New transition metal oxychalcogenides

在本提案中，我们申请资金用于研究各种新的过渡金属氧硫族化合物的合成，结构和电子/磁性能。这些是相对不寻常的材料，它们同时含有氧化物（O2-）和第二个硫族（S2-, Se2-, Te2-）阴离子，而不是更常见的物质，如硫酸盐或亚硫酸盐（SO42-和SO32-），其中的硫族具有正的形式电荷。混合阴离子材料很有趣，因为它们在不寻常的化学或电子环境中经常含有过渡金属。这可能导致材料具有意想不到的和迷人的电子，磁性或光学性质。一个经典的例子是2008年Hosono等人在氧nictide LaOFeAs衍生的材料中发现了26 K的超导性（现在已知温度高达55 K）。在这样的高温下，铁基系统中的超导性是前所未有的，完全出乎意料，引起了全世界的极大兴趣。其他有趣的混合阴离子相包括LnOCuS （Ln =镧系化物）和La2O2CdSe2等材料，它们是p型透明导体的罕见例子，可以在显示设备中找到一系列应用。在这项研究计划中，我们计划在三个主要领域开展工作。首先，我们想要调整Ln2O2M2OSe2 （Ln =镧系元素，M =过渡金属）组成的一个迷人而不寻常的材料家族的电子特性。它们与超导粒子系统密切相关，但在未掺杂状态下，它们位于绝缘体与金属边界的绝缘体一侧。我们计划用各种方法对它们进行化学修饰，以改变它们的导电性，理想情况下是朝着相图的超导区域，并了解它们的结构和物理性质。其次，我们的目标是扩展我们最近在制备与Ln2O2MSe2密切相关的新材料方面的成功。我们再次致力于理解、控制和利用它们的电学和光学特性。我们相信这里的发现也将有助于了解行星系统。在我们的最终工作链中，我们相信我们可以采用从我们的工作和其他人的工作中学到的各种想法来制备通式（LnOQ）1-xMx和（LnOQ）1-xMQx的新材料家族-我们称之为“4埃相”。我们的目的是探索这些新相的性质。我们工作的合成方面将通过各种表征和理论方法得到支持。我们将应用x射线和中子散射技术来探测材料的结构、结构变化和磁相互作用。有趣材料的物理性质（电导率、磁性、热容量等）将使用达勒姆可用的设备进行测量。平面波密度泛函理论将用于帮助我们预测和理解目标材料或制备材料的性质。我们相信，这种协同方法将使取得迅速和深刻的进展。

In this proposal we request funding to investigate the synthesis, structures and electronic/magnetic properties of a variety of new transition metal oxychalcogenides. These are relatively unusual materials which simultaneously contain an oxide (O2-) and a second chalcogenide (S2-, Se2-, Te2-) anion, as opposed to more commonly found species such as sulfates or sulfites (SO42- and SO32-) in which the chalcogen has a positive formal charge. Mixed anion materials are interesting as they frequently contain transition metals in unusual chemical or electronic environments. This can lead to materials with unexpected and fascinating electronic, magnetic or optical properties. A now-classic example of this was the 2008 discovery by Hosono et al. of 26 K superconductivity (now known at temperatures up to 55 K) in materials derived from a oxypnictide LaOFeAs. Superconductivity in an iron-based system such as this at such high temperatures was unprecedented, entirely unexpected and led to significant world-wide interest. Other interesting mixed anion phases include materials such as LnOCuS (Ln = lanthanide) and La2O2CdSe2, which are rare examples of p-type transparent conductors, and could find a range of applications in display devices.In this research programme we plan work in three main areas. Firstly, we want to tune the electronic properties of a fascinating and unusual family of materials of composition Ln2O2M2OSe2 (Ln = lanthanide, M = transition metal). These are closely related to the superconducting pnictide systems but, in their undoped state, lie on the insulator side of a insulator-to-metal boundary. We plan various approaches to chemically modify them to change their conductivity, ideally towards the superconducting region of the phase diagram, and to understand both their structural and physical properties. Secondly, we aim to extend our recent successes in the preparation of novel materials with the closely related composition Ln2O2MSe2. We again aim to understand, control and exploit their electrical and optical properties. We believe discoveries here will also help understand the pnictide systems. In our final work strand we believe that we can adopt a variety of ideas learned from our work and that of others to prepare new families of materials of general formula (LnOQ)1-xMx and (LnOQ)1-xMQx - what we call "4 Angstrom phases". Our aim is to explore the properties of these new phases. The synthetic side of our work will be supported via a variety of characterisation and theoretical methods. We will apply X-ray and neutron scattering techniques to probe the structures, structural changes and magnetic interactions in the materials. The physical properties of interesting materials (conductivity, magnetism, heat capacity, etc) will be measured using equipment available in Durham. Plane wave density functional theory will be used to help us predict and understand the properties of materials targetted or prepared. We believe this synergic approach will allow rapid and insightful progress.