Decrease of the required dopant concentration for δ-Bi2O3 crystal stabilization through thermal quenching during single-step flame spray pyrolysis. Issue 12 (16th February 2016)

• Record Type: Journal Article
• Authors: Dreyer, Jochen A. H.; Pokhrel, Suman; Birkenstock, Johannes; Hevia, Miguel G.; Schowalter, Marco; Rosenauer, Andreas; Urakawa, Atsushi; Teoh, Wey Yang; Mädler, Lutz
• Is Part Of: CrystEngComm. Volume 18:Issue 12(2016)
• Page Start: 2046
• Page End: 2056
• Publication Date: 2016-02-16
• Subjects: Crystals -- Periodicals; Crystal growth -- Periodicals; Crystallography -- Periodicals; Cristaux -- Périodiques; Cristaux -- Croissance -- Périodiques; Cristallographie -- Périodiques; 548
• DOI: 10.1039/c5ce02430g
• Languages: English
• ISSNs: 1466-8033

Abstract

Abstract : The extraordinarily high quenching rates during single-step flame spray pyrolysis enabled the stabilization of the oxygen ion conductor δ-Bi2 O3 with smaller dopant concentrations. Abstract : δ-Bi2 O3 is one of the best oxygen ion conductors known. However, due to its limited thermal stability and complicated synthesis techniques, its applications are limited. Here, the synthesis of stable nano-sized δ-Bi2 O3 using versatile and rapid flame spray pyrolysis (FSP) combined with in situ Ti and/or Mn doping for an enhanced thermal stability is reported for the first time. Exceptionally low Bi replacing cation concentrations (8 at% Ti) were sufficient to obtain phase-pure δ-Bi2 O3 which was attributed to the extraordinarily high temperature gradient during FSP. The required cation amount for δ-phase stabilization was even further reduced by introducing mixtures of Mn and Ti (2.5 at% Mn + 2.5 at% Ti). Rietveld analysis revealed that the δ-Bi2 O3 structure is best represented by the Fm 3̄ m space group containing two closely neighbored 8 c and 32 f Wyckoff positions. Depending on the amount of Mn/Ti cations, about 25% of the possible oxygen positions remain vacant, suggesting high bulk oxygen mobility. The enhanced oxygen mobility was confirmed by temperature programmed reduction (H2 -TPR) with bulk reduction for δ-Bi2 O3 in contrast to exclusive surface reduction for β-Bi2 O3 .