ZIRCONIUM DICHLORIDE PHASE REGION - SYNTHESIS, STRUCTURE, AND PHOTOELECTRON SPECTRAL STUDIES OF 3R-ZRCL2, 6T-ZR1.05CL2, AND RELATED PHASES

Homogenous compositions and several phases between ZrCl, 5 (Zr, 3C12) and ZrCl2.0 have been synthesized in sealed Ta tubing by both chemical transport reactions and isothermal equilibrations at 600-750 °C for 4-10 weeks. X-ray powder and single-crystal diffraction results indicate the breadth of the composition range is probably achieved through the formation of ordered superstructures derived from the basic three-layer slabs of the parent 3R-ZrCl2 type with ordered interstitial atoms and with extensive intergrowth and twinning, the individual phases showing small if not negligible homogeneity ranges. The structure of the stoichiometric 3R-ZrCl2.00(1) was refined using 98 independent reflections (2θ≤60°), space group [FORMULA OMMITED] The structure consists of homoatomic layers sequenced Cl-Zr-Cl with trigonal prismatic coordination of the metal by halide (D3h), isostructural with the isoelectronic 3R-MoS2. The phase could not be intercalated. A previously reported powder patern of ZrCl2 is found to be that of monoclinic ZrO2. A structure of 6T-Zr1.047(5)Cl2 (a=3.3791 (4) Å, c=38.713 (7) Å, space group P3ml) was approximated from a crystal in which it was a minor component coherently intergrown with 3R-ZrCl2 (obverse and reverse) through refinement of 266 I-odd reflections (R=0.256). The structure consists of three subcells of the 2Hb-MoS2 type together with a metal atom in an interslab octahedral hole with a partial occupancy of 0.28 (3). Single-crystal evidence was also found for an 18-slab structure (a=3.3820 (2) Å, c=116.31 (2) Å), and powder data indicated another six-slab cell with a tripled a dimension. Twinning of 3R-ZrCl2 only on slight reduction and the 6T-Zr, 1 0sCl2 structure appear to involve a common mechanism for substoichiometry—accommodation of extra metal atoms in octahedral interstices between slabs which share only edges (dZr-zr=3.77 Å) rather than faces (dZt-zr=3.23 Å) with filled trigonal prisms within the slas. Photoelectron spectra are reported for most of the reduced zirconium chlorides. ZrCl2 shows a narrow metal band 1.2 eV below EF, well above this feature in the isoelectronic MoS2, and is analogously a semiconductor (Eg≈0.3 eV). A metal valence band was not detected in ZrCl3, and there is an abrupt increase in the Zr(3d) core levels at that point relative to more reduced phases. © 1979, American Chemical Society. All rights reserved.