Crystalline and glassy phases in the Cs/Bi/As/S system

Area of Science:

• Materials Science
• Inorganic Chemistry
• Solid-State Chemistry

Background:

• Investigating quaternary systems like Cs2S/Bi/As/S is crucial for discovering novel materials with unique structural and electronic properties.
• Introducing asymmetric, isoelectronic building units ([Bi(III)(x)S(y)] and [As(III)(x)S(y)]) into a single structure presents a synthetic challenge and opportunity.

Purpose of the Study:

• To synthesize and characterize new crystalline and glassy compounds within the Cs2S/Bi/As/S quaternary system.
• To explore the structural diversity and the influence of arsenic content on the resulting material phases.
• To investigate the relationship between the structure, building units, and the optical properties (band gap) of the synthesized materials.

Main Methods:

• Solid-state reactions and fusion techniques were employed for material synthesis.
• X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and pair distribution function (PDF) analysis were used for structural and chemical characterization.
• Optical absorption measurements were performed to determine band gaps.

Main Results:

• Two crystalline compounds, Cs3Bi(AsS4)2 and Cs9Bi(AsS4)4, featuring tetrahedral [As(V)S4](3-) anions and Bi(III) centers, were synthesized.
• A glassy phase, Cs2BiAs3S7, containing As(III) species and [AsnS2n+1] fragments, was formed from arsenic-rich mixtures.
• The band gaps of the synthesized glasses (Cs(n-1)BiAs(n)S(2n+1)) range from 1.51 to 1.81 eV, while the crystalline Cs3Bi(AsS4)2 has a band gap of ~2.33 eV.

Conclusions:

• The Cs2S/Bi/As/S system can yield diverse crystalline and glassy materials by controlling the arsenic content and basicity.
• The presence of As(V) in crystalline phases and As(III) in glassy phases significantly influences the structural motifs and optical properties.
• The synthesized materials demonstrate tunable band gaps, suggesting potential applications in optoelectronics.