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AgSbSe 2 is a typical member of cubic I-V-VI 2 semiconductors, which are known for their extremely low lattice thermal conductivity (κ l ). However, the low electrical conductivity of AgSbSe 2 , below ∼10 S cm -1 at room temperature, has hindered its thermoelectric performance. In this work, single-phase AgSbSe 2 bulk samples with much higher electrical conductivity were synthesized via self-propagating high-temperature synthesis (SHS) combined with spark plasma sintering (SPS) for the first time. Pb doping through the nonequilibrium process further increases the electrical conductivity to >100 S cm -1 . Furthermore, continuously increased effective mass m d * can be achieved upon Pb doping because of the multiple degenerate valence bands of AgSbSe 2 and the energy-filtering effect induced by in situ -formed nanodots. The simultaneous enhancement of both the electrical conductivity and Seebeck coefficient contributes to an unprecedentedly high average power factor of 6.75 μW cm -1 K -2 . Meanwhile, the introduced dense grain boundaries and point defects enhance the phonon scattering and consequently suppress κ l , yielding a high ZT value of 1.2 at 723 K in AgSb 0.94 Pb 0.06 Se 2 . This study opens a new avenue for rapid, low-cost, large-scale production of AgSbSe 2 -based materials and demonstrates that Pb-doped AgSbSe 2 prepared via the SHS-SPS method is a promising candidate for thermoelectric applications.

Recent work on superionic conductors has demonstrated the influence of lattice dynamics and the softness of the lattice on ionic transport. When examining either the changes in the acoustic phonon spectrum or the whole phonon density of states, both a decreasing activation barrier of migration and a decreasing entropy of migration have been observed, highlighting that the paradigm of "the softer the lattice, the better" does not always hold true. However, both approaches to monitor the changing lattice dynamics probe different frequency ranges of the phonon spectrum, and thus, it is unclear if they are complementary. In this work, we investigate the lattice dynamics of the superionic conductor Na 3 PS 4- x Se x by probing the optical phonon modes and the acoustic phonon modes, as well as the phonon density of states via inelastic neutron scattering. Notably, Raman spectroscopy shows the evolution of multiple local symmetry reduced polyhedral species, which likely affect the local diffusion pathways. Meanwhile, density functional theory and the ionic transport data are used to compare the different approaches for assessing the lattice dynamics. This work shows that, while acoustic and inelastic methods may be used to experimentally assess the overall changing lattice stiffness, calculations of the average vibrational energies between the mobile ions and the anion framework are important to assess and computationally screen for ionic conductors.