New phases in the Yb-Au-Si and Ca-Au-Si systems

The YbAu2-xSix and CaAu2-xSix systems were studied by X-ray techniques in t he range 0.7 less than or equal to x less than or equal to 1.3. The YbAuSi compound forms peritectically at 1478 K and is stable till 1168 K in its hi gh-temperature form (EuAuGe type); below 1168 K the SrAgGe type occurs. No equiatomic compound exists in the Ca-Au-Si system. In the gold- and silicon -rich regions the two systems show similar structural behaviour: the gold-r ich phases belong to the CeCu2 or the EuAuGe type, while the silicon-rich p hases crystallize in the AlB2 type. The magnetic susceptibility at room tem perature indicates the divalency of ytterbium in YbAuSi.