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1.
ACS Nano ; 10(1): 1481-92, 2016 Jan 26.
Artigo em Inglês | MEDLINE | ID: mdl-26738414

RESUMO

The local electronic properties of tantalum oxide (TaOx, 2 ≤ x ≤ 2.5) and strontium ruthenate (SrRuO3) thin-film surfaces were studied under the influence of electric fields induced by a scanning tunneling microscope (STM) tip. The switching between different redox states in both oxides is achieved without the need for physical electrical contact by controlling the magnitude and polarity of the applied voltage between the STM tip and the sample surface. We demonstrate for TaOx films that two switching mechanisms operate. Reduced tantalum oxide shows resistive switching due to the formation of metallic Ta, but partial oxidation of the samples changes the switching mechanism to one mediated mainly by oxygen vacancies. For SrRuO3, we found that the switching mechanism depends on the polarity of the applied voltage and involves formation, annihilation, and migration of oxygen vacancies. Although TaOx and SrRuO3 differ significantly in their electronic and structural properties, the resistive switching mechanisms could be elaborated based on STM measurements, proving the general capability of this method for studying resistive switching phenomena in different classes of transition metal oxides.

2.
Phys Chem Chem Phys ; 16(10): 4942-51, 2014 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-24477488

RESUMO

The influence of line defects (dislocations) on the electrical properties of polycrystalline TiO2 was investigated. Line defects were created in TiO2 during spark plasma sintering at 1000 °C and 400 MPa. TEM characterisation indicates dislocations to be preferably oriented on {110} and {101} planes. The measured electrical conductivity as a function of oxygen partial pressure and temperature revealed that the dislocations play a vital role in modifying the defect chemistry of TiO2. The presence of dislocations enhanced the ionic conductivity over a wide range of oxygen partial pressures. The observed changes can be interpreted in terms of negatively charged dislocation cores and adjacent space charge accumulation layers. The present findings point towards an alternative method to tune the electrical properties of ionic solids.

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