| Summary: | Interest in the molybdenum double perovskites has increased since the discovery of high temperature, low field magnetresistance in Sr2FeMoO6. Molybdenum double perovskites of the form Ba2LnMoO6 (where Ln = Sm, Sm0.5Eu0.5, Eu, Gd, Pr) as well as Sr2ScMoO6 have been synthesized by solid-state reactions up to 1200°C. Laboratory X-ray diffraction, variable temperature neutron and synchrotron X-ray diffraction as well as DC-SQUID magnetometry have been employed, in order to investigate the intricate relationship between spin, lattice and orbital degrees of freedom within these compounds. A variable temperature neutron diffraction experiment has been performed on the molybdenum double perovskite Ba2154SmMoO6 between 353 and 877 K in order to further investigate the crystal structure into the high temperature regime. Variable temperature neutron diffraction studies of Ba2PrMoO6 have been performed to investigate the links between structure, spin and orbital order in this material. A synchrotron X-ray diffraction study of Ba2GdMoO6 is detailed. Ba2GdMoO6 exhibits a ferroelastic phase transition below 220 K; the first time this has been reported in a Mo5+ double perovskite. Furthermore, a study of the geometrically frustrated double perovskite Sr2ScMoO6 has been carried out, in order to further investigate the exotic new valence bond glass phase. The results shed new light on the complex relationship between spin, lattice and orbital degrees of freedom in Ba2LnMoO6 double perovskites.
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