Strontium doping in mullite-type bismuth aluminate: a vacancy investigation using neutrons, photons and electrons

Abstract

We report on strontium doped dibismuth-nonaoxoaluminate(III) produced at 1023 K. Partial substitution of bismuth by strontium in the structure yields oxygen vacancies for charge balance. Introducing oxygen vacancies rearranged the associated Al 2 O 7 double-tetrahedra forming ''Al 3 O 10 '' tri-clusters which were identified by multi-quantum 27 Al MAS NMR. Both STEM-EDX and XPSshowed homogeneous distribution of strontium in the bulk and on the surface, respectively. Moreover, XPS confirms the valence state of bismuth after doping. The orientations of bismuth 6s 2 lone electron pairs were calculated using DFT methods. The amount of strontium in the crystal structure was further confirmed from the decomposition product SrAl 12 O 19 formed during the temperature-dependent X-ray powder diffraction. The structural proof was carried out by refining the structure of (Bi 0.94 Sr 0.06 ) 2 Al 4 O 8.94 from powder neutron and X-ray diffraction data. Rietveld refinements clearly showed the under occupation of one oxygen site and the shift of two aluminum atoms from the doubletetrahedra to two tri-cluster sites.

Stabilization of high temperature hexagonal phase of SrAl2O4 at room temperature: role of ZnO

“…The peak at 530.3 eV is ascribed to the oxygen atoms of SAO, 531.3 eV is attributed to O 2− ions in oxygen deficient regions in SAO and 532.2 eV is assigned to the hydroxyl groups, chemisorbed oxygen and organic oxygen on the surface of the sample. [27][28][29][30] To compare the oxygen vacancies in different samples, we have calculated the area of the curve 1 and 2 after deconvolution and calculated the area ratio, A 2 /A 1 . Comparing A 2 /A 1 in SAO(2.5) and SAO(20) calcined at 700 °C (Fig.…”

“Forbidden” reflections in neutron diffraction on bismuth metal oxides: symmetry reduction, λ/2 effect or Umweganregung?

“…The two compounds, together with the isotypic Bi 2 Al 4 O 9 have attracted considerable technical interest as potential candidates for oxygen ion-conduction applications (see Schneider et al, 2012 andGesing et al, 2012 for further details). The crystal structures of the Bi 2 M 4 O 9 compounds were first described by Niizeki and Wachi (1968) after a brief description had been published by Levin and Roth (1964;cited after Niizeki and Wachi, 1968).…”

Effect of Al3+ substitution on the structural, magnetic, and electric properties in multiferroic Bi2Fe4O9 ceramics

“…Polycrystalline bulk samples of Bi 2 (Fe 1 À x Al x ) 4 Table 1 The lattice parameters of Bi 2 ( mixed solutions were adjusted to $7 by adding ammonia. Then, the obtained solutions were evaporated in a water bath at 373 K to get wet gel which was decomposed at 423 K for 4 h in a furnace, and the collected powders were ground and calcined at 773 K for 5 h. After that, the powder products were reground and pressed into pellets with 13 mm diameter and 1 mm thickness.…”

“…The structure analysis shows that the mullite-type structures are characterized by one dimensional chains of edge sharing MO 6 octahedra, and M 2 O 7 double tetrahedral units and BiO 6 E groups (where E refers to a 6s 2 lone electron pair) interconnect the octahedral chains in an alternating ordered manner along the caxis [4]. From the perspective of application, the phase should be stable up to a temperature of about 1200 K without showing any phase transition or decomposition.…”