Effect of heat treatment of pure and carbon-polluted rhodium samples on the low-temperature resistivity

We present a systematic investigation of conditions for heat treatment of R h with the aim of increasing the residual resistivity ratio (RRR). The maxi mal value of RRR for a 25 mum thick foil was found to be 1050 and the optim al treatment conditions were high temperatures, above 1400 degreesC, and a low pressure of pure oxygen, around 1 mu bar. Another batch of foils, conta ining less magnetic impurities, showed an RRR of only 600. A 0.4 mm thick s ingle crystal was heat treated to an RRR value of 740. Our findings are dis cussed in the light of a model with magnetic and non-magnetic impurities in Rh, where the latter is found to have an important contribution for this u nusual metal. Especially carbon impurities were found to be quite detriment al for the resistivity, and the recovery of the RRR after a carbon contamin ation is extremely slow in subsequent heat treatments. (C) 2001 Kluwer Acad emic Publishers.