Space charge effects at dislocations in TiO2

K. Adepalli, R. Merkle

The concentrations of point defects and thus the conductivity can be adjusted by several methods such as aliovalent doping, or introducing interfaces (grain boundaries, heterointerfaces). Line defects (with charged) cores represent an additional, intermediate possibility. Grain boundary cores of perovskite and fluorite structured oxides with large band gap such as SrTiO3, CeO2, Y-ZrO2 are typically positively charged due to the presence of excess anion vacancies. However, in case of TiO2 also negative core charges may be formed. For this reason, we decided to investigate the effect of dislocations on conductivity in rutile TiO2 which were generated by uniaxial hot-pressing. This changes the conductivity from p-type electronic (black symbols in fig. 1(a)) to predominant ionic (blue symbols). The concomitant increase of the hole conductivity (green symbols) indicates that accumulation of positive carriers (oxygen vacancies, Ti interstitials, electron holes) around negatively charged dislocation cores is responsible for the modified conductivity, cf. Fig. 1(b).

Fig. 1: (a) conductivity of pristine sample (black) and sample with dislocation created by compression (blue = ac conductivity » ionic, green = electronic conductivity measured with ionically blocking electrodes); (b) scheme of space charge accumulation zones adjacent to negatively charged dislocation cores.   from Adepalli (2013) with permission

see also annual report 2012   www.fkf.mpg.de/565342/I_04_04.pdf

Publications:

K. K. Adepalli, M. Kelsch, R. Merkle, and J. Maier
Influence of Line Defects on the Electrical Properties of Single Crystal TiO2
Advanced Functional Materials23(14), 1798–1806 (2013).  DOI: 10.1002/adfm.201202256

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