Etude cristallographique de sulfures et de seleniures de vanadium. Mise en evidence de deux composes nouveaux, V 7Se 8 ET V 7S 8 monocliniques

Abstract

Some vanadium selenides and sulfides are prepared close to the composition V 7X 8. The observed structures, with ordering of vacancies, are related to the NiAs type (hexagonal unit cell: a′, c′). Two hexagonal compounds already known, V 7Se 8 and V 7S 8 (a = 2a′, c = 4c′) and two new monoclinic compounds are obtained. Parameters of the F monoclinic unit cells (a ≈ 2a′ ⇔3, b ≈ 2a′, c ≈ 4c′) are: a = 12, 472 ± 0,004 A ̇ ; b = 7,152 ± 0,002 A ̇ ; c = 23,978 ± 0,006 A ̇ ; β = 90, 40° for V 7Se 8; a = 11,671 + 0,003 A ̇ ; b = 6,646 ± 0,002 A ̇ ; c = 23,118 ± 0,007 A ̇ ; β = 90,99° for V 7S 8.