Silver(I) selenide
Silver(I) selenide (Ag2Se) is an inorganic chemical compound composed of silver and selenium. It exists as a black solid at room temperature and is a well-known thermoelectric material.
Properties:
- Chemical Formula: Ag2Se
- Molar Mass: 341.68 g/mol
- Appearance: Black solid
- Crystal Structure: Exists in multiple crystalline phases depending on temperature. At low temperatures (below ~130 °C), it adopts a monoclinic structure (α-Ag2Se). Above this temperature, it transforms to a body-centered cubic (β-Ag2Se) structure. The high-temperature phase is a superionic conductor, exhibiting high silver ion mobility.
- Electrical Properties: Semiconductor in the low-temperature phase. The high-temperature phase exhibits mixed ionic and electronic conductivity.
- Thermoelectric Properties: Exhibits promising thermoelectric properties, particularly in the high-temperature superionic phase. This is due to the combination of high electrical conductivity and low thermal conductivity.
Synthesis:
Silver(I) selenide can be synthesized through various methods, including:
- Direct reaction of silver and selenium at elevated temperatures.
- Reaction of silver nitrate with a selenium source, such as sodium selenosulfate.
- Electrodeposition techniques.
Applications:
- Thermoelectric Materials: The most significant application of silver(I) selenide is in thermoelectric devices, which can convert heat energy directly into electrical energy and vice versa. The high thermoelectric figure of merit (ZT) in the high-temperature phase makes it suitable for high-temperature thermoelectric applications.
- Infrared Detectors: Its sensitivity to infrared radiation makes it useful in infrared detectors.
- Photovoltaic Cells: It has been explored as a potential material for use in thin-film photovoltaic cells.
- Chemical Sensors: Its electrical properties are sensitive to changes in the environment, making it useful in chemical sensors.
Safety:
Selenium compounds are generally considered toxic. Silver(I) selenide should be handled with care, using appropriate personal protective equipment (PPE) such as gloves and eye protection. Avoid inhalation and ingestion. Consult safety data sheets (SDS) for detailed safety information.