The physical properties of the 16 groups of elements in the periodic table change rapidly from top to bottom. Oxygen, of course, is a gas; polonium is a metal, but the ingredients in between, sulfur, selenium, and tellurium, are reliable, with their metallic properties enhanced in turn. I think tellurium (Te) is the most exciting element in this group, and its features are remarkably similar to those of most metals.
Tellurium is a rare metal. The amount in the earth's crust is about 1 PPB (one in a billion), more unique than gold, platinum, or other so-called "rare earth" elements. So why should we care about something so obscure? Borrow a phrase that George Mallory used to explain why he climbed Mount Everest, and one reason was "because it exists."
However, it is now wise to please the funders, so other reasons include meeting the essential industrial applications and developing more application potential. For realizing these applications, tellurium must satisfy industrial production as well as basic laboratory research, which brings us to the origin of tellurium.
Because tellurium is so rare and dispersed, it is not profitable to mine it. Tellurium, however, is often found in nature along with gold, silver, copper, and other valuable metals. Gold tellurides are the most common gold-bearing minerals. Tellurium, by the way, was discovered in 1782 by Austrian mineralogist Franz Josef Muller von Reichenstein in a gold mine in Hungary. Tellurium is, therefore, a by-product of the refining of the metals; The primary source is anode slime in the electrolysis of refined copper. The tellurium content in the mud averaged about two wt%. World production of tellurium has increased dramatically in recent years, reaching 500 tonnes in 2007. Moreover, the price of tellurium has been rising, as has demand.
The synthesis, structure, and properties of tellurium - containing compounds have attracted much attention in recent years. We can take tellurium compounds whose compositions have been characterized by X-ray diffraction as a reference. In the past several decades, the number of inorganic tellurium compounds has increased by about 40 percent; Organic and metallic organotellurium compounds increased by nearly 70 percent. This is a surprising number since tellurium is not essential to life. Moreover, many of the syntheses and products of tellurium chemistry smell even scarer than their sulfur homologs!
Personally, when we started working on ternary solid-state tellurides 25 years ago, we didn't know if these compounds were similar to ternary selenides. Some are similar, and some are different. The difference even extends to binary mixtures. For example, Nate exists, and NaSe is not known. If you ask a first-year chemistry student to describe Nate's structure and oxidation state, the answer is undoubtedly the well-known tendency of sulfur, selenium, and tellurium to form chains or rings, especially tellurium, unlike oxygen.
Nate is Na6Te(Te5), which contains Na+ cations and Te2− and the z-shaped Te54− anion. The z-shaped anion has two Te-Te bond lengths, 2.82 and 3.08 A, which is the difference between tellurium and sulfur. Pyrite (also known as "fool's gold" because of its golden luster) is found in FeS2, where the sulfur atoms are 2.08a apart and are of s-s single bond length. In the form of iron, the oxidation state is +II instead of the +IV that one might mistake by its formula.
All stable sulfur compounds containing s-s bonds are linked by single bonds. In contrast, stable compounds containing Te−Te may contain bonds 3.6 A or longer but still smaller than van der Waals bonds (4.1a), in addition to the regular Te−Te single relationship (2.74a). This makes the identification of formal oxidation states impossible. Tellurium's unique allotrope is stable at room temperature and appears as an infinite spiral (pictured above).In this helical structure, te-te spacing is approximately 2.83a, but there is also A short spacing of 3.49a adjacent interatomic interaction. The bonding of tellurium-bearing solid-state compounds has led to many theoretical studies that are far more interesting than their lighter homologs.
Tellurium is one of the most crucial alloy additives in the metallurgical industry. Steel and copper added with tellurium are more comfortable to process and can also be used in cast iron to minimize thermal shock and thus reduce fatigue. Another important industrial application of tellurium is as an accelerator and vulcanizer in the rubber industry. These applications do not require high purity tellurium. However, the need for high purity tellurium is growing in some new and evolving demands in the electronics industry. Tellurium, for example, is used in newly developed phase-shift memory chips and rewritable CDS, DVDs, and Blu-ray discs.
Bismuth telluride is widely used in thermoelectric cooling equipment. These devices are commonly used in electronics and consumer products. Recently more and more Bismuth telluride has been used in portable food coolers. Believe it or not, in car seat cooling systems. Tellurium's most significant impact on our lives is likely to come from cadmium telluride solar panels, which, while still in their infancy, are one of the most efficient generators. Tellurium may yet save humanity!