Sonochemical synthesis of supersaturated Ga–Al liquid-alloy fine particles and Al(3+)-doped γ-Ga(2)O(3) nanoparticles by direct oxidation at near room temperature

In this study, we investigated the fabrication of supersaturated gallium (Ga)–aluminum (Al) liquid alloy and Al(3+)-doped γ-Ga(2)O(3) 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 Al(2)O(3) or Al deposition. Thus, ultrafine Al(3+)-doped γ-Ga(2)O(3) 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-Ga(2)O(3)-based NPs were 59 nm and 181 m(2)/g, respectively. Compared with γ-Ga(2)O(3), the optical bandgap of the Al(3+)-doped γ-Ga(2)O(3) NPs was broadened, and the thermal stability improved, indicating Al(3+)-doping into the γ-Ga(2)O(3) lattice. However, the lattice constant of γ-Ga(2)O(3) was almost unchanged with or without Al(3+)-doping. Al(3+) was introduced into the defect sites of Ga(3+), 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.