Sonochemical synthesis of supersaturated Ga-Al liquid-alloy fine particles and Al3+-doped γ-Ga2O3 nanoparticles by direct oxidation at near room temperature

Toshiki Yamanaka; Yamato Hayashi; Hirotsugu Takizawa

doi:10.1016/j.ultsonch.2022.106114

Sonochemical synthesis of supersaturated Ga-Al liquid-alloy fine particles and Al³⁺-doped γ-Ga₂O₃ nanoparticles by direct oxidation at near room temperature

Ultrason Sonochem. 2022 Sep:89:106114. doi: 10.1016/j.ultsonch.2022.106114. Epub 2022 Aug 9.

Authors

Toshiki Yamanaka¹, Yamato Hayashi², Hirotsugu Takizawa¹

Affiliations

¹ Graduate School of Engineering, Department of Applied Chemistry, Tohoku University, 6-6 Aoba, Aramaki, Aobaku, Sendai 980-8579, Japan.
² Graduate School of Engineering, Department of Applied Chemistry, Tohoku University, 6-6 Aoba, Aramaki, Aobaku, Sendai 980-8579, Japan. Electronic address: yamato.hayashi.b6@tohoku.ac.jp.

Abstract

In this study, we investigated the fabrication of supersaturated gallium (Ga)-aluminum (Al) liquid alloy and Al³⁺-doped γ-Ga₂O₃ nanoparticles (NPs) at near room temperature (60 °C) using sonochemical and sonophysical effects. Supersaturated Ga-Al liquid alloy microparticles (D_av = 1.72 µm) were formed and stabilized at 60 °C by the thermal nonequilibrium field provided by sonochemical hot spots. Compared with liquid Ga, supersaturated Ga-Al liquid alloy was rapidly oxidized to a uniform oxide without Al₂O₃ or Al deposition. Thus, ultrafine Al³⁺-doped γ-Ga₂O₃ NPs were obtained after only 1 h of ultrasonic irradiation at 60 °C. The oxidation of liquid Ga was remarkably accelerated by alloying with metallic Al and ultrasonic irradiation, and the time was shortened. The average diameter and surface area of the γ-Ga₂O₃-based NPs were 59 nm and 181 m²/g, respectively. Compared with γ-Ga₂O₃, the optical bandgap of the Al³⁺-doped γ-Ga₂O₃ NPs was broadened, and the thermal stability improved, indicating Al³⁺-doping into the γ-Ga₂O₃ lattice. However, the lattice constant of γ-Ga₂O₃ was almost unchanged with or without Al³⁺-doping. Al³⁺ was introduced into the defect sites of Ga³⁺, which were massively induced in the defective spinel structure during ultrasonic processing. Therefore, sonochemical processing, which provides nonequilibrium reaction fields, is suitable for the synthesis of supersaturated and metastable materials in metals and ceramics fields.

Keywords: Direct oxidation; Liquid alloy; Nanoparticles; Room temperature; Supersaturation; Ultrasound.