  There has been considerable interest in chalcogenide alloys with high
concentrations of native vacancies that lead to properties desirable for
thermoelectric and phase-change materials. Recently, vacancy ordering has been
identified as the mechanism for metal-insulator transitions observed in
GeSb2Te4 and an unexpectedly low thermal conductivity in Ga2Te3. Here, we
report the direct observation of vacancy ordering in Ga2SeTe2 utilizing
aberration-corrected electron microscopy. Images reveal a cation-anion dumbbell
inversion associated with the accommodation of vacancy ordering across the
entire crystal. The result is a striking example of the interplay between
native defects and local structure.
