Conditions for the electrochemical synthesis of the CoPn(3) (Pn = P, As, Sb) skutterudites

The binary pnietide skutterudites, CoPn(3) (Pn = P, As, Sb), have been succ essfully synthesized for the first time by molten salt electrolysis. The me lt 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 si lver strip electrodes. Although COP3 powder was obtained in the crucible, n o COP3 deposit was found on the Pt cathode, which was attacked by the phosp horus present in the melt and produced platinum phosphide (PtP2). A low dep osition rate was observed for Ag cathodes, arid as a result, a very small a mount of material was deposited. This made it difficult to determine the ty pe and number of phases formed. Using graphite electrodes, two other cobalt skutterudites were prepared. CoAs3 was synthesized from a CoO + NaASO(2) m elt and CoSb3 from a CoO + Na2CO3 + Sb2O3 melt. While the skutterudite phas es were formed in these systems, the optimal melt compositions and other ex perimental conditions necessary to prepare single phase deposits still need to be determined. (C) 2001 The Electrochemical Society.