  We report a series of high-pressure electrical transport, magnetic
susceptibility, and x-ray diffraction measurements on single crystals of the
weak topological insulator Bi2TeI and the topological metal Bi3TeI. Room
temperature x-ray diffraction measurements show that both materials go through
a series of pressure-induced structural transitions and eventually adopt a
disordered bcc alloy structure at high pressure. A re-analysis of the published
data on BiTeI indicates that this material also adopts a disordered bcc
structure at high pressure, in contrast to the previously suggested P4/nmm
structure. We find that Bi2TeI and Bi3TeI become superconducting at 13 GPa and
11.5 GPa, respectively. The superconducting critical temperature Tc of the bcc
phase reaches maximum values of 7 K and 7.5 K for Bi2TeI and Bi3TeI,
respectively and dTc/dP < 0 in both cases. The results indicate that disordered
alloy bcc superconducting phases appear to be a universal feature of both the
Bi-Te and Bi-Te-I systems at high pressure.

Superconductivity;Materials Science