<p> Oxygen deficient SrTiO3-x with x = 0.28(2) was prepared in single crystal form and found to have a perovskite structure with a small tetragonal distortion. The structure was studied by powder and single crystal X-ray diffraction and electron diffraction. No long range order of the oxygen vacancies could be detected. The transport studies show that SrTiO2.72 is a metallic conductor. </p> <p> Some new K2NiF4 - type compounds, PrSrVO4, SmSrVO4, EuSrVO4 and PrSrGaO4, were prepared and studied by powder diffraction methods. The crystal structures of LaSrVO4, CeSrVO4, PrSrVO4 and NdSrVO4 were refined from powder neutron diffraction data. Powder X-ray diffraction data for all the new compounds above and for EuSrAlO4 are presented here. </p> <p> Magnetic susceptibilities are reported for SrTiO2.72 which exhibits metal-like Pauli-paramagnetism, PrSrGaO4, NdSrGaO4, EuSrAlO4 and LnSrVO4 where Ln = La, Ce, Pr and Nd. </p> / Thesis / Master of Science (MSc)

This study is a multi-proxy analysis of a 30-m section of a Barremian-Aptian succession of interbedded, grayish black (N2) and black (N1) limestones from a quarry of the Sierra de Prada. Index taxa include planktic foraminifera Globigerinelloides blowi and Hedbergella sigali, which combined with δ13C data from Cresmina and Gorgo a Cerbara sections indicate a late Barremian to early Aptian age. The rocks are organic-rich with 0.67 - 3.10 wt% total organic carbon (TOC). A marlstone interval (~1m) at 2.24 m has a low bioturbation index (1), TOC ~6.66 wt%, framboidal pyrite, and enrichment spikes of major, biolimiting, and redox-sensitive trace elements (Al, Si, Ti, P, Fe, and Mo, Cr, Cu, V, Th), indicating an anoxic episode. Biomarker analyses show a predominance of n-alkanes (≤nC20) at this level, suggesting an in situ origin of organic matter from phytoplankton. Pr/Phy ratios below 2 imply that organic matter did not reach overmaturity.

<p>A series of layered perovskite-based compounds were synthesized and studied as follows.</p> <p>La₅Mo_2.76(4)V_1.25(4)O₁₆ is a new pillared-perovskite synthesized by solid state chemistry method. It has layers of corner-sharing octahedra separated by dimers of edge-sharing octahedra, and is the first Mo-based pillared-perovskite whose magnetic structure was determined by neutron diffraction.</p> <p>Ca₂FeMnO₅ is an oxygen-deficient-perovskite with a brownmillerite-type ordering of oxygen vacancies, resulting in layers of corner-sharing octahedra separated by chains of corner-sharing tetrahedra. The octahedral layer contains mostly (~87%) Mn, while the tetrahedral layer is mainly (~91%) occupied by Fe. Long-range G-type magnetic ordering is present, where the moment on each site is coupled antiferromagnetically relative to all nearest neighbors.</p> <p>Ca₂FeCoO₅ has a brownmillerite superstructure with space group <em>Pcmb</em>, a rare space group for brownmillerites that requires doubling of one unit cell axis. Ca₂FeCoO₅is the first brownmillerite to contain intra-layer cation ordering. It has a long-range G-type ordering, and is the first brownmillerite to show spin re-orientation as function of temperature.</p> <p>Sr₂FeMnO_5+y was synthesized in both air (y~0.5) and argon (y~0), both of which resulted in vacancy-disordered cubic structures. The argon compound has a local brownmillerite structure, i.e. local ordering of vacancies. It has a superparamagnetic state below ~55K, with domains of short range (50Å) G-type ordering at 4K. For the air synthesized compound, y~0.5, long range G-type ordering is observed in ~4% of the sample.</p> <p>Sr₂Fe_1.9M_0.1O_5+y (M=Mn, Cr, Co; y= 0, 0.5) were synthesized in both air(y~0.5), and argon(y~0). All argon materials are brownmillerites with G-type magnetic ordering, but T_N’s are significantly different. The air-synthesized Co-material has long range vacancy ordering and magnetic ordering, while the Mn and Cr-materials (air) lack such orderings and both show spin-glass-like transitions.</p> <p>Sr₂Fe_1.5Cr_0.5O₅ has a vacancy-disordered cubic structure, but contains long range G-type magnetic ordering, unlike the other vacancy-disordered materials studied.</p> / Doctor of Philosophy (PhD)