Bismuth telluride‐based materials are already being commercially developed for thermoelectric (TE) cooling devices and power generators. However, the relatively low efficiency, which is characterized by a TE figure of merit, zT, is the main obstacle to more widespread application. Significant advances in the TE performance have been made through boundary engineering via embedding nanoinclusions or nanoscale grains. Herein, an effective approach to greatly enhance the TE performance of p‐type BiSbTe material by incorporating carbon microfibers is reported. A high zT of 1.4 at 375 K and high average zT of 1.25 for temperatures in the range of 300 to 500 K is achieved in the BiSbTe/carbon microfiber (BST/CF) composite materials. Their superior TE performance originates from the low thermal conductivity and the relatively high power factor. A TE unicouple device based on the p‐type BST/CF composite material and the commercially available n‐type bismuth telluride‐based material shows a huge cooling temperature drop in the operating temperature range of 299–375 K, and is greatly superior to the unicouple device made of both commercial p‐type and n‐type bismuth telluride‐based material. The materials demonstrate a high average zT and excellent mechanical properties and are strong candidates for practical applications.

A new category of five KBBF-analogy nonlinear optical (NLO) materials, AZn 2 BO 3 X 2 (A = K, Rb, NH 4 ; X = Cl, Br), are developed by the tetrahedron substitution of BeO 3 F for ZnO 3 X from KBe 2 BO 3 F 2 (KBBF). They preserve the structural merits of KBBF, consisting of the infinite planar [Zn 2 BO 3 X 2 ] ∞ layers. Optical measurements on this series of NLO crystals reveal that they are phase-matchable in the visible and UV region with powder second-harmonic generation (SHG) responses being more than twice that of isostructural KBBF. First-principles calculations and atomcutting analysis were carried out to demonstrate that enhanced SHG response originates from the cooperative effect of coparallel [BO 3 ] triangles and distorted ZnO 3 Cl/Br tetrahedra. The theoretical calculations and experimental results show that AZn 2 BO 3 X 2 exhibits a less-developed layer habit compared with KBBF. Especially, because of the existence of relatively strong hydrogen bond between NH 4 + groups and [Zn 2 BO 3 Cl 2 ] ∞ layers, NH 4 Zn 2 BO 3 Cl 2 crystal exhibits the best growth behavior along the c axis. These results show that they may have prospects as a kind of UV nonlinear optical material.

trical conductivity, S is Seebeck coefficient, T is the absolute temperature, and κ is the thermal conductivity (κ = electronic (κ e) + lattice thermal conductivity (κ L)). [2,3] The state-of-the-art bismuth telluride-based thermoelectric (TE) materials have been used for refrigeration applications. [4] However, their ZT is limited to about 1 at room temperature, making such cooling devices less powerful and cost-competitive than other conventional technologies such as mechanical vapor-compression cooling systems. Further improving the ZT would facilitate their widespread application in industrial waste heat harvesting and electronic device cooling. [5] Maximizing ZT requires the enhancement of the power factor (PF = S 2 σ) and the reduction of thermal conductivity. [6,7] Several approaches have recently been implemented to enhance ZT, including improvement of PF by optimizing carrier concentration, [8-10] band convergence, [11,12] resonant levels, [13] energy barrier filtering, [14] and reducing κ L by alloying, [15] all-scale hierarchical architectures [16-18] and nanostructuring. [19-21] In particular, reduction of κ L by nanostructuring or through formation of nanocomposites has been demonstrated to be an effective Based on the Seebeck and Peltier effects, state-of-the-art bismuth telluridebased thermoelectric materials, which are capable of direct and reversible conversion of thermal to electrical energy, have great potential in energy harvesting and solid-state refrigerators. However, their widespread use is limited by their low conversion efficiency, which is determined by the dimensionless figure-of-merit (ZT). Significant enhancement of ZT is a great challenge owing to the common interdependence of electrical and thermal conductivity. Here, it is demonstrated that by incorporating nanoamorphous boron into the p-type Bi 0.5 Sb 1.5 Te 3 , a record high ZT of 1.6 at 375 K is achieved. It is shown that a high density of nanostructures and dislocations due to the incorporation of the boron inclusions, leads to a significant reduction of thermal conductivity and improved charge transport. The findings represent an important step to further promote the development of thermoelectric technology and its widespread application in solid-state refrigeration and power generation from waste heat.

Crystals of KCdCO3F (I), RbCdCO3F (II), KZnCO3F (III), and RbZnCO3F (IV) are grown under subcritical hydrothermal conditions, using e.g. a 1:6:2 molar mixture of CdCl2, KF, and K2CO3 in H2O for KCdCO3F (autoclave, 220 °C, 5 d).

The first alkali-metal nitrate isocyanurates, A­(H3C3N3O3)­(NO3) (A = K, Rb), were synthesized by the tactic of introducing (NO3)− into isocyanurate with a mild hydrothermal technique. They crystallized into the same monoclinic centrosymmetric (CS) space group P21/c, which featured a 2D [(H3C3N3O3)­(NO3)]∞ layered structure separated by K+ and Rb+ cations, respectively. Both compounds exhibited short ultraviolet cutoff edges (λcutoff = 228 and 229 nm) and large birefringences (Δn = 0.253 and 0.224 at 546.1 nm). More importantly, in comparison with most of the isocyanurates and nitrates, they have better thermal stability with decomposition temperatures up to 319.8 and 324.4 °C. In addition, our theoretical calculations reveal that the π-conjugated groups play significant roles in improving the optical anisotropy. Remarkably, introducing a π-conjugated inorganic acid radical (NO3)− into isocyanurate is an extremely meaningful strategy to explore new UV birefringent crystals.

Research data are not shared.

A family of noncentrosymmetric alkali-metal bismuth selenite fluorides, A 2 Bi 2 (SeO 3 ) 3 F 2 [A = K(1) and Rb(2)], has been synthesized through a mild hydrothermal method. These isostructural compounds all had onedimensional [Bi 2 O 9 F 2 ] chains, which were further connected with neighbouring chains through bridged selenite groups to construct the 3D framework. Because of the relatively ordered alignment of [BiO x F y ] and SeO 3 groups, they have large second-harmonic generation (SHG) responses of about 15.0(1) and 14.4(2) times that of KH 2 PO 4 (KDP) under 1064 nm laser radiation and 0.40(1) and 0.36(2) times that of AgGaS 2 (AGS) under 2.05 μm laser radiation, respectively. In addition, the SHG response of (1) was the largest among those of all reported metal selenites. In addition, all of them had high thermal stability (∼400 °C), wide energy band gaps (over 3.72 eV), and an excellent IR transparent region, suggesting that they had great potential as high power mid-infrared nonlinear optical crystals.

Thermoelectric (TE) materials have attracted extensive interest because of their ability to achieve direct heat-to-electricity conversion. They provide an appealing renewable energy source in a variety of applications by harvesting waste heat. The record-breaking figure of merit reported for single crystal SnSe has stimulated related research on its polycrystalline counterpart. Boosting the TE conversion efficiency requires increases in the power factor and decreases in thermal conductivity. It is still a big challenge, however, to optimize these parameters independently because of their complex interrelationships. Herein, we propose an innovative approach to decouple electrical and thermal transport by incorporating carbon fiber (CF) into polycrystalline SnSe. We show that the incorporation of highly conductive CF can successfully enhance the electrical conductivity, while greatly reducing the thermal conductivity of polycrystalline SnSe. As a result, a high TE figure-of-merit (zT) of 1.3 at 823 K is obtained in p-type SnSe/CF composite polycrystalline materials. Furthermore, SnSe samples incorporated with CFs exhibit superior mechanical properties, which are favorable for device fabrication applications. Our results indicate that the dispersion of CF can be a good way to greatly improve both TE and mechanical performance.