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Chemistry of the Elements CHEMISTRY OF THE ELEMENTS Seminar Presentation Presented by Anh & Lotta Tellurium (Te) Content • Introduction • Discovery and development • Resources and production • Chemical properties • Reactivity • Compounds • Risks and hazard • Applications Introduction Group 16 Melting point 449.51°C Period 5 Boiling point 988°C Block p Density (g cm−3) 6.232 Atomic number 52 Atomic mass 127.60 State at 20°C Solid Key isotopes 130Te Electron [Kr] 4d105s25p4 configuration • The Earth-like reflects the origin of the element’s name, after tellus, the Latin word for Earth • The rarest stable solid element in the Earth’s crust: it’s abundance is about 1 μg/kg • Tellurium is used in alloys, mostly with copper and stainless steel, to improve their machinability • When added to lead it makes it more resistant to acids and improves its strength and hardness • Tellurium is a metalloid and very toxic Discovery and development • Tellurium was discovered in 1782 by Franz Joseph Müller von Reichenstein at Romania • Tellurium was first observed in ores mined in the gold district of Transylvania • He first assumed it was bismuth • After 3 years of researching ores, he proved it was a new element and called it metallum problematicum (difficult metal) • In 1796, Heinrich Klaproth confirmed his finding and decided to call it tellurium Tellurium resources and production • More than 90% of tellurium has been produced from anode slimes collected from electrolytic copper refining • The remainder was derived from skimming at lead refineries and from flue dusts and gases generated during the smelting of bismuth, copper, and lead-zinc ores • Potential sources of tellurium include bismuth telluride and gold telluride ores • China, Japan, and Sweden are the world leading Tellurium producers Refinery Production (In tons) Reserves in tons 2017 2018 United States W W 3500 Bulgaria 5 5 NA Canada 49 30 800 China 290 300 6600 Japan 38 36 _ Russia 44 35 NA South Africa 7 7 _ Sweden 35 32 670 Other Countries NA NA 16000 World Total 470 440 31000 (Rounded) Chemical properties ● Tellurium is rare, silver white, brittle metalloid ● Tellurium burns in air with greenish blue flame and forms white TeO2 ● When crystalline, Te is silvery white with metallic luster ● Te is chemically related to selenium and sulfur ● Common oxidation states: -2, 4, 6 Tellurium Reactivity • Te has great electrical conductivity and photoconductivity (conductivity increases when exposed to light) • Te has the highest boiling and melting points in group 6 • When Te is in molten state, it’s corrosive to copper, iron, and stainless steel • Tellurium is uneffected by water or hydrochloric acid, but dissolves in nitric acid Tellurium Compounds ● Hydrogen telluride H2Te ● Polytellurides ● Halides ○ Fluorides TeF4 and TeF6 ○ Chlorides TeCl4, Te2Cl and Te3Cl2 ● Oxides TeO2 and TeO3 ● Telluric acid H6TeO6 Risks and hazard • Elemental tellurium dusts may cause irritation of the respiratory tract and other symptoms like • metallic taste • loss of appetite • dryness of the mouth • nausea and headache • garlic odor of breath, sweat and urine • Tellurium compounds are more toxic than metallic tellurium • They are teratogenic (may affect the development of an embryo or fetus) • Te compounds are readily absorbed by the body and excreted to the breath and perspiration • Reacts vigorously with halogens causing fire hazard Tellurium Applications Photovoltaics 40 % Thermoelectrics 30 % Metallurgy 15 % • Tellurium was first used to improve the vulcanization of rubber Rubber 5 % Other 10 % • Tellurium can be used • to tint glass and ceramics • as a catalyst in oil refining • in semiconductor applications doped with silver, gold, copper or tin • in metallurgical alloys • Latest interest conserns the use of cadmiun telluride CdTe in photovoltaics and thermoelectric devices Overcoming Carrier Concentration Limits in Polycrystalline CdTe Thin Films with In Situ Doping McCandless, B.E., Buchanan, W.A., Thompson, C.P. et al. Overcoming Carrier Concentration Limits in Polycrystalline CdTe Thin Films with In Situ Doping. Sci Rep 8, 14519 (2018) doi:10.1038/s41598-018- 32746-y. • Thin film material CdTe offers the potential of lower solar module capital costs and improved performance of microcrystalline silicon • It has been difficult to control the hole and electron concentration in this material • Increasing CdTe hole density without compromising lifetime in thin polycrystalline CdTe films can increase solar cell efficiency significantly • Hole density exceeding 10-16/cm3 could be achieved with in-situ doping (process where impurity/dopant is added during deposition) coupled with manufacturing methods • Doping CdTe with group V elements (P/As/Sb) • A short post-growth anneal in Cd vapor • Fast cooling • P-type conductivity in CdTe could be obtained • This method improved the ability to incorporate dopant uniformly throughout the film • Conclusions • Longstanding carrier concentration limitations in polycrystalline CdTe films are overcome • Carefully controlled in-situ doping and anneals provide new paths for controlling carrier concentration in polycrystalline thin films → low cost solar energy and other thin film semiconductor applications References • Housecroft, C. E., Sharpe, A. G. 2012. Inorganic chemistry. 4th Edition. GB: Pearson Education. • Greenwood, N.N. Earnshaw, A. 1997. Chemistry of the Elements. 2nd Edition. Elsevier. • McCandless, B.E., Buchanan, W.A., Thompson, C.P. et al. 2018. Overcoming Carrier Concentration Limits in Polycrystalline CdTe Thin Films with In Situ Doping. Sci Rep 8, 14519. doi:10.1038/s41598-018- 32746-y. • National Minerals Information Center. 2019. Selenium and Tellurium Statistics and Information. Read 19.11.2019. https://www.usgs.gov/centers/nmic/selenium-and-tellurium-statistics-and- information • Trouba, J. & Anderson, C. 2019. Tellurium; Supply and Applications. Colorado School of Mines. Poster. https://www.researchgate.net/publication/330986012_Tellurium_Supply_and_Applications • Lenntech BV. nd. Periodic Table: Tellurium – Te. Read 19.11.2019. https://www.lenntech.com/periodic/elements/te.htm • Goldfarb, R. 2015. Tellurium - The Bright Future of Solar Energy. USGS Mineral Resources Program. https://pubs.usgs.gov/fs/2014/3077/pdf/fs2014-3077.pdf.
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