Magnetic influence on ion transport in concentrated solid solutions: An analytic investigation

It is well established that magnetic fields have a significant effect on transport in certain classes of electronic conductors. Less reported are similar effects in solid ionic conductors. Despite the rarity of Hall mobility measurements in ionic conductors, recent experimental work in batteries and other systems has demonstrated that an applied magnetic field can significantly and beneficially alter ionic transport and electrochemical processes in solid materials in a way that would not be predicted from naive Hall coefficient estimates. In this work, we analytically characterize the permissible magnetic-field dependence of the generalized mobility operator M for transport in solids, establishing that Lorentz-like current steering cannot increase longitudinal conductivity. Specific isotropic single- and binary-carrier models then identify the conditions under which magnetic influence may become significant. In particular, near-degenerate multicomponent transport can amplify the effective Hall response even when conventional Hall mobilities are small and the underlying transport coefficients are not strongly modified by the magnetic field. The isotropic binary-conductor model is also more consistent with the reported high-field magnetoresistance saturation in Pb_0.66Cd_0.34F_2 than the conventional single-carrier model. Finally, implications for reported conductivity and stability changes in solid Li-ion conductors are examined, and experimental tests for distinguishing the mechanisms are proposed.