High pressure structural phase transitions in the organic superconductor κ-(ET)2Cu[N(CN)2]Cl

✍ Scribed by A.J. Schultz; U. Geiser; H.H. Wang; J.M. Williams; L.W. Finger; R.M. Hazen

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 617 KB
• Volume: 208
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(93)90199-z

✦ Synopsis

A reversible symmetry-lowering structural phase transition is observed by X-ray diffraction techniques from single crystals of I¢-(ET)2Cu[N(CN)2]C1 (ET, or BEDT-TTF, is bis(ethylenedithio)tetrathiafulvalene, C~oHsSs) under applied pressure. At room temperature, by use of a diamond anvil cell, a transition above 8 kbar characterized by peak broadening begins to occur. The transition is also observed by cooling crystals coated with Apiezon N vacuum grease, which is a technique that is also used to produce the high pressure superconducting state (Tc = 12.8 K, P= 0.3 kbar). Given the anisotropic nature of the structure, the ambient pressure linear compressibilities are surprisingly isotropic, with values of fla=2.39(8)× 10 -3, fib=2.47(7)× 10 -3, flc=2.29(9) × 10 -3 kbar -~. At 3 kbar and room temperature, from a complete structure analysis it is shown that the ET molecule conformation is the same as that at ambient pressure although S.. -S contacts are reduced by as much as 0.05 A. A second transition, characterized by reversible disappearance of Bragg intensities consistent with pressure-induced amorphization, was observed between 11.4 and 11.8 kbar.