SYNTHESES, STRUCTURES, AND CHARACTERIZATION OF THE 2-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 measurement s show that both compounds crystallize in the space group Pn2(1)a of t he 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) Angstr om, b = 5.992(5) Angstrom, c = 20.562(14) Angstrom, V = 1012(1) Angstr om(3) at 113 K for M = Ta. The two compounds are isostructural. The st ructure 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 di storted tricapped trigonal prism. Both phases are highly resistive. (C ) 1996 Academic Press, Inc.