Interface-mediated ultrafast carrier conduction in oxide thin films and superlattices for energy

Abstract

Some recent observations on carrier (electronic and ionic) transport in thin film and nanostructured metal oxides and superlattices, where interfaces play a dominant role in overall conductivity response, are reviewed. Conduction in nominally pure oxides is compared to heavily aliovalently doped oxides (that correspond to changes in the Debye length over few orders of magnitude). The role of dopant segregation and their spatial variation in affecting transport is pointed out. The ability to utilize interfaces in enabling ultrafast-ion conduction as well as the creation of novel interfacial materials and implications in energy technologies as well as some scientific questions that may warrant further attention are highlighted.

A correlated nickelate synaptic transistor

“…To further increase the potentiation and depression rates, larger magnitude gate pulses may be applied. Solid-state electrolyte materials such as fast-ion conductors in thin films form with nanometre-scale thickness (ion diffusion length), which can sustain high potentials, can also be explored in future and would be of interest in this temperature range 58 . To realize STDP functionality, the source and drain of the SNO device can be connected to a multiplexer that converts the time difference between postneuron spikes (drain) and preneuron spikes (source) to a voltage pulse.…”

Applications of STEM-EELS to complex oxides

“…This possibility is of great use to study systems where localized fluctuations in the composition may alter their physical properties, such as grain boundaries. It is well known that the structural and chemical changes present within the dislocation cores at grain boundaries strongly influence the properties of fuel cells based on polycrystalline solid oxide electrolytes [105,106] and nanoionics devices [107,108]. In the past years, there has been a growing interest in ionic conducting materials, principally motivated by their wide range of applications in solid-state electrochemical devices such as solid oxide fuel cells which are devices capable of converting chemical energy in electrical energy with a high efficiency and without the generation of any polluting emission [109].…”

Ionic conductivity of nanocrystalline yttria-stabilized zirconia: Grain boundary and size effects

“…[23][24][25] While some authors have reported increases in the ionic conductivity in samples with nanometer size grains, 26 others have found no changes 27,28 or even decreases 29 of the conductivity in samples produced with different synthesis routes and with different grain sizes and dopant concentrations. 18 O tracer diffusion experiments assisted by secondary-ion mass spectroscopy also yield contradictory results while three orders of magnitude increase in the diffusion coefficient as compared with bulk samples has been reported in nanocrystalline thin films, 30 bulk nanocrys-talline ceramics show no change. 31 Moreover, the interpretations of the increases in conductivity in terms of spacecharge effect have to reconcile the fact that very small values of the Debye screening length ͑on the order of only 0.1 nm͒ result for typical dopant concentrations ͑8 -10 mol % YSZ͒ at intermediate temperatures ͑500°C͒.…”

“…[16][17][18] Space charge effects are an interesting family of nanoionic size effects which show up when sample dimensions are comparable to the extension of the space-charge region. 12,19,20 It is well known that the energy for defect generation may be different at surfaces or boundaries.…”