betaAs2S3

Beta-As2S3, or beta arsenic trisulfide, is a polymorph of arsenic sulfide (As2S3). Along with the more common alpha-As2S3, it represents one of the principal crystalline forms of the compound. The beta form is a high-temperature polymorph and is metastable at room temperature, typically transforming to the alpha phase upon heating or after long-term storage at ambient conditions.

Formation and transformation: Beta-As2S3 can be produced by heating alpha-As2S3 above its phase-transition temperature and then quenching to room temperature, or by crystallization from the melt under suitably controlled cooling. Under ordinary conditions, the beta phase is less common than the alpha phase.

Structure and properties: The beta polymorph has a different crystal structure from alpha-As2S3, as indicated by diffraction studies. This structural difference leads to distinct vibrational spectra and generally different optical and physical properties, including refractive index and band gap, though exact values are sample- and condition-dependent.

Applications and significance: Beta-As2S3 is mainly of scientific interest for studies of phase transitions in chalcogenide systems. While As2S3-based glasses and crystals are important in infrared optics, the crystalline beta phase itself is not a widely used commercial material.

See also: Arsenic sulfide, alpha-As2S3, orpiment, realgar.