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Low-temperature synthesis of transition/post-transition metal intermetallics and rare earth oxide perovskites.

机译：过渡/过渡金属间金属化合物和稀土氧化物钙钛矿的低温合成。

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摘要

Recent years have seen the emergence of numerous low-temperature synthetic approaches toward inorganic materials, including both intermetallic and oxide compounds. Many of these processes have focused on the synthesis, modification, and conversion of nanoparticles and deposited thin-films, which can overcome energetic barriers, such as the rate-limiting solid-solid diffusion step, associated with traditional metallurgical and ceramic techniques. Through a loss of dimensionality or drastically reduced diffusion distances these approaches can access a wide range of materials at much lower temperatures than typically employed. Additionally, low-temperature methods potentially provide for the discovery of nonequilibrium or kinetically stable phases. This dissertation details our work towards the development of alternative, non-traditional synthetic methods for accessing both intermetallic and oxide compounds at low-temperatures and ambient pressures.;We have used molten dispersions of low-melting metals as reactive precursors in the synthesis of various bimetallic materials, specifically M-Sn, M-Ga, M-Bi, and M-In phases ( M = late transition or post-transition metal). These compounds possess a range of different chemical and physical properties, such as superconductivity, and can be rapidly obtained in solution at temperatures below 300 °C. Additionally, we find that the choice of solvent is somewhat flexible, as several of these bimetallic phases were obtainable under similar conditions in renewable plant and seed oils, such as safflower and canola oil. This provides further support for our hypothesis that the solvent acts primarily as medium for dispersion and heat-transfer and that intermetallic formation occurs through a diffusion-based approach in solution.;With regards to oxide compounds, we have accessed layered perovskite-type Eu2Ti2O7, which is typically obtained through high-pressure techniques, at moderate temperatures and ambient pressure through mild oxidation of EuTiO3. This approach suppresses formation of the more thermodynamically stable pyrochlore structure and allows partial retention of the perovskite motif up to 900 °C. Our synthetic method is amenable to bulk-scaling and yields samples that possess an increased response toward second harmonic generation relative to previous reports. Finally, we have synthesized Ca-substituted EuTiO3 phases through a modified sol-gel approach. By varying the level of Ca content, we can systematically alter the length of the unit cell edge and suppress the antiferromagnetic ordering temperature, presumably through dilution of magnetic spins.
机译：近年来，已经出现了许多针对无机材料的低温合成方法，包括金属间化合物和氧化物化合物。这些过程中的许多过程都集中在纳米颗粒和沉积薄膜的合成，修饰和转化上，可以克服高能垒，例如与传统冶金和陶瓷技术相关的限速固-固扩散步骤。由于尺寸损失或扩散距离大大减少，这些方法可以在比通常采用的温度低得多的温度下接触各种材料。另外，低温方法可能提供发现非平衡或动力学稳定相的方法。本论文详细介绍了我们为开发可在低温和环境压力下接触金属间化合物和氧化物化合物的替代性非传统合成方法而开展的工作。；我们在各种合成过程中使用了低熔点金属的熔融分散体作为反应性前体双金属材料，特别是M-Sn，M-Ga，M-Bi和M-In相（M =后过渡金属或后过渡金属）。这些化合物具有一系列不同的化学和物理特性，例如超导性，可以在温度低于300°C的溶液中快速获得。此外，我们发现溶剂的选择有些灵活，因为在相似的条件下，可从可再生植物油和种子油（如红花油和低芥酸菜籽油）中获得这些双金属相中的几种。这进一步支持了我们的假设，即溶剂主要充当分散和传热的介质，并且金属间化合物的形成是通过在溶液中基于扩散的方法发生的。关于氧化物，我们已经研究了层状钙钛矿型Eu2Ti2O7，通常是通过高压技术，在中等温度和环境压力下通过EuTiO3的轻度氧化获得的。这种方法抑制了热力学更稳定的烧绿石结构的形成，并允许钙钛矿基序部分保留到900°C。我们的合成方法适用于批量缩放，并且产生的样品相对于以前的报告对二次谐波的产生具有增强的响应。最后，我们通过改进的溶胶-凝胶方法合成了Ca取代的EuTiO3相。通过改变Ca含量的水平，我们可以系统地改变晶胞边缘的长度并抑制反铁磁有序温度，这大概是通过稀释磁性自旋来实现的。

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  • 作者

    Henderson, Nathaniel L.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Inorganic chemistry.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 106 p.
  • 总页数 106
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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