TY - JOUR
T1 - Protonic conductivity of polycrystalline materials evaluated with effective medium percolation approach
T2 - A case study on lithium-carboxylate based MOF
AU - Zima, Vitezslav
AU - Shimakawa, Koichi
AU - Lin, Chia Her
N1 - Publisher Copyright:
© 2016 Elsevier B.V.
PY - 2016/9/1
Y1 - 2016/9/1
N2 - A model of random walk of protons previously proposed for the evaluation of conductivity data of polycrystalline metal-organic framework compound, lithium tetrahydrofuran-2,3,4,5-tetracarboxylate (LiTFTA), is reexamined using a percolation path approximation (PPA). PPA is a useful technique for analyzing electronic and ionic transports in inhomogeneous media and in this paper it is applied to interpret unclear effects encountered in the study of conductivity properties of LiTFTA measured in the form of a polycrystalline material. Random distribution of grain size produces dispersive conductivity, it means that ac conductivity of a polycrystalline sample depends on the frequency almost linearly, a phenomenon completely different from that observed in single crystals. The local conductance fluctuation due to the grain size variation is the origin of the dispersive conductivity. The frequency, at which dispersive loss occurs, is determined by macroscopic dielectric relaxation time but not by microscopic hopping time of protons. This reasoning leads to conductivity data analysis based on PPA, from which the values of conductivity inside the grains and at the interface of the grains can be determined. In addition, we were able to estimate the change of the density of the charge carriers in dependence on temperature, based on previously established idea of ionic diffusion.
AB - A model of random walk of protons previously proposed for the evaluation of conductivity data of polycrystalline metal-organic framework compound, lithium tetrahydrofuran-2,3,4,5-tetracarboxylate (LiTFTA), is reexamined using a percolation path approximation (PPA). PPA is a useful technique for analyzing electronic and ionic transports in inhomogeneous media and in this paper it is applied to interpret unclear effects encountered in the study of conductivity properties of LiTFTA measured in the form of a polycrystalline material. Random distribution of grain size produces dispersive conductivity, it means that ac conductivity of a polycrystalline sample depends on the frequency almost linearly, a phenomenon completely different from that observed in single crystals. The local conductance fluctuation due to the grain size variation is the origin of the dispersive conductivity. The frequency, at which dispersive loss occurs, is determined by macroscopic dielectric relaxation time but not by microscopic hopping time of protons. This reasoning leads to conductivity data analysis based on PPA, from which the values of conductivity inside the grains and at the interface of the grains can be determined. In addition, we were able to estimate the change of the density of the charge carriers in dependence on temperature, based on previously established idea of ionic diffusion.
KW - Dielectric relaxation time
KW - Dispersive ac conductivity
KW - Impedance spectroscopy
KW - Percolation path approximation
KW - Proton conductivity
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U2 - 10.1016/j.ssi.2016.05.015
DO - 10.1016/j.ssi.2016.05.015
M3 - Article
AN - SCOPUS:84971672828
SN - 0167-2738
VL - 292
SP - 98
EP - 102
JO - Solid State Ionics
JF - Solid State Ionics
ER -