Structures, Properties and Chemistry of Layered Oxide Chalcogenides

该项目将包括调查层状氧化物硫化物的结构和性质，并使用化学取代法调整其磁性和电子性质。氧化物硫化物是一类用途极其广泛的化合物，由于较小的氧化物阴离子和较大的、更易极化的硫化物阴离子的化学要求而观察到的阴离子分离，这导致这些材料具有层状结构。然后，这些层可能含有Li+等阳离子，然后循环使用以测试电池的正极适合性，这与EPSRC和其他政府资助机构(如法拉第研究所)的研究目标非常一致。氧化物硫化物的其他应用包括半导体、晶体管以及作为可再生能源的可能来源，例如在太阳能电池板中。该项目将在文献中的化合物的基础上生产多种新型化合物。如前所述，氧化物硫化物在组成上是灵活的，这意味着可以通过取代或掺杂从已知的结构中衍生出新的化合物。这些取代可以导致电学和磁学性质的微调。例如，在NaFeAs中就知道这一点，通过掺杂另一种过渡金属，如Co或Ni，可以诱导超导行为。尽管合成方法相对简单，只需称量反应物，在玛瑙研钵和研磨器中研磨，然后将其密封在真空的二氧化硅安瓶中；但该项目期间将产生的化合物的特征肯定不是微不足道的。将采用广泛的技术来补充内部X射线粉末衍射数据以及使用SQUID磁强计测量的磁化程度。将在钻石光源获得详细表征的高质量X射线数据，在ISIS设施获得中子衍射，以探测化合物内的磁性有序；ILL(法国格勒诺布尔)的中子源也将用于这一目的。有些样品可能无法在常压下合成，这些样品将在Element 6(Harwell)的帮助下进行，或者通过与JSPS(日本)新的核心到核心合作进行。其他不太常用的技术包括(但不限于)电子衍射(安特卫普)、穆斯堡尔谱(谢菲尔德哈勒姆)、电阻率和单晶生长。该项目的初始目标是来自Sr2NiO2Cu2S2(低自旋)和Sr2NiO2Cu2Se2(高自旋)的固溶体，这两种固溶体都位于密度泛函计算支持的自旋边界附近。初步结果表明，当系列化合物达到Sr2NiO2Cu2SeS时，已经发生了自旋态交叉，因此需要对已经合成的更富Se的化合物进行进一步的研究，以及通过共晶卤化物助熔剂合成更富S的化合物来证实这一发现。此外，在Se类似物中掺入钙以增加Ni2+的配位场以诱导自旋态交叉的尝试似乎是有希望的，尽管结果表明并不是所有预期的钙离子都被引入到结构中，这可能通过高压合成来克服。进一步的调查将包括含有其他过渡金属的类似物。该项目属于EPSRC“物理科学”研究领域。

The project will include investigating the structures and properties of layered oxide chalcogenides and tuning their magnetic and electronic properties using chemical substitution. Oxide chalcogenides are an extremely versatile class of compound, owing to the anion segregation observed due to the chemical requirements of the smaller oxide anion and larger, more polarisable chalcogenide anions, which leads to these materials having layered structures. These layers can then possibly host cations such as Li+, which can then be cycled to test battery cathode suitability which aligns well within the research goals of EPSRC and the other government-funded bodies such as the Faraday Institution). Other applications of oxide chalcogenides include semi-conductors, transistors and also as a possible source of renewable energy, for example, in solar panels.This project will produce multiple novel compounds based on compounds in the literature. As mentioned previously, oxide chalcogenides are compositionally flexible, this means that new compounds can be derived from already known structures via substitution or doping. These substitutions can lead to fine tuning of the electrical and magnetic properties. This is known in, for example, NaFeAs, whereby doping with another transition metal such as Co or Ni can induce superconducting behaviour. Although the synthetic methodology is relatively straightforward, involving weighing out reactants and grinding together in an agate mortar and pestle before sealing in an evacuated silica ampoule; the characterisation of the compounds that will be produced during this project is certainly not trivial. A wide range of techniques will be employed to complement the in-house X-ray powder diffraction data as well as the magnetisation as measured using a SQUID magnetometer. High quality X-ray data for detailed characterisation will be obtained at the Diamond Light source, and neutron diffraction at the ISIS Facility to probe magnetic ordering within the compounds; the neutron source at the ILL (Grenoble, France) will also be used for this. Some samples may not be able to be synthesised at ambient pressures and these will be carried out with help from Element 6 (Harwell) or via a new Core-to-Core collaboration with JSPS (Japan). Other techniques that will be less frequently used include (but not limited to), electron diffraction (Antwerp), Mössbauer spectroscopy (Sheffield Hallam), electrical resistivity and single crystal growth.The initial targets of the project are from the solid solution of Sr2NiO2Cu2S2 (low spin) and Sr2NiO2Cu2Se2 (high spin), which both lie close to the spin boundary as supported by density functional theory calculations. Preliminary results indicate that the spin-state crossover has already occurred by the time the series has reached Sr2NiO2Cu2SeS and so further investigation is needed into the already synthesised more Se rich compounds, as well as the synthesis of the more S rich compounds via a eutectic halide flux to confirm the findings. Furthermore, attempts to dope the Se analogue with calcium to increase the ligand field at Ni2+ to induce the spin-state crossover seem promising although results would suggest that all the intended Ca2+ is not being introduced into the structure, this could potentially be overcome via a high-pressure synthesis. Further investigations will include analogues containing other transition metals. This project falls within the EPSRC 'Physical Sciences' research area.