TY - JOUR

T1 - Ionic conductivity of nanocrystalline γ-AgI prepared by high-energy ball milling

AU - Jodlbauer, Anna

AU - Gombotz, Maria

AU - Gadermaier, Bernhard

AU - Heitjans, Paul

AU - Wilkening, H. R.Martin

N1 - Funding Information: Research funding: This study received funding from the Deutsche Forschungsgemeinschaft (recipient H.M.R. Wilkening, no. WI3600) and the State of Lower Saxony in the frame of a Niedersachsen Professorship (P. Heitjans).

PY - 2024/4/25

Y1 - 2024/4/25

N2 - The compound AgI crystallizes, depending on temperature and pressure, with various crystal structures. While α-AgI is the stable form at elevated temperatures, the β and the γ forms exist at lower temperatures. Variants with stacking sequences different than in pure β-AgI and γ-AgI enrich the complex crystallographic situation for AgI. In the study presented here, we converted a mixture of β-AgI and γ-AgI into nanostructured γ-AgI by mechanical treatment, that is, by high-energy ball milling of such a mixture under ambient conditions. Our work extends an earlier study by Ahmad (Z. Naturforsch. 2015, 70b, 17). We used variable-temperature, potentiostatic conductivity spectroscopy as well as electric modulus measurements to characterize the electric transport parameters. For the case that the sample is heated to temperatures near and above 420 K, preliminary information on the “resistance” of the electric conductivity against healing of defects are also collected. As compared to the unmilled but mixed sample, whose Ag+ ionic transport is dominated by those ions residing in the γ-phase of AgI (0.25 eV vs. 0.46 eV in β-AgI), ball milling only leads to a small increase in overall electric conductivity (by a factor of 3-4) for nanocrystalline γ-AgI (0.25 eV). This observation is perfectly in line with a recent observation for the fast ion conductor Li10GeP2S12 (Hogrefe et al., J. Am. Chem. Soc. 2022, 144, 9597): In materials with already rapid diffusion pathways, nanostructuring and the introduction of defects and distortions do not lead to significantly enhanced ion transport. Here, a careful analysis of data from conductivity and modulus spectroscopy helps identify which dynamic parameters are mainly responsible for the change in the overall conductivity upon mechanical treatment of coarse-grained γ-AgI.

AB - The compound AgI crystallizes, depending on temperature and pressure, with various crystal structures. While α-AgI is the stable form at elevated temperatures, the β and the γ forms exist at lower temperatures. Variants with stacking sequences different than in pure β-AgI and γ-AgI enrich the complex crystallographic situation for AgI. In the study presented here, we converted a mixture of β-AgI and γ-AgI into nanostructured γ-AgI by mechanical treatment, that is, by high-energy ball milling of such a mixture under ambient conditions. Our work extends an earlier study by Ahmad (Z. Naturforsch. 2015, 70b, 17). We used variable-temperature, potentiostatic conductivity spectroscopy as well as electric modulus measurements to characterize the electric transport parameters. For the case that the sample is heated to temperatures near and above 420 K, preliminary information on the “resistance” of the electric conductivity against healing of defects are also collected. As compared to the unmilled but mixed sample, whose Ag+ ionic transport is dominated by those ions residing in the γ-phase of AgI (0.25 eV vs. 0.46 eV in β-AgI), ball milling only leads to a small increase in overall electric conductivity (by a factor of 3-4) for nanocrystalline γ-AgI (0.25 eV). This observation is perfectly in line with a recent observation for the fast ion conductor Li10GeP2S12 (Hogrefe et al., J. Am. Chem. Soc. 2022, 144, 9597): In materials with already rapid diffusion pathways, nanostructuring and the introduction of defects and distortions do not lead to significantly enhanced ion transport. Here, a careful analysis of data from conductivity and modulus spectroscopy helps identify which dynamic parameters are mainly responsible for the change in the overall conductivity upon mechanical treatment of coarse-grained γ-AgI.

KW - AgI

KW - ion conductivity

KW - mechanical treatment

KW - nanostructured materials

UR - http://www.scopus.com/inward/record.url?scp=85190333787&partnerID=8YFLogxK

U2 - 10.1515/znb-2023-0081

DO - 10.1515/znb-2023-0081

M3 - Article

AN - SCOPUS:85190333787

VL - 79

SP - 155

EP - 161

JO - Zeitschrift fur Naturforschung - Section B Journal of Chemical Sciences

JF - Zeitschrift fur Naturforschung - Section B Journal of Chemical Sciences

SN - 0932-0776

IS - 4

ER -