Pleniglacial millennium-scale climate variations in northern China based on records from the Salawusu River Valley

Situated in the Salawusu River Valley, southeast of China＇s Mu Us Desert, the MGS2 （Milanggouwan section） portion of the Milanggouwan stratigraphic section records 5.5 sedimentary cycles consisting of alternations between dune sand deposits and fluvial or lacustrine facies. We analyzed the grain-size and CaCO3 distributions in MGS2, and found that Mz （mean particle diameter） and o （standard deviation） displayed clear variations in peaks and valleys within different sedimentary facies. The CaCO3 content averaged 0.4% in the dune sand deposits, 1.43% in the fluvial facies, and 8.82% in the lacustrine facies. Both the grain-size distribution and CaCO3 contents, which equal the indicators for the alternation among the sedimentary facies, suggest the occurrence of 5.5 cycles. These results suggest that the observed cycles mainly resulted from fluctuations between a cold and dry winter monsoon climate and a warm and humid summer monsoon climate, and that the MGS2 portion experienced at least 5.5 fluctuations between these two extremes. This high-frequency climatic fluctuation indicates a strong influence of millennium-scale variations in the strength of the East Asian winter and summer monsoons in our study area during the Pleniglacial.

构建准层状自空穴掺杂SnSe取向薄膜获得优异热电功率因子和输出功率密度

热电技术可以实现热能与电能的相互转换,其开发利用对于缓解能源危机具有重要意义.近10年来,SnSe因其潜在的高能量转换效率、绿色环保和低成本特性而备受关注.但SnSe的固有载流子浓度低(约10~(17)cm^(-3)),导致其功率因子偏低,从而限制了SnSe基器件的输出功率密度.因此,探索新的载流子浓度优化策略对于SnSe的应用至关重要.此外,与三维块体相比,二维薄膜更易和现代半导体工艺相兼容,在热电微纳米器件的构筑和应用方面具有独特优势.本文报道了一种利用非原位硒化技术,通过电荷转移和自空穴掺杂效应来优化a轴取向SnSe基薄膜的载流子浓度.当硒化时间为20 min时,薄膜载流子浓度可提高至10~(18)cm^(-3)数量级,形成了准层状的自空穴掺杂SnSe基薄膜,其功率因子在600 K时达到了5.9μW cm^(-1)K^(-2).由硒化处理的SnSe基取向薄膜构筑的热电发电机在50和90 K的温差下分别具有约83、838μW cm^(-2)的超高功率密度.非原位硒化技术可以有效提高SnSe基薄膜的载流子浓度,为其他热电材料性能优化提供了一种新策略.

Transparent conducting properties of c-axis-oriented NaxCoO2 epitaxial thin films

Transparent conducting oxides(TCOs)have attracted intensive attention because of their broad application in photoelectric devices such as solar cells,light-emitting diodes,and flat-panel displays.Current TCOs used in industry,including tin(IV)oxide(SnO_2),indium oxide(In_2O_3),indium tin oxide(ITO),and zinc oxide(ZnO),are primarily n-type semiconductors[1-3].Suitable p-type TCOs are still

Improving electrical and thermal properties synchronously via introducing CsPbBr_(3)QDs into higher manganese silicides

Higher manganese silicide(HMS)is a P-type medium temperature thermoelectric(TE)material,which has attracted widespread attention over the past few decades due to its remarkable mechanical properties,excellent chemical and thermal stability,as well as the non-toxicity,abundance and competitive price.The peak power factor(PF)of HMS is as high as~1.50×10^(-3)W m^(-1)K^(-2)because of its intrinsic high electrical conductivity and Seebeck coefficient.However,the thermal conductivity of HMS is also high,resulting in relatively low z T values.Introducing nano-dispersion in the matrix is one of the most effective methods to enhance the TE properties via reducing the lattice thermal conductivity significantly without drastic changes on the other parameters.In this study,Cs Pb BrQDs with uniform size were synthesized and introduced into HMS bulks.The PF(at 823 K)was enhanced to 1.71×10^(-3)W m^(-1)K^(-2),which is improved 14.0%approximately compared with that of pure HMS owing to the combined effect of element doping and energy filtering.The lattice thermal conductivity(at 823 K)decreased from 2.56W mKto 1.99 W mKsynchronously(~22.0%)due to the intensive phonon scattering caused by Cs doping,and the embedding of Pb riched CsPbBr_(3)QDs and Pb QDs.A maximum z T value of 0.57(823 K)is achieved in Cs Pb BrQDs/HMS composites,which is 36.0%higher than that of pure HMS.Predictably,for other TE materials,it is also feasible to improve the TE properties via introducing metastable quantum dots.

Effect of sintering temperature on thermoelectric properties of CdO ceramics

The effect of sintering temperature on thermoelectric properties of CdO ceramics was investigated by solid-state reaction method within the temperature range of 700-1000℃.With the increase of sintering temperature,both the grain size and the carrier concentration of these samples increased,while the Seebeck coefficient decreased.The highest dimensionless figure of merit ZT,0.34,was obtained at 1023 K for the sample sintered at 800℃,suggesting the potential application of CdO ceramics in thermoelectric(TE)devices.

Incorporating element doping and quantum dot embedding effects to enhance the thermoelectric properties of higher manganese silicides

Element doping and nano-inclusion embedding are effective approaches to enhance the electrical conductivities and decrease the lattice thermal conductivities of thermoelectric(TE)materials,respectively.However,the intrinsic low electrical thermal conductivities and high electrical properties are severely sacrificed,and the final figure of merit(ZT)is usually restricted.In this study,Ag doping and Pt quantum dot(QD)embedding were synchronously achieved via embedding Ag/Pt alloy QDs into the higher manganese silicides to avoid the conventional single-element doping strategy.The power factor(at 823 K)was enhanced from 1.57×10^(-3) W m^(-1) K^(-2) to 1.82×10^(-3) W m^(-1) K^(-2)(-16%)due to the-18%increase in carrier concentration that was derived from the Ag doping effect.Simultaneously,the lattice thermal conductivity(at 823 K)decreased from 2.65 W m^(-1) K^(-1) e1.92 W m^(-1) K^(-1)(-28%)because of the broadband phonon scattering effect that resulted from the residual Pt QDs inclusions.Synthetically,the optimal ZT value increased by-52%from 0.42 to 0.64 at 823 K.This study demonstrated that incorporating metastable alloy QDs to obtain element doping and nano-inclusion embedding effects is a novel and feasible means to enhance the ZT value of HMS.This method is also possibly applicable to other alloy QD/TE composites.