We have used systematic ab initio evolutionary structural
searching
to uncover the high-pressure transformation pathway of a promising
thermoelectric material, AgGaTe2. The global structures
of the ternary Ag–Ga–Te system have been predicted up
to 100 GPa. The known chalcopyrite phase at ambient pressure is validated
by the searching method. The B3-like structure with the space group
(s.g.) of P4̅m
2 exhibits a metastable one at a low-pressure range. The first structural
phase transition is calculated at about 4 GPa, processing the I4̅2
d phase to a B1-like
phase (s.g. Pmma). Other predicted structures, Pmn21 and Pm phases, are potentially
coexisting phases up to 30 GPa because of the slightly different enthalpy.
This finding reasonably explains the ambiguous results in the previous
experiments. The high-pressure phase beyond 30 GPa is proposed to
be a short-range alloy of bcc-Te and B2-AgGa rather than a cation-disordered
B2-like phase. The band gap of the I4̅2
d phase is increased with increasing pressure,
while the metastable P4̅m
2 phase is a narrow band gap semiconductor. The electron–phonon
coupling of the metallic phases of ternary IB-IIIA-VIA2 compounds is derived for the first time in AgGaTe2. They
exhibit superconductors with a maximum T
c of 2.4 K in the Pmma phase at 6 GPa. The findings
of this work not only provide a clear explanation of the high-pressure
transformation pathway of AgGaTe2 but also suggest promising
electronic properties guiding further applications, especially in
a thermometric device, of this material under high pressure.