TY - JOUR

T1 - Vacancy-driven extended stability of cubic metastable Ta-Al-N and Nb-Al-N phases

AU - Pacher, Ferdinand

AU - Mayrhofer, Paul Heinz

AU - Holec, David

PY - 2017

Y1 - 2017

N2 - Quantum mechanical calculations had been previously applied to predict phase stability in many ternary and multinary nitride systems. While the predictions were very accurate for the Ti-Al-N system, some discrepancies between theory and experiment were obtained in the case of other systems. Namely, in the case of Ta-Al-N, the calculations tend to overestimate the minimum Al content necessary to obtain a metastable solid solution with a cubic structure. In this work, we present a comprehensive study of the impact of vacancies on the phase fields in quasi-binary TaN-AlN and NbN-AlN systems. Our calculations clearly show that presence of point defects strongly enlarges the cubic phase field in the TaN-AlN system, while the effect is less pronounced in the NbN-AlN case. The present phase stability predictions agree better with experimental observations of physical vapour deposited thin films reported in the literature than that based on perfect, non-defected structures. This study shows that a representative structural model is crucial for a meaningful comparison with experimental data.

AB - Quantum mechanical calculations had been previously applied to predict phase stability in many ternary and multinary nitride systems. While the predictions were very accurate for the Ti-Al-N system, some discrepancies between theory and experiment were obtained in the case of other systems. Namely, in the case of Ta-Al-N, the calculations tend to overestimate the minimum Al content necessary to obtain a metastable solid solution with a cubic structure. In this work, we present a comprehensive study of the impact of vacancies on the phase fields in quasi-binary TaN-AlN and NbN-AlN systems. Our calculations clearly show that presence of point defects strongly enlarges the cubic phase field in the TaN-AlN system, while the effect is less pronounced in the NbN-AlN case. The present phase stability predictions agree better with experimental observations of physical vapour deposited thin films reported in the literature than that based on perfect, non-defected structures. This study shows that a representative structural model is crucial for a meaningful comparison with experimental data.

U2 - 10.1016/j.surfcoat.2017.07.012

DO - 10.1016/j.surfcoat.2017.07.012

M3 - Article

VL - 326.2017

SP - 37

EP - 44

JO - Surface & coatings technology

JF - Surface & coatings technology

SN - 0257-8972

IS - 15 October, Part A

ER -