Realising Sample Environments for X-ray and Neutron Powder Diffraction: Demonstrated through In Situ Studies of Magnetic Ferrites

Research output: Book/anthology/dissertation/reportPh.D. thesis

Advanced functional materials are indispensable in the modern day of life. They are included in all applications around us ranging from cars, cell phones to computers, etc. Some say that the development of new and better functional materials will be the solution to the current climate changes, others say they are necessary to expand beyond the planet earth to inhabit remote planet. No matter the cause, developing better advanced functional materials have become a huge topic in materials science. In order to improve materials it is important to understand the preparation process. For this we need methods to probe the reactions while they are occurring. An excellent tool for these, so-called in situ, studies is diffraction. With modern days 3rd generation high-brilliance synchrotrons and the new neutron facility, the European Spallation Source (ESS) being built in Sweden, we have the radiation sources needed to investigate the reaction mechanism with a very high time resolution. In order to take advantage of the improved time resolution, new sample environments must be developed.
The main topic of this dissertation is the development of sample environments for powder X-ray and Neutron diffraction. An in situ setup for an in-house X-ray diffractometer has been developed. The setup can be used to study solvothermal reaction as well as solid-gas reaction. The setup offers spatial sample resolution on a time scale of 15 s per diffraction pattern. Even though the achieved time-resolution is not comparable to the much better synchrotron radiation experiments, the setup has proved its relevance in preliminary investigations. The setup has been used to investigate the formation of Ni, and Cu nanoparticles through solvothermal synthesis and to follow the reduction of CoFe2O4 to create an exchange-spring nanocomposite material. A modified version of the heat-gun sample environment has been used at an X-ray synchrotron to repeat the reduction of CoFe2O4 with a better time resolution and bigger Q-range. The experiment has revealed a complicated three-step reaction mechanism of CoFe2O4 ® CoxFe1-xO ® CozFe2-z were each phase did initially form as Co-rich. With time Fe was observed to enter the structure
In an effort to follow the formation of magnetic transition metal doped nanocomposites a second in situ setup has been designed to follow solid-gas reaction using angular dispersive neutron powder diffraction (NPD). The setup offers a maximum temperature of 973K, and reach thermal equilibrium in less than 5 min. With this setup, the already well-known reduction of CoFe2O4 has been repeated. The experiment confirms the reaction mechanism observed in synchrotron experiments, and, additionally, reveals that the CoFe2O4 transforms into Fe3O4 at high temperatures and into -Fe2O3 at low temperatures. The setup has been used to perform multiple in situ experiments, but it has also been used to perform both annealing and solid-gas experiments ex situ.
A study of the crystallographic and magnetic structure of the W-type hexaferrite (WHF) SrMe2Fe16O27 doped with transition metals (Me = Mg, Co, NI, and Zn), prepared at temperatures above 1373 K, showed some interesting changes in the magnetic ordering. In order to follow the formation of the WHF a high-temperature induction furnace has been designed. It is designed for time-of-flight (ToF) NPD and can reach temperatures above 1811K in less than 5 min. It is built for heating experiments only but is being upgraded to include a press to follow powder compaction processes. The furnace has been successfully tested at the ToF neutron-powder diffractometer POLARIS at ISIS and is now ready to be used for real experiment. An in-house version of the setup has been made and is currently being used in ex situ experiment at our department.
Original languageDanish
Place of publicationAarhus
PublisherAarhus Universitet
Number of pages313
Publication statusPublished - 4 Feb 2020

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