Syntheses, properties, and electronic structure of materials with strongly correlated electrons. From thin film transition metal oxides to early actinide selenides

This work explores the chemistry and physics of transition metal oxides and early actinide chalcogenide and pnictide materials, two systems where the effects of electron-electron correlation can be large. The transition metal research focuses on theoretical investigations of ferromagnetic/ferroelectric coupling between ferrite spinel and oxide perovskite multilayer materials. Stable interfaces between Fe3O4 or CoFe2O 4 and BaTiO3, SrTiO3, or PbZrO3 are developed and several multilayer compositions are explored to establish physical and chemical variability. In one final relaxed interface, the A-site Fe of the spinel tries to retain its tetrahedral configuration, seeking out two perovskite oxygens to form a distorted tetrahedral geometry. This configuration has the advantage of maintaining a near octahedral oxygen environment for perovskite B-site cations, and encouraging cross-interface hybridization of Ti and Fe 3d-orbitals. This generates a slight magnetic polarization of the Ti 3d-electron cloud.;In the investigation of early actinide chalcogenide and pnictide materials, several Np analogues to U compounds have been synthesized along with several new U compounds. The compounds NpCuOP, AMNpS3 (A = K, Rb, and Cs; M = Cu or Ag), and ANp2Se6 (A = K and Cs) have been synthesized and their single-crystal X-ray structures solved. These compounds crystallizes isostructural to known U compounds. The modulated structure of CsNp2Se6 has been solved as a commensurate 5 a x 5b supercell confirming the presence of lone Se2- and Se22- anions rather than the long Se-Se interactions found in the average structure. NpCuSe2 has also been synthesized and crystallizes in a well known rare-earth structure-type. Through the syntheses of these compounds the intermediate nature of Np chemistry and its additional 5f-electron is explored.;Three new 5d-5f compounds: UTa 2O(S2)3Cl6, [Ta4(Se 2)8][UI6], and [Ta7(Se2) 14][U2I10]2, have been synthesized and their single-crystal X-ray structures solved. They contain interesting structural motifs including a heterobimetallic M3 cluster, 1D-[Ta(Se2)2]n chains, and the new [U 2I10]2- complex anion. The magnetic and transport properties of many of these U and Np compounds have been investigated and display properties such as antiferromagnetism, Mott-Heisenberg transitions, and semiconducting behavior. Ab initio density functional calculations have been used throughout to help understand the transport properties and predict the local magnetic structure at the actinide metal centers.