The conductivity is also suppressed by application of pressure (about 10 times decrease at 0.4 GPa) which reduces the mobility of lattice vacancies. It then sharply drops by two orders of magnitude because of the phase transition from the α-CsCl to β-CsCl phase. The conductivity increases with temperature up to about 450 ☌, with an activation energy changing from 0.6 to 1.3 eV at about 260 ☌. It occurs through nearest-neighbor jumps of lattice vacancies, and the mobility is much higher for the Cl - than Cs + vacancies. The conductivity has a value of the order 10 −7 S/cm at 300 ☌. ĭespite its wide band gap of about 8.35 eV at 80 K, caesium chloride weakly conducts electricity, and the conductivity is not electronic but ionic. Caesium chloride has also a relatively high solubility in formic acid (1077 g/L at 18 ☌) and hydrazine medium solubility in methanol (31.7 g/L at 25 ☌) and low solubility in ethanol (7.6 g/L at 25 ☌), sulfur dioxide (2.95 g/L at 25 ☌), ammonia (3.8 g/L at 0 ☌), acetone (0.004% at 18 °С), acetonitrile (0.083 g/L at 18 °С), ethylacetates and other complex ethers, butanone, acetophenone, pyridine and chlorobenzene. In contrast to sodium chloride and potassium chloride, caesium chloride readily dissolves in concentrated hydrochloric acid. The crystals are very hygroscopic and gradually disintegrate at ambient conditions. It readily dissolves in water with the maximum solubility increasing from 1865 g/L at 20 ☌ to 2705 g/L at 100 ☌. Physical propertiesĬaesium chloride is colorless in the form of large crystals and white when powdered. Upon heating to above 450 ☌, the normal caesium chloride structure (α-CsCl) converts to the β-CsCl form with the rocksalt structure ( space group Fm 3m). When both ions are similar in size (Cs + ionic radius 174 pm for this coordination number, Cl − 181 pm) the CsCl structure is adopted, when they are different (Na + ionic radius 102 pm, Cl − 181 pm) the sodium chloride structure is adopted. In contrast, the other alkaline halides have the sodium chloride (rocksalt) structure. This structure is shared with CsBr and CsI and many binary metallic alloys. The chloride atoms lie upon the lattice points at the edges of the cube, while the caesium atoms lie in the holes in the center of the cubes. The caesium chloride structure adopts a primitive cubic lattice with a two-atom basis, where both atoms have eightfold coordination. Spread of 137CsCl powder from a 93-gram container in 1987 in Goiânia, Brazil, resulted in one of the worst-ever radiation spill accidents killing four and directly affecting more than 100,000 people.īall-and-stick model of the coordination of Cs and Cl in CsCl Whereas conventional caesium chloride has a rather low toxicity to humans and animals, the radioactive form easily contaminates the environment due to the high solubility of CsCl in water. Another form of cancer treatment was studied using conventional non-radioactive CsCl. When enriched in radioisotopes, such as 137CsCl or 131CsCl, caesium chloride is used in nuclear medicine applications such as treatment of cancer and diagnosis of myocardial infarction. It is a reagent in analytical chemistry, where it is used to identify ions by the color and morphology of the precipitate. Ĭaesium chloride is widely used in isopycnic centrifugation for separating various types of DNA. Less than 20 tonnes of CsCl is produced annually worldwide, mostly from a caesium-bearing mineral pollucite. Caesium chloride occurs naturally in mineral waters and as an impurity in carnallite (up to 0.002%), sylvite and kainite. Caesium chloride crystals are thermally stable, but easily dissolve in water and concentrated hydrochloric acid, and therefore gradually disintegrate in the ambient conditions due to moisture. Its crystal structure forms a major structural type where each caesium ion is coordinated by 8 chlorine ions. This colorless solid is an important source of caesium ions in a variety of applications. 221, Pearson symbol cP2Įxcept where noted otherwise, data are given for materials in their standard state (at 25 ☌, 100 kPa)Ĭaesium chloride is the inorganic compound with the formula Cs Cl. Caesium chloride (see text), Pm 3m, space group No.
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