Chemistry of intercalation compounds: Metal guests in chalcogenide hosts

Intercalation of the layer type transition metal dichalcogenides by a variety of organic molecules, alkali metals, or ‘3d’ transition metals, provides a powerful way to finely tune the electron occupation of the relatively narrow ‘d’ bands met in these solids These transition metal dichalcogenides are highly anisotropic solids, sometimes referred to as ‘two-dimensional’ solids, and the intercalant molecules which are electron donors enter between the layers This can result in profound changes in the electronic properties of the host lattice, and these changes can be understood in terms of charge transfer and increased interlayer separation The phenomena discussed include optical properties, transport properties, super-conductivity, order-disorder phenomena and phase changes, staging, magnetic properties, metal-insulator transitions, Anderson localization, and fast-ion conduction Some possible practical applications are also considered

Electronic properties of intercalation complexes of the transition metal dichalcogenides

As a generic property, all substances transfer heat through microscopic collisions of constituent particles
 1
 . A solid conducts heat through both transverse and longitudinal acoustic phonons, but a liquid employs only longitudinal vibrations2,3. As a result, a solid is usually thermally more conductive than a liquid. In canonical viewpoints, such a difference also serves as the dynamic signature distinguishing a solid from a liquid. Here, we report liquid-like thermal conduction observed in the crystalline AgCrSe2. The transverse acoustic phonons are completely suppressed by the ultrafast dynamic disorder while the longitudinal acoustic phonons are strongly scattered but survive, and are thus responsible for the intrinsically ultralow thermal conductivity. This scenario is applicable to a wide variety of layered compounds with heavy intercalants in the van der Waals gaps, manifesting a broad implication on suppressing thermal conduction. These microscopic insights might reshape the fundamental understanding on thermal transport properties of matter and open up a general opportunity to optimize performances of thermoelectrics. Investigation of the thermal transport properties of AgCrSe2 reveals complete suppression of the transverse acoustic phonons by ultrafast dynamic disorder with only the longitudinal acoustic mode surviving, resembling the thermal conduction of liquids.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1131&context=ameslab_manuscripts

Liquid-like thermal conduction in intercalated layered crystalline solids

Intrinsically low lattice thermal conductivity ([Formula: see text]) in superionic conductors is of great interest for energy conversion applications in thermoelectrics. Yet, the complex atomic dynamics leading to superionicity and ultralow thermal conductivity remain poorly understood. Here, we report a comprehensive study of the lattice dynamics and superionic diffusion in [Formula: see text] from energy- and momentum-resolved neutron and X-ray scattering techniques, combined with first-principles calculations. Our results settle unresolved questions about the lattice dynamics and thermal conduction mechanism in [Formula: see text] We find that the heat-carrying long-wavelength transverse acoustic (TA) phonons coexist with the ultrafast diffusion of Ag ions in the superionic phase, while the short-wavelength nondispersive TA phonons break down. Strong scattering of phonon quasiparticles by anharmonicity and Ag disorder are the origin of intrinsically low [Formula: see text] The breakdown of short-wavelength TA phonons is directly related to the Ag diffusion, with the vibrational spectral weight associated to Ag oscillations evolving into stochastic decaying fluctuations. Furthermore, the origin of fast ionic diffusion is shown to arise from extended flat basins in the energy landscape and collective hopping behavior facilitated by strong repulsion between Ag ions. These results provide fundamental insights into the complex atomic dynamics of superionic conductors.

https://www.pnas.org/content/pnas/117/8/3930.full.pdf

Anharmonic lattice dynamics and superionic transition in AgCrSe2

Un nouveau conducteur ionique (LaO)AgS

Ionic and electronic conductivity has been measured in and. Ionic conductivity was measured by using as a blocking electrode for electronic conduction. Transference numbers were confirmed by cells of the type . Ionic conductivities were for and , respectively, at room temperature. The conductivity of increases abruptly at ∼170°C to ∼1 (Ω‐cm)−1. A transition at this temperature was observed by DSC.

H. S. Chen

Papers

Superionic Conduction in AgCrS2 and AgCrSe2

Superionic conduction in silver chromium disulfide and silver chromium diselenide