Effects of volume mismatch and electronic structure on the decomposition of ScAlN and TiAlN solid solutions

Abstract

Thin solid films of metastable rocksalt structure ͑c-͒ Sc 1−x Al x N and Ti 1−x Al x N were employed as model systems to investigate the relative influence of volume mismatch and electronic structure driving forces for phase separation. Reactive dual magnetron sputtering was used to deposit stoichiometric Sc 0.57 Al 0.43 N͑111͒ and Ti 0.51 Al 0.49 N͑111͒ thin films, at 675°C and 600°C, respectively, followed by stepwise annealing to a maximum temperature of 1100°C. Phase transformations during growth and annealing were followed in situ using x-ray scattering. The results show that the as-deposited Sc 0.57 Al 0.43 N films phase separate at 1000-1100°C into nonisostructural c-ScN and wurtzite structure ͑w-͒ AlN, via nucleation and growth at domain boundaries. Ti 0.51 Al 0.49 N, however, exhibits spinodal decomposition into isostructural coherent c-TiN and c-AlN, in the temperature interval of 800-1000°C. X-ray pole figures show the coherency between c-ScN and w-AlN, with AlN͑0001͒ ʈ ScN͑001͒ and AlN͗0110͘ ʈ ScN͗110͘. First-principles calculations of mixing energy-lattice spacing curves explain the results on a fundamental physics level and open a route for design of novel metastable pseudobinary phases for hard coatings and electronic materials.

Phase stability of ScN-based solid solutions for thermoelectric applications from first-principles calculations

“…For instance, it has been found that metastable nitride alloys might phase separate both by a spinodal-decomposition mechanism, for instance, in TiAlN, 26,27 and by nucleation and growth as in ScAlN. 28 The difference has been explained in terms of volume mismatch, favoring nucleation and growth, and the electronic structure as driving forces for phase separation, allowing for spinodal decomposition. [29][30][31] These decomposition mechanisms give a)…”

Stabilization of wurtzite Sc0.4Al0.6N in pseudomorphic epitaxial Sc Al1−N/In Al1−N superlattices

“…It has been theoretically predicted that epitaxial stabilization of ScxAl1-xN up to x=0.4 could hinder the material disintegration through spinodal decomposition [8]. However, phase separation through nucleation and growth of semicoherent wurtzite AlN phases in domain boundaries of cubic ScN has been demonstrated during annealing of cubic solid solutions [14] and might be a limiting factor for alloy formation during thin film growth.…”

Nonequilibrium ab initio molecular dynamics determination of Ti monovacancy migration rates in B1 TiN

“…This motivates us to undertake computational investigation of these challenging problems. Moreover, even though nitrogen vacancies are the most common type of defect in binary TM nitrides, experiments indicate that migration of metal vacancies may be the mechanism which primarily controls spinodal decomposition of (Ti,Al)N pseudobinary * davide.gambino@liu.se alloys at high (>1000 K) temperatures [30,31]. Titanium nitride (TiN), the prototype and most studied among all TM nitrides [32], crystallizes in the cubic B1 lattice structure over a wide range of temperatures (from 0 K up to its melting point, T m ≈ 3250 K [33]) and a wide range of stoichiometries TiN x , with 0.6 < x < 1.2 [16].…”