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Lars Börjesson - One of the best experts on this subject based on the ideXlab platform.

  • Ionic conductivity and the Mixed Alkali Effect in Li x Rb 1 − x PO 3 glasses
    Physical Review B, 2003
    Co-Authors: C. Karlsson, Jan Swenson, Andrea Mandanici, Aleksandar Matic, Lars Börjesson
    Abstract:

    The temperature and frequency dependent ionic conductivity in ${\mathrm{Li}}_{x}{\mathrm{Rb}}_{1\ensuremath{-}x}{\mathrm{PO}}_{3}$ glasses has been studied using dielectric spectroscopy. The dc conductivity decreases by more than six orders of magnitude on mixing the Alkali ions in the glass structure, that is, a strong Mixed Alkali Effect on the dc conductivity was observed. The results show that the Mixed Alkali Effect on the dc conductivity diminishes as the temperature is increased. An ac conductivity Mixed Alkali Effect can be observed up to high frequencies, although it gradually becomes weaker as the frequency is increased. A quantitative analysis of the conductivity spectra shows that the number of mobile cations in the single Alkali glasses is, within experimental uncertainty, temperature independent. The results are discussed in relation to a detailed microscopic structural model taking into account the random mixing of Alkali ions [Phys. Rev. B 63, 132202 (2001)].

  • ionic conductivity and the Mixed Alkali Effect in li x rb 1 x po 3 glasses
    Physical Review B, 2003
    Co-Authors: C. Karlsson, Jan Swenson, Andrea Mandanici, Aleksandar Matic, Lars Börjesson
    Abstract:

    The temperature and frequency dependent ionic conductivity in ${\mathrm{Li}}_{x}{\mathrm{Rb}}_{1\ensuremath{-}x}{\mathrm{PO}}_{3}$ glasses has been studied using dielectric spectroscopy. The dc conductivity decreases by more than six orders of magnitude on mixing the Alkali ions in the glass structure, that is, a strong Mixed Alkali Effect on the dc conductivity was observed. The results show that the Mixed Alkali Effect on the dc conductivity diminishes as the temperature is increased. An ac conductivity Mixed Alkali Effect can be observed up to high frequencies, although it gradually becomes weaker as the frequency is increased. A quantitative analysis of the conductivity spectra shows that the number of mobile cations in the single Alkali glasses is, within experimental uncertainty, temperature independent. The results are discussed in relation to a detailed microscopic structural model taking into account the random mixing of Alkali ions [Phys. Rev. B 63, 132202 (2001)].

  • Random ion distribution model: A structural approach to the Mixed-Alkali Effect in glasses
    Physical Review B, 2001
    Co-Authors: Jan Swenson, C. Karlsson, Aleksandar Matic, Lars Börjesson, Carlo Meneghini, W.s. Howells
    Abstract:

    We have performed structural studies of a series of Mixed-Alkali phosphate glasses using diffraction experiments and reverse Monte Carlo simulations. We find that the Alkali ions tend to preserve their local structural environment regardless of the glass composition. Furthermore, the distribution of the two types of cations in the structure is predominantly random. We propose that the long debated Mixed-Alkali Effect is a natural consequence of the structural findings; a large energy mismatch for ionic jumps to dissimilar Alkali sites resulting in blocking of low-dimensional migration pathways.

Jan Swenson - One of the best experts on this subject based on the ideXlab platform.

  • ionic conductivity and the Mixed Alkali Effect in li x rb 1 x po 3 glasses
    Physical Review B, 2003
    Co-Authors: C. Karlsson, Jan Swenson, Andrea Mandanici, Aleksandar Matic, Lars Börjesson
    Abstract:

    The temperature and frequency dependent ionic conductivity in ${\mathrm{Li}}_{x}{\mathrm{Rb}}_{1\ensuremath{-}x}{\mathrm{PO}}_{3}$ glasses has been studied using dielectric spectroscopy. The dc conductivity decreases by more than six orders of magnitude on mixing the Alkali ions in the glass structure, that is, a strong Mixed Alkali Effect on the dc conductivity was observed. The results show that the Mixed Alkali Effect on the dc conductivity diminishes as the temperature is increased. An ac conductivity Mixed Alkali Effect can be observed up to high frequencies, although it gradually becomes weaker as the frequency is increased. A quantitative analysis of the conductivity spectra shows that the number of mobile cations in the single Alkali glasses is, within experimental uncertainty, temperature independent. The results are discussed in relation to a detailed microscopic structural model taking into account the random mixing of Alkali ions [Phys. Rev. B 63, 132202 (2001)].

  • Ionic conductivity and the Mixed Alkali Effect in Li x Rb 1 − x PO 3 glasses
    Physical Review B, 2003
    Co-Authors: C. Karlsson, Jan Swenson, Andrea Mandanici, Aleksandar Matic, Lars Börjesson
    Abstract:

    The temperature and frequency dependent ionic conductivity in ${\mathrm{Li}}_{x}{\mathrm{Rb}}_{1\ensuremath{-}x}{\mathrm{PO}}_{3}$ glasses has been studied using dielectric spectroscopy. The dc conductivity decreases by more than six orders of magnitude on mixing the Alkali ions in the glass structure, that is, a strong Mixed Alkali Effect on the dc conductivity was observed. The results show that the Mixed Alkali Effect on the dc conductivity diminishes as the temperature is increased. An ac conductivity Mixed Alkali Effect can be observed up to high frequencies, although it gradually becomes weaker as the frequency is increased. A quantitative analysis of the conductivity spectra shows that the number of mobile cations in the single Alkali glasses is, within experimental uncertainty, temperature independent. The results are discussed in relation to a detailed microscopic structural model taking into account the random mixing of Alkali ions [Phys. Rev. B 63, 132202 (2001)].

  • Mixed Alkali Effect in glasses.
    Physical review letters, 2003
    Co-Authors: Jan Swenson, Stefan Adams
    Abstract:

    We have applied the bond-valence technique to reverse Monte Carlo produced structural models of Mixed Alkali phosphate glasses in order to elucidate the Mixed Alkali Effect (MAE) in glasses. For the first time, the MAE is reproduced and understood directly from structural models in quantitative agreement with available experimental results. The two types of Alkali ions are randomly Mixed and have distinctly different conduction pathways of low dimensionality. This implies that $A$ ions tend to block the pathways for the $B$ ions and vice versa, and this is the main reason for the MAE.

  • Random ion distribution model: A structural approach to the Mixed-Alkali Effect in glasses
    Physical Review B, 2001
    Co-Authors: Jan Swenson, C. Karlsson, Aleksandar Matic, Lars Börjesson, Carlo Meneghini, W.s. Howells
    Abstract:

    We have performed structural studies of a series of Mixed-Alkali phosphate glasses using diffraction experiments and reverse Monte Carlo simulations. We find that the Alkali ions tend to preserve their local structural environment regardless of the glass composition. Furthermore, the distribution of the two types of cations in the structure is predominantly random. We propose that the long debated Mixed-Alkali Effect is a natural consequence of the structural findings; a large energy mismatch for ionic jumps to dissimilar Alkali sites resulting in blocking of low-dimensional migration pathways.

Charisse M. Hill - One of the best experts on this subject based on the ideXlab platform.

  • Comparative study of the Mixed-Alkali Effect in poly(ethylene oxide) and poly(propylene oxide)-thiocyanate salt systems
    Solid State Ionics, 1994
    Co-Authors: Dale Teeters, Charisse M. Hill
    Abstract:

    Abstract The conductivity of poly(ethylene oxide), PEO, and poly(propylene oxide), PPO, polymers containing various mole fractions of potassium and sodium ions was measured in order to investigate the Mixed-Alkali Effect. The PEO and PPO polymers used in this work contained the same number of repeating units in the polymer backbone and the polymer-salt complexes were prepared in an identical fashion so that a comparison of the Mixed-Alkali Effect between the two polyether systems could be made. A Mixed-Alkali Effect was observed in the PEO-Na/KSCN complexes in the region of 0.2−0.6 mole fraction potassium while none was observed in the PPO-Na/KSCN systems. The difference in the Mixed-Alkali Effects seen in this study and in other studies in the literature were discussed in terms of the relaxation times of the local structure of the polymer matrix and the relaxation times of ion diffusion.

C. Karlsson - One of the best experts on this subject based on the ideXlab platform.

  • Ionic conductivity and the Mixed Alkali Effect in Li x Rb 1 − x PO 3 glasses
    Physical Review B, 2003
    Co-Authors: C. Karlsson, Jan Swenson, Andrea Mandanici, Aleksandar Matic, Lars Börjesson
    Abstract:

    The temperature and frequency dependent ionic conductivity in ${\mathrm{Li}}_{x}{\mathrm{Rb}}_{1\ensuremath{-}x}{\mathrm{PO}}_{3}$ glasses has been studied using dielectric spectroscopy. The dc conductivity decreases by more than six orders of magnitude on mixing the Alkali ions in the glass structure, that is, a strong Mixed Alkali Effect on the dc conductivity was observed. The results show that the Mixed Alkali Effect on the dc conductivity diminishes as the temperature is increased. An ac conductivity Mixed Alkali Effect can be observed up to high frequencies, although it gradually becomes weaker as the frequency is increased. A quantitative analysis of the conductivity spectra shows that the number of mobile cations in the single Alkali glasses is, within experimental uncertainty, temperature independent. The results are discussed in relation to a detailed microscopic structural model taking into account the random mixing of Alkali ions [Phys. Rev. B 63, 132202 (2001)].

  • ionic conductivity and the Mixed Alkali Effect in li x rb 1 x po 3 glasses
    Physical Review B, 2003
    Co-Authors: C. Karlsson, Jan Swenson, Andrea Mandanici, Aleksandar Matic, Lars Börjesson
    Abstract:

    The temperature and frequency dependent ionic conductivity in ${\mathrm{Li}}_{x}{\mathrm{Rb}}_{1\ensuremath{-}x}{\mathrm{PO}}_{3}$ glasses has been studied using dielectric spectroscopy. The dc conductivity decreases by more than six orders of magnitude on mixing the Alkali ions in the glass structure, that is, a strong Mixed Alkali Effect on the dc conductivity was observed. The results show that the Mixed Alkali Effect on the dc conductivity diminishes as the temperature is increased. An ac conductivity Mixed Alkali Effect can be observed up to high frequencies, although it gradually becomes weaker as the frequency is increased. A quantitative analysis of the conductivity spectra shows that the number of mobile cations in the single Alkali glasses is, within experimental uncertainty, temperature independent. The results are discussed in relation to a detailed microscopic structural model taking into account the random mixing of Alkali ions [Phys. Rev. B 63, 132202 (2001)].

  • Random ion distribution model: A structural approach to the Mixed-Alkali Effect in glasses
    Physical Review B, 2001
    Co-Authors: Jan Swenson, C. Karlsson, Aleksandar Matic, Lars Börjesson, Carlo Meneghini, W.s. Howells
    Abstract:

    We have performed structural studies of a series of Mixed-Alkali phosphate glasses using diffraction experiments and reverse Monte Carlo simulations. We find that the Alkali ions tend to preserve their local structural environment regardless of the glass composition. Furthermore, the distribution of the two types of cations in the structure is predominantly random. We propose that the long debated Mixed-Alkali Effect is a natural consequence of the structural findings; a large energy mismatch for ionic jumps to dissimilar Alkali sites resulting in blocking of low-dimensional migration pathways.

Minoru Tomozawa - One of the best experts on this subject based on the ideXlab platform.

  • The Mixed Alkali Effect and thermodynamic state of glasses
    Solid State Ionics, 1998
    Co-Authors: Minoru Tomozawa
    Abstract:

    Abstract The Mixed Alkali Effect, a pronounced reduction in electric conductivity when two or more dissimilar Alkali ions coexist, is most conspicuous under a d.c. electric field while it diminishes under high frequency. Correspondingly, low d.c. conductivity of the Mixed Alkali glass is accompanied by a large dielectric relaxation strength (dielectric loss and static dielectric constant). This larger dielectric relaxation strength of Mixed Alkali glasses compared with the corresponding single Alkali glasses appears due to a negative enthalpy of mixing of two dissimilar Alkali species. This fact has been experimentally confirmed. Correspondingly, the activity coefficient of one Alkali component decreases drastically by the addition of a second Alkali component and this behavior appears to be analogous to the pronounced decrease of a tracer diffusion coefficient when a second Alkali component is added. The thermodynamic state of glasses is controlled, primarily, by the charge interactions. The apparent correlation between the thermodynamics and the transport phenomena, as well as other features of the Mixed Alkali Effect, such as the diminishing Mixed Alkali Effect in a high electric field, can be explained, at least qualitatively, using the electrolyte theory based upon the Coulombic interactions of charged species originally developed by Debye and Huckel.

  • Mechanism of the Mixed Alkali Effect based upon the thermodynamic state of glass
    Journal of Non-Crystalline Solids, 1991
    Co-Authors: Minoru Tomozawa, Vincent J. Mcgahay
    Abstract:

    Abstract A new mechanism for the Mixed Alkali Effect of dc conductivity is proposed. It was shown earlier that the high frequency conductivity shows very little Mixed Alkali Effect and that Mixed Alkali glasses show a much larger dielectric relaxation strength than single Alkali glasses, indicating that the Mixed Alkali Effect in dc conductivity is related to the difference in the dielectric relaxation strength. An expression for dielectric relaxation strength in terms of the thermodynamic state was experimentally verified for single Alkali glasses. An analogous equation for dielectric relaxation strength of Mixed Alkali glasses was derived. Using the regular solution model, it was shown that the dielectric relaxation strength for Mixed Alkali glasses can show a large maximum if the enthalpy of mixing between the two Alkalis is negative. A large negative enthalpy of mixing between the two Alkali species was found experimentally from ion-exchange equilibrium, which, it is suggested, originates from the stress due to their ionic size difference. The proposed mechanism appears to be consistent with many experimental observations.