Control of Crystal Chemistry and Crystal Form in Complex Oxides by Mild Synthesis

我们的建议是研究新的合成化学，以制备复杂的无机材料，在材料制备中引入不同程度的控制，最终用于实际应用。用于技术应用的先进材料需要对样品的化学成分（样品中各种化学元素的比例及其化学状态）进行精确控制，并对样品的形式进行控制（从纳米到微米的长度尺度上的颗粒大小和形状）。基于一些初步结果，我们的假设是溶剂热条件（将溶剂和简单的化学前体结合在一个密封的反应容器中，加热到溶剂的沸点以上，就像家用压力锅一样）将允许在一步过程中实现这些水平的控制。这种合成方法已经应用于多孔材料的制备，但我们将转而研究陶瓷型材料，这种材料通常需要在超过1000摄氏度的极端温度下制备，需要反复研磨和烧制循环。这些材料都具有扩展的网络结构（实际上是无限的，在单个晶体的范围内），因此它们的合成和晶体生长必须在一步内控制：不像由分子单元的包装组成的固体，重结晶很容易实现。通过使用温和的条件和溶剂，我们的目标是首先进行探索性合成，以研究分离高温下未见的新材料的可能性，然后对组成样品的晶体生长进行控制，以优化其实际应用的性能。我们的合成方法的新颖性将包括与项目合作伙伴Baskerville Ltd合作设计和调试一个新的多电池反应器，用于高达500℃的常规操作。我们相信我们可以在三个层面上对晶体生长进行控制：(1)通过使用化学试剂控制金属氧化态（测量与金属原子相关的电子在固体结构中的位置），(2)通过选择伙伴金属来控制扩展固体结构中的原子排列，这将决定原子如何排列形成固体结构，(3)控制晶体形式，组成样品的单个晶体的形状和大小。这种精细的控制在无机材料的合成中很少实现，因此我们的工作将为新固体的“设计”提供重要的结果。为了测试这些想法，我们仔细选择了目标材料，其性质取决于化学环境和组成原子的氧化状态：这些材料用于催化，其中金属在固态氧化状态的转换产生了它们的性质（“氧化还原催化”）。与工业项目合作伙伴Johnson Matthey plc一起，将对这些特性进行初步评估，通过整个项目的合作，我们将能够使用结果来指导合成化学。这将是将材料投入实际应用的第一步：氧化还原催化剂构成了催化转换器的基础，用于破坏污染物分子，生产精细化学品，以及为未来能源生产和净化氢。虽然这是一个材料发现的基本合成化学项目，但我们的工作将因此扩展到研究我们在现实生活中应用的材料使用的第一步。

Our proposal is to investigate new synthetic chemistry for the preparation of complex inorganic materials that introduces various degree of control in the preparation of materials, ultimately for real-life uses. Advanced materials for technological applications require the synthesis of samples with precise control over the chemical composition of the sample (the ratio of various chemical elements in a sample and their chemical state) and also control over the form of the sample (particle size and shape over length scales from nanometres to micrometres). Our hypothesis, based on some preliminary results, is that solvothermal conditions (the combination of a solvent and simple chemical precursors in a sealed reaction vessel heated above the boiling point of the solvent, rather like a household pressure cooker) will permit these levels of control to be achieved in a one-step process. The synthetic method has already been applied for the preparation of porous materials, but we will instead study ceramic-type materials, materials that would usually be prepared using extreme temperature in excess of 1000 oC, with repeated grinding and firing cycles. These materials all have extended network structures (effectively infinite, within the bounds of an individual crystal) and therefore their synthesis and crystal growth must be controlled in one step: unlike solids made up by the packing of molecular units where recrystallisation is easily achieved. With the use of mild conditions and a solvent, we aim to first undertake exploratory synthesis to investigate the possibility of isolating new materials, not seen at high temperature, and then second develop control over the growth of crystals making up the sample, to optimise their properties for practical applications. The novelty of our synthetic approach will include the design and commissioning of a new multi-cell reactor in collaboration with a project partner, Baskerville Ltd for routine operation at up to 500 oC. We believe that we can introduce control of crystal growth at three levels: (1) the control of the metal oxidation state (a measure how the electrons holding together the solid structure are located in relation to the metal atoms) by use of chemical reagents, (2) control of the arrangement of atoms in the extended solid structure by choice of partner metals, which will dictate how atoms pack to form the solid structure, and (3) control over crystal form, the shape and size of individual crystals making up a specimen. Such fine control is rarely achieved in the synthesis of inorganic materials, and our work would therefore provide significant results for the 'design' of new solids. In order to test these ideas we have carefully chosen target materials whose properties are dictated by the chemical environment and oxidation state of constituent atoms: these materials are used in catalysis where the switching of metal oxidation states in the solid-state gives rise to their properties ('redox catalysis'). With industrial project partners, Johnson Matthey plc, preliminary assessment of these properties will be achieved, and by collaboration throughout the project, we will be able to use the results to inform and direct the synthetic chemistry. This will be the first step of putting materials into real life applications: redox catalysts form the base of catalytic converters for the destruction of pollutant molecules, production of fine chemicals, and in the production and purification of hydrogen for future energy sources. Although a fundamental synthetic chemistry programme in materials discovery, our work, will therefore extend into the first steps of investigating the use of the materials we make in real-life applications.