High pressure hydrothermal synthesis of magnetic and electronic materials

多功能钙钛矿结构已被证明在广泛的领域中是有用的，包括透明导体、光催化剂、多铁性和热电性。理想的钙钛矿结构ABX 3通常由大的金属阳离子（A）和较小的金属阳离子（B）以及阴离子（X）（通常是氧化物或卤化物）组成。在理想结构中，发现B离子处于6重八面体配位。材料性质与结构密切相关，并且钙钛矿结构耐受诸如八面体倾斜的变形。通过仔细选择元素和掺杂剂，可以微调材料的固有特性。将磁性阳离子引入非磁性结构可以将磁性行为引入先前非磁性材料中。当添加足够量的磁性掺杂剂时，可以形成交换路径以给出磁性结构。类似地，将异价掺杂剂引入到先前绝缘或半导体材料中可以导致转变成表现出更多导电行为的材料。钙钛矿结构的一个延伸是双钙钛矿，其中A或B位点含有多种元素并形成离子在结构上的有序排列。有两个有序的位置，其中至少一个元素具有未配对的d电子，可以形成有趣的磁性结构，导致奇异的行为。该项目将研究两种钙钛矿系统：锡酸钙钛矿和铁双钙钛矿。对于这两个系统，d-区掺杂剂和异价掺杂剂将用于诱导磁性和导电行为。在铁双钙钛矿体系中，将以B位点的有序化为目标，而对于锡酸盐钙钛矿，B位点将是无序的，因此将对取代量进行研究。将通过X射线衍射和HAADF-STEM技术分析结构。成分数据将通过ICP和EDX技术，XPS和XANES来确定本元素的氧化态。将使用SQUID磁力测量法来验证磁行为，并使用PPMS测量电阻率。

The versatile perovskite structure has shown to be useful within a wide range of areas including transparent conductors, photocatalysts, multiferroics and thermoelectrics. The ideal perovskite structure, ABX3, generally consists of a large metal cation (A) with a smaller metal cation (B) with an anion (X), often an oxide or halide. In the ideal structure, the B ion is found in a 6-fold octahedral coordination. Material properties are strongly related to the structure and the perovskite structure is tolerant to distortions such as octahedral tilting. By careful selection of elements and dopants, the intrinsic properties of the material can be finely tuned. Introducing magnetic cations to non-magnetic structures can induce magnetic behaviour into the previously non-magnetic material. When a sufficient amount of a magnetic dopant is added, exchange pathways can form to give a magnetic structure. Similarly, introducing aliovalent dopants into previously insulating or semiconducting materials can cause a transition into materials exhibiting more conductive behaviour. One extension of the perovskite structure is the double perovskite, where the A or B site contains multiple elements and forms an ordered arrangement of ions across the structure. Having two ordered sites where at least one element has unpaired d-electrons, interesting magnetic structures can form, leading to exotic behaviours.This project will look at two perovskite systems: stannate perovskites and iron double perovskites. For both systems, d-block dopants and aliovalent dopants will be used to induce both magnetic and conductive behaviour. In the iron double perovskite systems, ordering of the B sites will be targeted whereas for the stannate perovskites, the B site will be disordered and so an investigation into the substitution quantity will be performed. The structures will be analysed by X-ray diffraction and HAADF-STEM techniques. Compositional data will be found through ICP and EDX techniques, with XPS and XANES to characterise the oxidation states of the present elements. SQUID magnetometry will be used to characterise the magnetic behaviour and resistivity will be measured using a PPMS.