Pressure‐induced insulator–metal transition in a novel layer metalloorganic structure

A novel layer metalloorganic structure (Co(η 5 ‐C 5 H 5 ) 2 ) 0.25 TiSe 2 has been synthesized by intercalation of the cobaltocene, Co(η 5 ‐C 5 H 5 ) 2 [bis(eta‐5‐cyclopentadienyl)cobalt] (a representative of the metallocenes M(η 5 ‐C 5 H 5 ) 2 where M – is a metal) into van‐der‐Waals gaps of TiSe 2 matrix. The papers reports a study of the electrical resistance R , thermoelectric power S (Seebeck effect), and contraction of a sample's thickness (compressibility) under almost continuous variation of quasihydrostatic pressure P within 0–20 GPa at room temperature. We observed a gradual decrease of R ( P ) by ∼8 orders to 20 GPa. About P ∼ 10 GPa we established both an abrupt change of d R /d P and inversion of S from the electronic to the holes type of conductivity. To P ∼ 16 GPa the intercalate became a metal and exhibited a “close to zero” S , which was kept down to 8 GPa on decompression; all pressure‐induced changes were reversible. The synthesized compound (Co(η 5 ‐C 5 H 5 ) 2 ) 0.25 TiSe 2 is a novel functional material for wide application. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)