Crystal structure responses of corundum-type structures (α-Al2O3 and α-Fe2O3) under dynamic acoustic shocked conditions and their comparison between static high-temperature and high-pressure conditions: implications on volume-pressure-related phase transition types

Abstract

Universal behaviours of solid-state systems under static high pressures and temperatures are well known. With increasing pressure, the unit cell volume of materials decreases, and the materials frequently undergo high-pressure phases transitions. Acoustic shock waves can simultaneously offer dynamic thermal and high-pressure effects on materials. Herein, we investigate the corundum-type structures (α-Al₂O₃ and α-Fe₂O₃) of nanocrystalline particles under dynamic acoustic shocked conditions, and the observed structural results are compared with those obtained under static high-pressure and temperature conditions. According to the observed X-ray diffraction results, α-Al₂O₃ NPs’ unit cell volume remains unchanged, whereas α-Fe₂O₃ NPs’ unit cell volume increases under shocked conditions up to 150 shocks, and the Fe₂O₃ (Rc) to Fe₃O₄ (Fdm) transition is observed under the 200-shocked condition. The structural stability results of α-Al₂O₃ and α-Fe₂O₃ NPs under acoustic shocked conditions are explained by their lattice thermal conductivity values based on a superheating approach. From the observed results, it is confirmed that acoustic shock waves create a new stage, which requires a collective approach for reinvestigating/rewriting the classical P–T phase diagrams, conventional phase transition paths and compression behaviour of materials/minerals because of their unique structural results.