Boosting Thermoelectric Performance of PbBi2 Te4 via Reduced Carrier Scattering and Intensified Phonon Scattering.

Materials with low intrinsic lattice thermal conductivity are crucial in the pursuit of high-performance thermoelectric (TE) materials. Here, the TE properties of PbBi2 Te4-x Sex (0 ≤ x ≤ 0.6) samples are systematically investigated for the first time. Doping with Se in PbBi2 Te4 can simultaneously reduce carrier concentration and increase carrier mobility. The Seebeck coefficient is significantly increased by doping with Se, based on the density functional theory calculation, it is shown to be due to the increased bandgap and electronic density of states. In addition, the lattice strain is enhanced due to the difference in the size of Se and Te atoms, and the multidimensional defects formed by Se doping, such as vacancies, dislocations, and grain boundaries, enhance the phonon scattering and reduce the lattice thermal conductivity by about 37%. Finally, by using Se doping to reduce carrier concentration and thermal conductivity, a large ZTmax = 0.56 (at 574K) is achieved for PbBi2 Te3.5 Se0.5 , which is around 64% larger than those of the PbBi2 Te4 pristine sample. This work not only demonstrates that PbBi2 Te4 is a potential medium temperature thermoelectric material, but also provides a reference for enhancing thermoelectric properties through defect and energy band engineering.

Theoretical Study of Intrinsic and Extrinsic Point Defects and Their Effects on Thermoelectric Properties of Cu2SnSe3.

Current understanding of the intrinsic point defects and potential extrinsic dopants in p-type Cu2SnSe3 is limited, which hinders further improvement of its thermoelectric performance. Here, we show that the dominant intrinsic defects in Cu2SnSe3 are CuSn and VCu under different chemical conditions, respectively. The presence of VCu will damage the hole conduction network and reduce hole mobility. Besides, we find that the substitution of Al, Ga, In, Cd, Zn, Fe, and Mn for Sn can inhibit the formation of VCu; introducing CuSn, FeSn, MnSn, and NiCu defects can significantly enhance electronic density of states near the Fermi level due to the contribution of 3d orbitals. Therefore, increasing the Cu content and/or introducing the above beneficial dopants appropriately are expected to cause enhancement of carrier mobility and/or thermopower of Cu2SnSe3. Furthermore, introducing AgCu, AlSn, ZnSn, GeSn, and MnSn defects can induce large mass and strain field fluctuations, lowering lattice thermal conductivity remarkably. Present results not only deepen one's insights into point defects in Cu2SnSe3 but also provide us with a guide to improve its thermoelectric properties.

Design, Synthesis and Biological Evaluation of 4-Aryl-5,7-dihydro-6H-pyrrolo[2,3-d]pyrimidin-6-one Derivatives as a PI3Kα Inhibitor.

A novel series of 4-aryl-5,7-dihydro-6H-pyrrolo[2,3-d]pyrimidin-6-one derivatives were designed as a phosphoinositide 3-kinase α (PI3Kα) inhibitor by scaffold hopping. The target compounds, characterized by 1H-NMR, 13C-NMR and high resolution (HR)-MS, were synthesized from diethyl malonate and ethyl chloroacetate by nucleophilic substitution, ring-closure, chlorination and Suzuki reaction, etc. The biological activities were evaluated with cytotoxic activity in vitro on Uppsala 87 Malignant Glioma (U87MG) and prostate cancer-3 (PC-3) by Cell Counting Kit-8 (CCK-8). The results showed that compound 9c displayed the higher inhibition than the positive control PI-103, and high PI3Kα inhibitory activity with IC50 of 113 ± 9 nM in the same order of magnitude as BEZ235. In addition, the Log Kow values and molecular docking studies were performed to further investigate the drug-like properties of target compounds and interactions between 9c and PI3Kα.

Design, synthesis, and biological evaluation of 1,4-diaryl-1,4-dihydropyrazines as novel 11ß-HSD1 inhibitors.

The inhibition of 11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1) has demonstrated potential for the treatment of various components of metabolic syndrome. In this study, a series of 1,4-diaryl-1,4-dihydropyrazines were designed as inhibitors of 11ß-HSD1 based on the structure-activity relationship of known 11ß-HSD1 inhibitors through docking simulations. The docking simulation results supported the initial pharmacophore hypothesis: the docking results of the known inhibitors with 11ß-HSD1 suggested a similar interaction of 1,4-diaryl-1,4-dihydropyrazines with the catalytic site of 11ß-HSD1. Twelve of these compounds were synthesized through the cyclization of N,N-dialkylanilines with anilines, and their structures were determined by (1)H-NMR, (13)C-NMR, high resolution (HR)-MS, and single-crystal X-ray diffraction. The inhibitory activities of these compounds against human 11ß-HSD1 were investigated in vitro through a scintillation proximity assay using microsomes containing 11ß-HSD1.

High Thermoelectric Performance of n-type BiTeSe-Based Composites Incorporated with Both Inorganic and Organic Nanoinclusions.

N-type Bi2Te2.7Se0.3 (BTS) alloy has relatively low thermoelectric performance as compared to its p-type counterpart, which restricts its widespread applications. Herein, we designed and prepared a novel composite system, which consists of an n-type BTS matrix incorporated with both inorganic and organic nanoinclusions. The results indicate that the thermopower of the composite samples can be enhanced by more than 19% upon incorporating inorganic nanophase AgBi3S5 (ABS) due to the energy-dependent carrier scattering, which ensures a high power factor. On the other hand, further incorporation of organic nanophase polypyrrole (PPy) can drastically reduce its lattice thermal conductivity owing to the strong scattering of mid- and low-frequency phonons at these nanoinclusions. As a result, high figures of merit ZTmax = 1.3 at 348 K and ZTave = 1.17 (300-500 K) are achieved with improved mechanical properties in BTS-based composites incorporated with 1.5 wt % ABS and 0.5 wt % PPy, demonstrating that the incorporation of both inorganic and organic nanoinclusions is an effective way to improve its thermoelectric performance.

Enhancing Thermoelectric Performance of n-Type Bi2Te2.7Se0.3 through Incorporation of Amorphous Si3N4 Nanoparticles.

Bi2Te3-based thermoelectric (TE) materials are the state-of-the-art compounds for commercial applications near room temperature. Nevertheless, the application of the n-type Bi2Te2.7Se0.3 (BTS) is restricted by the comparatively low figure of merit (ZT) and intrinsic embrittlement. Here, we show that through dispersion of amorphous Si3N4 (a-Si3N4) nanoparticles both 14% increase in power factor (at 300 K) and 48% decrease in lattice thermal conductivity are simultaneously realized. The increased power factor comes from enhanced thermopower and reduced electrical resistivity while the reduced lattice thermal conductivity originates mainly from scattering of middle- and low-frequency phonons at the incorporated a-Si3N4 nanoparticles. As a result, a large ZTmax = 1.19 (at 373 K) and an average ZTave ∼ 1.12 (300-473 K) with better mechanical properties are achieved for the BTS/0.25 wt % Si3N4 sample. Present results demonstrate that the incorporation of a-Si3N4 is a promising way to improve TE performance.

Low Thermal Conductivity and High Thermoelectric Performance of Nb-Doped Quarternary Mixed Crystal Nb0.05W0.95-xMox(Se1-xSx)2.

Transition-metal dichalcogenide WSe2 has attracted increasing interest due to its large thermopower (S), low-cost, and environment-friendly constituents. However, its thermoelectric figure of merit, ZT, of WSe2 is limited due to its large lattice thermal conductivity (κL) and low electrical conductivity. In view of WSe2 and MoS2 having the same crystal structure, here we designed and prepared Nb-doped quarternary mixed crystal (MC) Nb0.05W0.95-xMox(Se1-xSx)2 (0 ≤ x ≤ 0.095). The results indicate that the κL of the MC can reach as low as 0.12 W m K-1 at 850 K, being 93% smaller than that of WSe2. Our analysis reveals that its low κL originates chiefly from intense scattering of both high-frequency phonons from point defects (mainly alloying elements) and mid/low-frequency phonons from MoS2 inclusions residual within MC. In addition, the alloying of WSe2 with MoS2 causes a 5-fold increase in cation vacancies (VW‴'), leading to a large increase in hole concentration and electrical conductivity, which gives rise to a ∼7.5 times increase in power factor (reaching 4.2 µ W cm-1 K-2 at 850 K). As a result, a record high ZTmax = 0.63 is achieved at 850 K for the MC sample with x = 0.076, which is 20 times larger than that of WSe2, demonstrating that MC Nb0.05W0.95-xMox(Se1-xSx)2 is a promising thermoelectric material.

Synthesis of 4H-1,4-oxazines as transthyretin amyloid fibril inhibitors.

4H-1,4-oxazines were designed as transthyretin (TTR) amyloid fibril inhibitors based on an analysis of the interactions between known small molecule inhibitors and TTR by molecular docking. A series of 2,4,6-triaryl-4H-1,4-oxazines was synthesized by the cyclization of N,N-bis(phenacyl)anilines with POCl3 in pyridine. Inhibition of TTR amyloid fibril was evaluated by a fibril formation assay. The results indicate that 4H-1,4-oxazines significantly inhibit TTR amyloid fibril at a concentration of 7.2 µM.

Attaining High Figure of Merit in the N-Type Bi2Te2.7Se0.3-Ag2Te Composite System via Comprehensive Regulation of Its Thermoelectric Properties.

n-Type Bi2Te2.7Se0.3 (BTS) is the state-of-the-art thermoelectric material near room temperature. However, the figure of merit ZT of commercial BTS ingots is still limited and further improvement is imperative for their wide applications. Here, the results show that through dispersion of the Ag2Te nanophase in BTS, one can not only elevate its power factor (PF) by as high as 14% (at 300 K) but also reduce its thermal conductivity κtot to as small as ∼29% (at 300 K). Experimental evidences show that the improved PF comes from both increased electron mobility via inhibited Te vacancies and enhanced thermopower due to energy filtering effect, while the reduction of κtot originates from the drop of both electronic thermal conductivity largely owing to the reduced number of vacancy VTe·· and intensified phonon scattering chiefly from the dispersed Ag2Te nanophase. Consequently, the largest ZTmax = 1.31 (at 350 K) and average ZTave = 1.16 (300-500 K) are achieved for the Bi2Te2.7Se0.3-0.3 wt % Ag2Te composite sample, leading to a projected conversion efficiency η = 8.3% (300-500 K). The present results demonstrate that incorporation of nanophase Ag2Te is an effective approach to boosting the thermoelectric performance of BTS.

Boosting Thermoelectric Performance of Cu2SnSe3 via Comprehensive Band Structure Regulation and Intensified Phonon Scattering by Multidimensional Defects.

As an eco-friendly thermoelectric material, Cu2SnSe3 has recently drawn much attention. However, its high electrical resistivity ρ and low thermopower S prohibit its thermoelectric performance. Herein, we show that a widened band gap and the increased density of states are achieved via S alloying, resulting in 1.6 times enhancement of S (from 170 to 277 µV/K). Moreover, doping In at the Sn site can cause a 19-fold decrease of ρ and a 2.2 times enhancement of S (at room temperature) due to both multivalence bands' participation in electrical transport and the further enhancement of the density of states effective mass, which allows a sharp increase in the power factor. As a result, PF = 9.3 µW cm-1 K-2 was achieved at ∼800 K for the Cu2Sn0.82In0.18Se2.7S0.3 sample. Besides, as large as 44% reduction of lattice thermal conductivity is obtained via intensified phonon scattering by In-doping-induced formation of multidimensional defects, such as Sn vacancies, dislocations, twin boundaries, and CuInSe2 nanoprecipitates. Consequently, a record high figure of merit of ZT = 1.51 at 858 K is acquired for Cu2Sn0.82In0.18Se2.7S0.3, which is 4.7-fold larger than that of pristine Cu2SnSe3.

Improving the thermoelectric performance of Cu2SnSe3via regulating micro- and electronic structures.

As a p-type thermoelectric material, Cu2SnSe3 (CSS) has recently drawn much attention, with its constituents being abundant and free of toxic elements. However, the low electrical conductivity σ and thermopower S of CSS prohibit its thermoelectric performance. Here, we show that through mechanical milling, a 14 times increase in σ, around a 2-fold rise in S and a 40% reduction in the lattice thermal conductivity κL (at 300 K) can be achieved, amazingly. Microstructural analysis combined with first-principles calculations reveal that the increased σ originates from the generated Sn vacancies , Se dangling bonds and the reconstructed Cu-Sn-terminated acceptor-like surface states; while the enhanced S comes mainly from the enhanced density of states effective mass caused by the Sn vacancies. In addition, the generated Sn vacancies and the in situ formed SnO2 nanoparticles give rise to strong phonon scattering, leading to the reduced κL. As a result, a maximum ZTm = 0.9 at 848 K is obtained for the CSS specimen milled for 2 h, which is ∼3 times larger than that of CSS milled for 0.5 h.

Achieving High Thermoelectric Performance in p-Type BST/PbSe Nanocomposites through the Scattering Engineering Strategy.

To achieve high thermoelectric conversion efficiency in Bi0.4Sb1.6Te3 (BST) alloy is vital for its applications in low-grade energy harvesting. Here, we show that 56% increase in the power factor (PF) (from 16 to 25 µW cm-1 K-2) and 32% reduction of lattice thermal conductivity κL (from 0.56 to 0.38 W m-1 K-1) as well as an approximately four-fold decrease in bipolar-effect contribution κb (from 0.48 to 0.12 W m-1 K-1) can be achieved at 512 K through the incorporation of 0.2 vol % PbSe nanoparticles in the BST matrix. Analyses indicate that the remarkable increase in PF for the composite samples can be mainly attributed to strong electron scattering at the large interface barriers, inhibiting effectively the electron contribution to the total thermopower at elevated temperatures, while the large drop of κL and κb originates from enhanced phonon scattering by PbSe nanoinclusions as well as phase boundaries (among BST and PbSe nanophase) and suppression of electron transport, respectively. As a result, a maximum figure of merit (ZT) of 1.56 (at 400 K) and an average ZT (ZTave) of 1.44 in the temperature range of 300-512 K are reached. Correspondingly, a record projected conversion efficiency η = 11% is achieved at the cold side 300 K and hot side 512 K in the BST-based composite incorporated with 0.2 vol % PbSe nanoinclusions.

Effects of Sb Deviation from Its Stoichiometric Ratio on the Micro- and Electronic Structures and Thermoelectric Properties of Cu12Sb4S13.

Thermoelectric material tetrahedrite Cu12Sb4S13 has attracted much attention because of its intrinsic low lattice thermal conductivity, excellent electrical transport property, and environment-friendly constituents. However, its thermoelectric figure merit, ZT, is limited because of the low Seebeck coefficient (S) and power factor (PF). Hence, it is indispensable to enhance its S and PF to increase its ZT. Here, we show that when Sb deviation from its stoichiometric ratio in the Cu12Sb4S13 band structure is modulated, it gives rise to increased density of states and enhancement of the Seebeck coefficient. Moreover, carrier concentration is tuned by changing sulfur and copper vacancies through controlling the Cu3SbS4 phase with an atomic ratio of Sb, leading to increased electrical conductivity. In addition, as large as ∼60% reduction of lattice thermal conductivity is obtained by intensified phonon scattering using an impurity phase/element and vacancy-like defects induced by different Sb contents. As a result, a high ZT = 0.86 is achieved at 723 K for the Cu12Sb4+δS13 sample with δ = 0.2, which is ∼50% larger than that of stoichiometric Cu12Sb4S13 studied here, indicating that ZT of Cu12Sb4S13 can be improved through simple modulation of the Sb stoichiometric ratio.

Design of Domain Structure and Realization of Ultralow Thermal Conductivity for Record-High Thermoelectric Performance in Chalcopyrite.

Chalcopyrite compound CuGaTe2 is the focus of much research interest due to its high power factor. However, its high intrinsic lattice thermal conductivity seriously impedes the promotion of its thermoelectric performance. Here, it is shown that through alloying of isoelectronic elements In and Ag in CuGaTe2 , a quinary alloy compound system Cu1- x Agx Ga0.4 In0.6 Te2 (0 ≤ x ≤ 0.4) with complex nanosized strain domain structure is prepared. Due to strong phonon scattering mainly by this domain structure, thermal conductivity (at 300 K) drops from 6.1 W m-1 K-1 for the host compound to 1.5 W m-1 K-1 for the sample with x = 0.4. As a result, the optimized chalcopyrite sample Cu0.7 Ag0.3 Ga0.4 In0.6 Te2 presents an outstanding performance, with record-high figure of merit (ZT) reaching 1.64 (at 873 K) and average ZT reaching 0.73 (between ≈300 and 873 K), which are ≈37 and ≈35% larger than the corresponding values for pristine CuGaTe2 , respectively, demonstrating that such domain structure arising from isoelectronic multielement alloying in chalcopyrite compound can effectively suppress its thermal conductivity and elevate its thermoelectric performance remarkably.

Enhanced thermoelectric performance of ß-Zn4Sb3 based nanocomposites through combined effects of density of states resonance and carrier energy filtering.

It is a major challenge to elevate the thermoelectric figure of merit ZT of materials through enhancing their power factor (PF) and reducing the thermal conductivity at the same time. Experience has shown that engineering of the electronic density of states (eDOS) and the energy filtering mechanism (EFM) are two different effective approaches to improve the PF. However, the successful combination of these two methods is elusive. Here we show that the PF of ß-Zn4Sb3 can greatly benefit from both effects. Simultaneous resonant distortion in eDOS via Pb-doping and energy filtering via introduction of interface potentials result in a ~40% increase of PF and an approximately twofold reduction of the lattice thermal conductivity due to interface scattering. Accordingly, the ZT of ß-Pb0.02Zn3.98Sb3 with 3 vol.% of Cu3SbSe4 nanoinclusions reaches a value of 1.4 at 648 K. The combination of eDOS engineering and EFM would potentially facilitate the development of high-performance thermoelectric materials.

Co-precipitation synthesis of nanostructured Cu3SbSe4 and its Sn-doped sample with high thermoelectric performance.

Large-scale fabrication of nanostructured Cu3SbSe4 and its Sn-doped sample Cu3Sb0.98Sn0.02Se4 through a low-temperature co-precipitation route is reported. The effects of hot-pressing temperatures, time and Sn doping on the thermoelectric properties of Cu3SbSe4 are explored. The maximum figure of merit ZTmax obtained here reaches 0.62 for the un-doped Cu3SbSe4, which is three times as large as that of Cu3SbSe4 synthesized by the fusion method. Due to the ameliorated power factor by optimized carrier concentration and the reduced lattice thermal conductivity by enhanced phonon scattering at grain interfaces, Sn doping leads to an improvement of thermoelectric performance as compared to Cu3SbSe4. The maximum ZT for Cu3Sb0.98Sn0.02Se4 is 1.05 in this work, which is 50% larger than the largest value reported.

Convenient ultrasound-mediated synthesis of 1,4-diazabutadienes under solvent-free conditions.

An ultrasound-assisted preparation of 1,4-diazabutadienes via smooth condensation of diketones with amines under solvent-free conditions is described. The generality of this method was examined by the synthesized N,N'-diaryl- and N,N'-dialkyl-1,4-diazabutadiene derivatives. In addition to experimental simplicity, the main advantages of the procedure are mild conditions, short reaction time (2-15 min) and high yields (71-98%).