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Samuel Gallego and Catalin Popescu at the MSPD beamline of ALBA.
Cerdanyola del Vallès, 28th July 2022 Gallium (III) sulphide (Ga2S3) is a compound of sulphur and gallium, that is a semiconductor that has a wide variety of applications in electronics and photonics: nano optoelectronics, photonic chips, electro-catalysis, energy conversion and storage, solar energy devices, gas sensors, laser-radiation detection, second harmonic generation, phase change memories or photocatalytic water splitting systems.
In this work published in Chemistry of Materials, scientists have shown relevant vibrational and structural fingerprints of a pressure-induced paraelectric to ferroelectric R-3m-to-R3m (β’-to-φ) phase transition under decompression on Ga2S3 chalcogenide.
This transition was theoretically predicted in several III−VI B2X3 compounds at high temperature (where B can be aluminium, gallium or indium and X, sulphur, selenium or tellurium). The novelty of this research stems from the synthesis of both phases: β-(R-3m) and α-In2Se3 (R3m)-like structures on Ga2S3 and tuning them via decreasing pressure. Within the III−VI B2X3 compounds, this R-3m-to-R3m (β’-to-φ-Ga2S3) phase transition had been observed experimentally only in the indium (III) selenide (In2Se3) compound, under varying temperature or pressure, to date.
This finding leads the way for designing cheap, nontoxic, nonrare-earth, and abundant element-based devices for second harmonic generation, photocatalytic splitting, ferroelectric, pyroelectric, and piezoelectric applications based on Ga2S3.
Hight pressure chemistry and synchrotron light
Regarding the methodology, the research team carried out high-pressure Raman scattering and X-ray diffraction measurements at the MSPD beamline of ALBA, supported by ab initio calculations at different pressures. The results shed light on several questions not resolved to date. On compression, scientists showed α’-Ga2S3 undergoes a phase transition above 16 GPa to β’-Ga2S3, isostructural with β-In2Se3. Unlike a previous work, researchers demonstrate that this transition proceeds without the need of laser heating. On decompression, the pressure-induced paraelectric-ferroelectric R-3m-to-R3m (β’-to-φ) phase transition was unveiled below 9.0 GPa. Finally, a new phase was proposed on downstroke below 1.0 GPa, the γ- Ga2S3, with a defective zincblende structure. These phases observed both increasing/decreasing pressure on Ga2S3 aimed scientists to reformulate the pressure-behaviour scheme for AGa2X4 ordered vacancy compounds (OVCs) by including the Ga2X3 chalcogenides, considered as another kind of OVCs. The theoretical prediction of getting R-3m and R3m phases in the latter compounds under increasing/decreasing pressure was discussed. In this sense, new high-pressure works are suggested to find paraelectric and ferroelectric phases in Ga2Se3 and Ga2Te3 compounds.
Schematic illustration of the phase transitions unveiled under compression/decompression on the Ga2S3 system. Selected (b) Raman scattering spectra and (c) X-ray diffraction patterns of the α’-, β’-, φ- and γ-Ga2S3 under compression/decompression.
Reference: Samuel Gallego-Parra, Rosario Vilaplana, Oscar Gomis, Plácida Rodríguez-Hernández, Alfonso Muñoz, Jesus Antonio González, Juan Angel Sans, Catalin Popescu, and Francisco Javier Manjón. High-Pressure Synthesis of β- and α‑In2Se3‑Like Structures in Ga2Se3. Chem. Mater (2022), 34, 13, 6068–6086. https://doi.org/10.1021/acs.chemmater.2c01169
With the collaboration of Fundación Española para la Ciencia y la Tecnología. The ALBA Synchrotron is part of the of the Unidades de Cultura Científica y de la Innovación (UCC+i) of the FECYT and has received support through the FCT-21-17088. project.
