Tellurium

Tellurium is a rare, brittle, silvery-white metalloid with the chemical symbol Te and atomic number 52. Chemically related to selenium and sulphur, it displays properties intermediate between metals and non-metals. Though discovered in 1782 by Franz-Joseph Müller von Reichenstein, tellurium remained little used for more than a century due to its scarcity and limited availability. In the modern era, however, tellurium has gained prominence owing to its valuable roles in metallurgy, electronics, solar energy, and thermoelectric applications. Its unique electrical and semiconductor characteristics make it a material of growing industrial and strategic interest.

Physical and Chemical Characteristics

Tellurium is a lustrous, brittle crystalline solid with a metallic sheen and relatively low abundance in the Earth’s crust—comparable to that of platinum. It melts at 449.5°C and boils at 989.8°C. In its crystalline form, tellurium conducts electricity better along certain directions, giving it semiconducting properties.
Chemically, tellurium exhibits multiple oxidation states ranging from –2 to +6, forming compounds with metals and non-metals alike. It readily combines with metals to form tellurides and with oxygen to form tellurium dioxide (TeO₂). Tellurium and its compounds are generally stable but can produce toxic fumes when heated or burned.
Tellurium is most often recovered as a by-product of copper, lead, or gold refining, since it occurs in small quantities within anode slimes during electrolytic extraction processes.

Everyday Applications

While tellurium does not appear directly in household items, its properties influence many technologies that affect everyday life.

• Electronics and Data Storage: Tellurium compounds are vital in optical data storage devices such as rewritable CDs, DVDs, and Blu-ray discs. In these systems, tellurium-based alloys (often with germanium and antimony) serve as the phase-change material that switches between amorphous and crystalline states to encode digital data.
• Solar Panels: Tellurium plays a key role in cadmium telluride (CdTe) thin-film solar cells, which are among the most cost-effective and efficient photovoltaic technologies available. CdTe panels convert sunlight into electricity efficiently even under diffuse light or high temperatures, making them widely used in large-scale solar farms.
• Thermoelectric Devices: Tellurium-based materials such as bismuth telluride (Bi₂Te₃) are used in thermoelectric modules that convert heat directly into electricity. These devices are found in refrigerators, portable coolers, power generators for spacecraft, and electronic temperature controllers.
• Alloying and Metallurgical Uses: Tellurium is used in small quantities to improve the machinability and performance of metals:
  • Steel and copper alloys containing tellurium exhibit greater ease of cutting, enhanced strength, and better electrical conductivity.
  • Lead-tellurium alloys improve the durability of lead-acid battery grids.
  • Stainless steel and cast iron alloys with tellurium resist fatigue and corrosion better, extending service life in industrial and mechanical components.
• Rubber and Glass Industries: Tellurium compounds act as vulcanising agents in rubber production and as colouring agents in glass and ceramics. Tellurium dioxide can impart a blue or brown tint to glass, and small additions improve optical and thermal properties.

Though tellurium is rarely visible in consumer products, it underpins the operation of many everyday technologies that rely on efficient energy conversion and durable materials.

Industrial Applications

Tellurium’s industrial relevance lies primarily in its semiconductor and metallurgical roles, where small quantities produce large performance improvements.

• Semiconductors and Electronics: Tellurium forms part of several key semiconductor materials used in high-performance applications:
  • Cadmium telluride (CdTe): for thin-film solar cells.
  • Bismuth telluride (Bi₂Te₃): for thermoelectric generators and coolers.
  • Mercury cadmium telluride (HgCdTe): for infrared detectors, night-vision equipment, and heat-seeking sensors.These compounds are valued for their tunable electrical and optical properties, allowing precise control of conductivity and light absorption.
• Metal Refining and Alloying: Small additions of tellurium to copper and steel improve machining performance, enabling faster manufacturing with reduced tool wear. Tellurium is also added to lead for producing corrosion-resistant cable sheathing and battery components.
• Chemical Industry: Tellurium compounds serve as catalysts, pigments, and vulcanising agents. Tellurium dioxide is used as a catalyst in synthetic fibre production, while organotellurium compounds find research applications in organic synthesis.
• Thermoelectric Power Generation: Tellurium-based thermoelectric materials are critical in aerospace and remote energy systems, where reliability and self-sufficiency are essential. Spacecraft such as satellites and planetary probes have utilised thermoelectric generators using tellurium compounds to convert heat from radioactive decay into electricity.

Economic Importance and Market Dynamics

Tellurium’s economic significance is disproportionate to its small global production. Its strategic role in renewable energy and high-technology sectors makes it a critical raw material.

• Production and Sources: Annual global tellurium production is estimated at around 500–600 tonnes, primarily as a by-product of copper refining. The largest producers include China, the United States, Japan, Russia, and Canada. Tellurium is also recovered from lead-zinc smelters and gold ore residues.
• Market Demand: The solar energy sector is the dominant consumer of tellurium, accounting for more than half of global demand due to its use in CdTe photovoltaic panels. Additional demand arises from thermoelectric devices, steel alloys, and electronic applications.
• Price and Availability: Because tellurium is produced only as a secondary by-product, its supply depends heavily on the volume of base-metal mining and refining. Market fluctuations in copper or gold output directly affect tellurium availability. Consequently, prices can vary significantly. In recent years, the increasing demand from the solar industry has raised concerns about long-term supply security.
• Recycling and Recovery: Recycling from end-of-life solar panels and electronic waste is emerging as an important source of tellurium. Efficient recovery processes are being developed to meet growing demand sustainably and reduce reliance on limited primary resources.

Environmental and Health Considerations

Tellurium and its inorganic compounds are relatively low in toxicity, but some volatile or organotellurium compounds can be hazardous if inhaled or ingested. A characteristic symptom of exposure is a garlic-like odour on the breath due to tellurium metabolism in the body.
Environmental concerns primarily relate to industrial waste and refining residues, which can release tellurium into soil or water systems. However, these risks are generally well managed under modern environmental regulations. The use of tellurium in solar and thermoelectric technologies contributes positively to sustainability by supporting renewable energy generation and reducing greenhouse gas emissions.

Emerging and Technological Applications

Tellurium continues to attract research interest due to its unusual electronic structure and compatibility with new technologies.

• Next-generation Semiconductors: Tellurium-based materials, such as two-dimensional tellurene, are being explored for flexible electronics, transistors, and quantum devices.
• Energy Storage: Tellurium is under investigation as an additive in lithium–tellurium and sodium–tellurium batteries, where it may improve energy density and cycling stability.
• Thermoelectric Innovation: New tellurium compounds with enhanced thermal-to-electric conversion efficiency promise applications in waste-heat recovery and wearable power generators.

These developments position tellurium as an essential element for the energy transition, bridging materials science, electronics, and sustainability.

Economic Outlook

The future outlook for tellurium is shaped by its strategic role in clean energy, particularly thin-film solar photovoltaics and thermoelectric devices. With increasing global emphasis on renewable energy and energy efficiency, demand for tellurium is expected to rise steadily.