Charge transport in transition metal oxides

Many of the functional oxide materials important to the IC industry are also critical for the energy storage systems necessary if intermittent sources such as wind and the Sun are to be effective. Despite this overlap, research on materials' properties related to the two fields has generally been separated.

The EU-funded project ELIOT (Electronic and ionic transport in functional oxides) formed a bridge, investigating how material production and physical properties affect charge transport in these oxides.

Scientists chose to study transition metal oxides, their electrochemical and physicochemical properties, and the effects of materials deposition techniques and conditions on charge transport. They targeted applications in non-volatile memory and energy storage with a focus on electronic and ionic mobility, respectively. Establishing mechanisms could lead to the engineering of better materials for both fields.

One promising alternative to flash memory devices to overcome imminent barriers in capacity and speed exploits metal oxides that exhibit resistive switching. The first objective of the project was to identify materials for which the large scalable change in resistance to applied pulsed voltages is due to correlated electron effects.

Transition metal oxides with high ionic mobility but low electrical conductivity are interesting as solid electrolytes for fuel cell applications. Materials with high lithium storage capacity (low mobility) and good electrical conductivity are potential candidates for electrode applications.

Studies covered simple binary oxides such as vanadium or titanium dioxide (VO2 and TiO2, respectively). They also evaluated more complex oxides such as samarium nickelate (SmNiO3) and lithium manganese oxide (LiMn2O4).

VO2 and SmNiO3 showed a metal to insulator transition, from good charge conductivity to low conductivity, with temperature. TiO2 and LiMn2O4 were identified as promising electrode materials for batteries, while a lithium magnesium oxide showed potential for use as a solid electrolyte.

enhanced knowledge about the factors affecting electronic and ionic mobility of transition metal oxides could lead to important breakthroughs in socioeconomically important areas such as volatile memory and energy storage. ELIOT has pointed the way to rational engineering of advanced materials for these and other applications.