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(C-0.5,N-0.5)(2), belonging to the M(n+1)AX(n) 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) A, 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 approximate to 50 GPa, no phase transformations were observed. The bulk modulus is 219 +/- 4 GPa, with a pressure derivative, K-o('), of 3.7 +/- 0.3. We also fabricated the ternary Ti3AlC2, with some Sn [nominal composition Ti-3(AlSn0.2)C-2]. Its a and c-lattice parameters are 3.0804(7) and 18.5426(7) A, respectively. Its bulk modulus is 226 +/- 3 GPa, with a pressure derivative, K-o('), of approximate to 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. (c) 2007 American Institute of Physics.