Ultrahigh‐pressure effects in metallo‐organics

The results are reported of the pressure ( P ) dependence of the electrical resistance ( R ), the thermoelectric power (Seebeck effect) ( S ), and compressibility as well as the time dependence of R at fixed P up to 20 GPa for four metallo‐organics based on the BEDT‐TTF (bisethylenedithiolo‐tetrathiofulvalene) group, θ ‐(BEDT‐TTF) 2 CsZn(SCN) 4 , α ‐(BEDT‐TTF) 2 I 3 , β ′‐(BEDT‐TTF) 2 PF 6 , and (BEDT‐TTF)‐TCNQ. X‐ray powder and single‐crystal diffraction studies were also made on θ ‐(BEDT‐TTF) 2 CsZn(SCN) 4 at high pressures up to P ∼ 10 GPa. The R values of all the crystals decreased with pressure up to P ∼ 3–5 GPa (low‐pressure regime), and then the sign of d R /d P inverted (high‐pressure regime). From the investigation of the mechanical and structural properties, these materials were found to have a large compressibility in the low‐pressure regime, and a small one in the high‐pressure region. In θ ‐(BEDT‐TTF) 2 CsZn(SCN) 4 we observed pressure‐ induced reversible degradation (amorphization) in structure without a solid‐phase reaction. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)