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 the range 0.7 ≤ x ≤ 1.3. The YbAuSi compound forms peritectically at 1478 K and is stable till 1168 K in its high-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-rich phases belong to the CeCu2 or the EuAuGe type, while the silicon-rich phases crystallize in the AlB2 type. The magnetic susceptibility at room temperature indicates the divalency of ytterbium in YbAuSi.