Phase stability and decomposition products of Ti-Al-Ta-N thin films

Ab initio calculations of quaternary alloys were used to predict the phase stability of ( Ti 1 − x Al x ) 1 − y Ta y N . Experimental observation of a dual phase structure containing wurtzite AlN and cubic Ti 1 − y Ta y N after thermal decomposition of sputter deposited thin films by vacuum annealing to 1400 ° C is in excellent agreement with the calculated phase stabilities of the investigated compositions. We found positive mixing enthalpies for Ti 1 − x Al x N and Al 1 − y Ta y N , with maximum values of 0.25 eV/atom and 0.30 eV/atom, respectively, but negative values for Ti 1 − y Ta y N over the whole composition range. The difference in lattice parameters obtained from experiments and ab initio calculations is within ∼ 1 % .