Syntheses, structures, and characterization of the two-dimensional tellurides CsCu(2)MTe(4) (M=Nb, Ta)

The new compounds CsCu(2)MTe(4) (M = Nb, Ta) have been synthesized at 900 degrees C through the reaction of Cu and Nb or Ta with a Cs2Te3/Te melt as a reactive flux. Single-crystal X-ray diffraction measurements show that both compounds crystallize in the space group Pn2(1)a of the orthorhombic system with four formula units in cells of dimensions a = 8.198(2) Angstrom, b = 5.988(2) Angstrom, c = 20.527(6) Angstrom, V = 1007.7(6) Angstrom(3) at 113 K for M = Nb, and a = 8.217(5) Angstrom, b = 5.992(5) Angstrom, c = 20.562(14) Angstrom, V = 1012(1) Angstrom(3) at 113 K for M = Ta. The two compounds are isostructural. The structure of CsCu2NbTe4 comprises infinite, two-dimensional layers of Cu- and Nb-centered tetrahedra; Cs+ cations separate the layers. Each Cs+ cation is coordinated by nine Te atoms at the corners of a highly distorted tricapped trigonal prism. Both phases are highly resistive. (C) 1996 Academic Press, Inc.