Thermodynamic assessment of the Al–Sc–N ternary system and phase-separated region of the strained wurtzite phase

• Published in: Journal of the European Ceramic Society Vol. 40; no. 15; pp. 5410 - 5422
• Main Authors: Hirata, K., Shobu, K., Yamada, H., Uehara, M., Anggraini, S.A., Akiyama, M.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2020
• Subjects: (Al, Sc)N; CALPHAD; First-principles calculation; Piezoelectric material; Thin film; Piezoelectric material; CALPHAD; (Al, Sc)N; First-principles calculation; Thin film
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2020.06.047

Sc-doped AlN with the wurtzite structure has excellent performance as a piezoelectric material. The phase stability of the (Al, Sc)N wurtzite phase is very important in designing highly functional piezoelectric materials. In this work, we assessed the thermodynamic parameters of the Al–Sc–N ternary system by incorporating the results of first-principles calculations into the calculation of phase diagrams (CALPHAD) method. The calculated Sc–N binary and Al–Sc–N ternary phase diagrams were consistent with the reported experimental results, where the (Al, Sc)N wurtzite phase exhibited phase separation. Because Sc-doped AlN is normally deposited on a substrate, we also evaluated the stability of the (Al, Sc)N wurtzite phase by considering the strain energy generated between the substrate and the thin film. It was found that the tendency to phase separation can be suppressed by decreasing the thickness of the thin film, which is qualitatively consistent with experimental reports.