孔隙率对水热合成Bi2Te3热电性能的影响

用水热法制备了晶粒尺寸为几十纳米到几百纳米的Bi₂Te₃粉末,再通过压片法制得不同孔隙率的Bi₂Te₃薄片材料,研究了孔隙率对Bi₂Te₃热电性能的影响。通过对热电性能的测试,研究发现压片法制得的Bi₂Te₃样品具有较高的孔隙率,且样品的热传导符合多孔材料的热传导规律。当Bi₂Te₃样品孔隙率较大时具有较低的热导率,在室温下测得孔隙率为43%的Bi₂Te₃薄片热导率为0.282W·m^-1·K^-1。材料热导率、电导率和ZT值均随孔隙率的增加而减小。     

非水溶液中电化学沉积制备Sb2Te3热电薄膜

采用电化学沉积法，从非水溶液DMSO中制备了Sb2Te3热电薄膜。并采用循环伏安、SEM、XRD、EPMA等技术分别对电化学沉积过程和产物的形貌、结构、组成进行了研究。结果表明，在非水溶液二甲亚砜（DMSO）中，当电解液中Sb原子和Te原子的摩尔比为2：3，沉积电位为-2．2V时，在室温下即可得到单相的Sb2Te3热电薄膜，元素的组成接近化学计量比，组成薄膜的为大小均匀的球状颗粒，直径约为2～3岬左右。沉积电位对薄膜的组成影响明显，通过改变沉积电位，可以分别得到Te微过量的薄膜和近化学计量比的薄膜。     

定向凝固Ag掺杂Mg3Sb2合金热电性能

通过定向凝固方法可以高效制备Mg₃Sb₂晶体,根据凝固理论计算了平界面生长临界速率,在此速率下可以有效抑制第二相Sb的析出。对不同的凝固速率下的Mg₃Sb₂晶体微观组织进行了分析,表明凝固速率为5μm·s^-1时可以有效减少Mg空位的出现,并在晶体中获得过量Mg原子,有利于更好地提升热电性能。通过消除晶界和Ag元素掺杂有效提升了Mg₃Sb₂晶体的载流子迁移率和浓度,在测试温度区间(300～800K)内,最大电导率值可达309S·cm^-1,同时保持了较高的Seebeck系数值,从而获得了更好的电子传输性能(PF_max=1.2mW·m^-1·K^-2),通过Hall测试和第一性原理计算对此结果进行了验证。Ag掺杂浓度为2.5at%下相应的热电优值最高可以达到0.67,此方法为Mg₃Sb₂基热电材料性能优化提供了新的...     

CaMnO3热电薄膜的制备及其性能表征

采用溶胶-凝胶旋转涂覆法制备CaMnO3热电薄膜。通过XRD、SEM、Raman对薄膜显微结构进行了表征,并采用PPMS对其热电性能进行了测试。XRD、SEM以及Raman测试结果表明,CaMnO3的成相温度高于700℃,并且随着热处理温度升高,晶粒增大。络合剂比例及薄膜厚度对CaMnO3质量影响显著。PPMS测试发现,薄膜热导率随着热处理温度的升高而降低。     

Bi2Te3合金熔体结构变化对凝固行为及凝固组织的影响

根据Bi2Te3合金熔体的电阻率随温度而发生的异常行为,从熔体结构变化的视角探索了材料凝固行为与熔体热历史的依存关系。实验证明,Bi2Te3合金熔体结构在686～707℃范围内发生了异常转变,这种结构变化导致其熔体凝固过冷度增大,释放凝固潜热更加剧烈,并且凝固组织细化。这一结果表明通过控制熔体热历史,可更为有效地获得理想的凝固组织。     

Ba0.5Sr0.5TiO3铁电薄膜的微弧氧化成膜研究

以0.2 mol/L Ba(OH)2+0.2 mol/L Sr(OH)2溶液为电解液,采用微弧氧化法,在Ti板表面原位生长铁电薄膜,并对薄膜的物相构成、元素分布情况、截面结构及介电性能进行表征。结果表明:该工艺下制备的薄膜主要由四方相Ba0.5Sr0.5TiO3构成,薄膜致密层内,Ba,Sr,Ti和O元素分布都较均匀,但在微弧氧化孔洞附近存在含量波动;该薄膜在1 kHz下的介电常数较优,为411.3。最后对微弧氧化沉积铁电薄膜的成膜过程进行了分析,提出了微弧氧化过程中可能存在的化学反应。     

Bi_2Te_3和Bi_(0.5)Sb_(1.5)Te_3的机械合金化法制备及其热电性能

用机械合金法制备了Bi2 Te3和Bi0 .5Sb1 .5Te3两种热电材料。XRD分析表明两种材料分别在球磨 1 75h和 31 5h后完全合金化。机械合金化合金粉末冷压后在不同温度烧结并测量了热电性能 ,其中Bi0 .5Sb1 .5Te3材料480℃烧结样的最高Seebeck系数约为 2 0 0 μV/K。     

热电Bi2Te3/Bi2Se3纳米“弹簧”材料的电化学组装

为了探索制备具有高热电优值的一维纳米材料,采用脉冲电化学技术制备了一种热电Bi₂Te₃/Bi₂Se₃多层纳米线材料。对电沉积过程的监测结果表明,电沉积过程中体系电阻不断增大,随着电沉积的不断进行,体系电阻增大幅度越来越小。对电沉积产物进行退火处理,然后溶解掉模板,进行XRD测试,结果表明,所制备的产物是Bi₂Te₃/Bi₂Se₃,同时,有很多“卫星峰”出现在衍射图上,表明所制备的材料具有超晶格结构。运用FE-SEM、TEM对产物形貌进行分析,结果发现,所制备的材料是像“弹簧”一样形状的Bi₂Te₃/Bi₂Se₃多层纳米线。通过对脉冲时间的调节,可以实现对多层纳米线周期的调制。     

球形高电压LiNi0.5Mn1.5O4的制备及其电化学性能

以化学共沉淀法制备的球形Ni0.25Mn0.75CO3为前驱体合成高电压正极材料LiNi0.5Mn1.5O4,探讨用前驱体与Li2CO3直接反应和用前驱体分解后的氧化物与Li2CO3反应两种工艺路线对LiNi0.5Mn1.5O4形貌和电化学性能的影响。用扫描电镜(SEM)和X射线衍射(XRD)对Ni0.25Mn0.75CO3前驱体和LiNi0.5Mn1.5O4样品进行表征,用充放电测试和循环伏安法对LiNi0.5Mn1.5O4样品进行电化学性能研究。结果表明:两种方法合成的LiNi0.5Mn1.5O4均具有尖晶石型结构。但以前驱体Ni0.25Mn0.75CO3直接与Li2CO3反应合成的LiNi0.5Mn1.5O4的一次粒子颗粒较大,形貌较差,性能也较差;而以前驱体分解后的氧化物与Li2CO3反应合成的LiNi0.5Mn1.5O4的形貌及性能均较好。在3.0~4.9 V的电压范围内,1C倍率下电池的放电比容量达到136.3 mA.h/g,循环100次仍有126.5 mA.h/g,且材料具有较好的倍率性能;5C倍率下的首次放电比容量高达120.7 mA.h/g。     

退火对高压烧结Gd掺杂Bi_2Te_(2.7)Se_(0.3)纳米晶热电性能的影响

以Bi粉、Te粉、Se粉、Sb I3粉、Gd粉为原料,用高压烧结法制备了Gd掺杂的n型Bi2Te2.7Se0.3热电材料,对制备的样品分别在573、603、633 K真空退火36 h。用粉末XRD和FE-SEM研究了样品的物相及显微形貌;在298~473K范围内测定了样品的热电性能。建立了Bi2Te3基材料的禁带宽度与压力和体积的近似关系式,利用此关系式较好解释了高压烧结样品在退火前后热电性能的变化特性。研究结果表明制备的样品在退火前后均为纳米结构。高压烧结和Gd掺杂使样品晶胞尺寸变大,禁带宽度减小。退火使高压烧结样品的电导率提高,塞贝克系数增大,热导率降低。样品于633 K退火36 h后具有较好的热电性能,在423 K时其ZT达到最大值为0.74。     

Bi0.5Sb1.5Te3/Bi2Te2.4Se0.6 thin film thermoelectric sensors

In order to make thin film thermoelectric sensors, p-type (Bi_0.5Sb_1.5Te₃) and n-type (Bi₂Te_2.4Se_0.6) thermoelectric thin films were deposited on Pyrex and Teflon substrates by the flash evaporation technique. Their thermoelectric properties were investigated for annealed (473 K, 1 h) films. Thin film temperature sensors were fabricated and their thermal emf, sensitivity, and time constant were measured and evaluated. The sensor deposited on Teflon substrate showed better performance than that on the Pyrex substrate. The sensitivity and time constant were 2.54 V/W and 13.7 s, respectively, for the sensor with a leg size of 3 mm (w)×16mm (l)×4μm (t).     

Effects of hot pressing on electric performances of Bi0.5Sb1.5Te3

The effects of hot pressing on electric performance and mechanical strength of Bi0.5Sb1.5Te3 thermoelectric material prepared through vacuum melting and milling were studied. The phase constituent and microstructure were analyzed by X-ray Diffraction and cold field emission Scanning Electric Microscope. Aeolotropisms of the material on microstructure and electric performances are approved. With the rise of hot pressing temperature (from 300-500 ℃) and pressure (30-70 Mpa), electric conductivity and power factor are improved. Moreover, Bi0.5Sb1.5Te3 material can gain ideal thermoelectric performances and increased mechanical strength by hot pressing.     

Diffusion Soldering of Bi0.5Sb1.5Te3 Thermoelectric Material with Cu Electrode

For the production of thermoelectric modules, Bi_0.5Sb_1.5Te₃ was sequentially electroplated with a 4-μm Ni barrier layer and a 10-μm Ag layer and then diffusion soldered with the Cu electrode, which was also electroplated with 4-μm Ag and 4-μm Sn layers. The Bi_0.5Sb_1.5Te₃ and Ni interface with no sufficient chemical bonds resulted in a bonding strength lower than 3 MPa. Through the pre-coating of a 1-μm Sn thin film on Bi_0.5Sb_1.5Te₃ and heating at 250 °C for 3 min before the electroplating of the Ni barrier layer, the bonding strengths of Bi_0.5Sb_1.5Te₃/Cu assemblies increased to a maximal value of 10.7 MPa. The intermetallic compounds formed at various interfaces in the Bi_0.5Sb_1.5Te₃/Cu modules after diffusion soldering at temperatures ranging from 250 to 325 °C for 5-60 min and their growth kinetics was analyzed.     

Sn掺杂Bi2Te2.7Se0.3薄膜材料的微结构及热电性能研究

采用真空熔炼法合成(Bi<,1-x>Sn<,x>)<,2>Te<,2.7>Se<,0.3>合金,再通过热蒸发技术在473K玻璃基体上沉积了厚800nm的Sn掺杂Bi<,2>Te<,2.7>Se<,0.3>热电薄膜.利用X射线衍射技术对薄膜的相结构进行表征;采用表面粗糙度测量仪测定薄膜厚度;采用四探针法和温差电动势法分别测量薄膜的电阻率和Seebeck系数:采用薄膜的电阻率和Seebeck系数Sn掺杂浓度对(Bi<,1-x>Sn<,x>)<,2>Te<,2.7>Se<,0.3>薄膜热电性进行分析.结果表明,Sn掺杂浓度为0.003时,热电功率因子提高到12.8μW/K<'2>·cm;Sn掺杂浓度从0.004增加到0.01,薄膜为P型半导体,热电功率因子减小.     

Electric and mechanical performances of Bi0.5Sb1.5Te3 prepared by spark plasma sintering

Thermoelectric (TE) materials are a kind of functional materials which can be used to convert directly heat energy to electricity or reversely.The thermoelectric effects hold great potential for application in power generation and refrigeration.Bi2Te3 and its alloys are well known as best TE materials currently available near room temperature.This paper studies respectively the effects of spark plasma sintering (SPS) on electric performance of Bi0.5Sb1.5Te3 thermoelectric materials that are prepared through vacuum melting and ball milling.Through X-ray Diffraction and cold field emission scanning electric microscope s4800, the phase constituent and microstructure of the TE materials samples were analyzed.Electric conductivity and power factor can be improved with the rise of Spark Plasma Sintering temperature (from 300 to 500 ℃) and pressure(from 30 to 60 MPa), and the density and mechanical strength of Bi0.5Sb1.5Te3 thermoelectric material increase, too.     

PEDOT:PSS(聚3,4-乙撑二氧噻吩/聚苯乙烯磺酸盐)/ Bi0.5Sb1.5Te3复合材料热电性能研究

将PEDOT:PSS(聚3,4-乙撑二氧噻吩/聚苯乙烯磺酸盐)与Bi0.5Sb1.5Te3粉末混合烘干,在液氮下研磨成粉,将粉末经过热压工艺致密化,获得复合热电材料。通过XRD和FESEM表征其相结构和微观形貌,对该样品的电传输性能和热传输性能进行测试,结果表明：在75℃时,质量比90%的Bi0.5Sb1.5Te3复合PEDOT:PSS样品ZT值为0.1,比纯PEDOT:PSS样品高出40倍;复合材料样品Seebeck系数随着Bi0.5Sb1.5Te3的增加大幅提升,无机相连续分布是提高复合材料Seebeck系数的关键。     

Ga、K双掺杂P型Bi_(0.5)Sb_(1.5)Te_3材料的制备及热电性能

采用真空熔炼和热压方法制备了Ga和K双掺杂Bi0.5Sb1.5Te3热电材料。XRD结果表明,Ga0.02Bi0.5Sb1.48-x Kx Te3块体材料的XRD图谱与Bi0.5Sb1.5Te3的XRD图谱对应一致,但双掺杂样品的衍射峰略微向左偏移。热压块体材料中存在明显的(00l)晶面择优取向。SEM形貌表明材料组织致密且有层状结构特征。Ga和K双掺杂可使Bi0.5Sb1.5Te3在室温附近的Seebeck系数有一定的提高,而双掺杂样品的电导率均得到了不同程度的提高,其中Ga0.02Bi0.5Sb1.42K0.06Te3样品的电导率得到较明显的改善。在300~500 K测量温度范围内,所有双掺杂样品的热导率高于Bi0.5Sb1.5Te3的热导率,在300 K附近双掺杂样品的ZT值得到提高,其中Ga0.02Bi0.5Sb1.42K0.06Te3样品在300 K时ZT值达到1.5。     

Effect of cooling rate on the thermoelectric and mechanical performance of Bi0.5Sb1.5Te3 prepared under a high magnetic field

Given the thermoelectric and mechanical performance of a given material is closely related to its microstructure, in this paper, the microstructure of p-type Bi_0.5Sb_1.5Te₃, fabricated by a high magnetic field assisted melting-solidification (HMAMS) process, is successfully tuned by regulating the cooling rate during the solidification process, and a systematic investigation has been carried out to the effect of the cooling rate on the crystal orientation, microstructure, thermoelectric and mechanical performance of the obtained materials. By this approach, the thermal conductivity is sharply reduced due to the intensive phonon scattering by the massive BST/Te and Te/BST_Ⅱ interfaces, while the power factor is less affected, and the flexural strength is enhanced owing to the narrowing of eutectic strip and spacing. Eventually, a highest ZT of 1.23 at 323 K with a maximal flexural strength 23.2 MPa has been obtained in the sample prepared under a 6 T magnetic field at a cooling rate of 16 K/min.     

Enhanced thermoelectric and mechanical performance of polycrystalline p-type Bi0.5Sb1.5Te3 by a traditional physical metallurgical strategy

In this paper, p-type Bi_0.5Sb_1.5Te₃ polycrystalline materials have been fabricated by a traditional vacuum melting method, and the effects of cooling rate and MoSi₂ addition on the microstructure, thermoelectric and mechanical performance of the polycrystalline materials have been studied detailedly. It shows that the amount of Te-rich eutectic phase increases and the lamellar microstructure has been refined with the increase of the cooling rate. Due to the combined effect of cooling rate on the carrier concentration and mobility, the air cooled sample has higher figure of merit than the furnace cooled, water cooled and liquid nitrogen cooled samples, and a maximal ZT of 1.02 at 50 °C was obtained for the air cooled polycrystalline sample. Under the same air cooling condition, the inhomogeneous nucleation sites increase with increasing the amount of MoSi₂ particles, therefore the amount of Te-rich eutectic phase increases and the lamellar microstructure get refined, and the thermal conductivity of the sample decreases significantly due to the extra phonon scattering by the refined microstructure and MoSi₂ particles. The resulted figure of merit ZT increases with increasing the amount of MoSi₂ particles, and it decreases with further increasing the MoSi₂ content after attaining the vertex of ZT = 1.33 at 100 °C at a content of 0.2 wt.% MoSi₂. The flexural strength of the air cooled polycrystalline sample also increases with the amount of MoSi₂ increasing from 0 to 0.3 wt.%, and a nearly 56% enhancement was achieved for the 0.2 wt.% MoSi₂ sample (28.0 MPa) compared with the MoSi₂ free sample. The improvement of flexural strength is in agreement with the Hall–Petch strengthening mechanism due to the lamellar microstructure refinement induced by MoSi₂.