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Figure 6
Illustration of the transformation of VS6 octahedra into VS5 pyramids as a general underlying principle for changes in the BaVS3 structure as a function of temperature. The interatomic distances are given in Å. Arched arrows point to the transformation of short apical V–S contacts in VS6 octahedra. The numerical values of the distances are highlighted in red, which change as a result of the corresponding structural phase transitions. Straight red arrows show displacements of V atoms, which initiate the transformation of the structure. (a) Compression of the apical V–S contacts in the hexagonal phase results in a too-short V–V contact, indicated in brown. During the TS transition, this contact relaxes due to its increase as a result of the V-atom displacement, which leads to a zigzag deformation of the V-chain. (b) At the TLOCK phase transition, further compression of the apical V–S contact for one V atom occurs due to its predominant displacement, which leads to the loss of the inversion centre (black crosses) in the V-chain. This results in two sites, V1 and V2, for the V atom instead of one. (c) During the TMI structural transition, the uniformly compressed apical V–S contact for each V atom is realized due to different displacements of the V atoms along the c axis. As a consequence, the number of V sites increases from two to four (V1, V2, V3 and V4). A side effect is a significant difference of the intra-chain V–V distances, indicated in brown.

Journal logoSTRUCTURAL SCIENCE
CRYSTAL ENGINEERING
MATERIALS
ISSN: 2052-5206
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