Theoretical and experimental comparative study of the stability and phase transformations of sesquichalcogenides M<sub>2</sub>Q<sub>3</sub> (M = Nb, Mo; Q = S, Se)

Ivanova, Mariia N.; Enyashin, Andrey N.; Grayfer, Ekaterina D.; Fedorov, V. E.

doi:10.1039/c8cp07150k

“…However, due to the strong Nb-Nb interactions the Nb (x = 0.1) SI system is found to be the least favorable. The close free energy ΔG values at high temperature suggest that facile phase transition between the two polytypes may occur, as established between Nb 2 Se 3 and Nb 1.33 Se 2 polytypes (Ivanova et al, 2019). These results can explain the experimental stability of both 2H and 3R between 0 < x < 0.07, and confirm the hypothesis of a phase transition from 2H to 3R beyond x = 0.1.…”

Section: Chemistry Journalssupporting

confidence: 77%

Peer Review #2 of "X-ray diffraction and theoretical study of the transition 2H-3R polytypes in Nb1+xSe2 (0 < x < 0.1) (v0.2)"

2021

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Single crystals of 2H and 3R niobium diselenide were grown by a chemical transport reaction. The current determinations by single crystals X-ray diffraction reveal a nonstoichiometric composition. The structures are built from Se-Nb-Se slabs with Nb in trigonal prismatic coordination whereas the extra or additional Nb atoms are located in the octahedral holes between the slabs giving rise to the formula 2H and 3R-Nb 1+x Se 2 with 0.07< x <0.118. In particular, vacancy and Nb-Nb interactions may play an important role on the non-stoichiometry and the stacking mode in NbSe 2 . By increasing the number of additional Nb atoms in the pure 2H-NbSe 2 , a transition 2H to 3R polytype should occur in order to minimize the Nb layer -Nb extra -Nb layer repulsions between these adjacent slabs. The theoretical study shows that both 2H and 3R-Nb 1+x Se 2 are thermodynamically stable in the range 0< x <0.1.

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“…The calculated free energy ΔG at typical synthesis temperatures of 760 and 1050 °C only include configurational entropy due to intercalation, according to Ivanova et al, 2019.…”

Section: Chemistry Journalsmentioning

confidence: 99%

Peer Review #2 of "X-ray diffraction and theoretical study of the transition 2H-3R polytypes in Nb1+xSe2 (0 < x < 0.1) (v0.1)"

2021

0

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Single crystals of 2H and 3R niobium diselenide were grown by a chemical transport reaction. The current determinations by single crystals X-ray diffraction reveal a nonstoichiometric composition. The structures are built from Se-Nb-Se slabs with Nb in trigonal prismatic coordination whereas the extra or additional Nb atoms are located in the octahedral holes between the slabs giving rise to the formula 2H and 3R-Nb 1+x Se 2 with 0.07< x <0.118. In particular, vacancy and Nb-Nb interactions may play an important role on the non-stoichiometry and the stacking mode in NbSe 2 . By increasing the number of additional Nb atoms in the pure 2H-NbSe 2 , a transition 2H to 3R polytype should occur in order to minimize the Nb layer -Nb extra -Nb layer repulsions between these adjacent slabs. The theoretical study shows that both 2H and 3R-Nb 1+x Se 2 are thermodynamically stable in the range 0< x <0.1.

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“…However, and according to the recent findings (Ivanova et al, 2019), the diagram may contain some ambiguous data and should be revisited…”

Section: Introductionmentioning

confidence: 99%

Peer Review #1 of "X-ray diffraction and theoretical study of the transition 2H-3R polytypes in Nb1+xSe2 (0 < x < 0.1) (v0.1)"

2021

0

View full text Add to dashboard Cite

Single crystals of 2H and 3R niobium diselenide were grown by a chemical transport reaction. The current determinations by single crystals X-ray diffraction reveal a nonstoichiometric composition. The structures are built from Se-Nb-Se slabs with Nb in trigonal prismatic coordination whereas the extra or additional Nb atoms are located in the octahedral holes between the slabs giving rise to the formula 2H and 3R-Nb 1+x Se 2 with 0.07< x <0.118. In particular, vacancy and Nb-Nb interactions may play an important role on the non-stoichiometry and the stacking mode in NbSe 2 . By increasing the number of additional Nb atoms in the pure 2H-NbSe 2 , a transition 2H to 3R polytype should occur in order to minimize the Nb layer -Nb extra -Nb layer repulsions between these adjacent slabs. The theoretical study shows that both 2H and 3R-Nb 1+x Se 2 are thermodynamically stable in the range 0< x <0.1.

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Theoretical and experimental comparative study of the stability and phase transformations of sesquichalcogenides M₂Q₃ (M = Nb, Mo; Q = S, Se)

Abstract: We have analyzed the discrepancies in the behavior of seemingly related chalcogenides with a stoichiometry of M : Q = 2 : 3.

Cited by 14 publications

References 51 publications

Peer Review #2 of "X-ray diffraction and theoretical study of the transition 2H-3R polytypes in Nb1+xSe2 (0 < x < 0.1) (v0.2)"

Peer Review #2 of "X-ray diffraction and theoretical study of the transition 2H-3R polytypes in Nb1+xSe2 (0 < x < 0.1) (v0.2)"

Peer Review #2 of "X-ray diffraction and theoretical study of the transition 2H-3R polytypes in Nb1+xSe2 (0 < x < 0.1) (v0.1)"

Peer Review #1 of "X-ray diffraction and theoretical study of the transition 2H-3R polytypes in Nb1+xSe2 (0 < x < 0.1) (v0.1)"

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Theoretical and experimental comparative study of the stability and phase transformations of sesquichalcogenides M2Q3 (M = Nb, Mo; Q = S, Se)

Abstract: We have analyzed the discrepancies in the behavior of seemingly related chalcogenides with a stoichiometry of M : Q = 2 : 3.

Cited by 14 publications

References 51 publications

Peer Review #2 of "X-ray diffraction and theoretical study of the transition 2H-3R polytypes in Nb1+xSe2 (0 < x < 0.1) (v0.2)"

Peer Review #2 of "X-ray diffraction and theoretical study of the transition 2H-3R polytypes in Nb1+xSe2 (0 < x < 0.1) (v0.2)"

Peer Review #2 of "X-ray diffraction and theoretical study of the transition 2H-3R polytypes in Nb1+xSe2 (0 < x < 0.1) (v0.1)"

Peer Review #1 of "X-ray diffraction and theoretical study of the transition 2H-3R polytypes in Nb1+xSe2 (0 < x < 0.1) (v0.1)"

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Theoretical and experimental comparative study of the stability and phase transformations of sesquichalcogenides M₂Q₃ (M = Nb, Mo; Q = S, Se)