Seebeck coefficient in multiphase thin films

Abstract

Mg-Ag-Sb thin films were deposited by magnetron sputtering using a commercial Mg 1/3 Ag 1/3 Sb 1/3 target. All the films contain principally the two phases Ag 3 Sb and -MgAgSb in same proportions but exhibit different microstructures. The films have the same Seebeck coefficient despite the difference of interface density and structure. Theoretical calculations show that the film effective Seebeck coefficient S film is depending only on the volume of each phase present in the film and their Seebeck coefficients. The multiple interfaces between the different phases have no effect on S film .

Influence of the Mn5Ge3/Ge ohmic-contact interface on the Seebeck coefficient of the Mn5Ge3/Ge bilayer

“…The thickness of the Mn layer was maintained the same for all the samples, while the thickness of the Ge film was varied in order to obtain a 160 nm-thick Mn 5 Ge 3 layer on a Ge layer of different thicknesses. Hall measurements and sample resistivity were measured in the Van der Pauw geometry using a lab-made setup operating between 20 and 350 K. The applied magnetic field for Hall measurements was 0.5 T. The Seebeck coefficients of the films were measured using a home-made setup 48 , 53 , 55 , 71 between T = 225 and 325 K. The distance d between the two electrodes allowing to simultaneously determine the potential difference Δ V as well as the temperature gradient Δ T = T h − T c was 1 cm (Fig. 4 a).…”

“…Despite theoretical models 37 , 39 – 42 and numerical calculations 18 , 43 , 44 showing a possible increase of S due to interface-mediated energy filtering, the effect of interfaces on S still needs further experimental investigations in order to improve TE property engineering of multiphase materials. For example, the dependence of S with interface area in multiphase materials exhibiting enhanced S has been poorly studied 45 , and some experimental results shown no modification of S with the presence of interfaces 21 , 25 , 28 , 29 , 45 – 48 . Furthermore, the increase of S in multiphase materials has been shown as possibly due to a significant gradient of charge mobility resulting from the temperature gradient 49 .…”

High-entropy materials for thermoelectric applications: towards performance and reliability

“…Several strategies have been implemented to improve TE performance (ZT), with a particular emphasis on reducing k L by decoupling the electron and phonon transport. [98][99][100] This includes hierarchical architectures, [67][68][69] band structure engineering, 16,101 nano-structuring, [102][103][104][105] energy filtering, [106][107][108] and exploring materials possessing intrinsically low k. 11 A recent addition to the array of promising strategies is the high-entropy approach, which has garnered significant attention in solving the interdependence of TE properties. 39 The entropy-driven approach can be adopted to modify the electronic/thermal transport properties of a material and to maintain the crystal symmetry to achieve high a.…”

Effect of Annealing Conditions on Thermoelectric Properties of Magnetron Sputtered MgO-Ag3Sb-Sb2O4 Flexible Films

“…近几年来, 可穿戴电子设备在人们社会生活中 越来越受欢迎, 与此同时电源供给问题越来越突出, 引起了研究人员的极大关注 [1][2] 。在众多供电方式中, 热电发电机(TEGs)是一种理想的能源供应方式, 能 够直接将人体与外界环境之间的温差转化为电能, 无机械振动且无需维护 [3][4] 。热电发电机的转换效率 主要取决于热电材料的热电优值 ZT(ZT=S 2 σT/κ, 其 中 S、σ、κ 和 T 分别是塞贝克系数、电导率、热导 率和热力学温度)。为了获得较高的热电优值, 热电 材料应当具有较高的功率因子(PF=S 2 σ)和较低的热 导率 [4][5] 。 传统的热电块体材料制造工艺价格昂贵, 通常 涉及许多工序, 如粉末热压、抛光、切割和组装 [6][7] , 存在材料浪费现象。此外, 块体材料所制备的器件 结构体积较大、柔性较差, 存在器件穿戴不便、难 以有效贴合人体等缺点。相比而言, 柔性热电薄膜 省去了昂贵的加工步骤, 便于大面积制备, 减少了 材料浪费, 可以满足多种空间和复杂器件的设计加 工要求, 更易于穿戴集成。常见的热电薄膜制备方 法有化学气相沉积 [8] 、喷墨打印 [9] 、丝网印刷 [10][11] 和溅射 [12][13][14] 等。如 Han 等 [10] 采用低成本的丝网印刷 制备了 PbTe-SrTe 基热电薄膜, 623 K 下 ZT 超过 1.0。 Akihiro 等 [13] 采用磁控溅射获得了 n 型 Bi 2 Te 3 和 p 型 Sb 2 Te 3 热电薄膜, 制备了管状薄膜热电发电机, 当温差 20 K 时, 其输出功率达到 306.8 nW。 目前含 Te 材料在无机热电材料中研究较多, 但 Te 元素在 地壳中含量较少且具有毒性, 不适用于可穿戴应用, 因此探究和发展无 Te 热电材料已成为目前的研究 热点。MgAgSb 作为一种新型 p 型近室温热电材料, 其各元素地壳含量丰富且无毒。MgAgSb 最早作为 热电材料被研究是在 2012 年, Kirkham 等 [15] 采用真 空熔炼和高温热压的方法制备了 MgAgSb 合金, 并 对其晶体结构与热电性能进行了系统研究。随后, Zhao 等 [16] 采用两步球磨法及低温热压法制备了致 密的 MgAgSb 块状样品, 测得其室温下 ZT 接近 1, 并随着温度升高而增大, 在 475 K 达到最大值 1.4。 Liu 等 [17][18][19][20][21] 采用高能球磨法结合快速烧结法制备 MgAgSb 合金, 并通过调节烧结温度、热压温度 [17][18] 或多种元素掺杂 [19][20][21] 提高热电性能, 系统研究了多 种变量对合金微观结构和热电性能的影响。但目前 鲜有对 MgAgSb 热电薄膜的详细研究。2020 年 Oueldna 等 [22] 首次在玻璃和氧化硅衬底上溅射制备 了含杂相的 MgAgSb 薄膜, 仅对该薄膜的总 Seebeck 系数与各相组成 Seebeck 系数和含量占比关系进行 了研究。随后又共溅射制备了 MgAgSb 薄膜, 利用 原位 X 衍射谱图详细研究了薄膜相变情况 [23] 。由于 MgAgSb 自身易氧化和生成多相结构, 因此退火气 氛将导致其结构组成变化, 退火温度对于薄膜相结 构形成、结晶度以及晶粒尺度变化影响较大, 进而 改变热电参数。此外, 磁控溅射在柔性热电大面积 镀膜方面具有明显优势, 获得了较大关注 [12][13][14] [24] 。考虑到热电薄膜厚度较小, 自身热 容很小, 面内热导率不易准确测量, 所以暂不考虑 热导率 …”