Ruthenium Oxide, Pb

Submitted by H. S. HOROWITZ, J. M. LONGO, and J. T. LEWANDOWSKI Checked by J. MURPHYt 

All the cited literature references to the above compounds have described solid-state syntheses at temperatures of 700-1200°. Such synthesis conditions will always lead to pyrochlore structure compounds in which all of the octa-hedrally coordinated sites are occupied by the noble metal cation, thus requiring the post-transition metal to noble metal molar ratio always to be 1.0. This paper focuses on solution medium syntheses at quite low temperatures ( 75°), thereby stabilizing a new class of pyrochlore compounds in which a variable fraction of the octahedrally coordinated sites are occupied by post-transition element cations. The specific example here involves the Pb2[Ru2 cPbJ ]06.5 series. The synthesis conditions may be simply adapted, however, to accommodate preparation of a wider range of pyrochlores which can be described by the formula A2[B2 cAx]07 j, where A is typically Pb or Bi, B is typically Ru or Ir and 0 jc 1, and 0 1. 

The synthesis method involves reacting the appropriate metal ions to yield a pyrochlore oxide by precipitation and subsequent crystallization of the precipitate in a liquid alkaline medium in the presence of oxygen. The alkaline solution serves both as a precipitating agent and as a reaction medium for crystallizing the pyrochlore, thus eliminating the need for subsequent heat treatment. 

A pyrochlore of the approximate composition Pb2[Rui.33Pbo g7]06.s may be synthesized by first preparing an aqueous solution source of lead and ruthenium cations in a 2 1 lead-to-ruthenium ratio as follows S.O g of commercially available Ru(N03)3 solution, 10% (wt.) ruthenium metal (0.005 mole ruthenium metal) is diluted with 25 mL of distilled water. Reagent grade Pb(N03)2 (3.277 g, 0.010 mole) is dissolved in 100 mL of distilled water and added to the ruthenium aqueous solution. This aqueous solution of lead and ruthenium is then stirred for approximately 10 min. 

The precipitate is then separated from the still-hot reaction medium by vacuum nitration using a fritted glass filter fuimel (350-mL Pyrex, fine frit). At the point when the precipitate is still submerged under a minimal volume of alkaline liquid, distilled water (at 75°) is added to the filtration fuimel and allowed to wash the precipitate, always taking care to keep the precipitate submerged under liquid until the nitration is complete. This procedure is carried out in the manner speciRed until all KOH is removed from the precipitate. (Phenolphthalein 

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