Soft chemistry of layered chalcogenides

Thesis

This thesis reports the synthesis and characterisation of several new layered chalcogenides. Low temperature intercalation methods have been used to synthesise new metastable materials which retain the general structure of their precursors, but modify their properties.

Chapters 3 and 4 focus on the intercalation chemistry of excitonic insulator candidate Ta2NiSe5 and structurally related compound Ta2NiSe7. Several species can be intercalated into Ta2NiSe5, all cause significant, but similar, rearrangement of the Ta-Ni-Se layers. Conversely, Li intercalation into Ta2NiSe7 is found to be topotactic in nature and highly reversible. High resolution synchrotron XRD data reveals two distinct phases are formed depending on Li content, and neutron diffraction is used to characterise each phase. Electrochemical studies show continuous filling of the Li sites, and are presented as a comparison to the chemical synthesis.

Chapters 5 and 6 of this work explores the manipulation of layered near room temperature ferromagnetic compounds Fe3GeTe2 and Fe5GeTe2, by insertion of Li(NH2) or K into the interlayer spacing. Intercalation into Fe3GeTe2 results in rearrangement of the Fe-Ge-Te layers and an increase in the Curie temperature by approximately 25 K. In contrast, intercalation into Fe5GeTe2 results in no layer rearrangement and very little change to the ferromagnetic behaviour of Fe5GeTe2. The magnetic properties are characterised through SQUID magnetometry, neutron diffraction and Mössbauer spectroscopy on polycrystalline samples.

Authors: Hyde, PA

• DOI: 10.5287/ora-m8zj0o2go
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: layered compounds; magnetometry; intercalation; x-ray diffraction; chalcogenides