Hf2.64Zr0.36Te4 and MIxZr3Te4 (MI = Na, K, Rb, Cs), new compounds of the Nb3Te4-structure type
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The synthesis of the pseudo-binary telluride Hf2.64Zr0.36Te4 and new ternary tellurides MIx)Zr3Te4 (MIx = Na, K, Rb, Cs; 0.2 < x < 0.5) is reported. The single crystal structures of Hf2.64Zr0.36Te4, K0.25Zr3Te4, and Rb0.29Zr3Te4 have been determined. The structures of these tellurides were refined in the hexagonal space group P63/m (No. 176, Z = 2) with lattice parameters determined from the Guinier powder diffraction data as follows: a = 10.892(1) A , c = 3.9084(5) A for Hf2.64Zr0.36Te4, a = 11.009(2) A , c = 3.9374(8) A for Na0.42Zr3Te4; a = 11.034(2) A , c = 3.9340(6) A for K0.25Zr3Te4; a = 11.061(1) A , c = 3.9278(5) A for Rb0.29Zr3Te4; and a = 11.100(1) A , c = 3.9188 (5) A for Cs0.35Zr3Te4. All compounds adopt the Nb3Te4 structure type, which is built up by edge and face sharing of distorted MTe6 (M = Zr, Hf) octahedra. MTe6 octahedra share edges to form zigzag M-M chains running along the c-axis. Distorted MTe6 octahedra in these zigzag metal-metal chains are further condensed by sharing faces. MM bond distances in these tellurides are quite a bit longer (0.5 ) than those of Nb3Te4, as expected for compounds with fewer electrons for metal-metal bonding. Large hexagonal channels are partially occupied by alkali cations in the ternary zirconium tellurides. Four-probe single crystal resistivity measurements (77-300 K) show these ternary tellurides to be metallic with resistivities of 1.2 10-3 -cm (Na0.42Zr3Te4), 2.8 10-4 -cm (K0.25Zr3Te4), 4.9 10-4 -cm (Rb0.29Zr3Te4), and 1.7 10-4 -cm (Cs0.35Zr3Te4) at 273 K. Hf2.64Zr0.36Te4 also shows metallic behavior. 1995.
