  We did extensive research for the typical nanolaminate Mn+1AXn (n=1, 2, 3)
ceramics focusing on the structural stability, the phase transition pressure of
Ti2GaN (160 GPa) is far higher than that of Zr2GaN (92 GPa), meaning the strong
M dependence of the same group, whereas Zr2AlN (98 GPa) has similar value with
that of Zr2GaN, meaning the weak A dependence. Mo2GaC shows lowest phase
transition pressure among all of the known MAX, meaning that C-containing phase
has lower phase transition pressure than that of N-containing counterparts. All
of the metastable phases of the selected MAX transition almost at the same
time, such as all of the metastable phases of Zr2AlN transition at the similar
pressure, about 90-110 GPa, with a very narrow pressure range of less than 20
GPa, as is also the case for Zr2GaN corresponding to 90-115 GPa and for Mo2GaC
corresponding to 10-25 GPa. Mo2GaC presents multi-phase co-existence status at
high pressure, whose P63/mmc alpha-beta phase transition is the more commonly
and frequently occurred route in this kind of MAX structure. The hexagonal
P63-mmc to tetragonal P4-mmm transition is the common direct route for the
N-containing MAX due probably to the high transition pressure. P63/mmc
alpha-beta-P4-mmm transition might be the common route for the C-containing MAX
due probably to the low alpha-beta transition pressure. Nb2InN(Nb2GaN) and
Mo2InN present c-axis abnormal elongation at low pressures, these compounds
have negative formation of energy at ambient conditions, meaning that all of
them are stable or experimentally synthesizeable.
