Etude structurale des composés MxTiSe 2 ( M = Fe, Co, Ni)

Abstract

New compounds M x TiSe 2 have been prepared with M = Fe ( x ⩽ 0.66), M = Co or Ni ( x ⩽ 0.50). The metal M is located in vacant octahedral sites of the TiSe 2 host lattice (hexagonal unit cell a′, c′). An ordering of vacancies occurs if x ⩾ 0.20. With M = Co or Ni ( x = 0.50) and with M = Fe (0.25 ⩽ x ⩽ 0.66) isotypic compounds of Ti 3Se 4 can be obtained ( M 3 □ X 4 type; monoclinic unit cell a ≈ a′ √3, b ≈ a′, c ≈ 2 c′). The compounds Fe 0.38TiSe 2 and Co 0.38TiSe 2 (hexagonal unit cell a ≈ a′ √3, c ≈ 2 c′) are of the M 2 □ X 3 type, variety 2 c′. The Fe 0.25TiSe 2 and Co 0.25TiSe 2 monoclinic unit cells ( a ≈ 2 a′ √3, b ≈ 2 a′, c ≈ 2 c′) allow us to assume, for these two compounds, a structure of the M 5 □ 3 X 8 type, variety 2 c′, identical to the Ti 5Se 8 one. The compound Ni 0.25TiSe 2 has an hexagonal unit cell ( a ≈ 2 a′, c ≈ 3 c′); it belongs to a so-called 3 c′ variety of the M 5 □ 3 X 8 type.