STRUCTURAL AND PHYSICAL-PROPERTIES OF THE MISFIT INTERCALATION COMPOUNDS HGXTAS2 (X=0.58, 1.19, AND 1.3)

Time-differential perturbed angular correlation (TDPAC) and x-ray powd er diffraction (XPD) have been used to investigate the complex physica l and structural properties of mercury intercalation compounds derived from 1T-TaS2 and 2H-TaS2, respectively. In situ TDPAC studies of the Ta-181 nuclear quadrupole interaction during Hg intercalation and ther mal deintercalation proved the complete reversibility of the intercala tion process and revealed the formation of three distinct phases (alph a-Hg1.19TaS2, beta-Hg1.3TaS2, and a disordered second-stage phase Hg0. 58TaS2 derived from alpha-Hg1.19TaS2) The stage-1 compounds alpha-Hg1. 19TaS2 and beta-Hg1.3TaS2 are characterized by two different structura l arrangements of the intercalated Hg that bear a strong resemblance t o those realized in solid-state phases of beta-Hg and alpha-Hg, respec tively. alpha-Hg1.19TaS2 adopts an unusual (3 + 1)-dimensional composi te crystal structure which can be described as two interpenetrating su blattices formed by the TaS2 host and the Hg guest. These C-face-cente red orthorhombic sublattices share common a and c axes but are incomme nsurate along the b axis [a = 5.765(1) Angstrom, b = 3.309(1) Angstrom , c = 17.842(1) Angstrom, and b(Hg) = 2.782(1) Angstrom]. The in-plane Hg-Hg distances of 2.782 and 3.201 Angstrom indicate a chainlike Hg a rrangement similar to that found in Hg1.24TiS2. In the case of beta-Hg 1.3TaS2 the Hg arrangement is such that the TaS2 host lattice (a = 3.3 18 Angstrom) can be considered as a 2X2 superstructure formed upon hex agonal close-packed Hg layers (a(Hg) = 2.902 Angstrom). Hg intercalati on into 1T-TaS2 requires an elevated reaction temperature of 423 K, wh ereas 2H-TaS2 intercalates Hg already at ambient temperature. Both the TDPAC and x-ray-diffraction data indicate that in the case of 1T-TaS2 the Hg intercalation process is accompanied by an irreversible change of the TaS2 host layers from octahedral to a trigonal-prismatic arran gement.