Synthesis and characterisation of new layered oxychalcogenide materials

Abstract

Chapter one describes oxychalcogenide phases found in the literature with layered and three- dimensional structures. An attempt is made to systematise the structures of a range of materials to help understand their structural chemistry. Synthetic details and physical properties are also reported. Potential applications of these materials are discussed, with emphasis placed on compounds similar to those discussed in later chapters. Chapter Two gives full details of the synthetic methods, characterisation techniques and physical property measurements employed in the work described in the following chapters. Chapter Three contains the results of experiments on ԼaշՕՅMշՏBշ (M = Μn, Co) materials, including synthesis, room temperature structure and thermal behaviour by powder X-ray and neutron diffraction, magnetic and conductivity properties. The low temperature magnetic structures of both compounds have been determined and reveal antiferromagnetic ordering of spins within MշՕ layers. Chapter Four reports the synthesis and room temperature structure of the AշMCսշՕշXշ (A = Sr, Ba; M = Μn, Co, Ni, Zn; χ = s, Se) family of compounds. The results of variable temperature powder X-ray diffraction, magnetometry and conductivity experiments on these compounds are also discussed. They show smooth thermal expansion properties except BaշCoCuշՕշՏշ and SrշNiCuշOշSeշ, which show deviations between 100 and 200 K, indicative of structural/magnetic phase transitions at low temperature. Varying magnetic properties are found and a number of the compounds are found to be semiconductors. Chapter Five discusses attempts to prepare the Aշ MOշ Lnշ Oշ Xշ (A = Sr, Ba; M = Co, Mn, Fe; Ln = La, Y, Gd; X = S, Se) family of compounds. The potential stability of such compounds is investigated using bond valence calculations. Chapter Six outlines the work done in indexing, solving and refining the crystal structure of an α,α thiophene tin tetramer from powder X-ray diffraction data.