Elektro 041 Analysis of Acoustic Spectra Reflecting Ion Transport Processes in Glassy Electrolytes P. Hockicko a), P. Bury a), S. Jurečka b), M. Jamnický c) and I. Jamnický a) a) University of Žilina, Department of Physics, Žilina, b) University of Žilina, Department of Engineering Fundamentals, Liptovký Mikuláš, c) Slovak Technical University, Department of Ceramic, Glass and Cement, Bratislava

Elektro 042 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

Elektro Ion Conductive Glasses Characterization Attention Attention due to the possible application in modern electrochemical devices (solid electrolytes) Advantages Advantages compared to crystalline materials:  absence of grain boundaries  isotropic properties  composition variability  easy preparation Important criterion Important criterion – high ionic conductivity at room temperatures  Glasses containing Ag + ions can have the highest conductivity  25   -1 cm -1.  Theoretically the glasses that contain Cu + ions should achieve comparable conductivity because of similar electronic configuration and smaller ionic radii:  Interest  Interest in ion conductive glasses that contain Cu + ions In the present contribution the glasses of the system CuI - CuBr - Cu 2 O - P 2 O 5 CuI - CuBr - Cu 2 O - P 2 O 5 are investigated.

Elektro Experimental details melting melting reagent of the powders CuI, CuBr, Cu 2 O and P 2 O 5 P 2 O 5 – glass forming components Cu 2 O – modificator CuI + CuBr – cuprous halides mixing mixing under a dry argon atmosphere in appropiate portions in silica ampule at 933 K for 90 min. rapid quenching rapid quenching of glass melts pressing them between two brass plates of the area  1 cm 2 final thicknees  2.0 mm a) Glasses preparation procedure:

Elektro Experimental details Starting composition (in mol. %) at prepared ion conductive glasses: Glass sample Composition (in mol.%)CuBrCuI Cu 2 O P2O5P2O5P2O5P2O5 BIDP BIDP BIDP BIDP BDP Table 1 Starting glass compositions (in mol.%)

Elektro 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. Fig. 1. Experimental arrangement for acoustic attenuation measurement

Elektro Experimental details Fig. 2. Fig. 2. Temperature dependence of acoustic attenuation of ion conductive glasses of the system CuI-CuBr-Cu 2 O- P 2 O 5 for different glass compositions. The individual spectra are shifted for better resolution. 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.

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

Elektro Theoretical models power-law 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] [1] D. Almond, A. West: Solid State Ionics 26 (1988) 265 (2) 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).  power-law model model

Elektro Theoretical models Two functions have mainly been used to fit mechanical loss data [3]. [3] B. Roling, M. Ingram: Physical Review B 57 (1998) (3) with 0 <   1 Kohlrausch-Williams- Watts (KWW) - The first function is the Kohlrausch-Williams- Watts (KWW) function  (t) double power law (DPL) - The second function is the double power law (DPL) (4)  KWW model  DPL model

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

Elektro Results Analysis and Discussion Fig. 4. Fig. 4. Acoustics attenuation spectrum of sample BIDP5 (full line) and its theoretical supposing fit is superposition of two supposed relaxation processes (dashed lines). DPL model The complete spectrum of this 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.

Elektro Results Analysis and Discussion DPL model 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. Fig. 5. Acoustics spectrum of sample BIDP1 (full line). Dashed lines represent the best fit for two relaxation processes and their superposition.

Elektro Conclusion The experimental and theoretical investigation of ion conductive glasses in system CuI-CuBr-Cu 2 O-P 2 O 5 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,

Elektro Conclusion - the acoustic attenuation spectra of all investigated ion conducting glasses prepared in the system CuI-CuBr- Cu 2 O-P 2 O 5 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.

Elektro 0416 Thank You for Your Attention Peter Hockicko