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Defect‐Mediated Anisotropic Lattice Expansion in Ceramics as Evidence for Nonthermal Coupling between Electromagnetic Fields and Matter
Advanced Engineering Materials ( IF 3.6 ) Pub Date : 2019-09-26 , DOI: 10.1002/adem.201900762
Shikhar Krishn Jha 1 , Nathan Nakamura 1 , Shuyan Zhang 1 , Laisuo Su 1 , Phil M. Smith 1 , Xin L. Phuah 2 , Han Wang 2 , Haiyan Wang 2 , John S. Okasinski 3 , Alan J. H. McGaughey 1 , B. Reeja-Jayan 1
Affiliation  

Electromagnetic (EM) fields can trigger a range of surprising responses in materials. Microwave radiation (MWR), a type of EM field in the frequency range of 0.3–300 GHz, can lower the synthesis temperature required for ceramics such as TiO2 and induces mixed amorphous–crystalline phase compositions. To better understand the effects of MWR on matter, structural changes during microwave heating and MWR‐assisted synthesis using in situ synchrotron X‐ray diffraction are studied. Anisotropic expansion–contraction of lattice parameters under microwave‐radiation is observed, which contradicts the results from conventional thermal heating. When as‐received TiO2 powders are heated with MWR, an instantaneous decrease in the intensities of diffraction peaks indicates decrystallization/amorphization. High‐resolution electron microscopy supports these observations. Raman spectroscopy and X‐ray photoemission spectroscopy indicate increased defect‐generation under microwave exposure. Molecular dynamics simulations on the anatase phase of TiO2 suggests that introducing an oxygen vacancy can lead to the formation of an interstitial–vacancy pair resulting in anisotropic expansion–contraction of the lattice. These unique responses of ceramics under externally applied fields provide direct evidence for nonthermal coupling between EM fields and matter. Understanding such nonthermal, field‐driven processes has implications in engineering low‐temperature processes for integrating ceramics with polymers for flexible electronics, energy harnessing, and storage applications.

中文翻译:

陶瓷中介导的各向异性晶格膨胀作为电磁场与物质之间非热耦合的证据

电磁(EM)场会触发材料中一系列令人惊讶的响应。微波辐射(MWR)是0.3–300 GHz频率范围内的一种电磁场,可以降低TiO 2等陶瓷的合成温度,并诱导混合的非晶-晶相成分。为了更好地了解MWR对物质的影响,研究了微波加热和使用原位同步加速器X射线衍射的MWR辅助合成过程中的结构变化。观察到微波辐射下晶格参数的各向异性膨胀-收缩,这与常规热加热的结果相矛盾。收到TiO 2时粉末用MWR加热,衍射峰强度的瞬时降低表明发生了去结晶/非晶化。高分辨率电子显微镜支持这些观察。拉曼光谱法和X射线光发射光谱法表明,在微波照射下缺陷生成增加。TiO 2锐钛矿相的分子动力学模拟这表明引入氧空位可以导致间隙-空位对的形成,从而导致晶格的各向异性膨胀-收缩。陶瓷在外部施加场下的这些独特响应为电磁场与物质之间的非热耦合提供了直接证据。理解此类非热场驱动过程对工程低温过程具有重要意义,该过程将陶瓷与聚合物集成在一起,用于柔性电子,能源利用和存储应用。
更新日期:2019-09-26
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