10 listed 68 quaternary MAX phases compositions already reported. partial substitution of the M, A or X elements, hence broadening to a quasi-infinite number of possible combinations. Furthermore, MAX phases are also of interest as precursors for MXenes (M n + 1X n two-dimensional nanosheets with properties analogues to graphene) currently only synthesizable by selective chemical etching of mostly Al-based MAX phases 6, 7.įrom 1996 to 2004, intensive research expanded the MAX phase family to more than 60 compositions that included 9 different “M” elements, 12 different “A” elements and n values of 1, 2, and 3 1, 8, 9, Since then, new discoveries reported have mainly focused on MAX phases with higher n values and on solid solutions 9, 10, 11, i.e. Like most metals and alloys, they possess high thermal shock resistance, have a good machinability, and high thermal and electrical conductivities while like most ceramics they have high decomposition or melting temperature and high elastic stiffness 1. Indeed, due to their structure consisting of the stacking of n “ceramic” layer(s) of MX interleaved by an A “metallic” plane, MAX phases are characterized by a combination of both ceramic and metallic behavior. 2 They were little studied for more than two decades until Barsoum and El-Raghy reported in 1996 the remarkable properties of Ti 3SiC 2 3 and further demonstrated these properties were shared by the other MAX phases 4, 5. More than half of known MAX phases were first synthesized in the 1960s by Nowotny et al. To be designated as a MAX phase, a compound should crystallize with the hexagonal P6 3/ mmc structure in the general formula M n + 1AX n with n being an integer, M being an early transition metal, A being a group 13–16 element and X being C and/or N 1. The MAX phases are a family of ternary carbides and nitrides.
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