Enhanced thermoelectric properties of p-type polycrystalline SnSe by regulating the anisotropic crystal growth and Sn vacancy

Thermoelectric selenides have attracted more and more attentions recently.Herein,p-type Sn Se polycrystalline bulk materials with good thermoelectric properties are presented.By using the SnSe_2 nanostructures synthesized via a wetchemistry route as the precursor,polycrystalline Sn Se bulk materials were successfully obtained by a combined heattreating process under reducing atmosphere and following spark plasma sintering procedure.As a reference,the Sn Se nanostructures synthesized via a wet-chemistry route were also fabricated into polycrystalline bulk materials through the same process.The thermoelectric properties of the Sn Se polycrystalline transformed from SnSe_2 nanostructures indicate that the increasing of heattreating temperature could effectively decrease the electrical resistivity,whereas the decrease in Seebeck coefficient is nearly invisible.As a result,the maximum power factor is enhanced from 5.06×10~(-4)W/m·K~2to 8.08×10~(-4)W/m·K~2at 612~?C.On the other hand,the reference sample,which was obtained by using Sn Se nanostructures as the precursor,displays very poor power factor of only 1.30×10~(-4)W/m·K~2at 537~?C.The x-ray diffraction(XRD),scanning electron microscope(SEM),x-ray fluorescence(XRF),and Hall effect characterizations suggest that the anisotropic crystal growth and existing Sn vacancy might be responsible for the enhanced electrical transport in the polycrystalline Sn Se prepared by using SnSe_2 precursor.On the other hand,the impact of heat-treating temperature on thermal conductivity is not obvious.Owing to the boosting of power factor,a high z T value of 1.07 at 612~?C is achieved.This study provides a new method to synthesize polycrystalline Sn Se and pave a way to improve the thermoelectric properties of polycrystalline bulk materials with similar layered structure.     

排队论及其BASIC程序

排队论(Queueing Theory)也称随机服务系统理论。在生产活动和日常生活中有各种各样的随机服务系统,经常会遇到许多有形或无形的排队现象。例如,到火车站售票口买票的旅客,到理发店理发的顾客,到医院就诊的患者,到商店购买商品的用户,早晚上下班时乘坐公共汽车、电车的职工,常常都需要排队等候,才能得到或接受服务。医生到患者家出诊,修理工到各车间去修理机床,推销员访问用户,从前一道工序流送来的待加工的在制品,电子计算机中心处理来自各终端的上机作业也是一类排队问题。还有电话的传呼与交换台占线问题,水库存水量的调节问题,车站、码…     

水热法合成Ni(OH)2/SiO2催化剂制备碳纳米管:镍含量对碳纳米管管径和产率的影响

以硝酸镍和正硅酸乙酯为主要原料，采用前驱物水热法制得不同镍含量的纳米Ni(0H)2／SiO2复合粉体，用复合粉体做催化剂催化裂解C2H2制得多壁碳纳米管粗产物。研究表明：在复合粉体Ni(OH)2／SiO2催化剂中，硅镍比在一定范围内(1：2～1：14)，随着镍含量增加，粒径增大，结晶程度提高，催化剂活性先提高后下降，制得的碳纳米管纯度及产量先增后降，碳管的管径分布范围先窄后宽。催化剂硅镍比为1：12时，制得的碳纳米管纯度高，管径细而均匀(10～18nm)，且粗产物数量较多(1g催化剂合成3．3g碳纳米管粗产物)。     

库存论简介

引言 库存论也称为库存管理或存■论.在人类生产活动与日常生活中,存■系统是常见的普遍存在着的一种系统.人们往往要将一定量的材料、产品、商品、食品、用品等暂时存■起来,以备将来在需要时使用、销售或消费.现举例如下. 在工厂里,为了制造某一产品,甚至加工某一零件往往需要经过多路工序、需要各种材料、加工工具等等,因此一般要建立各种仓库,如有存■原材料的材料库,存■零部件的零件库,存■在制品的在制品库,存放工具的工具库,存放劳保用品的用品库,存放产品的成品库等等,这些仓库内存■着生产中所需的物资,以备在需要时出库,满足消费…