T-P Phase Diagram of β-(ET)2I3

Molecular Conductors and Superconductors Based on Trihalides of BEDT-TTF and Some of Its Analogues

“…Although no detailed crystal structures of the β t samples are available, the similarities of the T c values and the values and anisotropy of the upper critical fields as well as the unit-cell parameters strongly suggest that the β t state is probably very similar to the β H state of (ET) 2 I 3 , which usually arises under pressure. As it is known, the increase of T c up to 8 K in a high-pressure phase is due to a suppression of incommensurate structure modulation in the β crystals. , It was shown 99 that internal strains can stabilize the β H state in the β-(ET) 2 I 3 crystals at ambient pressure. The occurrence of the β H state in thermolized crystals is probably associated with internal strains arising in crystals during the ε → β and ζ → β conversions.…”

“…While studying the effect of electrocrystallization conditions on conducting properties of the crystals, it was found that some crystals of β-(ET) 2 I 3 exhibited the acceleration of the resistivity fall starting from ∼4 and/or ∼8 K (Figures and ). , The application of magnetic field suppressed this fall that indicated the existence of one and/or two more superconducting phases of (ET) 2 I 3 with higher T c . The behavior of the β-(ET) 2 I 3 crystals under pressure was studied, and a drastic change in superconductivity was found, with the increase of T c to 8 K at a low pressure (Figure ). , The T − P phase diagram was investigated and it was established that the β-(ET) 2 I 3 crystals can exist in two superconducting states: a low-temperature one (β L ) with T c of 1.5 K under ambient pressure and a high-temperature one (β H ) with T c of 8 K at P ≈ 400 bar. − The limits of stability of both phases were determined. The β H phase can be retained at ambient pressure by cooling the sample under pressure ( P > 400 bar) followed by the pressure release at low temperatures. , On such a treatment, the β H phase exists at atmospheric pressure at T < 150 K, above which it converts to the β L phase (Figure ). − It was asserted in ref that the high- T c state in β-(ET) 2 I 3 cannot be accessed by only hydrostatic pressure but requires, in addition, a substantial shear component.…”

“…The behavior of the β-(ET) 2 I 3 crystals under pressure was studied, and a drastic change in superconductivity was found, with the increase of T c to 8 K at a low pressure (Figure ). , The T − P phase diagram was investigated and it was established that the β-(ET) 2 I 3 crystals can exist in two superconducting states: a low-temperature one (β L ) with T c of 1.5 K under ambient pressure and a high-temperature one (β H ) with T c of 8 K at P ≈ 400 bar. − The limits of stability of both phases were determined. The β H phase can be retained at ambient pressure by cooling the sample under pressure ( P > 400 bar) followed by the pressure release at low temperatures. , On such a treatment, the β H phase exists at atmospheric pressure at T < 150 K, above which it converts to the β L phase (Figure ). − It was asserted in ref that the high- T c state in β-(ET) 2 I 3 cannot be accessed by only hydrostatic pressure but requires, in addition, a substantial shear component. When pure hydrostatic pressure was applied to a sample through careful isobaric freezing of He, a high- T c state was not observed.…”

Time-Resolved Photoresponse Measurements of the Electrical Conductivity of the Quasi-Two-Dimensional Organic Superconductor β-(BEDT-TTF)2I3 Using a Nanosecond Laser Pulse

“…15,16 Diffraction experiments have suggested that an incommensurate superlattice structure is present in the low-T c state, and at pressures higher than 0.5 kbar, the incommensurate structure disappears. 17,18 It is certain that the incommensurate structure is related to the disorder of a conformation of the terminal ethylene groups of the BEDT-TTF molecule.…”

“…In a single crystal of β-(BEDT-TTF) 2 I 3 , two superconducting states, a low- T c state that shows a phase transition to a superconducting state at a critical temperature T c ≅ 1.5 K and a high- T c state with T c = 7–8 K, can coexist. − The superconducting phase transition temperature of the crystal which initially shows T c ≅ 1.5 K in the low- T c state rises to ∼7 K at the pressure of ∼1 kbar . After releasing the applied pressure (higher than 0.4 kbar) at temperatures below 125 K, a pure crystal of the high- T c state is obtained at ambient pressure. , Diffraction experiments have suggested that an incommensurate superlattice structure is present in the low- T c state, and at pressures higher than 0.5 kbar, the incommensurate structure disappears. , It is certain that the incommensurate structure is related to the disorder of a conformation of the terminal ethylene groups of the BEDT-TTF molecule …”