Tellurium (Te, atomic number 52) is a naturally occurring element that exists as a solid under Standard Temperature and Pressure (STP) conditions. Its name comes from the Latin word tellus meaning “Earth.” Tellurium is a relatively rare material found in the Earth’s crust, often as a byproduct of copper and lead refining processes. This element possesses characteristics that place it on the boundary between metals and nonmetals, defying simple classification.
The Physical State of Tellurium
At standard room temperature, tellurium is a silvery-white solid with a metallic luster, resembling elements like tin or antimony. This crystalline form is the most stable state, existing in a hexagonal structure of parallel chains of atoms. Despite its metallic appearance, pure tellurium is noticeably brittle and can be easily pulverized into a gray powder, a trait associated with nonmetallic elements.
Tellurium remains a solid until it reaches its melting point of approximately 449.5°C (841°F), where it transforms into a liquid state. Its boiling point is reached at about 988°C (1,810°F), converting the element into a gas. The wide range between its melting and boiling points shows that substantial heat energy is required to complete these phase changes.
Classification as a Metalloid
Tellurium is located in Group 16 of the Periodic Table, alongside oxygen, sulfur, and selenium (the chalcogens). Unlike its lighter counterparts, tellurium sits on the dividing line between metals and nonmetals, earning it the designation of a metalloid or semimetal. This classification means the element exhibits a mix of properties from both major groups.
Tellurium’s defining characteristic as a metalloid is its behavior as a semiconductor. This means its ability to conduct electricity is greater than that of nonmetals, but significantly lower than that of true metals. Furthermore, its conductivity is not uniform; it shows greater electrical flow in certain directions depending on the alignment of its atoms in the crystal structure.
Tellurium also exhibits a property known as photoconductivity, where its electrical conductivity increases upon exposure to light. This sensitivity to light, coupled with its tunable electrical properties, makes it an invaluable material in the construction of sophisticated electronic components.
Key Applications in Modern Technology
The unique semiconducting and thermal properties of tellurium have secured its place in modern high-tech industries. One recognized use is in the production of thin-film solar cells, which utilize cadmium telluride (CdTe). These CdTe solar panels efficiently convert sunlight into electricity and are a major component of the renewable energy sector.
Tellurium plays a significant role in devices that manage or generate energy from heat. When alloyed with elements like bismuth or lead, it forms compounds used in thermoelectric applications. These devices can generate electrical power from a temperature difference, such as capturing waste heat, or use electricity to create a cooling effect for refrigeration or cooling electronic components.
A substantial portion of tellurium is used as an alloying agent in metallurgy. Adding a small amount of tellurium to materials like copper and stainless steel greatly improves their machinability, allowing them to be cut and shaped more easily in manufacturing processes. This alloying property increases the production efficiency of metal parts for various industries. Tellurium compounds are also utilized in phase-change memory chips, which are a type of non-volatile computer memory, as well as in rewritable optical discs like DVDs.