High pressure hydrothermal synthesis of magnetic and electronic materials

点击翻译按钮获取中文摘要

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.