Absence of a space-charge-derived enhancement of ionic conductivity in β|γ- heterostructured 7H- and 9R-AgI.
Extreme room temperature conductivity enhancements have been reported for nanocrystalline AgI of up to  × 10(4) relative to bulk β-AgI (Guo et al 2005 Adv. Mater.  17 2815-9). These samples were identified as possessing 7H and 9R polytype structures, which can be considered as heterostructures composed of thin, commensurate layers in the β (wurtzite) and γ (zincblende) phases. It has been proposed that space-charge layer formation at β|γ-interfaces causes near complete disordering of the Ag(+) sublattice in these polytypes, resulting in a massive intrinsic enhancement of ionic conductivity. We have performed molecular dynamics simulations of β- and γ-AgI and mixed β|γ superlattices, to study the effect of heterostructuring on intrinsic defect populations and Ag(+) transport. The ionic conductivities and Ag(+) diffusion coefficients vary as β > 7H ≈ 9R ≈ 10L > γ. The β|γ-heterostructured polytypes show no enhancement in defect populations or Ag(+) mobilities relative to the β-AgI phase, and instead behave as simple composites of β- and γ-AgI. This contradicts the proposal that the extreme conductivity enhancement observed for 7H and 9R polytypes is explained by extensive space-charge formation.
Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK. benjamin.morgan@materials.ox.ac.uk
B J
BJ
Morgan
P A
PA
Madden
D004058:Diffusion; D004553:Electric Conductivity; D007454:Iodides / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D007477:Ions; D056004:Molecular Dynamics Simulation; D018030:Silver Compounds / Q000737:chemistry*; D013237:Stereoisomerism; D013816:Thermodynamics
D007454:Iodides; D052578:Ionic Liquids; D007477:Ions; D018030:Silver Compounds; C030584:silver iodide