RbCa3 is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. Rb(1) is bonded to four equivalent Ca(2) and eight equivalent Ca(1) atoms to form RbCa12 cuboctahedra that share corners with four equivalent Rb(1)Ca12 cuboctahedra, corners with eight equivalent Ca(2)Rb4Ca8 cuboctahedra, edges with eight equivalent Rb(1)Ca12 cuboctahedra, edges with sixteen equivalent Ca(1)Rb4Ca8 cuboctahedra, faces with four equivalent Rb(1)Ca12 cuboctahedra, faces with six equivalent Ca(2)Rb4Ca8 cuboctahedra, and faces with eight equivalent Ca(1)Rb4Ca8 cuboctahedra. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to four equivalent Rb(1), four equivalent Ca(1), and four equivalent Ca(2) atoms to form CaRb4Ca8 cuboctahedra that share corners with twelve equivalent Ca(1)Rb4Ca8 cuboctahedra, edges with eight equivalent Rb(1)Ca12 cuboctahedra, edges with eight equivalent Ca(1)Rb4Ca8 cuboctahedra, edges with eight equivalent Ca(2)Rb4Ca8 cuboctahedra, faces with four equivalent Rb(1)Ca12 cuboctahedra, faces with four equivalent Ca(2)Rb4Ca8 cuboctahedra, and faces with ten equivalent Ca(1)Rb4Ca8 cuboctahedra. In the second Ca site, Ca(2) is bonded to four equivalent Rb(1) and eight equivalent Ca(1) atoms to form CaRb4Ca8 cuboctahedra that share corners with four equivalent Ca(2)Rb4Ca8 cuboctahedra, corners with eight equivalent Rb(1)Ca12 cuboctahedra, edges with eight equivalent Ca(2)Rb4Ca8 cuboctahedra, edges with sixteen equivalent Ca(1)Rb4Ca8 cuboctahedra, faces with four equivalent Ca(2)Rb4Ca8 cuboctahedra, faces with six equivalent Rb(1)Ca12 cuboctahedra, and faces with eight equivalent Ca(1)Rb4Ca8 cuboctahedra.
RbCa3 is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. Rb(1) is bonded to four equivalent Ca(2) and eight equivalent Ca(1) atoms to form RbCa12 cuboctahedra that share corners with four equivalent Rb(1)Ca12 cuboctahedra, corners with eight equivalent Ca(2)Rb4Ca8 cuboctahedra, edges with eight equivalent Rb(1)Ca12 cuboctahedra, edges with sixteen equivalent Ca(1)Rb4Ca8 cuboctahedra, faces with four equivalent Rb(1)Ca12 cuboctahedra, faces with six equivalent Ca(2)Rb4Ca8 cuboctahedra, and faces with eight equivalent Ca(1)Rb4Ca8 cuboctahedra. All Rb(1)-Ca(2) bond lengths are 4.12 Å. All Rb(1)-Ca(1) bond lengths are 4.13 Å. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to four equivalent Rb(1), four equivalent Ca(1), and four equivalent Ca(2) atoms to form CaRb4Ca8 cuboctahedra that share corners with twelve equivalent Ca(1)Rb4Ca8 cuboctahedra, edges with eight equivalent Rb(1)Ca12 cuboctahedra, edges with eight equivalent Ca(1)Rb4Ca8 cuboctahedra, edges with eight equivalent Ca(2)Rb4Ca8 cuboctahedra, faces with four equivalent Rb(1)Ca12 cuboctahedra, faces with four equivalent Ca(2)Rb4Ca8 cuboctahedra, and faces with ten equivalent Ca(1)Rb4Ca8 cuboctahedra. All Ca(1)-Ca(1) bond lengths are 4.12 Å. All Ca(1)-Ca(2) bond lengths are 4.13 Å. In the second Ca site, Ca(2) is bonded to four equivalent Rb(1) and eight equivalent Ca(1) atoms to form CaRb4Ca8 cuboctahedra that share corners with four equivalent Ca(2)Rb4Ca8 cuboctahedra, corners with eight equivalent Rb(1)Ca12 cuboctahedra, edges with eight equivalent Ca(2)Rb4Ca8 cuboctahedra, edges with sixteen equivalent Ca(1)Rb4Ca8 cuboctahedra, faces with four equivalent Ca(2)Rb4Ca8 cuboctahedra, faces with six equivalent Rb(1)Ca12 cuboctahedra, and faces with eight equivalent Ca(1)Rb4Ca8 cuboctahedra.