Exploration of Multi-Component Vanadium and Titanium Pnictides Using Flux Growth and Conventional High-Temperature Methods.

Alexander Ovchinnikov,Svilen Bobev

doi:10.3389/fchem.2019.00909

Alexander Ovchinnikov, Svilen Bobev

Open Access

https://doi.org/10.3389/fchem.2019.00909

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Abstract

The flux growth method was successfully employed to synthesize millimeter-sized single crystals of the ternary barium vanadium pnictides Ba5V12As19+x (x ≈ 0.02) and Ba5V12Sb19+x (x ≈ 0.36), using molten Pb and Sb, respectively. Both compositions crystallize in space group P3m and adopt a structure similar to those of the barium titanium pnictides Ba5Ti12Pn19+x (Pn = Sb, Bi), yet with a subtly different disorder, involving the pnictogen and barium atoms. Attempts to obtain an arsenide analog of Ba5Ti12Pn19+x using a Pb flux technique yielded binary arsenides. High-temperature treatment of the elements Ba, Ti, and As in Nb or Ta tubes resulted in side reactions with the crucible materials and produced two isostructural compositions Ba8Ti13−xMxAs21 (M = Nb, Ta; x ≈ 4), representing a new structure type. The latter structure displays fcc-type metal clusters comprised of statistically distributed Ti and M atoms (M = Nb, Ta) with multi-center and two-center bonding within the clusters, as suggested by our first-principle calculations.

Highlights

The application of molten metals as inert or reactive solvents for the crystal growth of intermetallic compounds is an actively used synthetic approach in solid-state chemistry
The flux material can be removed by inverting the reactor at a temperature above the flux melting point and letting the molten flux pass through the filter, leaving the grown crystals behind
We explored the application of the metal flux approach to the synthesis of multinary vanadium pnictides

Summary

INTRODUCTION

The application of molten metals as inert or reactive solvents for the crystal growth of intermetallic compounds is an actively used synthetic approach in solid-state chemistry. Careful optimization of the flux growth procedure resulted in large single crystals of these recently discovered compounds. In this contribution, we explored the application of the metal flux approach to the synthesis of multinary vanadium pnictides. Flux-assisted single crystal growth was employed for the synthesis of Ba5V12As19.02(1) and Ba5V12Sb19.36(2) For the former compound, metallic Pb was utilized as a flux. Besides some inhomogeneously looking powder, which was revealed by powder X-ray diffraction to be a mixture of binary Ba and V arsenides, well-formed single crystals of isotropic polyhedral shape and dimensions up to 1 mm were clearly visible. Subsequent single crystal data collection and refinement confirmed a new structure with the chemical formula Ba8Ti9.24(6)Ta3.76As21. Electron density was integrated using the program Critic (Otero-de-la-Roza et al, 2014)

Findings

DISCUSSION

CONCLUSIONS