Thermoelectric materials with crystal-amorphicity duality induced by large atomic size mismatch

•Discovering a material series with crystal structure not previously reported•Large S/Te size mismatch in (Cu,Ag)2(Te,S) inducing crystal-amorphicity duality•Ultralow thermal conductivity and high thermoelectric figure of merit zT Exploration discovering novel high-performance materials are the “fountain youth” for science, engineering, technology. Here, we report series, (Cu1?xAgx)2(Te1?ySy), structurally featured by mismatch-induced duality. The entanglement highly disordered yet crystalline anionic sublattice an amorphous cationic gives rise to extremely low conductivities state-of-the-art 2.0 x = y 0.22 sample. These results attest duality as paradigm-shifting approach beyond classic “phonon-glass electron-crystal” “phonon-liquid paradigm development thermoelectrics. Discovering attaining higher performance eternal pursuit research. (Cu1?xAgx)2(Te1?ySy) (0.16 ? 0.24, 0.16 0.24), which adopts complex orthorhombic differing from any known (Cu/Ag)2(S/Te). This is induced large mismatch: size-mismatched anions Te/S coexists amorphous-like cations Cu/Ag. In context structure-property correlation, gave only interesting electrical properties but also exceptionally lattice 300 1,000 K. A obtained sample at give insights into design develop materials. Nowadays, concerns about environmental issues fossil fuel usage have made sustainable energy technologies urgent front-burner task. To this end, (TE) technology, enables direct green conversion between electricity heat, holds promise waste heat harvesting, distributive spot-size cooling, etc.1Shi X.L. Zou J. Chen Z.G. Advanced design: structures devices.Chem. Rev. 2020; 120: 7399-7515Crossref PubMed Scopus (476) Google Scholar, 2He Tritt T.M. Advances research: looking back moving forward.Science. 2017; 357: 6358Crossref (962) 3Zhang Z. Zhao Wei T.-R. Qiu P. L. Shi X. Cu2Se-Based liquid-like materials: stepping forward.Energy Environ. Sci. 13: 3307-3329Crossref 4Tan G. L.D. Kanatzidis M.G. 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Mixed phononic non-phononic lead halide perovskites: glass-crystal dynamical disorder, anharmonicity.Energy 216-229Crossref following, display stemming mismatch. average solved single-crystal X-ray diffraction (XRD) data, revealing both ordered components particular, form periodic Cu/Ag short-range ordered, properties, value ?2.0 K (Cu0.78Ag0.22)2(Te0.78S0.22) Doping and/or alloying semiconductors semimetals main route, major restriction solubility limit doping element, governed dopant host substituted. (> 15%) tends facilitate separation.23Hume-Rothery Cu2S, Cu2Te, Ag2S, Ag2Te their potentials TEs. Given (1.35 Å), Ag (1.60 S (1.00 Te (1.40 Å),25Slater J.C. Atomic radii crystals.J. 1964; 41: 3199-3204Crossref (1563) especially Te, what would happen, solid solutions separation, if melt cool admixture Cu, Ag, Te? efforts answer question, observed intriguing phenomena formation nominal compositions 0.13 0.26; 0.16, 0.24; 0.16. characterize purity, microstructures, conducted scanning microscopy (SEM), dispersive (EDS) analysis, powder XRD measurements. As shown Figures 1A S1, elemental segregations impurity phases samples 0.26, consistent previous nearly immiscible Cu2X Te).26Zhao Yue Guan Zhu al.Are Cu2Te-based materials?.Adv. 31e1903480Crossref (42) Scholar,27Guan Enhanced quaternary Cu2-2xAg2xSe1-xSx chalcogenides.ACS Appl. Interfaces. 13433-13440Crossref (21) Notably, homogeneous element distributions ranging quantitative analysis accordance compositions. patterns depicted 1B S2. When content all peaks can well indexed suggesting over wide composition range. 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For simplicity, assume solely site structural model follow-up discussion calculations. At stage, unable differentiate preferred occupation because disorder. partially ions. Each anion surrounded multiple different polyhedrons, S3. S-Cu/Ag bond distance 2.2697–2.4996 shorter Te-Cu/Ag 2.3956–2.7944 expected. That being said, take appropriate relax sublattice. fully occupied, forming largely (cf. 1E), occupancy factors (SOFs) 0.138 0.561. total, there 48 spread 140 each cell, resulting 1F). We infer drives state; latter former separation.Table 1Crystallographic information KSample(Cu2Te)0.82(Ag2S)0.18a / Å16.3803(8)b Å7.3157(4)c Å11.1689(6)Volume Å31,338.4(1)Space groupImmaCrystal systemorthorhombic?calc g cm?36.965 Open table new tab 2Refined coordinates, occupancies, isotropic displacement parameters KSitesWyckoffXyZOccupancyU (Å2)Te18i0.7194(1)0.250.4153(2)10.0293(9)Te28i0.3756(2)0.250.8011(2)10.046(1)Te34e0.50.750.8523(4)10.0652(14)S4a0.500.510.027(3)Cu/Ag116j0.7295(4)0.3885(11)0.6347(5)0.522(16)0.048(3)Cu/Ag216j0.6488(5)0.5983(12)0.7938(9)0.561(18)0.083(4)Cu/Ag38i0.5873(9)0.250.5775(12)0.52(2)0.077(5)Cu/Ag48i0.5541(10)0.750.6303(11)0.45(3)0.077(8)Cu/Ag516j0.5870(8)0.581(2)0.6687(18)0.374(19)0.102(8)Cu/Ag68h0.50.410(3)0.945(2)0.31(3)0.098(15)Cu/Ag78h0.50.427(3)0.817(3)0.21(2)0.064(14)Cu/Ag88g0.750.479(4)0.750.25(2)0.080(12)Cu/Ag916j0.6303(12)0.415(3)0.5858(15)0.264(18)0.087(10)Cu/Ag1016j0.6295(14)0.575(5)0.968(4)0.19(3)0.064(14)Cu/Ag118f0.580(7)0.510.26(7)0.12(4)Cu/Ag124e0.50.250.628(5)0.18(2)0.077(7)Cu/Ag138h0.50.445(7)0.700(5)0.138(16)0.077(7) super-structure along axis corresponding super triple length. 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Nevertheless, rough linear trend implies substitutionally dope Other hump capacity anomaly near room temperature S6) small change SOF Tables S2–S4), unchanged 100 stable 800 K, undergoes orthorhombic-to-cubic transition, demonstrated high-temperature measurements S6). feature pattern less salient still discernible compared counterpart low-temperature phase. cross-check supplement derived means aberration-corrected transmission (STEM) high-angle annular dark-field (HAADF) detector loss spectroscopy (EELS). 2A 2B atomically resolved HAADF-STEM images [111] zone axis. discern. Nonetheless, composed captured 2B, agreement 2C). dimmer spots, marked pink arrows indicate more these Concomitantly, brighter red squares, better features, turn [010] axis, columns separated. 2D 2E, ring-like arrangement center locate Te. aforementioned 2F). 2D, substitutions defects effectively short-wavelength elevated Besides, sign (red circles) direction, although clear EELS S7 further confirm elements, determined model. All above-mentioned evidences corroborate as-formed dual defects. How does coexistence impact behavior? dependence total plotted 3A. discontinuous jumps approximately attributed exhibit very values significantly lower Cu2Te. reduction caused decreased (?e) S8). (?L), calculated subtracting 3B. show extraordinarily ?L 0.2–0.3 W m?1 K?1 those well-known Bi2Te3 PbTe,34Hao Tang Xing Chu H.-S. 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