Functional Monochalcogenides: Raman Evidence Linking Properties, Structure, and Metavalent Bonding

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Germanium (Ge), Selenium (Se), Tin (Sn), and Tellurium (Te) based chalcogenides are technologically important materials.
• Understanding their phase transitions under extreme conditions is crucial for novel applications.
• Raman spectroscopy is a powerful tool for probing vibrational and electronic properties of materials.

Purpose of the Study:

• To investigate the pressure- and temperature-dependent Raman scattering of GeSe, SnSe, and GeTe.
• To identify structural and electronic phase transitions in these materials.
• To elucidate the differences in bonding and defect formation between GeTe and the GeSe/SnSe systems.

Main Methods:

• High-pressure and variable-temperature Raman spectroscopy up to 50 GPa and 800 K.
• First-principles calculations.
• Analysis of vibrational and electronic properties.

Main Results:

• Observed distinct structural and electronic phase transitions in GeSe, SnSe, and GeTe.
• Identified similarities between GeSe and SnSe, and highlighted differences with GeTe.
• Calculations indicated a propensity for defect formation and doping in GeTe, leading to strong Raman damping.
• Anomalous anharmonicity was observed in GeTe.

Conclusions:

• The study reveals unique properties of GeTe, including defect formation and doping, distinguishing it from GeSe and SnSe.
• These properties are linked to GeTe's distinct chemical bonding, consistent with its classification as an "incipient" metal.
• Raman scattering provides insights into the complex behavior of chalcogenides under extreme conditions.