A New Bi₄Mn_1/3W_2/3O₈Cl Sillén–Aurivillius Intergrowth: Synthesis and Structural Characterisation by Quantitative Transmission Electron Microscopy

Abstract

The synthesis and structural characterisation of a new phase with nominal composition Bi4Mn1/3W2/3O8Cl is presented. Conventional and analytical transmission electron microscopy are used to determine the composition, unit‐cell symmetry and space group of the compound, whereas a structural model is deducted by exit‐wave reconstruction in the transmission electron microscope. This technique allows the microscope information limit of 1.1 Å to be reached and the (light) oxygen atoms in the presence of heavier atoms (Bi, W, Mn) to be imaged. The average structure is refined from X‐ray powder diffraction data using the Rietveld method yielding an orthorhombic unit cell with lattice parameters a = 5.467(4) Å, b = 5.466(7) Å and c = 14.159(3) Å and space group Cm2m, which could be described as a Sillén–Aurivillius intergrowth. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Statistical Estimation of Atomic Positions from Exit Wave Reconstruction with a Precision in the Picometer Range

“…Alternatively, the exit wave can also be reconstructed using off-axis holography [11] and can be used as a starting point for further refinement as well. Here, we will first demonstrate that results obtained with a precision in the picometer range using the statistical parameter estimation theory are comparable to the x-ray diffraction data acquired for the Bi 4 W 2=3 Mn 1=3 O 8 Cl compound [1]. Next, we will show that local deviations in the interatomic distances can be detected and quantified using this method.…”

“…Part of the W cations along the columns is replaced by Mn cations and it is known that Mn 3 cations cause a Jahn-Teller effect (compression or elongation) of the O octahedra surrounding Mn 3 in order to break down the degeneration of their Table I are indicated. energy levels [19]. Since magnetic susceptibility measurements for Bi 4 Mn 1=3 W 2=3 O 8 Cl indeed indicate Mn 3 [1], we can thus expect a Jahn-Teller distortion to be present in this case. In Table I, it can be seen that the projected distance d 3 from the W=Mn columns to the O columns at the apical position is smaller compared to the projected distances d 1 and d 2 between the W=Mn columns and the O columns at the equatorial position.…”

“…new phase with nominal composition Bi 4 W 2=3 Mn 1=3 O 8 Cl has recently been synthesized [1]. The interest in this compound, which is based on a Sillén-Aurivillius intergrowth [2], is found in the resemblance of the structure with, e.g., the high T c superconducting bismuth phases [3,4] and the manganese based CMR materials [5,6].…”

“…In order to judge the adequateness of the model used, the so-called residual plot, normal probability plot, and quantitative test for zero mean of the residuals have been performed [10,13]. In addition, the reliability of the method is confirmed by comparing the computed interatomic distances to the corresponding distances as obtained from Rietveld refinement [1].…”

Sillen–Aurivillius Intergrowth Phases as Templates for Naturally Layered Multiferroics

“…11 An alternative, arguably more simplistic, approach is to build ferroelectric and ferromagnetic layers into naturally-layered structures. Sharma et al 15,16 17,18 with Avila-Brande 18 achieving up to 1 3 magnetic transition metal substitution into the single perovskite layer. Aurivillius phases consist of n perovskite layers 'sandwiched' between α-PbO-type [Bi 2 O 2 ] 2+ layers.…”