Ba2Cu(18-x)As10: A new mixed-valent ternary copper-rich arsenide with metallic properties

Abstract

The new barium copper pnictide Ba2Cu(18-x)As10 (x ≃ 1.67) was obtained from a direct element combination reaction in a sealed graphite tube at 700 °C, and its structure was determined by single-crystal X-ray diffraction methods. It crystallizes in the trigonal space group P31c (No. 163) with a = 6.7329(1) Å, c = 11.6747(2) Å, and Z = 1. Ba2Cu(18-x)As10 has a three-dimensional structure with straight bottle-shape parallel tunnels running along the c-direction. The Ba atoms reside in the tunnels. The [Cu(18-x)As10]4- framework features Cu atom vacancies with x = 1.67. The compound is metallic with a room-temperature resistivity along the c-axis of 1.7 x 10-4 Ω·cm and a Seebeck coefficient of ~+2.5 μV/K. Band structure calculations in the extended Huckel approximation suggest that the defects on the Cu sites enhance its metallic character.