Alkali, Chalcogen, Energy gap for indirect transition

• Na-O-Si
• Ba-Na-O-Sr-Ti
• Cu-K-S-Sb
• Bi-Na-O-W
• Bi-Rb-Se
• alkali
• chalcogen
• non-disordered
• ternary
• transitional
• trigonal
• monoclinic
• tetragonal
• orthorhombic
• cubic