Structural Phase Transition of θ-(BEDT-TTF)2RbZn(SCN)4 under High Pressure

θ-(BEDT-TTF) 2 RbZn(SCN) 4 is known as a two-dimensional organic conductor exhibiting a metal–insulator phase transition associated with a charge ordering phenomena at T MI =200 K under ambient pressure. The transition temperature increases with applied pressure and reaches room temperature at 1.1 GPa. The structural change by pressure induced phase transition was investigated by X-ray diffraction using synchrotron radiation. A superlattice formation of 2 c was found above 1.1 GPa. A single crystal structural analysis taking account of the superlattice was carried out at 1.2 GPa. Displacements of BEDT-TTF molecules were found to be similar to the displacements in the low temperature phase at the ambient pressure. However, the shrinkage of the c -axis under pressure was four times as large as that under cooling at the transition point. Decreases in the intermolecular distances between BEDT-TTF molecules resulted in increases of the intersite Coulomb energies V and an increase of the electric bandwidth W . ...

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