Heterostructured ($\beta /\gamma$)-AgI exhibits a spontaneous lattice polarization not accounted for in standard space-charge models. This polarization field dominates the positional variation of energies of isolated defects, and ${\mathrm{Ag}}^{+}$ vacancies and interstitials are stabilized at alternate [$\beta /\gamma$] interfaces. This suggests enhanced Frenkel pair separation, analogous to electronic charge separation in polar semiconductor heterostructures. Stoichiometric systems are, however, characterized by associated Frenkel pairs due to strong $V_{\mathrm{Ag}}\mathrm{\text{−}}{\mathrm{Ag}}_i$ interactions and show no enhancement of defect numbers. In nonstoichiometric systems, lattice polarization does direct the distribution of the excess defect species, and defect-defect interactions enhance local Frenkel pair concentrations at interfaces, suggesting that nonstoichiometry is critical to the extreme room-temperature ionic conductivities observed in heterostructured AgI nanoplates.

• Received 11 June 2011

DOI:https://doi.org/10.1103/PhysRevLett.107.206102