Phase Relations and Crystal Structures in the Ternary Systems Sr‐{Ag, Au}‐{Si, Ge}

Phase equilibria in the isothermal sections of the ternary systems Sr‐{Ag, Au}‐{Si, Ge} were determined in the (Si) or (Ge) rich part up to 33.3 at % Sr after annealing at 700 °C (Sr‐{Ag, Au}‐Ge) or 800 °C (Sr‐{Ag, Au}‐Si). Tentative liquidus projections were constructed for the Si, Ge‐rich part of all the four phase diagrams. These systems are characterized by a series of ternary compounds, exhibiting in some cases extended homogeneity regions at a constant Sr content. Compounds in the Si, Ge‐rich region essentially form along two sections: at 33.3 at % Sr (AlB 2 ‐family) and at 20 at % Sr (BaAl 4 ‐family of structure types). The crystal structures of the novel equilibrium phases were derived by X‐ray single crystal diffraction: Sr 2 Ag 1+ x Si 3– x – y □ y [Sr 2 LiSi 3 type; x = 0.17, y = 0.43: a = 8.4488(2), b = 14.6376(2), c = 18.4018(2) Å], SrAg 2– x Si 2+ x [ThCr 2 Si 2 type; x = 0.1: a = 4.37664(6), c = 10.4517(2) Å], Sr(Au 1– y □ y )(Si 1– x Au x ) 3 [BaNiSn 3 type; x = 0.59, y = 0.64: a = 4.4594(2), c = 10.1013(6) Å] and SrAu 5– x □ x Si 2 [BaAu 5 Si 2 type; x = 0.7: a = 8.7557(3), b = 6.9945(2), c = 9.8873(3) Å]. The crystal structures of Sr(Ag x Ge 1– x ) 2 [AlB 2 type; x = 0.25: a = 4.3431(2), c = 4.5938(1) Å], SrAg 2– x Ge 2+ x [ThCr 2 Si 2 type; x = 0.2: a = 4.4476(2), c = 10.822(1) Å] and Sr(Au x Ge 1– x ) 2 [AlB 2 type; x = 0.25: a = 4.3263(2), c = 4.5852(7) Å] were evaluated by X‐ray powder Rietveld analysis. Composition dependent polymorphism was observed among the BaAl 4 ‐type derivative structures for SrAu 2– x Ge 2+ x : CaBe 2 Ge 2 type [ x = 0.45: a = 4.4796(2), c = 10.6315(5) Å], BaCu 2 Sb 2 type [ x = 0.35: a = 4.4866(2), c = 31.808(1) Å] and ThCr 2 Si 2 type [ x = 0.2: a = 4.5214(4), c = 10.336(1) Å]. Similarly, Sr(Au x Si 1– x ) 2 exhibits the Ca 2 AgSi 3 structure type [ x = 0.25: a = 8.3407(2), b = 14.4465(2) and c = 9.2664(3) Å] and the AlB 2 type [ x = 0.375: a = 4.2241(2), c = 4.5799(3) Å]. The structural chemistry of the BaAl 4 derivative structures within the sections SrT 2– x X 2+ x is discussed.