Rubidium silver iodide

Rubidium silver iodide, formula RbAg₄I₅, is an unusually conductive crystal, with the conductivity involving movement of the silver ions within the crystal lattice. It was discovered while searching for chemicals which had the ionic-conductivity properties of alpha-phase silver iodide at temperatures below the 146 °C for AgI.cite book |title=Solid State Chemistry: An Introduction |author=Smart, Lesley and Elaine A. Moore |year=2005 |publisher=CRC Press |pages=p. 192 |isbn=0748775161 |url=http://books.google.com/books?id=vDPZLVAoRqQC&pg=PA192&lpg=PA192&dq=rbag4i5&source=web&ots=RSbWo9uwAP&sig=TxjgzGpzB1vUbQ1EwLXaGW3f89A]

It can be formed by melting together [cite journal |title=Phase analysis of RbAg4I5 crystals grown in microgravity |author=Popov, A. S.; Kostandinov, I. Z.; Mateev, M. D.; Alexandrov, A. P.; Regel, Liia L. |journal=Microgravity Science and Technology |volume=3 |year=1990 |pages= 41–43 |month=May | bibcode = 1990MiST....3...41P] or grinding together [cite journal |title=Mechano-chemical Synthesis of RbAg4I5 and KAg4I5 Crystals and Their Silver Ion Conducting Properties |author=Peng H.; Machida N. Shigematsu T. |journal=Journal of the Japan Society of Powder and Powder Metallurgy
volume=49 |issue=2 |pages= 69–74 |year=2002 |url=http://sciencelinks.jp/j-east/article/200207/000020020702A0227545.php] stoichiometric quantities of rubidium iodide and silver (I) iodide. The published conductivity is 25 siemens per metre (IE a 1mm x 1mm x 1cm bar would have a resistance of 400 ohms along the long axis).

The crystal structure is composed of sets of iodine tetrahedra sharing faces, through which the silver ions are able to diffuse. [cite journal |title=Crystal Structure of the Solid Electrolyte, RbAg4I5 |first=S. |last=Geller |journal=Science |month=July |year=1967 |volume=157 |issue=3786 |doi=10.1126/science.157.3786.310 |pages= 310–312]

It was proposed around 1970 as a solid electrolyte for batteries, and has been used in conjunction with electrodes of silver and of RbI₃.

Rubidium silver iodide –family is a group of compounds and solid solutions which are isostructural with the RbAg₄I₅ alpha modification. The examples of such advanced superionic conductors with mobile Ag⁺- and Cu⁺-cations are: KAg₄I₅, NH₄Ag₄I₅, K_1-xCs_xAg₄I₅, Rb_1-xCs_xAg₄I₅, CsAg₄Br_1-xI_2+x, CsAg₄ClBr₂I₂, CsAg₄Cl₃I₂, RbCu₄Cl₃I₂, KCu₄I₅ and others [5-8] .

References

[5] Geller S., Akridge J.R., Wilber S.A. Crystal structure and conductivity of the solid electrolyte α-RbCu₄Cl₃I₂ // Phys. Rev. B 1979. V.19. P. 5396 – 5402.

[6] Hull S. Keen D.A., Sivia D.S., Berastegui P. Crystal Structures and Ionic Conductivities of Ternary Derivatives of the Silver and Copper Monohalides - I. Superionic Phases of Stoichiometry MAg₄I₅: RbAg₄I₅, KAg₄I₅, and KCu₄I₅ // J.Solid State Chemistry 2002. V. 165. P. 363-371.

[7] Despotuli A.L., Zagorodnev V.N., Lichkova N.V., Minenkova N.A. New high conductive CsAg₄Br_1-xI_2+x (0.25 < x <1) solid electrolytes // Sov. Phys. Solid State 1989. V.31. P. 242-244.

[8] Lichkova N.V., Despotuli A.L., Zagorodnev V.N., Minenkova N.A., Shahlevich K.V. Ionic conductivity of solid electrolytes in the two- and three-components AgX –CsX (X = Cl, Br, I) glass-forming systems // Sov. Electrochem. 1989. V.25. P.1636-1640.