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AgBi3S5 is a new n-type thermoelectric material that is environmentally friendly and composed of elements of earth-abundant, non-toxic and high performance-cost ratio. This compound features an intrinsically low thermal conductivity derived from its complex monoclinic structure. However, the terrible electrical transport properties greatly limited the improvement of thermoelectric performance. Most previous studies considered that carrier concentration is the main reason for low electrical conductivity and focused on improving carrier concentration by aliovalent ion doping. In this work, we found that the critical parameter that restricts the electric transport performance of AgBi3S5 was the extremely low carrier mobility instead of the carrier concentration. According to the Pisarenko relationships and density functional theory calculations, Nb doping can sharpen the conduction band of AgBi3S5, which contributes to reducing the effective mass and improving the carrier mobility. With a further increase of the Nb doping content, the conduction band convergence can enlarge the effective mass and preserve the carrier mobility. Combined with the decrease in lattice thermal conductivity due to the intensive phone scattering, a maximum ZT value of ∼0.50 at 773 K was achieved in Ag0.97Nb0.03Bi3S5, which was ∼109.6% higher than that of pure AgBi3S5. This work will stimulate the new exploration of high-performance thermoelectric materials in ternary metal sulfides.

In this study, we present a metal/Ba0.6Sr0.4TiO3/SiO2/Si (MBOS) structure for charge trapping memory, where the single Ba0.6Sr0.4TiO3 film acts as the blocking layer and charge trapping layer. This MBOS device structure demonstrates excellent charge trapping characteristics, a large memory window up to 8.4V under an applied voltage of ± 12 V, robust charge retention of only 4% charge loss after 1.08 x 104 s, fast switching rate, and great program/erase endurance. These attractive features are attributed to the high density of defect states in the Ba0.6Sr0.4TiO3 film and its interdiffusion interface with SiO2. The properties of defect states in the Ba0.6Sr0.4TiO3 film are investigated through measurements of photoluminescence and photoluminescence excitation spectroscopy. The energy levels of these defect states are found to be distributed between 2.66 eV and 4.05 eV above the valence band. The inter-diffusion at the Ba0.6Sr0.4TiO3/SiO2 interface is observed by high-resolution transmission electron microscopy. More defect sites were created to obtain a better charge trapping capability and retention characteristics. [ABSTRACT FROM AUTHOR]