The　Ag-based　superionic　argyrodites　with　liquid-like　ultralow　lattice　thermal　conductivity　have　garnered　widespread　attention　as　promising　thermoelectric　materials.　However,　the　inferior　performance　of　n-type　argyrodites　does　not　match　the　p-type　counterpart　for　device　construction.　Here,　the　two　new　cubic　n-type　Ag-based　argyrodite　compounds　Ag4M0.5S2Te　(M　=　Sn　and　Ge)　are　synthesized.　They　crystallize　in　the　(Formula　presented.)　space　group　with　excellent　structural　stability.　The　unique　triangular　[AgS2Te]5−,　rod-like　[AgSTe]3−,　and　complex　cage-like　[Te4Ag36]28+　clusters　together　with　the　vibrations　of　weakly　bonded　Ag+　ions　result　in　large　lattice　anharmonicity　and　enhance　the　scatter　of　acoustic　phonons.　These　structure　characters　lead　to　the　ultralow　lattice　thermal　conductivity　(κlat)　of　0.30–0.32 W　m−1　K−1　near　the　amorphous　limit　0.24 W　m−1　K−1　at　525–823　K.　Moreover,　the　power　factor　enhanced　from　1.53　µW　cm−1　K−2　for　Ag4Sn0.5S2Te　to　2.61　µW　cm−1　K−2　by　introducing　Te　deficiencies,　resulting　in　a　high　ZT　of　0.74　at　823　K　for　Ag4Sn0.5S2Te0.92,　which　is　95　%　higher　than　that　of　the　pristine　sample.　©　2025　Wiley-VCH　GmbH.