Tin tetrabromide at high pressures: Reversible crystalline-to-amorphous and electronic transitions

Abstract

Several phase transitions have been observed in SnBr4 up to 23 GPa. Measurements of the Raman spectra show that additional modes are observed in the lattice region at about 4 GPa, suggesting that the symmetry of the unit cell is changing. All lattice modes disappear and the internal vibrational modes lose their splitting in the 13 -15-GPa region, indicating that a crystal-to-amorphous transition occurs in this pressure range. Upon release of pressure, the amorphous phase is stable to about 1 GPa. A crystalline phase is observed below 1 GPa. Optical absorption experiments indicate that the optical band gap displays a continuous (and reversible) closure with increasing pressure. A photoluminescence signal is observed to red shift with increasing pressure and is quenched in the amorphous state.

Size criterion for amorphization of molecular ionic solids

“…This is consistent with the already observed amorphization of all examined members of this family at pressures above 8 to 10 GPa. 2,[21][22][23][24] There are distinct analogies between the ionic size ratio systematics identified here for crystalline to noncrystalline transitions and those found to dictate crystal-crystal phase transitions in a variety of simpler system such as alkali halides. For example in sodium halides, NaF and NaCl undergo the well documented B1-B2 transition at pressure.…”

Pressure‐Induced Amorphization of LiInGe

“…LiInGe is an example for an reversible pressure induced amorphization of a compound with zincblende-like partial structure. L r X Structural memory behaviour has also been reported for Alp04 [23], [24] and several other compounds, for example molecular solids like SnBr4 1251, [26], SnI4 [27] to [29] and GeI4 [30]. This effect suggests that the atomic disorder produced by pressure derives from a relative small perturbation of the crystalline structure.…”

Pressure-induced transformations in molecular crystals

“…Previous Raman and reflectiwty studies by Williams and Lee [9 ] have shown that to the highest pressure measured (25 GPa) there is no gap closure and SnBr4 remains a bonajde insulator. Fig.…”