1s² 2s²p⁶ 3s²p⁶d¹⁰ 4s²p⁶d¹⁰ 5s²p⁴

Characteristics

Tellurium is a relatively rare element, in the same chemical family as Oxygen, Sulfur, Selenium, and Polonium (the Chalcogens).

Silvery white metal-looking non-metal that is usually obtained as a dark grey powder.  It is unaffected by water and HCl, but burns in air or oxygen and dissolves in HNO₃.

When crystalline, Tellurium is silvery-white and when it is in its pure state it has a metallic luster.  This is a brittle and easily pulverized metalloid.  Amorphous Tellurium is found by precipitating it from a solution of Tellurous or Telluric Acid (Te(OH)₆). However, there is some debate whether this form is really amorphous or made of minute crystals.

Tellurium is a p-type semiconductor that shows a greater conductivity in certain directions which depends on atomic alignment.  Chemically related to Selenium and Sulfur, the conductivity of this element increases slightly when exposed to light.

It can be doped with Copper, Gold, Silver, Tin, or other metals. When in its molten state, Tellurium is corrosive to Copper, Iron, and stainless steel.

Tellurium gives a greenish-blue flame when burned in normal air and forms Tellurium Dioxide as a result.

Occurrence

Tellurium is found free in nature (native elemental form), but is most often found in the Telluride ores of Gold: Sylvanite (AgAuTe₄), Calaverite (AuTe₂) and Krennerite (AuTe₂).  Tellurium compounds are the only chemical compounds of Gold found in nature, but Tellurium itself (unlike Gold) is also found combined with other elements (in metallic salts). The principal source of Tellurium is from anode sludges produced during the electrolytic refining of blister Copper.  It is a component of dusts from blast furnace refining of Lead.  Tellurium is produced mainly in the United States, Canada, Peru, and Japan.

Commercial-grade Tellurium is usually marketed as minus 200-mesh powder but is also available as slabs, ingots, sticks, or lumps. The year-end price for Tellurium in 2000 was $14 per pound.

Applications

Metal Alloys

• It is mostly used in alloys with other metals.  It is added to Lead, Pb, to improve its strength and durability, and to decrease the corrosive action of Sulfuric Acid, H₂SO₄.   When added to stainless steel and Copper, Cu, it makes these metals more workable.   It is alloyed into cast iron for chill control.

Semiconductor Industry Uses:

• Bismuth Telluride (Bi₂Te₃) has found use in thermoelectric devices.

• Tellurium has potential applications in Cadmium Telluride (CdTe) solar panels.   Some of the highest efficiencies for solar cell electric power generation have been obtained by using this material, but this application has not yet caused demand to increase significantly.  If some of the Cadmium in CdTe is replaced by Zinc then CdZnTe is formed which is used in solid-state x-ray detectors.

• Alloyed with both Cadmium, Cd,  and Mercury, Hg, to form Mercury Cadmium Telluride, an infrared sensitive semiconductor material is formed.  Organotellurium compounds such as Dimethyl Telluride (CH₃)₂Te, Diethyl Telluride (CH₃CH₂)₂Te, Diisopropyl Telluride (CH₃)₂CHTe, Diallyl Telluride and Methyl Allyl Telluride are used as precursors for MOVPE growth of II-VI compound semicondictors.  Diisopropyl Telluride (DIPTe) is employed as the preferred precursor for achieving the low temperature growth of CdHgTe by MOVPE.

Other Uses:

• Used in ceramics. 
• It is used in chalcogenide glasses. 
• Tellurium is also used in blasting caps.
• Organic tellurides have also been employed as initiators for living radical polymerisation and electron-rich mono- and di-tellurides possess antioxidant activity.

High purity metalorganics of both Selenium and Tellurium are reported to be obtained by using innovative chemical purification strategy, also called adduct purification. These high purities are often required for semiconductor industry uses.

Compounds

Tellurium forms many compounds, but none that are commercially important.  They include:

Tellurium is in the same series as Sulfur and Selenium and forms similar compounds.   A compound with metal or Hydrogen and similar ions is called a Telluride.   Gold and Silver Tellurides are considered good ores.  Compounds with tellurate ions complexes TeO₄^2- or TeO₆^6- are known as Tellurates.  Also Tellurites, TeO₃^2-.  Also Tellurols –TeH, named with prefix tellanyl- or suffix -tellurol.

Isotopes

There are 30 known isotopes of Tellurium with atomic masses that range from 108 to 137. Naturally found tellurium consists of eight isotopes (listed in the table to the right); three of them are observed to be radioactive. ¹²⁸Te has the longest known half-life, 2.2×10²⁴ years, among all radioactive isotopes. Tellurium is the first element which can undergo Alpha Decay, with isotopes ¹⁰⁶Te to ¹¹⁰Te being able to undergo this mode of decay.

Precautions

Tellurium and Tellurium compounds should be considered to be mildly toxic and need to be handled with care.  Acute poisoning is rare.  Tellurium is not reported to be carcinogenic.

Humans exposed to as little as 0.01 mg/m³ or less in air develop "Tellurium Breath", which has a garlic-like odor.  The garlic odor that is associated with human intake of Tellurium compounds is caused from the Tellurium being metabolized by the body. When the body metabolizes Tellurium in any oxidation state, the Tellurium gets converted into Dimethyl Telluride, (CH₃)₂Te.  Dimethyl Telluride is volatile and produces the garlic-like smell.

(L. tellus, earth) Discovered by Muller von Reichenstein in 1782; named by Klaproth, who isolated it in 1798.  Tellurium is occasionally found native, but is more often found as the telluride of Gold (Calaverite), and combined with other metals.  It is recovered commercially from the anode muds produced during the electrolytic refining of blister copper.  The U.S., Canada, Peru, and Japan are the largest Free World producers of the element.  Crystalline Tellurium has a silvery-white appearance, and when pure exhibits a metallic luster.  It is brittle and easily pulverized.   Amorphous Tellurium is found by precipitating Tellurium from a solution of Telluric or Tellurous Acid, (Te(OH)₆).  Whether this form is truly amorphous, or made of minute crystals, is open to question.  Tellurium is a p-type semiconductor, and shows greater conductivity in certain directions, depending on alignment of the atoms.  Its conductivity increases slightly with exposure to light.  It can be doped with Silver, Copper, Gold, Tin, or other elements.  In air, Tellurium burns with a greenish-blue flames, forming the dioxide.  Molten Tellurium corrodes Iron, Copper, and stainless steel.   Tellurium and its compounds are probably toxic and should be handled with care. Workmen exposed to as little as 0.01 mg/m³ of air, or less, develop "Tellurium Breath," which has a garlic-like odor.  Thirty isotopes of tellurium are known, with atomic masses ranging from 108 to 137.  Natural Tellurium consists of eight isotopes. Tellurium improves the machinability of Copper and stainless steel, and its addition to lead decreases the corrosive action of Sulfuric Acid, H₂SO₄, on Lead and improves its strength and hardness.   Tellurium is used as a basic ingredient in blasting caps, and is added to cast Iron for chill control. Tellurium is used in ceramics.  Bismuth Telluride (Bi₂Te₃) has been used in thermoelectric devices. Tellurium costs about $100/lb, with a purity of about 99.5%.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond

Tellurium was discovered by Franz Joseph Müller von Reichenstein, a Romanian mining official, in 1782.  Reichenstein was the chief inspector of all mines, smelters and saltworks in Transylvania.  He also had an interest in chemistry and extracted a new metal from an ore of Gold, known as Aurum Album, which he believed was Antimony.  He shortly realized that the metal he had produced wasn't antimony at all, but a previously unknown element.  Reichenstein's work was forgotten until 1798 when Martin Heinrich Klaproth, a German chemist, mentioned the substance in a paper.   Klaproth named the new element Tellurium but gave full credit for its discovery to Reichenstein.