AUTHOR=Ovchinnikov Alexander , Bobev Svilen 

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

JOURNAL=Frontiers in Chemistry

VOLUME=7

YEAR=2020

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2019.00909

DOI=10.3389/fchem.2019.00909

ISSN=2296-2646

ABSTRACT=<p>The flux growth method was successfully employed to synthesize millimeter-sized single crystals of the ternary barium vanadium pnictides Ba<sub>5</sub>V<sub>12</sub>As<sub>19+x</sub> (<italic>x</italic> ≈ 0.02) and Ba<sub>5</sub>V<sub>12</sub>Sb<sub>19+x</sub> (<italic>x</italic> ≈ 0.36), using molten Pb and Sb, respectively. Both compositions crystallize in space group <italic>P</italic><inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mo>̄</mml:mo></mml:mover></mml:math></inline-formula>3<italic>m</italic> and adopt a structure similar to those of the barium titanium pnictides Ba<sub>5</sub>Ti<sub>12</sub><italic>Pn</italic><sub>19+x</sub> (<italic>Pn</italic> = Sb, Bi), yet with a subtly different disorder, involving the pnictogen and barium atoms. Attempts to obtain an arsenide analog of Ba<sub>5</sub>Ti<sub>12</sub><italic>Pn</italic><sub>19+x</sub> 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 Ba<sub>8</sub>Ti<sub>13−x</sub><italic>M</italic><sub><italic>x</italic></sub>As<sub>21</sub> (<italic>M</italic> = Nb, Ta; <italic>x</italic> ≈ 4), representing a new structure type. The latter structure displays <italic>fcc</italic>-type metal clusters comprised of statistically distributed Ti and <italic>M</italic> atoms (<italic>M</italic> = Nb, Ta) with multi-center and two-center bonding within the clusters, as suggested by our first-principle calculations.</p>