Synthesis, Structure and Properties of Metal Oxychalcogenides

Abstract

Chapter 1 gives a brief review of oxychalcogenide materials and their properties, with particular focus on structures similar to the systems discussed in the later chapters. These oxychalcogenides, are of interest due to their potentially interesting magnetic and electronic properties.
Chapter 2 discusses the synthetic methods and characterisation techniques used throughout this thesis. The theory behind both single crystal and powder diffraction techniques used in this work is described.
Chapter 3 describes the synthesis of a new ZrCuSiAs-related transition metal containing oxychalcogenide La2O2ZnSe2. The structure of La2O2ZnSe2 is reported, deduced from symmetry adapted distortion mode analysis of laboratory X-ray powder diffraction data, and confirmed by Rietveld analysis of combined X-ray and neutron powder diffraction data. The variable temperature structural properties of La2O2ZnSe2 are also reported alongside diffuse reflectance measurements.
Chapter 4 discusses the variable temperature structural, electronic and magnetic properties of A4O4TiSe4 (A = Sm, Gd, Tb, Dy, Ho, Er, & Y). The variable temperature structural properties of the compounds are also reported. Electronic measurements show these materials are semiconductors while SQUID magnetometry measurements suggest these materials order antiferromagnetically at low temperatures.

Chapter 5 reports the synthesis of an extended family of ternary oxychalcogenides with A4O4Se3 composition. Three new structures for this composition have been solved using a combination of single crystal and powder X-ray diffraction. The new γ and δ-structures have been shown to contain a highly disordered layer of selenium anions. The variable temperature structural properties of the series are also reported.
Chapter 6 discusses the synthesis of single crystals of La2O2Se2Fe2O, La2O2Se2Mn2O and Pr2O2Se2Mn2O. A comparison of the structural properties of the A2O2Se2Mn2O materials is given, alongside determination of the incommensurately modulated cell of La2O2Se2Mn2O.
Chapter 7 reports synthesis a new 3D oxychalcogenide LaInS2O. Its structure is solved from X-ray powder diffraction measurements.
Chapter 8 describes the method of temperature calibration used for variable temperature X-ray powder diffraction measurements used in this work.