Synthesis and compressibility of Ti3(Al,Sn0.2)C2 and Ti3Al(C0.5,N0.5)2

In this paper we report on the synthesis of a composition, Ti3Al(C0.5,N0.5)2, belonging to the Mn+1AXn family of ternary layered carbides and nitrides. X-ray and selected area diffraction confirm that this compound is isostructural with Ti3SiC2; its a and c-lattice parameters are 3.0404(5) and 18.414(6) Å, respectively. Chemical analysis performed by electron dispersive and electron energy loss spectroscopy confirmed the Ti3AlCN chemistry. Using a synchrotron radiation source and a diamond anvil cell, we also measured the pressure dependencies of the lattice parameters. Up to a pressure of ≈50 GPa, no phase transformations were observed. The bulk modulus is 219±4 GPa, with a pressure derivative, Ko′, of 3.7±0.3. We also fabricated the ternary Ti3AlC2, with some Sn [nominal composition Ti3(AlSn0.2)C2]. Its a and c-lattice parameters are 3.0804(7) and 18.5426(7) Å, respectively. Its bulk modulus is 226±3 GPa, with a pressure derivative, Ko′, of ≈4. In both cases, the compressibility was greater along the c than along the a axes. We also show that in the case of Tin+1AlCn MAX-phases, replacing C by N results in a decrease in both lattice parameters and bulk moduli. The apparent contradiction inherent in this observation can be reconciled by assuming that the addition of N results in the formation of vacancies on the Al and/or X-sites.