Synthesis of ferroelectric perovskite oxynitride with perfect trans-anion order and its application for photovoltaic energy conversion

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K22227
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 36:Inorganic materials chemistry, energy-related chemistry, and related fields
• Research Institution: The University of Tokyo
• Principal Investigator: HIROSE Yasushi 東京大学, 大学院理学系研究科(理学部), 准教授 (50399557)
• Project Period (FY): 2019-06-28 – 2022-03-31
• Keywords: 機能性薄膜材料 / 酸窒化物 / 強誘電体 / アニオン配列 / エピタキシャル成長 / 太陽電池

Outline of Final Research Achievements

The synthesis of perovskite oxynitride thin films with trans-type anion arrangement, a candidate for narrow-bandgap ferroelectric material, was studied. Although it was theoretically predicted that A3+B4+O2N-type oxynitrides would stabilize the trans-type arrangement with charge-neutral AN and BO2 planes, no increase in the trans-type arrangement in the synthesized thin films was confirmed. Depth-profile analysis of the N modulation-doped thin films revealed that the diffusion of N in the crystals must be suppressed by low-temperature growth. As another approach, Sn2+ with electron lone pairs was introduced into the A site, which enhances the tetragonal distortion stabilizing the trans-type arrangement. However, the synthesis of such compounds was difficult due to the desorption of SnNx. It was concluded that a solid-phase epitaxy, which can suppress nitride desorption, is promising.

Free Research Field

応用物理学

Academic Significance and Societal Importance of the Research Achievements

目標としていた完全trans型ペロブスカイト酸窒化物の合成には至らなかったが、課題（酸窒化物結晶中のアニオン拡散および熱力学的に不安定な窒化物の分解脱離）とその解決に向けた方策を明らかにした。また、酸化物/酸窒化物人工超格子の合成、エピタキシャル酸化物薄膜を前駆体に用いたトポタクティック窒化反応、逆光電子ホログラフィーによる単結晶薄膜中のアニオン配列評価といった新たな技術の開発に成功した。