The ability of solid electrolytes to allow ion transport in the solid state makes them useful for a range of applications, including fuel cells and solid-state batteries . As a consequence, a considerable amount of research has focussed on understanding how the structure and chemical composition of particular solid electrolytes modulate their ionic conductivity . In addition to providing insight into the atomic-scale mechanisms of ionic conductivity within specific families of solid electrolytes, this body of research has also produced various "design principles"-general conceptual models that seek to explain, and predict, trends in ionic conductivity across different families of solid electrolytes . Many of these solid electrolyte design principles reflect how changes to the structure and composition of the host framework-the set of non-diffusive ions within a solid electrolyte-modulate the potential energy surface for the mobile ions, and hence influence overall ionic conductivity .