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Johnson, Ian D.

Publications and source records attributed to Johnson, Ian D..

How machine learning can extend electroanalytical measurements beyond analytical interpretation

Electroanalytical measurements are routinely used to estimate material properties exhibiting current and voltage signatures. Analysis of such measurements relies on analytical expressions of material properties to describe the experiments. The need for analytical expressions limits the experiments that can be used to measure properties as well as the properties that can be estimated from a given experiment. Such analytical relations are essentially solutions of the physics-based differential equations (with properties as coefficients) describing the material behavior under certain specific conditions. In recent years, a new machine learning-based approach has been gaining popularity wherein the differential equations are numerically solved to interpret the electroanalytical experiments in terms of corresponding material properties. Since the physics-based differential equations are solved, one can additionally estimate underlying fields, e.g., concentration profile, using such an approach. To exemplify the characteristics of such a machine learning assisted interpretation of electroanalytical measurements, we use data from the Hebb–Wagner test on a magnesium spinel intercalation host. In conclusion, as compared to the traditional analytical expression-based interpretation, the emerging approach decreases experimental efforts to characterize relevant material properties as well as provides field information that was previously inaccessible.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Elucidating Structural Transition Dynamics in the Magnesium Cathode MgCr 2 O 4

Multivalent batteries, e.g., those based on magnesium (Mg), are promising candidates for next-generation energy storage due to their high volumetric energy densities and low cost. However, the corresponding ion migration and structural transition mechanisms are often linked and difficult to observe directly. Here, in this paper, we report the direct investigation of atomic transport pathways of cations in spinel magnesium chromate (MgCr 2 O 4 ) by using aberration-corrected scanning transmission electron microscopy (STEM). Cr atoms are directly observed to reversibly occupy the otherwise vacant octahedrally coordinated interstitial sites, passing through tetrahedral sites normally occupied by Mg. Furthermore, imaging and electron energy loss spectroscopy show that electron irradiation induces the formation of Mg and O vacancies, facilitating the migration of Cr and leading to an irreversible phase transition. These results demonstrate the ability of STEM to capture the pathway of deleterious point defects that can result in undesirable phase transitions.

25 ENERGY STORAGE↗