Exfoliation and thermal transformations of Nb-substituted layered titanates

Publication: Research - peer-reviewJournal article – Annual report year: 2011

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Single-layer Nb-substituted titanate nanosheets of ca. 1 nm thickness were obtained by exfoliating tetrabutylammonium (TBA)-intercalated Nb-substituted titanates in water. AFM images and turbidity measurements reveal that the exfoliated nanosheets crack and corrugate when sonicated. Upon heating, the thermal transformation into anatase and further to rutile is retarded. This suppression of the phase transition upon higher valent substitution may promote technological applications of anatase thin films, hereunder development of films with TCO properties. Depending on the oxygen partial pressure during the transformation, the Nb-substitution into TiO2 provokes different defect situations and also electronic properties. At reducing conditions, Nb is incorporated as NbV and an equivalent amount of TiIV is transformed to TiIII as evidenced by XPS. Magnetic susceptibility data show accordingly paramagnetic behavior. For samples heated in air TiIV and NbV cations prevail, the latter is compensated by cation vacancies. 93Nb MAS NMR data prove that Nb is finely dispersed into the transformed (Ti,Nb)O2 oxide matrices without sign of Nb2O5 (nano)precipitates. The Nb–O–Ti bonds and defects at cation sites are considered key factors for increasing the transformation temperatures for conversion of the nanosheets to anatase and finally into rutile. It is further tempting to link the delay in crystallization to morphology limitations originating from the nanosheets. The present work shows that layered Nb-titanates are appropriate precursors for formation of highly oriented Nb-substituted anatase thin films via delamination, reconstruction and subsequent heat treatment.
Original languageEnglish
JournalJournal of Solid State Chemistry
Publication date2011
Volume184
Issue12
Pages3135-3143
ISSN0022-4596
DOIs
StatePublished
CitationsWeb of Science® Times Cited: 1

Keywords

  • Batteries and carbon-free energy storage
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