AC and DC Conductivity in Nano- and Microcrystalline Li₂O : B₂O₃ Composites: Experimental Results and Theoretical Models

Abstract

Nanocrystalline Composites / Li Ion Conductor / Impedance Spectroscopy / Percolation ModelsWe report on impedance measurements of nano-and microcrystalline composites of the Li ion conductor Li 2 O and the ionic insulator B 2 O 3 as well as their interpretation in the frame of percolation models. In the experimental part, besides the dc conductivity and its dependence on composition and temperature (i.e. its activation energy) also the ac conductivity and its dependence on composition, temperature and frequency (i.e. the conductivity exponent) are presented. Striking differences between the nanocrystalline and the corresponding microcrystalline composites were found. Deviations of the ac from the dc results can be explained by the fact that the experiments probe ion dynamics on different time and thus length scales. In the theoretical part, a continuum percolation model, a brick-layer type bond percolation approach and a Voronoi construction are alternatively used to model the dc behaviour. Based merely on the largely different volume fractions of the interfaces between ionic conductor and insulator grains in the nano-and microcrystalline composites, good overall agreement with the experimental dc results is obtained. The high critical insulator content above which the experimental conductivity vanishes in the nanocrystalline composites suggests the presence of an additional Li diffusion passageway of nanometer length in the interface between nanocrystalline insulator grains.

Motion of Li+ in Nanoengineered LiBH4 and LiBH4:Al2O3 Comparison with the Microcrystalline Form

“…[5,[29][30][31][32] Moreover, without changing the chemical composition of the ion conductor, the formation of so-called dispersed ion conductors consisting of the conducting phase and an insulator, such as B 2 O 3 or Al 2 O 3 , is also reported to lead to rather high conductivities. [4,[33][34][35][36][37][38] In the case of a nanocrystalline two-phase composite, the large volume fraction of ion conductor/insulator interfaces formed by adjacent crystallites enable the ions to use fast (percolating) migration pathways. [35,37] Herein, results for the mechanosynthesized, nanocrystalline LiBH 4 :Al 2 O 3 com-The introduction of structural disorder and large volume fractions of different kinds of interfaces enables the manipulation of ion dynamics in solids.…”

Ionic conductivity and activation energy for oxygen ion transport in superlattices — The multilayer system CSZ (ZrO2+CaO)/Al2O3

“…in LiI/Al 2 O 3 as one of the prototype materials [1]. In recent years this heterogeneous doping was intensively studied because of the great interest in the increase of ionic conductivity at low temperatures [2][3][4][5][6][7][8][9][10].…”

Dielectric Properties of RhombohedralPbNb2O6

“…Here, is the time constant of the equivalent circuit (also called relaxation time), and this has been calculated using Nyquist diagram [9,23] as detailed previously. Value of DC activation energy ( dc ), due to DC conductivity [9], has been calculated using the Arrhenius relation dc = 0 exp(− dc / ) [26], where 0 is the preexponential factor, is the Boltzmann constant that equals 8.617343 × 10 −5 eV⋅K −1 , and is the temperature in Kelvin. The values of dc = and 0 have been summarized in Table 4.…”