Structural and physical properties of the misfit intercalation compounds HgxTaS2 (x=0.58, 1.19, and 1.3).

Abstract

Time-differential perturbed angular correlation (TDPAC) and x-ray powder diffraction (XPD) have been used to investigate the complex physical and structural properties of mercury intercalation compounds derived from 1T-${\mathrm{TaS}}_{2}$ and 2H-${\mathrm{TaS}}_{2}$, respectively. In situ TDPAC studies of the $^{181}\mathrm{Ta}$ nuclear quadrupole interaction during Hg intercalation and thermal deintercalation proved the complete reversibility of the intercalation process and revealed the formation of three distinct phases (\ensuremath{\alpha}-${\mathrm{Hg}}_{1.19}$${\mathrm{TaS}}_{2}$, \ensuremath{\beta}-${\mathrm{Hg}}_{1.3}$${\mathrm{TaS}}_{2}$, and a disordered second-stage phase ${\mathrm{Hg}}_{0.58}$${\mathrm{TaS}}_{2}$ derived from \ensuremath{\alpha}-${\mathrm{Hg}}_{1.19}$${\mathrm{TaS}}_{2}$). The stage-1 compounds \ensuremath{\alpha}-${\mathrm{Hg}}_{1.19}$${\mathrm{TaS}}_{2}$ and \ensuremath{\beta}-${\mathrm{Hg}}_{1.3}$${\mathrm{TaS}}_{2}$ are characterized by two different structural arrangements of the intercalated Hg that bear a strong resemblance to those realized in solid-state phases of \ensuremath{\beta}-Hg and \ensuremath{\alpha}-Hg, respectively. \ensuremath{\alpha}-${\mathrm{Hg}}_{1.19}$${\mathrm{TaS}}_{2}$ adopts an unusual (3+1)-dimensional composite crystal structure which can be described as two interpenetrating sublattices formed by the ${\mathrm{TaS}}_{2}$ host and the Hg guest.These C-face-centered orthorhombic sublattices share common a and c axes but are incommensurate along the b axis [a=5.765(1) \AA{}, b=3.309(1) \AA{}, c=17.842(1) \AA{}, and ${\mathit{b}}_{\mathrm{Hg}}$=2.782(1) \AA{}]. The in-plane Hg-Hg distances of 2.782 and 3.201 \AA{} indicate a chainlike Hg arrangement similar to that found in ${\mathrm{Hg}}_{1.24}$${\mathrm{TiS}}_{2}$. In the case of \ensuremath{\beta}-${\mathrm{Hg}}_{1.3}$${\mathrm{TaS}}_{2}$ the Hg arrangement is such that the ${\mathrm{TaS}}_{2}$ host lattice (a=3.318 \AA{}) can be considered as a 2\ifmmode\times\else\texttimes\fi{}2 superstructure formed upon hexagonal close-packed Hg layers (${\mathit{a}}_{\mathrm{Hg}}$=2.902 \AA{}). Hg intercalation into 1T-${\mathrm{TaS}}_{2}$ requires an elevated reaction temperature of 423 K, whereas 2H-${\mathrm{TaS}}_{2}$ intercalates Hg already at ambient temperature. Both the TDPAC and x-ray-diffraction data indicate that in the case of 1T-${\mathrm{TaS}}_{2}$ the Hg intercalation process is accompanied by an irreversible change of the ${\mathrm{TaS}}_{2}$ host layers from octahedral to a trigonal-prismatic arrangement.