电沉积Bi2Te3基薄膜的电化学阻抗谱研究

以不锈钢为基底,利用电化学沉积方法制备Bi2Te3基薄膜材料,并采用X射线衍射技术、电子探针微观分析等方法对薄膜进行结构和成分表征,通过电化学阻抗谱技术对不锈钢表面Bi2Te3的电化学沉积机理进行了初步探讨.结果表明Bi-Te和Bi-Te-Se体系具有相似的电化学沉积机理,即Bi3+和2HTeO+或H2SeO3首先被还原为Bi单质和Te或Se单质,然后Bi单质与Te或Se单质反应生成Bi2Te3基化合物,而Bi-Sb-Te体系中,2HTeO+首先被还原为Te单质,生成的Te再与Bi3+和Sb(III)反应生成Bi2Te3基化合物,三种体系的沉积都受电化学极化控制.     

La掺杂Bi2O3的制备、表征与可见光催化活性

采用浸渍法制备了La掺杂Bi2O3(La-Bi2O3)光催化剂,利用X射线荧光光谱(XRF)、X射线衍射(XRD)、扫描电子显微镜(SEM)、傅立叶变换红外光谱(FT-IR)、X射线光电子能谱(XPS)、紫外-可见吸收光谱(UV-Vis)和光致发光谱(PL)等分析测试手段对样品的La掺杂量、晶体结构和光谱特征等进行了表征,并以2,4-二氯苯酚(2,4-DCP)水溶液的降解作为探针反应,考察了样品的可见光催化性能.结果表明,适量的La掺杂能有效抑制Bi2O3由四方相向单斜相转变,并将光吸收范围拓展到550 nm以上.掺杂的La可取代Bi2O3晶格中部分Bi,形成Bi—O—La键,并生成了少量镧铋复合氧化物(La0.176Bi0.824O1.5),它们的存在能有效抑制光生电子-空穴对的复合,从而提高光催化量子产率.可见光照射下2,4-DCP的光催化降解实验表明,La-Bi2O3具有良好的可见光催化性能,并且当La的掺杂量为3%(摩尔分数)时,催化剂的可见光催化效率最高.     

Bi4(Ti1/3Sn2/3)3O12掺杂BaTiO3基X8R陶瓷微观结构与介电性能

研究了Bi4(Ti1/3Sn2/3)3O12掺杂对钛酸钡基陶瓷微观结构和介电性能影响。结果表明,掺杂Bi4(Ti1/3Sn2/3)3O12后钛酸钡基陶瓷晶粒明显长大,同时烧结温度可由1 280℃降低至1 180℃。系统的介电性能和Bi4(Ti1/3Sn2/3)3O12的掺杂量有密切关系。当Bi4(Ti1/3Sn2/3)3O12的掺杂量从0.5mol%增加到2mol%,体系的居里峰被明显压低和展宽,当掺杂量为2mol%时居里峰变得不明显。当Bi4(Ti1/3Sn2/3)3O12的掺杂量从0.5mol%增加到2mol%,系统的居里温度由131℃升高至139℃。当Bi4(Ti1/3Sn2/3)3O12的掺杂量为1mol%时,钛酸钡基陶瓷介电常数为1 930,介电常数温度变化率为5%(-55℃),13%(134℃),-8%(150℃),满足X8R标准。     

(Ce, La)yFe1.0Co3.0Sb12热电化合物的固相反应合成及性能研究

研究了以Co，Sb，Fe及稀土Ce，La为起始原料，采用固相反应-放电等离子烧结(SPS)技术合成二元稀土填充式Skutterudite化合物(Ce，La)yFexCo4-xSb12(x=1．0，y=0—0．3)，并对化合物的热电性能进行了研究。实验结果表明：在y=0—0．3组成范围内，采用固相反应-SPS法在900-1000K温度范围内合成了(Ce，La)yFexCo4-xSb12化合物，并伴有极少量的Sb相。(Ce，La)，FexCo4-xSb12化合物呈现P型传导，化合物的晶格常数和Seebeck系数随Ce，La复合填充分数y的增加而增加，电导率和热导率由于Ce，La的复合填充大幅度降低，并且随着填充分数的增加进一步降低。当Ce，La复合填充分数为0．3时热导率达到最小值。在773K，富Co组成Ce0.1La0．2FeCo3Sb12化合物的最大无量纲热电性能指数ZTmax达0．46。     

原位溶解-沉积法制备高可见光活性BiOI/Bi2O3光催化剂

以Bi2O3为前驱体,通过原位溶解-沉积法在KI溶液中制备了BiOI/Bi2O3光催化剂。用X射线衍射(XRD)、扫描电子显微镜(SEM)和紫外-可见漫反射光谱(UV-Vis DRS)等对样品进行了表征。结果表明Bi2O3球形颗粒紧密地贴在BiOI片上。随着KI溶液pH值的降低,Bi2O3逐渐转变为BiOI,且样品的吸收带边逐渐红移。在可见光(λ≥420 nm)下降解甲基橙,在pH=3下制备的BiOI/Bi2O3的活性最强,其原因是BiOI/Bi2O3 p-n异质结促进了光生载流子的分离。     

纳米结构Bi2Te3化合物的低温湿化学合成

通过对溶液pH值和颜色以及粉末结构的原位分析, 研究了低温湿化学Bi₂Te₃纳米粉末合成过程中的化学和物理反应机制. 结果表明, 碱性添加剂对合成Bi₂Te₃是必要的. 采用65 ℃低温湿化学合成方法, 在添加乙二胺四乙酸二钠(EDTA)的情况下, 制备了Bi₂Te₃纳米囊. 高分辨电镜观察表明, 这种内空管状结构纳米囊的壁厚约为6 nm.     

纳米结构Bi2Te3化合物的低温湿化学合成

通过对溶液pH值和颜色以及粉末结构的原位分析, 研究了低温湿化学Bi₂Te₃纳米粉末合成过程中的化学和物理反应机制. 结果表明, 碱性添加剂对合成Bi₂Te₃是必要的. 采用65 ℃低温湿化学合成方法, 在添加乙二胺四乙酸二钠(EDTA)的情况下, 制备了Bi₂Te₃纳米囊. 高分辨电镜观察表明, 这种内空管状结构纳米囊的壁厚约为6 nm.     

用电沉积法制备稀土填充热电材料Bi_2Sb_3Re_x

分别以脉冲电沉积法和直流电沉积法制备了稀土填充热电材料Bi2Sb3Rex(Re=Ce,Nd)。结果表明,采用脉冲电沉积法,在通断脉宽为Ton=10ms(电流1A),Toff=40ms(电流0A),电流密度2000A.m-2,电沉积时间180s的条件下制得的电沉积膜Bi2Sb3Ce2,表面均匀、光滑、致密;在通断脉宽为Ton=0.4ms(电流1A),Toff=2.4ms(电流0A),电流密度2800A.m-2,电沉积时间120s,占空比为0.142的条件下制得的电沉积膜Bi2Sb3Nd0.1,表面均匀、光滑、致密。     

Bi掺杂对La0.1Sr0.9TiO3陶瓷热电性能的影响

在5% H₂+95% N₂（V/V）还原气氛中1 500℃烧结4 h制备La_0.1Bi_xSr_0.9-xTiO₃（x=0、0.05、0.075、0.1）陶瓷,并对其组成、显微结构和热电性能进行研究。结果表明：掺Bi试样的主晶相均为SrTiO₃,当Bi掺杂量大于0.075时,样品中出现少量Bi₂O₃杂相;掺Bi试样的晶粒发育完全,形状规则,结合紧密,显示出Bi₂O₃良好的助烧效果。另外,Bi元素掺入使La_0.1Sr_0.9TiO₃陶瓷的电导率和Seebeck系数绝对值显著增加,说明Bi元素的掺入可有效提高材料的载流子浓度和载流子迁移率。其中,x=0.075时试样的功率因子最大,在400℃时为692 μW·m^-1·K^-2。虽然其热导率比未掺杂Bi试样有所提高,x=0.075时试样的ZT值在500℃时仍可达0.172,比未掺杂Bi试样提高了130%。     

Ga掺杂La9+x/3(GeO4)6-x(GaO4)xO1.5的合成及导电性能研究

利用固相法合成系列Ga掺杂缺陷氧锗氧基磷灰石La9+x/3(GeO4)6-x(GaO4)xO1.5(sx=0,0.5,1,1.5).X射线粉末衍射结果表明:反应物在1350℃烧结24 h即可得到磷灰石结构的纯相产物.700℃时La9.5((GeO4)4.5(GaO4)1.5O1.5的电导率达到3.162×10-3 S·cm-1,是同温度La9(GeO4)6O1.5(1.259×10-3 S·cm-1)电导率的2.5倍.氧分压测试结果表明:材料的电导率在Po2=1～105 Pa保持不变,证明材料在较宽的氧分压范围内为O2-导电.     

Electrochemical aspects and structure characterization of VA-VIA compound semiconductor Bi2Te3/Sb2Te3 superlattice thin films via electrochemical atomic layer epitaxy

This paper concerns the electrochemical atom-by-atom growth of VA-VIA compound semiconductor thin film superlattice structures using electrochemical atomic layer epitaxy. The combination of the Bi2Te3 and Sb2Te3 programs and Bi2Te3/Sb2Te3 thin film superlattice with 18 periods, where each period involved 21 cycles of Bi2Te3 followed by 21 cycles of Sb2Te3, is reported here. According to the angular distance between the satellite and the Bragg peak, a period of 23 nm for the superlattice was indicated from the X-ray diffraction (XRD) spectrum. An overall composition of Bi 0.25Sb0.16Te0.58, suggesting the 2:3 stoichiometric ratio of total content of Bi and Sb to Te, as expected for the format of the Bi2Te3/Sb2Te3 compound, was further verified by energy dispersive X-ray quantitative analysis. Both field-emission scanning electron microscopy and XRD data indicated the deposit grows by a complex mechanism involving some 3D nucleation and growth in parallel with underpotential deposition. The optical band gap of the deposited superlattice film was determined as 0.15 eV by Fourier transform infrared spectroscopy and depicts an allowed direct type of transition. Raman spectrum observation with annealed and unannealed superlattice sample showed that the LIF mode has presented, suggesting a perfect AB/CB bonding in the superlattice interface.     

Nanostructures versus solid solutions: low lattice thermal conductivity and enhanced thermoelectric figure of merit in Pb9.6Sb0.2Te10-xSex bulk materials

The series of Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) compounds with different Se content (x) were prepared, and their structure was investigated at the atomic and nanosized regime level. Thermoelectric properties were measured in the temperature range from 300 to 700 K. The Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) series was designed after the refinement of the single-crystal structure of Pb(3.82)Sb(0.12)Te(4) (Pb(9.6)Sb(0.3)Te(10); S.G. Pmm) by substituting isoelectronically in anion positions Te by Se. The Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x)() compounds show significantly lower lattice thermal conductivity (kappa(L)) compared to the well-known PbTe(1)(-)(x)Se(x) solid solutions. For Pb(9.6)Sb(0.2)Te(3)Se(7) (x = 7), a kappa(L) value as low as 0.40 W/m.K was determined at 700 K. High-resolution transmission electron microscopy of several Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) samples showed widely distributed Sb-rich nanocrystals in the samples which is the key feature for the strong reduction of the lattice thermal conductivity. The reduction of kappa(L) results in a significantly enhanced thermoelectric figure of merit of Pb(9.6)Sb(0.2)Te(10)(-)(x)Se(x) compared to the corresponding PbTe(1)(-)(x)Se(x) solid solution alloys. For Pb(9.6)Sb(0.2)Te(3)Se(7) (x = 7), a maximum figure of merit of ZT approximately 1.2 was obtained at approximately 650 K. This value is about 50% higher than that of the state-of-the-art n-type PbTe. The work provides experimental validation of the theoretical concept that embedded nanocrystals can promote strong scattering of acoustic phonons.     

Bismuth telluride (Bi2Te3) nanowires: synthesis by cyclic electrodeposition/stripping, thinning by electrooxidation, and electrical power generation

Nanowires composed of the thermoelectric material Bi2Te3 were synthesized on highly oriented pyrolytic graphite (HOPG) electrodes using the electrochemical step edge decoration (ESED) method. Nanowire synthesis was initiated by applying a voltage pulse of -0.75 V versus SCE for 5 ms to an HOPG electrode in an aqueous solution containing both Bi3+ and TeO22-, thereby producing nuclei at the step edges. Bi2Te3 was electrodeposited onto these nuclei using a cyclic electrodeposition-stripping scheme that involved the electrodeposition of bismuth-rich Bi2Te3 on a negative-going voltammetric scan (to -0.05 V) and the subsequent anodic stripping of excess bismuth from these nanowires during a positive-going scan (to +0.35 V). When this cycle was repeated 10-50 times, Bi2Te3 nanowires in the 100-300-nm-diameter range were obtained. These nanowires were narrowly dispersed in diameter (RSDdia = 10-20%), were more than 100 microm in length, and were organized into parallel arrays containing hundreds of wires. Smaller nanowires, with diameters down to 30 nm, were obtained by electrooxidizing 150-nm-diameter Bi2Te3 nanowires at +0.37 V under conditions of kinetic control. This oxidation process unexpectedly improved the uniformity of Bi2Te3 nanowires, and X-ray photoelectron spectroscopy (XPS) shows that these nanowires retain a Bi2Te3 core but also have a thin surface layer composed of Bi and Te oxides. The ability of Bi2Te3 nanowires to generate electrical power was assessed by transferring ensembles of these nanowires onto cyanoacrylate-coated glass surfaces and evaporating 4-point nickel contacts. A dimensionless figure of merit, ZT, ranging from 0 to 0.85 was measured for fresh samples that were less than 1 day old. XPS reveals that Bi2Te3 nanowires are oxidized within a week to Bi2O3 and TeO2. These oxides may interfere with the application by evaporation of electrical contacts to these nanowires.     

Pressure-induced disordered substitution alloy in Sb2Te3

A new type of disordered substitution alloy of Sb and Te at above 15.1 GPa was discovered by performing in situ high-pressure angle-dispersive X-ray diffraction experiments on antimony telluride (Sb(2)Te(3)), a topological insulator and thermoelectric material, at room temperature. In this disordered substitution alloy, Sb(2)Te(3) crystallizes into a monoclinic structure with the space group C2/m, which is different from the corresponding high-pressure phase of the similar isostructural compound Bi(2)Te(3). Above 19.8 GPa, Sb(2)Te(3) adopts a body-centered-cubic structure with the disordered atomic array in the crystal lattice. The in situ high-pressure experiments down to about 13 K show that Sb(2)Te(3) undergoes the same phase-transition sequence with increasing pressure at low temperature, with almost the same phase-transition pressures.     

Design in solid state chemistry based on phase homologies. Sb4Te3 and Sb8Te9 as new members of the series (Sb2Te3)m.(Sb2)n

Sb4Te3 and Sb8Te9 are members of the homology (Sb2Te3)m.(Sb2)n, with structures consisting of Sb2- and Sb2Te3-type slabs stacked along [001]; electrical conductivity and thermopower are reported for several members of this family.     

Elemental distribution and thermoelectric properties of layered tellurides 39R-M(0.067)Sb(0.667)Te(0.266) (M=Ge, Sn)

The isostructural phases 39R‐Ge_0.067Sb_0.667Te_0.266 (R$\bar 3The isostructural phases 39R-Ge(0.067)Sb(0.667)Te(0.266) (R3m, a=4.2649(1), c=75.061(2) ?) and 39R-Sn(0.067)Sb(0.667)Te(0.266) (R3m, a=4.2959(1), c=75.392(2) ?) were prepared by quenching stoichiometric melts of the pure elements and subsequent annealing at moderate temperatures. Their structures are comparable to "superlattices" synthesized by layer-by-layer deposition onto a substrate. These structures show no stacking disorder by electron microscopy. The structure of the metastable layered phases are similar to that of 39R-Sb(10)Te(3) (equivalent to Sb(0.769)Te(0.231)), which contains four A7 gray-arsenic-type layers of antimony alternating with Sb(2)Te(3) slabs. Joint refinements on single-crystal diffraction data using synchrotron radiation at several K edges were performed to enhance the scattering contrast. These refinements show that the elemental distributions at some atom positions are disordered whereas otherwise the structures are long-range ordered. The variation of the elemental concentration correlates with the variation in interatomic distance. Z-contrast scanning transmission electron microscopy (HAADF-STEM) on 39R-Ge(0.067)Sb(0.667)Te(0.266) confirms the presence of concentration gradients. The carrier-type of the isostructural metal (A7-type lamellae)-semiconductor heterostructures (Ge/Sn-doped Sb(2)Te(3) slabs) varies from n-type (Ge(0.067)Sb(0.667)Te(0.266)) to p-type (Sn(0.067)Sb(0.667)Te(0.266)). Although the absolute values of the Seebeck coefficient reached about 50-70 μV/K and the electrical conductivity is relatively high, the two isotypic phases exhibit a maximal thermoelectric figure of merit (ZT) of 0.06 at 400 °C as their thermal conductivity (κ≈8-9.5 W/mK at 400 °C) lies interestingly in between that of antimony and pure Sb(2)Te(3).     

CsPb3Bi3Te8 and CsPb4Bi3Te9: low-dimensional compounds and the homologous series CsPbmBi3Te5 + m

Two new thermoelectric materials of quaternary bismuth telluride CsPb3Bi3Te8 and CsPb4Bi3Te9 are reported, which are members of a homologous series featuring anionic slabs [PbmBi3Te5 + m]- (m = 1-4) of monotonically increasing thickness.     

Direct tuning of electrical properties in nano-structured Bi2Se0.3Te2.7 by reversible electrochemical lithium reactions

Lithium intercalation and de-intercalation processes have been used to fabricate bulk Bi(2)Se(0.3)Te(2.7) with internal nanostructures. The doped Li content can be precisely controlled through this method. It provides a chance to directly optimize electrical properties when preparing nano-structured materials, leading to the optimum carrier concentration for improved thermoelectric figure of merit.     

Direct synthesis of Te/Bi2Te3 nanocomposite powders by a polyol process

Research on Chemical Intermediates - Tellurium nanotube-based bismuth telluride (Te/Bi2Te3) nanocomposite powders have been synthesized by the polyol process using Bi (NO3)3, TeCl4 as the metal...     

Synthesis in ionic liquids: [Bi2Te2Br](AlCl4), a direct gap semiconductor with a cationic framework

The Lewis acidic ionic liquid EMIMBr-AlCl(3) (EMIM = 1-ethyl-3-methylimidazolium) allows a novel synthetic route to the semiconducting layered metal chalcogenides halide [Bi(2)Te(2)Br](AlCl(4)) and its Sb analogue. [Bi(2)Te(2)Br](AlCl(4)) is a direct band gap, strongly anisotropic semiconductor and consists of cationic infinite layers of [Bi(2)Te(2)Br](+) and [AlCl(4)](-) anions inserted between the layers.