The design of crystalline precursors for the synthesis of Mn-1AXn phases and their application to Ti3AlC2

A methodology to allow the deliberate design of solid precursors to affect the solid-state synthesis of materials has proven elusive. We have designed a conceptual synthesis route for M(n+1)AX(n) phases that does not involve the usual intermediate phases. Instead, it is proposed that the common structural units within a solid-state precursor Mn+1Xn containing vacancy ordering should be the basis for direct synthesis of the desired M(n+1)AX(n) phase. The method is demonstrated to be successful in producing titanium aluminum carbide (Ti3AlC2) by the rapid intercalation of Al into TiC0.67 at 400 degrees-600 degrees C below the conventional synthesis temperature. Time-resolved neutron diffraction at 1 min time-resolution has confirmed the reaction sequence. The vacancy ordering in TiC0.67 occurred simultaneously to, and appeared to be greatly facilitated by, the ingress of aluminum. There is considerable scope for adaptation of the method to other M(n+1)AX(n) phases.