High-pressure metallization and amorphization of the molecular crystal Sn(IBr)₂

An insulator-to-metal transition concurring with amorphization is found in the cubic (Pa3̄) molecular crystal Sn(IBr)₂ at P ≈ 20 GPa. Measurements were carried out with diamond-anvil cells at pressures up to approx. 30 GPa using resistance measurements, X-ray diffraction (XRD), and ¹¹⁹Sn Mossbauer spectroscopy (MS). With increasing pressure a new crystalline phase is observed in the 10-23 GPa range; at P ≈ 16 GPa, a gradual onset of structural disorder is first observed, and full amorphization takes place at P ≥ 23 GPa. Both electronic properties as measured by R(P, T) and MS data are consistent with a gradual growth of disordered (SnI₂Br₂)_n polymeric chains, formed by intermolecular I-I bonding allowing for electronic delocalization to occur. Upon decompression both XRD and ¹¹⁹Sn MS show a significant pressure hysteresis.