Conditions for the electrochemical synthesis of the CoPn3 (Pn = P, As, Sb) skutterudites

The binary pnietide skutterudites, CoPn(3) (Pn = P, As, Sb), have been successfully synthesized for the first time by molten salt electrolysis. The melt for depositing CoP3 contained Coo and (NaPO3)(3), and graphite rods were used for both anode and cathode. All experiments were run in a flowing N-2 gas atmosphere. By adjusting the melt composition, single phase COP3 could be prepared. Attempts were also made to deposit CoP3 using platinum and silver strip electrodes. Although COP3 powder was obtained in the crucible, no COP3 deposit was found on the Pt cathode, which was attacked by the phosphorus present in the melt and produced platinum phosphide (PtP2). A low deposition rate was observed for Ag cathodes, arid as a result, a very small amount of material was deposited. This made it difficult to determine the type and number of phases formed. Using graphite electrodes, two other cobalt skutterudites were prepared. CoAs3 was synthesized from a CoO + NaASO(2) melt and CoSb3 from a CoO + Na2CO3 + Sb2O3 melt. While the skutterudite phases were formed in these systems, the optimal melt compositions and other experimental conditions necessary to prepare single phase deposits still need to be determined. (C) 2001 The Electrochemical Society.