放电等离子烧结设备中使用的钛酸锶双晶体的形成
Summary
A viable technique for the formation of strontium titanate bicrystals at high pressure and fast heating rate via the spark plasma sintering apparatus is developed.
Abstract
A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with one twist grain boundary. This apparatus utilizes high uniaxial pressure and a pulsed direct current for rapid consolidation of material. Diffusion bonding of strontium titanate bicrystals without fracture, in a spark plasma sintering apparatus, is possible at high pressures due to the unusual temperature dependent plasticity behavior of strontium titanate. We demonstrate a method for the successful formation of bicrystals at accelerated time scales and lower temperatures in a spark plasma sintering apparatus compared to bicrystals formed by conventional diffusion bonding parameters. Bond quality was verified by scanning electron microscopy. A clean and atomically abrupt interface containing no secondary phases was observed using transmission electron microscopy techniques. Local changes in bonding across the boundary was characterized by simultaneous scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy.
Introduction
放电等离子烧结（SPS）是其中应用高的单轴压力，脉冲直流电引线的粉末的快速致密化压块1的技术。这种技术也导致由各种材料，包括氮化硅/碳化硅，硼化锆/碳化硅或碳化硅的成功形成复合结构，没有额外的烧结助剂需要2，3，4，5。这些复合结构通过常规热压已经过去有挑战性的合成。同时通过SPS技术高的单向压力和快速升温速率的应用提高粉末和复合材料的整理，的现象，造成文献2,3辩论这种增强致密化，类=“外部参照”> 6，7。此外，还存在对于电场在晶界形成的影响只有有限的信息和晶界芯8,9的所得原子结构。这些芯结构确定的SPS烧结材料的功能特性，包括高电压电容器的电击穿和陶瓷氧化物10的机械强度和韧性。因此，了解基本晶界结构的SPS加工参数，如施加的电流的函数，是必需的材料的整体物理性能的操作。系统地阐明支撑SPS的基本物理机制的一种方法是特定晶界结构， 即 ，双晶的形成。一个双晶是由两个单晶，然后将它们的操作创建diffu锡永的具体取向差角度保税11。此方法提供了一种可控制的方式来研究的基本晶界芯结构作为处理参数的函数，掺杂剂浓度，并且杂质偏析12，13，14。
扩散接合是依赖于四个参数：温度，时间，压力，和键合气氛15。钛酸锶的常规扩散接合（的SrTiO 3，STO）双晶通常发生在低于1兆帕的压力下，温度范围为1,400-1,500℃的范围内，和时间尺度从3至20小时13，14，16，17。在这项研究中，接合在一个SPS装置以在C显著较低的温度和时间尺度达到omparison常规方法。对于多晶材料，降低温度和时间尺度通过SPS显著限制晶粒长大，从而通过其微操纵提供了物质属性的有利控制。
所述SPS的装置，对于一个5×5 平方毫米的样品，施加140兆帕的最小压力。内的常规扩散接合温度范围，哈特等人。当粘结压力超过10兆帕18日报道STO瞬间断裂。然而，STO具有温度依赖性可塑性的行为，表示连接压力可在特定的温度超过10兆帕。以上1200℃和低于700℃，STO具有一些延展性，在其中强调大于120兆帕可以在没有样品的瞬时断裂被应用。在中间温度范围的700-1,200°C，申通快递在s脆性和经验瞬时断裂秀发大于10兆帕。在800℃，STO具有应力断裂小于200兆帕19，20，21之前轻微变形。因此，粘合温度为经由SPS装置的STO双晶的形成必须根据材料的塑性行为进行选择。
Protocol
Representative Results
Discussion
被选择的1200℃的接合温度最大化扩散由于温度的微小变化可以大大地影响所有扩散接合机制的动力学。 1200℃的温度是脆韧转变温度范围STO之外。然而，样品在该温度下进行脆性断裂。申通快递双晶的灾难性故障并不出乎意料，因为申通快递有〜1200℃，0.5％的延展性。此外，该样品在140兆帕的整个加热过程中的压力保持和STO在该加热过程，其中具有0％延性21通过其脆性阶段过渡…
Divulgations
The authors have nothing to disclose.
Acknowledgements
LH非常感谢在加州大学戴维斯分校1148897.批准号：电子显微镜表征和SPS处理由美国国家科学基金会研究生研究奖学金的财政支持由美国加利福尼亚大学的实验室费用奖项是财政支持（＃12-LR-238313）。 在分子铸造工作是由科学，基础能源科学办公室的办公室，能源合同号DE-AC02-05CH11231美国能源部的支持。
Materials
| Strontium titanate single crystal (100) | MTI Corporation | STOa101005S1-JP | |
| Buffered oxide etch, hyrofluoric acid 6:1 | JT Baker | MBI 1178-03 | |
| Scanning electron microscope (SEM) | FEI | Model: 430 NanoSEM | |
| SPS apparatus | Sumitomo Coal Mining Co | Model: Dr. Sinter 5000 SPS Apparatus | |
| High Temperature Furnace | Thermolyne | Model: 41600 | |
| Ultrasonic Cleaner | Bransonic | Model: 221 | |
| Mechanical polisher | Allied High Tech Products | 15-2100-TEM | |
| Diamond lapping film | 3M | 660XV | 1 um to 9 um Grit Size |
| Diamond lapping film | 3M | 661X | 0.5 um to 0.1 um Grit Size |
| Colloidal silica | Allied High Tech Products | 180-20000 | .05 um Grit Size |
| Sputter coater | QuorumTech | Model: Q150RES | |
| Focused ion beam (FIB) instrument | FEI | Model: Scios dual-beamed focused ion beam (FIB) instrument | |
| Nanomill TEM specimen preparation system | Fischione Instruments | Model: 1040 | |
| Transmission electron microscope (TEM) | JEOL | Model: JEM2500 SE | |
| Scanning transmission electron microscope (STEM) | FEI | Model: TEAM 0.5 |
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