Thermodynamic stability and material design of piezoelectric nitride with wurtzite structure

2020 Fiscal Year Final Research Report

• Project/Area Number: 19K15302
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 26030:Composite materials and interfaces-related
• Research Institution: National Institute of Advanced Industrial Science and Technology
• Principal Investigator: Hirata Kenji 国立研究開発法人産業技術総合研究所, エレクトロニクス・製造領域, 研究員 (40828282)
• Project Period (FY): 2019-04-01 – 2021-03-31
• Keywords: 圧電材料 / 平衡状態図 / 第一原理計算 / 窒化物

Outline of Final Research Achievements

In Al-Sc-N ternary system, the phase stability of wurtzite phase is very important in designing highly functional piezoelectric material. In this study, we have assessed the thermodynamic parameters of Al-Sc-N ternary system by incorporating the results of first-principles calculation into the CALPHAD method. From the calculated phase diagram, it has been found that the (Al, Sc)N wurtzite phase exhibits phase separation. On the other hand, (Al, Sc)N solid solution with wurtzite phase can be formed in thin film which was fabricated by sputtering. This contradiction is thought to be derived from different phase equilibria between a thin film and a bulk sample. In this work, we evaluated the solid solution behavior of (Al, Sc)N wurtzite phase by considering the strain energy generated between the substrate and the thin film. It was found that the tendency of phase separation was suppressed with decreasing thickness of thin film.

Free Research Field

無機材料

Academic Significance and Societal Importance of the Research Achievements

Al-Sc-N 3元系の相平衡は不明な点が多く、これまでに熱力学データベースは構築されていなかった。そこで本研究では、第一原理計算やデバイグリュナイゼン近似をCALPHAD法に援用することで相平衡を計算することが可能となった。構築した熱力学データベースにより計算した状態図は実験報告をよく再現しており、信頼性が高いものと考えられる。また、基板と薄膜の間に生じる歪エネルギーにより、ウルツ鉱相の二相分離が抑制される新しい知見も得ることができた。