Basic properties, such as the phase relationship, crystal structure, and energy gap Eg, have been investigated in Sr-rich Sr1-xBaxSi2. Sr1-xBaxSi2 (0 <= x <= 1.0) has two phases: one with the SrSi2-type structure and another with the BaSi2-type structure. The SrSi2 phase exists at x ranging from 0 to 0.13, and the BaSi2 phase exists at x ranging from 0.24 to 1.0. The volume increases with x in both the SrSi2 and BaSi2 phases. A volume jump of 13.7% appears at the structural phase transition from the SrSi2 phase to the BaSi2 phase. Eg increases with x in SrSi2-phase Sr1-xBaxSi2 but Eg decreases with x in the BaSi2-phase Sr1-xBaxSi2. In Sr-rich BaSi2-phase Sr1-xBaxSi2, Ba atoms at a specific crystallographic site, the A1 site, are preferentially substituted by Sr atoms, as well as in Ba-rich BaSi2-phase Sr1-xBaxSi2. (C) 2011 Elsevier B. V. All rights reserved.