Ultralow Glassy Thermal Conductivity and Controllable, Promising Thermoelectric Properties in Crystalline o-CsCu5S3

We thoroughly investigated the anharmonic lattice dynamics and microscopic mechanisms of the thermal and electronic transport characteristics in orthorhombic o-CsCu5S3 at the atomic level. Taking into account the phonon energy shifts and the wave-like tunneling phonon channel, we predict an ultralow κL of 0.42 w/mK at 300 K with an extremely weak temperature dependence following ∼T-0.33. These findings agree well with experimental values along with the parallel to the Bridgman growth direction. The κL in o-CsCu5S3 is suppressed down to the amorphous limit, primarily due to the unconventional Cu-S bonding induced by the p-d hybridization antibonding state coupled with the stochastic oscillation of Cs atoms. The nonstandard temperature dependence of κL can be traced back to the critical or dominant role of wave-like tunneling of phonon contributions in thermal transport. Moreover, the p-d hybridization of Cu(3)-S bonding results in the formation of a valence band with "pudding-mold" and high-degeneracy valleys, ensuring highly efficient electron transport characteristics. By properly adjusting the carrier concentration, excellent thermoelectric performance is achieved with a maximum thermoelectric conversion efficiency of 18.4% observed at 800 K in p-type o-CsCu5S3. Our work not only elucidates the anomalous electronic and thermal transport behavior in the copper-based chalcogenide o-CsCu5S3 but also provides insights for manipulating its thermal and electronic properties for potential thermoelectric applications.

Graphene-Edge Electrode on a Cu-Based Chalcogenide Selector for 3D Vertical Memristor Cells

Resistive memristors are considered to be key components in the hardware implementation of complex neuromorphic networks because of their simplicity, compactness, and manageable power dissipation. However, breakthroughs with respect to both the selector material technology and the bit-cost-effective three-dimensional (3D) device architecture are necessary to provide sufficient device density while maintaining the advantages of a two-terminal device. Despite substantial progress in the scaling of the memristor devices, the scaling potential of the selector materials remains unclear. A majority of the selector materials are unlikely to form conductive filaments, and the effect of the highly concentrated electrical fields on such materials is not well understood. In this study, the atomically thin graphene edge in a 3D vertical memory architecture is utilized to study the effect of highly focused electrical fields on a CuGeS chalcogenide selector layer. We demonstrate that additional interface resistance can improve the nonlinearity and reduce leakage current by almost three orders of magnitude; however, even a relatively low Cu⁺ ion density can adversely affect leakage because of the highly asymmetric electrode configuration. This study presents a meaningful step toward understanding the characteristics of mobile ions in solid chalcogenide electrolytes and the potential for ultrascaled selector devices.