The spinel structure with a general formula AB 2 X 4 consists of a cubic close-packed arrangement of X atoms. In its conventional crystal structure, the A cations occupy 1/8 of the tetrahedral sites, while the B cations occupy 1/2 of the octahedral sites, as depicted in Fig- At high temperatures, numerous spinels exhibit cubic symmetry; however, the presence of distorted BO 6 octahedra cannot be dismissed. The octahedra undergo a trigonal distortion, leading to a transformation from O h octahedral symmetry to D 3h octahedral symmetry. In addition, migration in the spinel structure is mediated by intermediate octahedral sites whose relative stability to the initial tetrahedral site, called site preference, strongly influences the resulting migration barriers. In the ideal scenario in which the site preference tends towards zero, the activation barriers minimize and any deviations towards higher or lower values result in an increased barrier. This observation can be inferred from the relationship between the activation barrier and the site preference, as depicted in Figure . As a result, this phenomenon presents potential avenues for augmenting charge carrier mobility through deliberate choices of B-group transition metals and anion chemistry that satisfy the site preference criterion. Such improvements are evident in the low migration barriers of Ca in d 0 -metal oxide spinels. Migration barriers in spinel materials have recently been used to derive a descriptor for the ion mobility based on ionic radii, oxidation states, and electronegativities, as mentioned in the previous section. Additionally, it was shown that transport properties of spinel compounds are impacted by transition metal cations, discovering that these metals have a notable impact on the barriers for Mg 2+ migration in such compounds. By utilizing this principle, it was demonstrated that oxide spinels incorporating electronegative transition metal cations of substantial size hold the potential for showcasing elevated Mg 2+ mobility.