Events

Linear diffusion model for the grain boundary resistance of ionic conductors

Speaker :
Prof. Igor Lubomirsky
Department of Materials Science, Weizmann Institute of Science, Rehovot, Israel
Date : 24 Apr 2019 (Wed)
Time : 10:30 am
Venue : Room 3598, HKUST (3/F., Lift #27/28)

Abstract

We have demonstrated that current-voltage characteristics of grain boundaries in prominent solid oxygen or proton conductors can be accurately described using a simple linear diffusion formalism (I-V model).[1-3] The model assumes that: (1) the grain boundaries do not represent physical blocking layers and (2) the ions follow Boltzmann distribution. Despite its simplicity, the model successfully reproduces the ‘‘power law’’: current proportional to voltage power Igb~(Ugb(n. The model also correctly predicts that the product n·T, where T is the temperature in K, is constant and the grain boundary potential, φgb, can be determened as φgb=n/fKL, where fKL=0.41 is an empirical factor.

Prior to our model, the value of φgb has been determined exclusively by the ratio of an effective resistivity of a single grain boundary to that of grain interior (RR model [4]). This approach assumes that the grain boundary resistance arises solely from the depletion of charge carriers in the space charge zone. Such cases are relatively rare, like for instance, doped LaGaO3 [5], for which φgb determined by both methods, are very close. However, in general, grain boundary resistance may have various sources, causing the RR model to overestimate the value of gb. Using the I-V model, φgb can be determined accurately even if multiple factors are responsible for the grain boundary resistance [6]. The linear diffusion model can also be applicable to the case of the grain boundaries in electronic conductors, for instance, in Fe-doped SrTiO3 [7], in which the conductivity is dominated by only one electronic carrier.

The ability of the linear diffusion model to distinguish between the various contributions to the grain boundary resistance makes it into a powerful and versatile tool to analyze grain boundaries of ionic and, sometimes, electronic conductors.

Funding by US-Israel BSF (grant no. 2016006) is acknowledged.

References
[1]    S. K. Kim, S. Khodorov, C. T. Chen, S. Kim, I. Lubomirsky, Phys Chem Chem Phys 2013, 15, 8716.
[2]    S. K. Kim, S. Khodorov, I. Lubomirsky, S. Kim, Phys Chem Chem Phys 2014, 16, 14961.
[3]    S. Kim, S. K. Kim, S. Khodorov, J. Maier, I. Lubomirsky, Phys Chem Chem Phys 2016, 18, 3023.
[4]    J. Fleig, S. Rodewald, J. Maier, J. Appl. Phys. 2000, 87, 2372.
[5]    C. Y. S. Chang, I. Lubomirsky, S. Kim, Phys Chem Chem Phys 2018, 20, 8719.
[6]    C.-Y. S. Chang, I. Lubomirsky, S. Kim, The Journal of Physical Chemistry C 2019.
[7]    C. Y. S. Chang, I. Lubomirsky, S. Kim, Phys Chem Chem Phys 2018, 20, 19250.

Bio

Igor Lubomirsky, Prof. at the Dept. of Materials & Interfaces, Weizmann Institute of Science (WIS), Israel;  B.Sc. in Chemical Engineering, Kharkov Polytechnic Institute (Ukraine); Ph.D. Solid State Chemistry at WIS; postdoc in Electrical Engineering of UCLA  and Max Planck Institute for Solid State Research (Stuttgart, Germany). I.L. studies local symmetry reduction leading to anelastic and electrostrictive effects in solids with a large concentration of point defects, in general, and in ion conductors in particular. I.L. worked for the last six years to develop a method to distinguish the various contributions to the grain boundary resistance.