非均匀掺Pr的SrTiO的合成<sub> 3</sub>陶瓷及其热电性能
Summary
A protocol for the synthesis and processing of polycrystalline SrTiO3 ceramics doped non-uniformly with Pr is presented along with the investigation of their thermoelectric properties.
Abstract
We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using X-ray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy. It was observed that the grains of these bulk Pr-doped SrTiO3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration. Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO3.
Introduction
氧化物热电被证明是有前途的候选高温热电应用，从稳定性和成本的观点，以电子输运性质。之间的n型氧化物热电，高度掺杂的钛酸锶（STO）已经引起了人们的注意，因为它有趣的电子特性。然而，大的总热导率（κ〜12瓦米-1 K -1，在300°K的单结晶）1和低载流子迁移率（μ〜6cm 2的V -1秒-1，在300°K的单结晶） 1不利地影响热电性能是由优点的一个无量纲的数字计算，ZT =α2σT/κ，其中α是塞贝克系数，σ电导率，T为绝对温度以开尔文，以及κ的总热导率。这里我们定义的分子作为功率因数，PF =α263;吨。为了使该氧化物热电材料与其他高温热电（例如SiGe合金）进行竞争，在功率因数和/或减少晶格热导率更明显的增加是必需的。
为了提高STO的热电性能的大多数实验研究主要集中在热导率通过应变场和声子的质量波动散射的降低。这些尝试包括：（i）单或双掺杂锶2+和/或Ti 4+的网站，如相对于主要的努力这个方向，自然超晶格Ruddlesden -波普尔结构的2,3（二）合成为了通过加入纳米第二相绝缘的SrO层，4和（iii）复合工程进一步降低热导率不过5，直到最近，无增强策略已报道substantially增加这些氧化物热电功率因数。散装单和多晶的STO所报告的最大功率因数（PF）的值被限制于PF <1.0 W M -1 K -1的上限。
各种合成方法和处理技术已经被用于实现上述尝试的想法。粉末合成途径包括传统的固态反应，6溶胶-凝胶，水热7，图8和燃烧合成，9而常规烧结，6热压10和最近放电等离子体烧结12顷之间用于将粉末压实成普通技术散装陶瓷。然而，对于一个类似的掺杂剂（ 例如，La）的和掺杂浓度，将得到的块状陶瓷表现出范围的电子和热传输性能。这在很大程度上是由于钛酸锶<的强烈过程相关的缺陷化学子> 3，这导致合成依赖特性。只有少数报告的优化合成和加工参数，以造福热电运输。值得一提的是，由于非常小的声子平均中的SrTiO 3自由程（升pH值 〜2在300K纳米），11纳米结构是不是一个可行的选择的散装STO陶瓷在TE性能主要是通过减少的改善的晶格热导率。
最近，我们报导优点在非均匀掺Pr的SrTiO 3陶瓷从同时提高热电功率因数始发热电数字超过30％的改善，并降低热导率。12,13在此详细的视频协议中，我们提出与讨论我们的综合战略，这些编制的步骤镨掺杂STO陶瓷具有改进的电子和热电性能。
Protocol
Representative Results
Discussion
在这个协议中，我们已经提出，为了成功地批量制备多晶硅镨掺杂的SrTiO 3陶瓷具有改进的电子和热电性能的综合战略的步骤。该协议的主要步骤包括：（i）固态合成掺杂的SrTiO 3粉末在空气中在常压下与放电等离子体烧结法的能力（ⅱ）利用致密所制备的粉末成高密度散装陶瓷，并在同一时间，以进一步掺杂有镨的样品的晶界。据证实，通过施加高的SPS加热速度（300-400℃，分…
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
The authors wish to acknowledge the competitive faculty-initiated collaboration (FIC) grant from KAUST.
Materials
| SrCO3 Powder, 99.9% | Sigma Aldrich | 472018 | |
| TiO2 Nanopowder, 99.5% | Sigma Aldrich | 718467 | |
| Pr2O3 Sintered Lumps, 99.9% | Alfa Aesar | 35663 | |
| Name of Equipment | |||
| Spark Plasma Sintering | Dr. Sinter Lab | SPS-515S | |
| Resistivity/Seebeck Coefficient Measurement System | Ulvac-Riko | ZEM-2 | |
| Laser Flash Thermal Diffusivity Measurement System | Netzsch | LFA-457 Microflash | |
| Differential Scanning Calorimetry (DSC) System | Netzsch | 404C Pegasus | |
| Physical Property Measurement system (PPMS) | Quantum Design | ||
| Field Emission Scanning Electron Microscope (FE-SEM) | Hitachi | SU-6600 | |
| Energyy-dispersive X-ray Spectroscopy (EDS) | Oxford Instruments | ||
| X-ray Diffractometer | Rigaku | Ultima IV | |
| Bench-top Sputter Coater | Denton Vacuum | Desk II | |
| Diamond Wheel Saw | South Bay Technology |
Riferimenti
- Ohta, S., Nomura, T., Ohta, H., Koumoto, K. High-temperature Carrier Transport and Thermoelectric Properties of Heavily La-or Nb-doped SrTiO3 Single Crystals. J. Appl. Phys. 97, (2005).
- Wang, H. C., et al. Enhancement of Thermoelectric Figure of Merit by Doping Dy in La0.1Sr0.9TiO3 Ceramic. Mater. Res. Bull. 45, 809-812 (2010).
- Bhattacharya, S., Mehdizadeh Dehkordi, A., Alshareef, H. N., Tritt, T. M. Synthesis–Property Relationship in Thermoelectric Sr1−xYbxTiO3−δ Ceramics. J. Phys. D: Appl. Phys. 47, 385302 (2014).
- Wang, Y., Lee, K. H., Ohta, H., Koumoto, K. Thermoelectric Properties of Electron Doped SrO(SrTiO3)n (n=1,2) Ceramics. J. Appl. Phys. 105, 1037011-1037016 (2009).
- Wang, N., et al. Effects of YSZ Additions on Thermoelectric Properties of Nb-Doped Strontium Titanate. J. Electron. Mater. 39, 1777-1781 (2010).
- Muta, H., Kurosaki, K., Yamanaka, S. Thermoelectric Properties of Rare Earth Doped SrTiO3. J. Alloys Compd. 350, 292-295 (2003).
- Shang, P. -. P., Zhang, B. -. P., Li, J. -. F., Ma, N. Effect of Sintering Temperature on Thermoelectric Properties of La-doped SrTiO3 Ceramics Prepared by Sol-gel Process and Spark Plasma Sintering. Solid State Sciences. 12, 1341-1346 (2010).
- Wang, Y., Fan, H. J. Sr1-xLaxTiO3 Nanoparticles: Synthesis, Characterization and Enhanced Thermoelectric Response. Scripta Materialia. 65, 190-193 (2011).
- Kikuchi, A., Okinakab, N., Akiyama, T. A Large Thermoelectric Figure of Merit of La-doped SrTiO3 Prepared by Combustion Synthesis with Post-Spark Plasma Sintering. Scripta Materialia. 63, 407-410 (2010).
- Obara, H., et al. Thermoelectric Properties of Y-Doped Polycrystalline SrTiO3.Jpn. J. Appl. Phys. 43, L540-L542 (2004).
- Koumoto, K., Wang, Y., Zhang, R., Kosuga, A., Funahashi, R. Oxide Thermoelectric Materials: A Nanostructuring Approach. Annu. Rev. Mater. Res. 40, 363-394 (2010).
- Mehdizadeh Dehkordi, A., et al. Large Thermoelectric Power Factor in Pr-Doped SrTiO3−δ Ceramics via Grain-Boundary-Induced Mobility Enhancement. Chem. Mater. 26, 2478-2485 (2014).
- Mehdizadeh Dehkordi, A., Bhattacharya, S., He, J., Alshareef, H. N., Tritt, T. M. Significant Enhancement in Thermoelectric Properties of Polycrystalline Pr-doped SrTiO3 Ceramics Originating from Nonuniform distribution of Pr dopants. Appl. Phys. Lett. 104, 1939021-1939024 (2014).
- . . Standard Test Methods for Density of Compacted or Sintered Powder Metallurgy (PM) Products Using Archimedes’ Principle. , (2015).
- Parker, W. J., Jenkins, R. J., Butler, C. P., Abbott, G. L. Flash Method of Determining Thermal Diffusivity, Heat Capacity and Thermal Conductivity. J. Appl. Phys. 32, 1679-1684 (1961).
- Cowan, R. D. Pulse Method of Measuring Thermal Diffusivity at High Temperatures. J. Appl. Phys. 34, 926-927 (1963).
- Mehdizadeh-Dehkordi, A. . An Experimental Investigation Towards Improvement of Thermoelectric Properties of Strontium Titanate Ceramics. , (2014).
- . . DSC Pegasus 404C Operating Manual. , (1999).
- Daw, J. E. Measurement of Specific Heat Capacity Using Differential Scanning Calorimeter. Report of US Department of Energy. , (2008).
- Tritt, T. M. . Thermal Conductivity: Theory, Properties and Applications. , (2004).
- . . SC7610 Sputter Coater Operating Manual. , (2002).
- Tritt, T. M., Rowe, D. M. Electrical and Thermal Transport Measurement Techniques for Evaluation of the figure-of-Merit of Bulk Thermoelectric Materials. Thermoelectrics Handbook: Macro to Nano. , 23-1-23-17 (2006).
- Burkov, A. T., Rowe, D. M. Measurements of Resistivity and Thermopower: Principles and Practical Realization. Thermoelectrics Handbook: Macro to Nano. , 22-1 (2006).
- . . Physical Property Measurement System: AC Transport Option User’s Manual. , (2003).
- Ohta, S., Ohta, H. Grain Size Dependence of Thermoelectric Performance of Nb-doped SrTiO3. Polycrystals. J. Ceram. Soc. Jpn. 114, 102 (2006).
- Wang, N., He, H., Ba, Y., Wan, C., Koumoto, K. Thermoelectric Properties of Nb-doped SrTiO3 Ceramics Enhanced by Potassium Titanate Nanowires Addition. J. Ceram. Soc. Jpn. 118, 1098 (2010).
- Ohta, S., et al. Large Thermoelectric Performance of Heavily Nb-doped SrTiO3 Epitaxial Film at High Temperature. Appl. Phys. Lett. 87, 092108 (2005).
- Kovalevsky, A., Yaremchenko, A., Populoh, S., Weidenkaff, A., Frade, J. Enhancement of Thermoelectric Performance in Strontium Titanate by Praseodymium Substitution. J. Appl. Phys. 113, 053704 (2013).
- Kovalevsky, A. V., et al. Towards a High Thermoelectric Performance in Rare-Earth Substituted SrTiO3: Effects Provided by Strongly-Reducing Sintering Conditions. Phys. Chem. 16, 26946 (2014).
- Dawson, J. A., Tanaka, I. Local Structure and Energetics of Pr- and La-Doped SrTiO3 Grain Boundaries and the Influence on Core–Shell Structure Formation. J. Phys. Chem. C. 118, 25765-25778 (2014).
- Mehdizadeh Dehkordi, A., et al. New Insights on the Synthesis and Electronic Transport in Bulk Polycrystalline Pr-doped SrTiO3−δ. Appl. Phys. Lett. 117, 055102 (2015).
