The different ionic conductivity responses to supervalent versus subvalent doping, under lithium-rich and lithium-poor conditions, are compared graphically in fig. . As noted above, subvalent doping is predicted to give no net increase in ionic conductivity except at very high dopant levels. Even at sufficient subvalent doping levels to produce a net increase in ionic conductivity, the resulting conductivity increase remains orders of magnitude smaller than for supervalent doping at comparable dopant concentrations, and we conclude, therefore, that subvalent doping to increase lithium interstitial concentrations is not an effective strategy for enhancing the ionic conductivity of Li 3 OCl. Our analysis also indicates that subvalent doping will be maximally effective under Li-poor synthesis conditions, due the associated low formation energy of V Li .