Revealing the Elusive Structure and Reactivity of Iron Boride α-FeB

Abstract

Crystal structures can strongly deviate from bulk states when confined into nanodomains. These deviations may deeply affect properties and reactivity and then call for a close examination. In this work, we address the case where extended crystal defects spread through a whole solid and then yield an aperiodic structure and specific reactivity. We focus on iron boride, α-FeB, whose structure has not been elucidated yet, thus hindering the understanding of its properties. We synthesize the two known phases, α-FeB and β-FeB, in molten salts at 600 and 1100 °C, respectively. The experimental X-ray diffraction (XRD) data cannot be satisfactorily accounted for by a periodic crystal structure. We then model the compound as a stochastic assembly of layers of two structure types. Refinement of the powder XRD pattern by considering the explicit scattering interference of the different layers allows quantitative evaluation of the size of these domains and of the stacking faults between them. We, therefore, demonstrate that α-FeB is an intergrowth of nanometer-thick slabs of two structure types, β-FeB and CrB-type structures, in similar proportions. We finally discuss the implications of this novel structure on the reactivity of the material and its ability to perform insertion reactions by comparing the reactivities of α-FeB and β-FeB as reagents in the synthesis of a model layered material: Fe 2 AlB 2 . Using synchrotron-based in situ X-ray diffraction, we elucidate the mechanisms of the formation of Fe 2 AlB 2 . We highlight the higher reactivity of the intergrowth α-FeB in agreement with structural relationships.

Breaking New Ground: MBene Route toward Selective Vinyl Double Bond Hydrogenation in Nitroarenes

“…However, MnB and FeB have both high-temperature FeB-type and low-temperature CrB-type polymorphs and can also form peculiar intergrowths of both CrB- and FeB- fragments when synthesized at lower temperatures. Similar cases of polymorphism are seen in other intermetallic compounds. − …”

Galvanic Replacement and Etching of MAX-Related Phases in Molten Salts toward MXenes: An In Situ Study

“…18 keV, where the reaction media are sufficiently transparent to enable XRD detection in transmission mode through a capillary. We used a capillary oven setup inspired by a previous work. , To ensure homogeneity of the reaction medium, the capillary containing the reaction mixture was continuously scanned through 4 vertical positions. An XRD pattern was recorded at each position every 8.4 s with an acquisition time of 5 s. The same capillary oven used for in situ XRD was also used for in situ XAS at an energy corresponding to the K -edge of the probed element and in fluorescence detection mode, where X-ray fluorescence was collected from the capillary at an angle of ca.…”

“…Galvanic reactions of MAX and MAX-related phases occur at 400–700 °C, where it is difficult to probe reaction media in situ . In this context, in situ XRD and in situ X-ray absorption spectroscopy (XAS), which are sporadically used to probe molten salts, – appear as ideal techniques to study the mechanisms of galvanic reactions of MAX and MAX-related phases. The combination of in situ XRD and in situ XAS to study molten salts is, however, not reported to the best of our knowledge.…”

Influence of the Hubbard U Parameter on the Structural, Electronic, Magnetic, and Transport Properties of Cr/Fe/Zr-Based MBenes

“…On the other hand, in the P 6/ mmm structures, the honeycomb, graphene-like, boron layer is sandwiched between two TM layers on both sides, with every TM atom located above or below the centroid of the honeycomb structure. Their bulk counterparts, all widely studied both experimentally and theoretically, – are the ferromagnetic (FM) α and β modifications of FeB and the nonmagnetic (NM) CrB and ZrB compounds. The structure of α-FeB is debatable, whereas β-FeB and CrB are orthorhombic crystals with Pnma (no.…”

“…Their bulk counterparts, all widely studied both experimentally and theoretically, – are the ferromagnetic (FM) α and β modifications of FeB and the nonmagnetic (NM) CrB and ZrB compounds. The structure of α-FeB is debatable, whereas β-FeB and CrB are orthorhombic crystals with Pnma (no. 62) and Cmcm (no.…”