Particular structural defects in Ta2O5 from crystallisation of amorphous thin films in O2–H2O atmosphere
(a,b) HRTEM images of structural defects in mL-Ta2O5 monoclinic structures resulting of a crystallisation of amorphous thin films in O2–H2O atmosphere compared in (c) to simulated images of the 11L-Ta2O5 structure with [001] columns of Ta5+–O2− vacancies or only Ta5+ vacancies; (d) ToF-SIMS depth pr...
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Published in | Acta materialia Vol. 94; pp. 181 - 192 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier Ltd
01.08.2015
Elsevier |
Subjects | |
Online Access | Get full text |
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Summary: | (a,b) HRTEM images of structural defects in mL-Ta2O5 monoclinic structures resulting of a crystallisation of amorphous thin films in O2–H2O atmosphere compared in (c) to simulated images of the 11L-Ta2O5 structure with [001] columns of Ta5+–O2− vacancies or only Ta5+ vacancies; (d) ToF-SIMS depth profiles of H−, 18O−, TaO− and 30Si− through a Ta2O5 thin film on Si substrate. [Display omitted]
Structural defects within Ta2O5 monoclinic structures were obtained by crystallisation at 850°C in atmosphere O2–H2O of amorphous thin films deposited by injection metal-organic chemical vapour deposition (i-MOCVD) on Si substrates. These defects, observed by high resolution transmission electron microscopy (HRTEM), contain alignments of Ta5+ vacancies along a crystallographic direction [001]. H2O gas of different partial pressures was obtained by bubbling O2 gas through deionised water or Na2CO3–K2CO3 aqueous solution maintained at different temperatures in a range of 25–45°C. The amount of structural defects increases dramatically with H2O partial pressure and annealing time from HRTEM observations and X-ray diffraction results. Such defects are thermally stable, at least up to 850°C. Using Na2CO3–K2CO3 aqueous solution, similar structural defects including mainly K+ species were formed. Na+ species contributes mostly to the formation of another phase of composition close to (Na0.8K0.2)2Ta4O11 of natrotantite type structure. Assuming that Ta5+ vacancies are occupied by H+ in a form of bridging hydroxyl groups Ta–OH–Ta in order to satisfy electrical neutrality, the presence of significant levels of hydrogen atoms within Ta2O5 concordant with H enrichment at defects was identified by time-of-flight secondary ion mass spectrometry (ToF-SIMS). |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1359-6454 1873-2453 |
DOI: | 10.1016/j.actamat.2015.04.041 |