New Layered Zirconium Tellurides: Zr0.30ZrTe2, Zr0.29Zr2Te2As, and NaZr2Te2As
journal contributionposted on 22.01.1998, 00:00 by Chwanchin Wang, Cahit Eylem, Timothy Hughbanks
The synthesis and crystal structure determinations of Zr0.30ZrTe2 and MxZr2Te2As (M = Zr, Na) compounds are reported. The structure of Zr0.30ZrTe2 was refined in the hexagonal space group P63mc (No. 186, Z = 2) with lattice parameters a = 3.9840(3) Å and c = 13.366(3) Å; Zr0.29Zr2Te2As was refined in the rhombohedral space group R3̄m (No. 166, Z = 3) with lattice parameters a = 3.9329(4) Å and c = 29.564(5) Å. Zr0.30ZrTe2 and Zr0.29Zr2Te2As have close structural similarities to Zr2Se3 and Ta2S2C, respectively, and are built up by stacking hexagonal layers with [Zr0.30−Te−Zr−Te] and [Zr0.29−Te−Zr−As−Zr−Te] sequences. Four-probe resistivity measurements (77−300 K) show both Zr0.30ZrTe2 and Zr0.29Zr2Te2As to be metallic (Zr0.29Zr2Te2As: 8.9 × 10-5 Ω cm at 273 K). Both compounds exhibit structures wherein Zr atoms are included between layers (ZrTe2 and Zr2Te2As) by partially filling trigonal antiprismatic holes. The replacement of the included Zr ions in Zr0.29Zr2Te2As by Na ions has been demonstrated. Powder diffraction data showed that NaZr2Te2As is isostructural with Zr0.29Zr2Te2As. By use of Rietveld refinements, sodium ions were found to reside in the trigonal antiprismatic sites between the layers. Extended Hückel band calculations on the [Zr2Te2As]1.16- layer indicate that it should be a metallic conductor and that the [Zr2Te2As] layer can bear a greater negative charge than has so far been observed. We suggest that the [Zr2Te2As] layered compounds may offer new opportunities as electron-donating hosts.