Synthesis and thermoelectric properties of Rashba semiconductor BiTeBr with intensive texture.

Bismuth tellurohalides with Rashba-type spin splitting exhibit unique Fermi surface topology and are developed as promising thermoelectric materials. However, BiTeBr, which belongs to this class of materials, is rarely investigated in terms of the thermoelectric transport properties. In the study, polycrystalline bulk BiTeBr with intensive texture was synthesized via spark plasma sintering (SPS). Additionally, its thermoelectric properties above room temperature were investigated along both the in-plane and out-plane directions, and they exhibit strong anisotropy. Low sound velocity along two directions is found and contributes to its low lattice thermal conductivity. Polycrystalline BiTeBr exhibits relatively good thermoelectric performance along the in-plane direction, with a maximum dimensionless figure of merit (ZT) of 0.35 at 560 K. Further enhancements of ZT are expected by utilizing systematic optimization strategies.

Structure, Magnetism, and Thermoelectric Properties of Magnesium-Containing Antimonide Zintl Phases Sr14MgSb11 and Eu14MgSb11.

New Mg-containing antimonide Zintl phases, Sr14MgSb11 and Eu14MgSb11, were synthesized from high-temperature solid-state reactions in Ta tubes at 1323 K. Their structures can be viewed as derived from the Ca14AlSb11 structure type, which adopt the tetragonal space group I41/acd (No. 142, Z = 8) with the cell parameters of a = 17.5691(14)/17.3442(11) Å and c = 23.399(4)/22.981(3) Å for the Sr- and Eu-containing compounds, respectively. The corresponding thermoelectric properties were probed, which demonstrated high potential of these compounds as new thermoelectrics for their very low thermal conductivity and moderate Seebeck coefficient. Magnetism studies and theoretical calculations were conducted as well to better understand the structure-and-property correlation of these materials.

Enhancing Thermoelectric Performance of n-Type Hot Deformed Bismuth-Telluride-Based Solid Solutions by Nonstoichiometry-Mediated Intrinsic Point Defects.

Bismuth-telluride-based solid solutions are the unique thermoelectric (TE) materials near room temperature. Various approaches have been applied to enhance the thermoelectric performance, and much progress has been made in their p-type materials. However, for the n-type counterparts, little breakthrough has been obtained. We herein report on enhancing thermoelectric performance of n-type bismuth-telluride-based alloys by nonstoichiometry to mediate the point defects, combined with one-time hot deformation. The improved power factor of 3.3 × 10-3 W m-1 K-2 and reduced lattice thermal conductivity contribute to a high figure-of-merit, zT, of 1.2 at 450 K for n-type Bi2Te2.3Se0.69 alloys with Se deficiency. The high zT is comparable to that of Bi2Te2.3Se0.7 hot deformed three times, which is a practically complicated process. The results demonstrate that nonstoichiometry can be an effective and simple strategy in mediating intrinsic point defects and enhancing the thermoelectric performance of bismuth-telluride-based alloys.

[Negative air ions generated by plants upon pulsed electric field stimulation applied to soil].

This paper investigated the capacity of plants (Schlumbergera truncata, Aloe vera var. chinensis, Chlorophytum comosum, Schlumbergera bridgesii, Gymnocalycium mihanovichii var. friedrichii, Aspidistra elatior, Cymbidium kanran, Echinocactus grusonii, Agave americana var. marginata, Asparagus setaceus) to generate negative air ions (NAI) under pulsed electric field stimulation. The results showed that single plant generated low amounts of NAI in natural condition. The capacity of C. comosum and G. mihanovichii var. friedrichii generated most NAI among the above ten species, with a daily average of 43 ion · cm(-3). The least one was A. americana var. marginata with the value of 19 ion · cm(-3). When proper pulsed electric field stimulation was applied to soil, the NAI of ten plant species were greatly improved. The effect of pulsed electric field u3 (average voltage over the pulse period was 2.0 x 10(4) V, pulse frequency was 1 Hz, and pulse duration was 50 ms) was the greatest. The mean NAI concentration of C. kanran was the highest 1454967 ion · cm(-3), which was 48498.9 times as much as that in natural condition. The lowest one was S. truncata with the value of 34567 ion · cm(-3), which was 843.1 times as much as that in natural condition. The capacity of the same plants to generate negative air ion varied extremely under different intensity pulsed electric fields.

[Effects of 1alpha,25-dihydroxyvitamin D(3) and UVB on cell proliferation and melanin synthesis of cultured human melanocyte].

OBJECTIVE: To study the effects of 1alpha,25-dihydroxyvitamin D(3) and UVB on cell proliferation and melanin synthesis of normal human melanocytes. METHODS: Melanocytes of foreskins of healthy men were cultured and treated with various concentration of 1alpha,25-dihydroxyvitamin D(3) or UVB (55 mJ/cm(2)),or both. Cell proliferation was measured with MTT assay .The synthesis of melanin was determined by chromatography. RESULTS: 1alpha,25-dihydroxyvitamin D(3) and UVB could promote the proliferation of cultured melanocyte,and 1alpha,25-dihydroxyvitamin D(3) could promote the melanin synthesis. The significant concentration of 1alpha,25-dihydroxyvitamin D(3) ranging from 10(-7) to 10(-10) mol/L. CONCLUSION: 1alpha,25-dihydroxyvitamin D(3) and UVB irradiation could promote the proliferation of melanocyte,which indicates that they might be effective in the treatment of vitiligo.