The phase diagram of the Ca–Si system

The phase diagram of the Ca-Si system has been investigated across almost the whole composition range (0 to 70 at% Si) using differential thermal analysis, metallographic analysis, X-ray diffraction and electron microscopy. Six intermediate phases have been found: CaSi2 (CaSi2-type), Ca14Si19 (Ca14Si19-type), Ca3Si4 (Ca3Si4-type), CaSi (CrB-type), Ca5Si3 (Cr5B3-type) and Ca2Si (anti-PbCl2-type). Ca3Si4, not previously known, is a Zintl phase representative of a new structural type: hexagonal hP42, a=854.1, c=1490.6 pm, space group P63/m. Three eutectics occur in this system: at about 3.5 at% Si and 795°C, 42.5 at% Si and 1230°C, 72.0 at% Si and 1020°C.