Structural Evolution of Iron Antimonides from Amorphous Precursors to Crystalline Products Studied by Total Scattering Techniques

Abstract

Homogeneous reaction precursors may be used to form several solid-state compounds inaccessible by traditional synthetic routes, but there has been little development of techniques that allow for a priori prediction of what may crystallize in a given material system. Here, the local structures of FeSbx designed precursors are determined and compared with the structural motifs of their crystalline products. X-ray total scattering and atomic pair distribution function (PDF) analysis are used to show that precursors that first nucleate a metastable FeSb3 compound share similar local structure to the product. Interestingly, precursors that directly crystallize to thermodynamically stable FeSb2 products also contain local structural motifs of the metastable phase, despite their compositional disagreement. While both crystalline phases consist of distorted FeSb6 octahedra with Sb shared between either two or three octahedra as required for stoichiometry, a corner-sharing arrangement indicative of AX3-type structures is the only motif apparent in the PDF of either precursor. Prior speculation was that local composition controlled which compounds nucleate from amorphous intermediates, with different compositions favoring different local arrangements and hence different products. This data suggests that local environments in these amorphous intermediates may not be very sensitive to overall composition. This can provide insight into potential metastable phases which may form in a material system, even with a precursor that does not crystallize to the kinetically stabilized product. Determination of local structure in homogeneous amorphous reaction intermediates from techniques such as PDF can be a valuable asset in the development of systematic methods to prepare targeted solid-state compounds from designed precursors.

Pair distribution functions of amorphous organic thin films from synchrotron X-ray scattering in transmission mode

“…A solution to the problem of thin-film characterization is to take advantage of the highly penetrating X-ray beams available at third-generation synchrotron facilities. To this end, Jensen et al (2015) reported the first measurement of a strongly scattering FeSb 3 film 360 nm thick deposited on a 170 mm thick borosilicate glass substrate, and their result is consistent with that of Bauers et al (2015) on the same film material that had been exfoliated and gathered in a Kapton tube. In this short communication, we extend this technique to weakly scattering organic glass films.…”

The chemistry of ZnWO4 nanoparticle formation

“…This observation fits in with the emerging understanding that the local structure of precursors play a vital role in directing structural evolution in various systems. 64 …”

Multistep Crystallization Pathways in the Ambient‐Temperature Synthesis of a New Alkali‐Activated Binder

“…[39][40][41] This "activated precursor" containing a statistically "frozen" mixture of educts was generated mechanochemically. [42] Different from solid-state reactions, where diffusion is intristically slow, and solution reactions, where diffusion is fast, water/acetonitrile mixtures were then used to retard the crystallization process while still allowing structural reorganization to occur. [43] Our approach experimentally mimics the "simulated annealing" concept, which has been employed for predicting inorganic solids and their crystal structures [44] and allows to explore the energy landscape of a reaction system by controlling supersaturation via solvent concentration.…”

“…[ 39–41 ] This “activated precursor” containing a statistically “frozen” mixture of educts was generated mechanochemically. [ 42 ]…”