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是有用的，包括透明导体，光催化剂，多铁质和热电材料。理想的钙钛矿结构，ABX3，通常由一个大的金属阳离子(a)和一个小的金属阳离子(B)和一个阴离子(X)组成，通常是氧化物或卤化物。在理想结构中，B离子呈6重八面体配位。材料性能与结构密切相关，钙钛矿结构对八面体倾斜等变形具有耐受性。通过仔细选择元素和掺杂剂，可以很好地调整材料的固有特性。将磁性阳离子引入到非磁性结构中可以诱导先前非磁性材料的磁性行为。当加入足够量的磁性掺杂剂时，可以形成交换途径以获得磁性结构。类似地，将共价掺杂剂引入先前绝缘或半导体的材料中可以导致过渡到表现出更导电行为的材料。钙钛矿结构的一种延伸是双钙钛矿，其中A或B位点包含多个元素，并在结构上形成有序的离子排列。有两个有序的位置，其中至少有一个元素有未配对的d电子，可以形成有趣的磁性结构，导致奇异的行为。本项目将研究两种钙钛矿体系：锡酸钙钛矿和铁双钙钛矿。对于这两种体系，将使用d-嵌段掺杂剂和共价掺杂剂来诱导磁性和导电性。在铁双钙钛矿体系中，B位的有序将是目标，而对于锡酸钙钛矿，B位将是无序的，因此将对取代量进行研究。这些结构将通过x射线衍射和HAADF-STEM技术进行分析。成分数据将通过ICP和EDX技术获得，XPS和XANES将表征当前元素的氧化态。SQUID磁强计将用于表征磁性行为，电阻率将使用PPMS测量。

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.