortions of the I^--lattice is presented which is in agreement with experiment.     

Raman results in the superionic conductor RbAg4I5

Raman measurements between 77°K and 296°K are reported for the superionic conductor RbAg₄I₅. Careful attention is paid to the temperature region of the two phase transitions at 121°K and 208°K. We can detect no shifts in any of the numerous phonon modes except one at 22.9 cm^-1, which abruptly and reversibly appears in the lowest temperature phase. Raman results for the isomorphic material KAg₄I₅ are the same with the same mode appearing in the low temperature phase. Thus, the results in these systems are markedly different from those in AgI, where there are very large changes at the superionic conducting transition temperature.     

Proprietes electrogalvaniques et electroniques du sulfure d'argent β: Domaine d'existence

The study of electrogalvanic and electronic properties of the form β of silver sulfide has been performed on polycrystalline samples whose non stoichiometry is controled by coulometric titration with the cell Ag/RbAg₄I₅/Ag₂₊?S/Pt.The data obtained lead to the adoption of an electronic model according to which the Frenkel defects of the silver sublattice are completly ionized. The variation with temperature of the electronic properties near the stoichiometric composition between 23 and 176°C, the temperature of transition between the two forms β and α of Ag₂S, enables the forbidden gap E_i = (1,35?1,5 × 10^?3T) eV to be computed. The existence range has been drawn between 69°C and the α ? β transition temperature.The study of the ionic conductivity has made it possible to detect two ranges of preferential conduction and to determine the mechanism of migrations of the intersticial silver ions.     

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)     

Proprietes electroniques et electrogalvaniques du seleniure d'argent β: Domaine d'existence

A study of the electronic and electrogalvanic properties of β silver selenide has been performed on polycrystalline samples whose non-stoichiometry is controlled by eoulometric titration with the cell Ag/RbAg₄I₅/Ag_2+? Se/Pt. The adoption of an electronic model according to which the Frenkel defects of the silver sublattice are completely ionised allows us to compute independently the non-stoichiometry with the two formulaes δ = [Ag^o_i] ? [V'_Ag] and δ = n ? p. The homogeneity range has been drawn at positive temperatures and the formation enthalpy of the Frenkel defects is H'_F = 0,40 eV.     

Solid state reactions and transport properties in the quasibinary system AgI/RbI

The reactions between AgI and Rb₂AgI₃, RbI and RbAg₄I₅ and AgI and RbI have been investigated by measurements of reaction layer thickness and by experiments with inert markers. A theoretical derivation of the growth kinetics for reactions with double layers is given. The Rb⁺-diffusion coefficients, which are needed to apply these relations to the reaction between AgI and RbI, have been obtained from an investigation of the other two reactions which form only a single product layer. The diffusion coefficient of Ag⁺in Rb₂AgI₃ was also determined from conductivity measurements on Rb₂AgI₃.     

Hyperfine structure measurements in the4 I 9/2 ground state of141Pr

Using the atomic beam magnetic resonance method, the five hyperfine structure separations in the 4f ³ 6s ^{2 4}I_9/2 ground state of ₅₉ ¹⁴¹ Pr have been measured. The results are:F F′ E _FF′ ^* /h (MHz) 7 6 6477.913423(17) 6 5 5556.359848 (6) 5 4 4633.023306 (2) 4 3 3708.201146 (5) 3 2 2782.190601(15) From these quantities, the multipole interaction constantsA _k,k=1, 2, 3, 4 between the nucleus and the electron shell have been calculated.A ₄ especially then served to give the following limit for the intrinsic hexadecapole moment: ¦Q ₄₀¦<0.4eb ². Furthermore, theg _J -factors of the⁴ I multiplet have been measured at magnetic fields of 300 Oe. The results are:g _J(⁴ I _9/2)=0.7310371(15)g _J(⁴ I _11/2)=0.9651476(20)g _J(⁴ I _13/2)=1.1063197(40)g _J(⁴ I _15/2)=1.197963 (30) Small corrections due to perturbations by neighbouring fine structure levels are included.     

Thermal expansivity in superionic RbAg4I5

We have measured the length of a RbAg₄I₅ crystal in the temperature range between 130 K and 300 K using a fused silica LVDT dilatometer system. The expansivity is a smooth, nearly linear function of temperature. There is no anomaly such as a kink, discontinuity, or critical behavior at T_c = 209 K where the superionic β to superionic α phase transition occurs.