Comment on 'Shear stiffness in nanolaminar Ti3SiC2 challenges ab initio calculations'

In a recent publication by Kisi et al (2010 J. Phys.: Condens. Matter 22 162202) the authors present experimentally measured elastic constants for the M(n + 1)AX(n) (MAX) phase, Ti(3)SiC(2), that differ from density functional theory calculations. They then conclude that 'prediction [by ab initio calculation] of the full elasticity tensor for Ti(3)SiC(2) has not been successful'. However the authors do not compare with previous experimental work in which Finkel et al measure the elastic moduli (Finkel et al 2000 J. Appl. Phys. 87 1701). The predictions of ab initio calculations (Yu et al 2005 J. Mater. Res. 20 1180) agree with the measurements of Finkel et al as well as with most other experimentally measured elastic moduli for MAX phases (Cover et al 2008 10 935; Cover et al 2009 J. Phys.: Condens. Matter 21 305403). The unrealistically high value of the C(44) constant obtained by Kisi et al, which would mean that Ti(3)SiC(2) is almost as resistant to shear as diamond, undermines confidence in their results.