Synthesis, Single Crystal Growth and Crystal Structure of Ta 7 Cu 10 Ga 34 – a 8 × 4 × 2 Super Structure of CsCl

Single crystals of Ta 7 Cu 10 Ga 34 were grown from the elements in a Cu/Ga melt. Ta 7 Cu 10 Ga 34 represents the first ternary compound of the system Ta/Cu/Ga. The crystal structure ( Cmmm , oC102, Z = 2, a = 23.803(1), b = 12.2087(4), c = 5.7487(2) Å, 1291 refl. 78 parameters, R 1 = 0.037, wR 2 = 0.070). The crystal structure is characterized by rods of pentagonal prisms M Ga 10 , which are alternatingly occupied by Ta and Cu. Four of these rods are connected to columns running in direction (001). These columns are linked by cubic units TaGa 8 , CuGa 8 , and GaGa 8 . According to the characteristic structural elements and the size of the unit cell Ta 7 Cu 10 Ga 34 represents a 8 × 4 × 2 super structure of CsCl or bcc . With respect to the underlying CsCl structure the formula can be written as [Ta 7 Cu 10 Ga 2 □ 13 ]Ga 32 , i.e. a cubic primitive packing of 32 Ga atoms with Ta, Cu, and Ga in cubic voids and 13 vacancies. The pentagonal‐prismatic coordination of Ta and Cu can formally be obtained from the cubic primitive packing of Ga atoms by a 45° rotation of a part of the Ga 8 cubes. There is a close similarity to the binary compounds Ta 8 Ga 41 and Ta 2–x Ga 5+ x . The first one is also related to a CsCl‐like structure, the latter one contains rods of pentagonal prisms, which form the same columns. There are also relations to the ternaries V 2 Cu 3 Ga 8 and V 11 Cu 9 Ga 46 , whose cubic structures are more or less complex variants of CsCl.