Optical and thermoelectric characterizations of electroplated n-Bi2(Te0.9Se0.1)3

Bismuth selenotelluride (Bi₂(Te_0.9Se_0.1)₃) films were electrodeposited at constant current density from acidic aqueous solutions with Arabic gum in order to produce thin films for miniaturized thermoelectric devices. X-ray fluorescence spectroscopy determined film compositions. X-ray diffraction pattern shows that the films as deposited are polycrystalline, isostructural to Bi₂Te₃ and covered by crystallites. Mueller-matrix analysis reveals that the electroplated layers are optically like an isotropic medium. Their pseudo-dielectric functions were determined using mid-infrared spectroscopic ellipsometry. Tauc-Lorentz combined with Drude dispersion relations were successfully used. The energy band gap E_g was found to be about 0.15 eV. Moreover, the fundamental absorption edge was described by an indirect optical band-to-band transition. From Seebeck coefficient measurement, films exhibit n-type charge carrier and the value of thermoelectric power is about −40 μV/K.     

Electrodeposition of BixSb2−xTey thermoelectric thin films from nitric acid and hydrochloric acid systems

The electrochemical behaviors of Bi^III, Te^IV and Sb^III single ions and their mixtures were investigated in nitric acid and hydrochloric acid system separately. Based on which, Bi_xSb_2−xTe_y thermoelectric films were prepared by potentiostatic electrodeposition from the solutions with different concentrations of Bi^III, Te^IV and Sb^III in the two acid systems. The morphologies, compositions, structures, Seebeck coefficients and resistivities of the deposited thin films were characterized and compared by ESEM (or FESEM), EDS, XRD, Seebeck coefficient measurement system and four-probe resistivity measuring device respectively. The results show that although Bi_xSb_2−xTe_y thermoelectric thin film which structure is consistent with the standard pattern of Bi_0.5Sb_1.5Te₃ can be gained in both of the two acid solutions by adjusting the deposition potential, their morphologies and thermoelectric properties have big differences in different acid solutions.     

Bi-Sb-Te基热电薄膜温差电池离子束溅射制备与表征

本文采用离子束溅射Bi/Te和Sb/Te二元复合靶,直接制备n型Bi₂Te₃热电薄膜和p型Sb₂Te₃热电薄膜.在退火时间同为1 h的条件下,对所制备的Bi₂Te₃薄膜和Sb₂Te₃薄膜进行不同温度的退火处理,并对其热电性能进行表征.结果表明,在退火温度为150 ℃时,制备的n型Bi₂Te₃关键词： 薄膜温差电池 2Te₃薄膜')" href="#">Sb₂Te₃薄膜 2Te₃薄膜')" href="#">Bi₂Te₃薄膜 离子束溅射     

Annealing temperature influence on electrical properties of ion beam sputtered Bi2Te3 thin films

Ion beam sputtering process was used to deposit n-type fine-grained Bi₂Te₃ thin films on BK7 glass substrates at room temperature. In order to enhance the thermoelectric properties, thin films are annealed at the temperatures ranging from 100 to 400 °C. X-ray diffraction (XRD) shows that the films have preferred orientations in the c-axis direction. It is confirmed that grain growth and crystallization along the c-axis are enhanced as the annealing temperature increased. However, broad impurity peaks related to some oxygen traces increase when the annealing temperature reached 400 °C. Thermoelectric properties of Bi₂Te₃ thin films were investigated at room temperature. The Bi₂Te₃ thin films, including as-deposited, exhibit the Seebeck coefficients of −90 to −168 μV K⁻¹ and the electrical conductivities of 3.92×10²-7.20×10² S cm⁻¹ after annealing. The Bi₂Te₃ film with a maximum power factor of 1.10×10⁻³ Wm⁻¹ K⁻² is achieved when annealed at 300 °C. As a result, both structural and transport properties have been found to be strongly affected by annealing treatment. It was considered that the annealing conditions reduce the number of potential scattering sites at grain boundaries and defects, thus improving the thermoelectric properties.     

Laser synthesis of thin layers of In4Se3, In4Te3 and modification of their structure and characteristics

Trends of structural modifications and phase composition occurring in In₄Se₃ thin films and In₄Se₃-In₄Te₃ epitaxial heterojunctions under laser irradiations have been investigated. Dynamics of the layer structure modification, depending on laser modes, i.e. pulse duration τ = 2-4 ms, irradiation intensity I₀ = 10-50 kW/cm², number of pulses N = 5-50, was studied by electron microscopy. An increase in laser influence promotes enlargement of the layer grains and transformation of their polycrystalline structure towards higher degree of stoichiometry. As a result of laser solid restructuring heterojunctions of In₄Se₃-In₄Te₃, being photosensitive within 1.0-2.0 μm and showing fast time of response, have been obtained. Laser modification of structure enables one to optimize electrical and optical properties of functional elements on the base of thin films and layers of In₄Se₃, In₄Te₃, widely used as infrared detectors and filters.     

TeI4掺杂量对n型Bi2Te3基烧结材料热电性能的影响

采用区熔法结合放电等离子体快速烧结(SPS)技术制备了n型Bi₂Te₃基热电材料.在300—500K的温度范围内测量了各热电性能参数，包括电导率(σ)、塞贝克系数(α)和热导率(κ)，研究了掺杂剂TeI₄的含量(质量百分比分别为0，0.05，0.08，0.10，0.13和0.15wt%)对热电性能的影响.结果表明：试样的载流子浓度(n)随TeI₄含量增加而增大，使电导率增大、塞贝克系数的绝对值先增大而后减小，从而导致品质因子(α²σ)呈先增加后降低的变化趋势；同时，由于异质离子(I^-)以及载流子对声子的散射作用增强，可显著降低其晶格热导率.烧结材料的性能优值(ZT=α²σT/κ)对应于TeI₄含量为0.08wt%有其最大值，约为0.92.此外，烧结材料的抗弯强度增加至80MPa左右，从而可以显著改善材料的可加工性以及元器件的使用可靠性. 关键词： 2Te₃')" href="#">Bi₂Te₃ 放电等离子体快速烧结 热电性能     

Low temperature thermoelectric properties of Pb- or Sn-doped Bi-Sb alloys

Pb- or Sn-doped Bi₈₈Sb₁₂ alloys were prepared by direct melting, quenching, and annealing. The Bi-Sb alloy phase was predominant in all samples. Pb or Sn atoms were distributed almost uniformly in Bi₈₈Sb_12, while some segregation was confirmed at the grain boundaries when Pb or Sn was involved heavily. The thermoelectric properties of these doped materials were investigated by measuring the Hall coefficient, electrical resistivity, and Seebeck coefficient between 20 K and 300 K. The Hall and Seebeck coefficients of Pb- or Sn-doped samples were positive at low temperatures, indicating that the doping element acted as an acceptor. Temperatures resulting in positive Hall and Seebeck coefficients further increased with increasing doping amount and with respect to the annealing process. As a result, a large power factor of 1.2 W/mK² could be obtained in the 3-at% Sn-doped sample at 220 K, with a large positive Seebeck coefficient.     

Formation of highly textured (1 1 1) Bi2O3 films by anodization of electrodeposited bismuth films

Highly textured bismuth oxide (Bi₂O₃) thin films have been prepared using anodic oxidation of electrodeposited bismuth films onto stainless steel substrates. The Bi₂O₃ films were uniform and adherent to substrate. The Bi₂O₃ films were characterized for their structural and electrical properties by means of X-ray diffraction (XRD), electrical resistivity and dielectric measurement techniques. The X-ray diffraction pattern showed that Bi₂O₃ films are highly textured along (1 1 1) plane. The room temperature electrical resistivity of the Bi₂O₃ films was 10⁵ Ω cm. Dielectric measurement revealed normal oxide behavior with frequency.     

Characterization of chemically deposited ZnSe/SnO2/glass films: Influence of annealing in Ar atmosphere on physical properties

The Zinc Selenide (ZnSe) thin films have been deposited on SnO₂/glass substrates by a simple and inexpensive chemical bath deposition (CBD). The structural, optical and electrical properties of ZnSe films have been characterized by X-ray diffraction (XRD), Energy Dispersive X-ray Analysis (EDAX), optical absorption spectroscopy, and four point probe techniques, respectively. The films have been subjected to different annealing temperature in Argon (Ar) atmosphere. An increase in annealing temperature does not cause a complete phase transformation whereas it affects the crystallite size, dislocation density and strain. The optical band gap (E_g) of the as-deposited film is estimated to be 3.08 eV and decreases with increasing annealing temperature down to 2.43 eV at 773 K. The as-deposited and annealed films show typical semiconducting behaviour, dρ/dT > 0. Interestingly, the films annealed at 373 K, 473 K, and 573 K show two distinct temperature dependent regions of electrical resistivity; exponential region at high temperature, linear region at low temperature. The temperature at which the transition takes place from exponential to linear region strongly depends on the annealing temperature.     

Structural, electrical and optical properties of TiO2 doped WO3 thin films

TiO₂ doped WO₃ thin films were deposited onto glass substrates and fluorine doped tin oxide (FTO) coated conducting glass substrates, maintained at 500 °C by pyrolytic decomposition of adequate precursor solution. Equimolar ammonium tungstate ((NH₄)₂WO₄) and titanyl acetyl acetonate (TiAcAc) solutions were mixed together at pH 9 in volume proportions and used as a precursor solution for the deposition of TiO₂ doped WO₃ thin films. Doping concentrations were varied between 4 and 38%. The effect of TiO₂ doping concentration on structural, electrical and optical properties of TiO₂ doped WO₃ thin films were studied. Values of room temperature electrical resistivity, thermoelectric power and band gap energy (E_g) were estimated. The films with 38% TiO₂ doping in WO₃ exhibited lowest resistivity, n-type electrical conductivity and improved electrochromic performance among all the samples. The values of thermoelectric power (TEP) were in the range of 23-56 μV/K and the direct band gap energy varied between 2.72 and 2.86 eV.     

Effect of annealing temperature on photoelectrochemical properties of nanocrystalline MoBi2(Se0.5Te0.5)5 thin films

Nanocrystalline MoBi₂(Se_0.5Te_0.5)₅ thermoelectric thin films have been deposited on ultrasonically cleaned glass and FTO-coated glass substrates by Arrested Precipitation Technique. The change in properties of MoBi₂(Se_0.5Te_0.5)₅ thin films were examined after annealing at the temperature 473 K for 3 h. The structural, morphological, compositional and electrical properties of thin films were characterized by X-ray Diffraction, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, etc. Thermoelectric properties of the thin films have been evaluated by measurements of electrical conductivity and Seebeck coefficient in the temperature range 300–500 K. Our aim is to investigate the effect of annealing on behaviour of MoBi₂(Se_0.5Te_0.5)₅ thin films along with photoelectrochemical properties.     

Thermoelectric power and phase transition of polycrystalline As2Te3 under pressure

The pressure dependence of the thermoelectric power of monoclinic As₂Te₃ is measured up to 10 GPa using a Mao-Bell diamond anvil cell. The thermoelectric power never reaches an absolute value greater than the ambient pressure value of 242 μV/K. Evidence of a phase transition is present between 6 and 8 GPa where the thermoelectric power reaches an absolute value of 225 μV/K after passing through a minimum of S≈75 μV/K. X-ray diffraction experiments confirm that the resulting structure is β-As₂Te₃, which is isostructural with Bi₂Te₃ and Sb₂Te₃.     

Influence of substrate temperature on structures and dielectric properties of pyrochlore Bi1.5Zn1.0Nb1.5O7 thin films prepared by pulsed laser deposition

The influence of substrate temperature on structural and dielectric properties of cubic pyrochlore Bi_1.5Zn_1.0Nb_1.5O₇ (BZN) thin films prepared by pulsed laser deposition process has been investigated. BZN thin films were deposited on Pt/Ti/SiO₂/Si(1 0 0) substrate and in situ annealed at 700 °C. The results indicate that the substrate temperature has a significant effect on the structural and dielectric properties of BZN thin films. The films exhibit a cubic pyrochlore structure in the substrate temperature range from 550 °C to 700 °C and at the annealing temperature of 700 °C. With further increase of substrate temperature to 750 °C, the phases of Bi₂O₃, BiNbO₄ and Bi₅Nb₃O₁₅ can be detected in the XRD pattern due to the Zn loss. The dielectric constant and loss tangent of the films deposited at 650 °C are 192 and 6 × 10⁻⁴ at 10 kHz, respectively. The tunability is 10% at a dc bias field of 0.9 MV/cm.     

High temperature thermoelectric properties of highly c-axis oriented Bi2Sr2Co2Oy thin films fabricated by pulsed laser deposition

High-temperature thermoelectric transport property measurements have been performed on the highly c-axis oriented Bi2Sr2Co20v thin films prepared by pulsed laser deposition on LaA1Oa （001）. Both the electric resistivity p and the seebeck coefficient S of the film exhibit an increasing trend with the temperature from 300 K-1000 K and reach up to 4.8 m. cm and 202 V/K at 980 K, resulting in a power factor of 0.85 mW/mK which are comparable to those of the single crystalline samples. A small polaron hopping conduction can be responsible for the conduction mechanism of the film at high temperature. The results demonstrate that the Bi2Sr2Co2Oy thin film has potential application has high temperature thin film thermoelectric devices,     

Transverse laser induced thermoelectric voltage effect in tilted La0.5Sr0.5CoO3 thin films

The transverse laser induced thermoelectric voltage effect has been investigated in tilted La_0.5Sr_0.5CoO₃ thin films grown on vicinal cut LaAlO₃ (1 0 0) substrates when films are irradiated by pulse laser at room temperature. The detected voltage signals are demonstrated to originate from the transverse Seebeck effect as the linear dependence of voltage on tilted angle in the range of small tilted angle. The Seebeck coefficient anisotropy ΔS of 0.03 μV/K at room temperature is calculated and its distorted cubic structure is thought to be responsible for this. Films grown on a series of substrates with different tilted angles show the optimum angle of 19.8° for the maximum voltage. Film thickness dependence of voltage has also been studied.     

Growth of superconducting FeSe0.5Te0.5 thin films by pulsed-laser deposition

FeSe_0.5Te_0.5 thin films with PbO-type structure are successfully grown on MgO(1 0 0) and LaSrAlO₄(0 0 1) substrates from FeSe_0.5Te_0.5 or FeSe_0.5Te_0.75 polycrystalline targets by pulsed-laser deposition. The film deposited on the MgO substrate (film thickness ∼ 55 nm) shows superconductivity at 10.6 K (onset) and 9.2 K (zero resistivity). On the other hand, the film deposited on the LaSrAlO₄ substrate (film thickness ∼ 250 nm) exhibits superconductivity at 5.4 K (onset) and 2.7 K (zero resistivity). This suggests the strong influence of substrate materials and/or the c-axis length to superconducting properties of FeSe_0.5Te_0.5 thin films.     

High-throughput characterization of BixY3−xFe5O12 combinatorial thin films by magneto-optical imaging technique

Bi_xY_3−xFe₅O₁₂ thin films have been grown on GGG (Gd₃Ga₅O₁₂) (1 1 1) substrates by the combinatorial composition-spread techniques under substrate temperature (T_sub) ranging from 410 to 700 °C and O₂ pressure of 200 mTorr. In order to study the effect of substrates on the deposition of Bi_xY_3−xFe₅O₁₂ thin films, garnet substrates annealed at 1300 °C for 3 h were also used. Magneto-optical properties were characterized by our home-designed magneto-optical imaging system. From the maps of Faraday rotation angle θ_F, it was evident that the Faraday effect appears only when T_sub = 430-630 °C. θ_F reaches to the maximum value (∼6°/μm, λ = 632 nm) at 500 °C, and is proportional to the Bi contents. XRD and EPMA analyses showed that Bi ions are easier to substitute for Y sites and better crystallinity is obtained for annealed substrates than for commercial ones.     

Structural and electrical properties of (Na0.85K0.15)0.5Bi0.5TiO3 thin films deposited on LaNiO3 and Pt bottom electrodes

(Na_0.85K_0.15)_0.5Bi_0.5TiO₃ thin films were deposited on LaNiO₃(LNO)/SiO₂/Si(1 0 0) and Pt/Ti/SiO₂/Si(1 0 0) substrates by metal-organic decomposition, and the effects of bottom electrodes LNO and Pt on the ferroelectric, dielectric and piezoelectric properties were investigated by ferroelectric tester, impedance analyzer and scanning probe microscopy, respectively. For the thin films deposited on LNO and Pt electrodes, the remnant polarization 2P_r are about 22.6 and 8.8 μC/cm² under 375 kV/cm, the dielectric constants 238 and 579 at 10 kHz, the dielectric losses 0.06 and 0.30 at 10 kHz, the statistic d_33eff values 95 and 81 pm/V. The improved piezoelectric properties could make (Na_1−xK_x)_0.5Bi_0.5TiO₃ thin film as a promising candidate for piezoelectric thin film devices.     

Doping effects on the thermoelectric properties of Cu-intercalated Bi2Te2.7Se0.3

We herein report an enhancement of the thermoelectric performance of spark plasma sintered polycrystalline n-type Bi₂Te_2.7Se_0.3 by the intercalation of Cu and the doping of Al on Bi-sites. Through the intercalation of a small amount of Cu (0.008), the reproducibility could be significantly improved, with ZT was enhanced from 0.64 to 0.73 at 300 K due to the reduced lattice thermal conductivity benefiting from intensified point-defect phonon scattering. We also found that Al is an effective doping element for power factor enhancement and for reducing the lattice thermal conductivity of Cu-intercalated Bi₂Te_2.7Se_0.3. With these synergetic effects, an enhanced ZT values of 0.78 at 300 K and 0.81 at 360 K were obtained in 1 at% Al-doped Cu_0.008Bi₂Te_2.7Se_0.3 (Cu_0.008Bi_1.98Al_0.02Te_2.7Se_0.3).     

Thermoelectric properties in Mn-doped Bi2Se3

Using n-type and p-type Mn-doped Bi₂Se₃ single crystals, a thin-film-type thermoelectric (TE) module was fabricated and the TE characteristics were investigated. The Seebeck coefficient at room temperature was about 100 μV K⁻¹ with different sign for both materials. From the Seebeck coefficient and resistivity values, the electric power of our TE module was evaluated to be 90 μW for a single couple at the temperature difference of 10 K. This value is compared to that (∼21 μW) of commercialized TE device. Nevertheless, the actual power was measured to be quite small around 0.74 μW, which is much higher than other homemade TE power level. This small power is attributed to the high electrical contact resistance between the TE material and the heat source and sink. Assuming the contact resistance level ∼0.1 Ω similar to that of commercialized TE devices, the electric power should be about 41 μW, which is almost 2 times higher than that in commercialized TE devices. These results propose that the Mn-doped Bi₂Se₃ system is another promising TE material, which can be replaced with the commercialized Bi₂Te₃ system.