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P. Hockicko a ) , P. Bury a) , S. Jure č ka b) , M. Jamnický c) and I. Jamnický a)

Analysis of A coustic S pectra R eflecting I on T ransport P rocesses in G lassy E lectrolytes. P. Hockicko a ) , P. Bury a) , S. Jure č ka b) , M. Jamnický c) and I. Jamnický a) a) University of Žilina, Department of Physics, 010 26 Žilina,

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P. Hockicko a ) , P. Bury a) , S. Jure č ka b) , M. Jamnický c) and I. Jamnický a)

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  1. Analysis of Acoustic SpectraReflectingIon Transport Processes in Glassy Electrolytes P. Hockickoa), P. Bury a) , S. Jurečka b), M. Jamnický c)and I. Jamnický a) a) University of Žilina, Department of Physics, 010 26 Žilina, b) University of Žilina, Department of Engineering Fundamentals, 031 01 Liptovký Mikuláš, c) Slovak Technical University, Department of Ceramic, Glass and Cement, 812 19 Bratislava • hockicko@fyzika.utc.sk, • http://hockicko.utc.sk

  2. Introduction 1) Ion Conductive Glasses Characterization 2) Experimental Details of Measurements • Glasses preparation procedure • Acoustical measurement details 3) Theoretical models 4) Results Analysis and Discussion • Fitting of the acoustic attenuation spectra • Comparison of the models 5) Conclusion

  3. 1. Ion Conductive Glasses Characterization Attention due to the possible application in modern electrochemical devices (solid electrolytes) Advantages compared to crystalline materials:  absence of grain boundaries  isotropic properties  composition variability  easy preparation Important criterion – high ionic conductivity at room temperatures  Glasses containing Ag+ ions can have the highest conductivity 25 10-2-1cm-1.  Theoretically the glasses that contain Cu+ ions should achieve comparable conductivity because of similar electronic configuration and smaller ionic radii: Interest in ion conductive glasses that contain Cu+ ions In the present contribution the glasses of the system CuI - CuBr - Cu2O - P2O5 are investigated.

  4. 2. Experimental details • a) Glasses preparation procedure: melting reagent of the powders CuI, CuBr, Cu2O and P2O5 P2O5– glass forming components Cu2O – modificator CuI + CuBr – cuprous halides mixing under a dry argon atmosphere in appropiate portions in silica ampule at 933 Kfor 90 min. rapid quenching of glass melts pressing them between two brass plates of thearea  1 cm2 final thicknees 2.0 mm

  5. 2. Experimental details Starting composition (in mol. %) at prepared ion conductive glasses: Table 1 Starting glass compositions (in mol.%)

  6. 2. Experimental details • b)Acoustical measurement details: Experimental details: - measurement equipment:MATEC attenuation comparator - longitudinal acoustic wave: f = 18 MHz - quartz rod buffer - temperature range: 140 – 365 K Fig. 1.Experimental arrangement for acoustic attenuation measurement

  7. 2. Experimental details The existence of two thermally activated relaxation processes of ions in connection with different kinds of sites. Low temperature peaks are usually related to faster ion transport and high temperature peaks are related to slower mobile ions. Fig. 2.Temperature dependence ofacoustic attenuationof ion conductive glasses of the system CuI-CuBr-Cu2O-P2O5 for different glass compositions. The individual spectra are shifted for better resolution.

  8. 3. Theoretical models The attenuation may be described as a Debye-like, single relaxation time processes [1] • Debye model • - attenuation, - relaxation strength, - angular frequency, -relaxation time, , [2] B - deformation potential, N- number of mobile ions, v- velocity of the sound wave, - density of the solid, T - absolute temperature, kB- Boltzmann constant EA- activation energy, 1/0 1013– 1014 s-1 - typical relaxation frequency of ion hopping when = 1= max [1]D.Almond, A. West: Solid State Ionics 26 (1988) 265 [2] G. Carini et al.: Physical Review B 30 (1984) 7219

  9. 3. Theoretical models The relaxation phenomena observed in a wide variety of materials exhibit a power-law type of frequency dependence. The relationship to Debye behaviour is expressed in the form [1] • power-law model m,n - power-law exponents, (take values between 0 and 1) When m = 1 and n = 0, equation (2) reduces to the equation for a single Debye-like process (1). [1]D. Almond, A. West: Solid State Ionics 26 (1988) 265

  10. 3. Theoretical models Two functions have mainly been used to fit mechanical loss data [3]. - The first function is the Kohlrausch-Williams-Watts (KWW) functionF (t) • KWW model with 0 < b 1 • DPL model - The second function is the double power law(DPL) [3]B. Roling, M. Ingram: Physical Review B 57 (1998) 14192

  11. 4. Results Analysis and Discussion To fit the acoustic spectrum using the Debye model (Eq. (1)) was applied. Themeasured spectrum in intermediate and high temperature ranges is represented by spotted line in the acoustic spectrum. Fig. 3.The acoustic spectrum of sample BIDP5 (full line) and the Debye fit of the two relaxation processes (dashed lines).

  12. 4. Results Analysis and Discussion The complete spectrum ofthis sample cannot be fitted using DPL model similarly as in the case of supposing only two relaxation processes. The additional third relaxation process should be taken into account with maximum at the temperature about 270 K. Fig. 4.Acoustics attenuation spectrum of sample BIDP5 (full line) and its theoretical supposing fit is superposition of two supposed relaxation processes (dashed lines).

  13. 4. Results Analysis and Discussion To fit the acoustic spectrum using the DPL model (Eq. (4)) was applied and the calculated lines gave an excellent agreement with measured spectrum in intermediate and high temperature range represented by dashed lines in the acoustic spectrum. Fig. 5.Acoustics spectrum of sample BIDP1 (full line). Dashed lines represent the best fit for two relaxation processesand theirsuperposition.

  14. 5. Conclusion The experimental and theoretical investigation of ion conductive glasses in system CuI-CuBr-Cu2O-P2O5 showed that: • the acoustical spectroscopy can be a very useful technique for the study of transport processes in fast ion conductive glasses, • the investigated relaxation process could be described by a relaxation theory, • the superposition attenuation peaks described by theoretical models can fit all acoustic attenuation spectra, • using the theoretical models we can describe the relaxation processes and find some ion parameters,

  15. 5. Conclusion - the acoustic attenuation spectra of all investigated ion conducting glasses prepared in the system CuI-CuBr-Cu2O-P2O5 consist of more then two thermally activated relaxation processes for temperatures over 220 K, • the DPL model provides a slightly better fit than the KWW model or the Debye model, • the superposition of three loss peaks with different activation energies can better fit the investigated spectrum of the glasses, • further analyses of acoustic spectra obtained by investigation of glass samples with different compositions in wider temperature and frequency range should be done for better understanding of ion transport mechanisms for various types of the investigated ion conducting glasses.

  16. Thank You for Your Attention Peter Hockicko • hockicko@fyzika.utc.sk, • http://hockicko.utc.sk

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