Stairlike Aurivillius Phases in the Pseudobinary Bi₅Nb₃O₁₅–ABi₂Nb₂O₉ (A = Ba and Sr) System: A Comprehensive Analysis Using Superspace Group Formalism

Abstract

We report the possibility of extending the so-called stairlike Aurivilius phases in the pseudobinary BiNbO-ABiNbO (A = Ba and Sr) over a wide range of compositions. These phases are characterized by a discontinuous stacking of [BiO] slabs and perovskite blocks, leading to long-period intergrowths stabilized as a single phase. When analyses from precession electron diffraction tomography and X-ray and neutron powder diffraction are combined, the monoclinic incommensurately modulated structure with q = αa* + γc* previously proposed for the ABiNbO composition could be generalized to the BiNbO-ABiNbO (A = Ba and Sr) compounds. Considering the compositions expressed as (A,Bi)Nb O, the stacking sequence associated with compositions ranging from x = / to / is governed by the component γ of the modulation vector and can be predicted following a Farey tree hierarchy independently to the A cation. The length of the steps, characteristic of the stairlike nature, is controlled by the α component and depends on the substitution ratio A/Bi and the nature of A (A = Ba and Sr). This study highlights the compositional flexibility of stairlike Aurivillius phases.

3D Electron Diffraction: The Nanocrystallography Revolution

“…3D ED is an extremely promising technique for the structure determination of functional layered oxides, even if characterized by disorder , or incommensurate modulations. ,,, 3D ED was also used for the analysis of structure modifications caused by the thermal annealing of Ni/Au electrodes, and for the study of materials engineered for electrochemical applications. ,, In this regard, Karakulina et al . performed the first in situ charge/discharge experiment on a (Li)­FePO 4 electrode.…”

“…Since 2007, the three-dimensional ED method has spread with an exponential trend. Very soon, still in the hand of few specialists, it allowed the structure determination of landmark samples, mostly inorganic, that were considered impracticable for X-ray methods. − Later, the introduction of ultrafast data acquisition procedures and of more sensitive detectors allowed establishing robust experimental protocols also for organic and metalorganic materials. − Finally, three-dimensional ED found successful applications for macromolecules − and other structures of biologic interest. − The growing attention on three-dimensional ED is confirmed by the number and impact of related publications in the very last year, − and by the fact that this method has been considered one of the most important recent scientific breakthroughs …”

3D electron diffraction study of terrestrial iron oxide alteration in the Mineo pallasite

“…This results in a reduction of the total electron dose on the sample, which is crucial for beam-sensitive materials. The 3D ED method is currently applied to the structural characterisation of nanocrystalline functional materials (Mugnaioli et al , 2018; Steciuk et al , 2018; Wang et al , 2018), pharmaceuticals (Jones et al , 2018; Brázda et al , 2019) and macromolecules (Nannenga et al , 2014; Xu et al , 2019). A comprehensive review of 3D ED was published recently by Gemmi et al (2019).…”

NEXAFS–Spectra and Magnetic Susceptibility of Nickel and Chromium Doped of Bismuth Niobate

“…Along with usual layered compounds there are also so-called mixed or hybrid layered compounds (Bi 2 O 2 ) (A n-1 B n O 3n+1 )…(Bi 2 O 2 )(A m-1 B m O 3m+1 ), in the structure of which the perovskite-like fragments of different thickness alternate. Bismuth niobate Bi 5 Nb 3 O 15 belongs to the mixed layered compounds, whose structure is characterized by an ordered alternation of fragments one and two niobium thick -oxygen octahedron, so that its structure can be described as (Bi 2 О 2 )(NbO 4 )(Bi 2 O 2 )(BiNb 2 O 7 ), when n=1 и m=3 [4,[7][8][9][10][11].…”