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The rational design of crystal structures, in particular noncentrosymmetric materials, and how to differentiate polar, polar-chiral, and chiral structures, is an ongoing theme in crystal engineering. In KNaNbOF5, the combination of a second-order Jahn Teller active d0 transition metal oxyfluoride anionic unit and mixed K/Na cation coordination environments are shown to result in a polar structure (space group Pna21). The crystal structure analysis of the Na/K-O/F interactions reveals that the potassium cations form one of the two contacts to the under-bonded oxide ions. These interactions satisfy the expected bond valence sums and Pauling's second crystal rule (PSCR), leading to O/F ordering and acentric packing of the [NbOF5]2− anionic unit.
A new series of low-melting, highly volatile, thermally and air-stable cadmium MOCVD precursors have been synthesized and characterized. Cd(hfa)2(N, N-DE-N', N'-DMEDA) has been successfully utilized in the growth of highly conductive and transparent CdO thin films. Hall measurements conducted on films deposited simultaneously on MgO (100) single crystal and Corning 1737F glass substrates reveal that the films on MgO have significantly enhanced carrier mobilities. Owing to similar grain sizes and carrier concentrations we attribute this effect to improved texture and associated improvements crystalline order. Conductivities as high as 8,590 S/cm are obtained which is to our knowledge the highest value reported to date for CdO films without aliovalent dopants.
Perovskite-like mixed metal ruthenates are of interest owing to their varied electronic and magnetic properties, which are heavily dependent on the ordering of the transition metals. We report the synthesis and structural characterization of the first 1:2 ordered perovskite ruthenate, Sr3CaRu2O9. The structure was determined from a combination of powder X-ray, electron and neutron diffraction data and is characterized by a 1:2 ordering of Ca2+ and Ru5+ over the sixcoordinate B-sites of the perovskite lattice. Sr3CaRu2O9 is the first example of this structure-type to include a majority metal with d electrons (Ru(V), d3). The relationship of this material to the K2NiF4-type Sr1.5Ca0.5RuO4 (i.e., Sr3CaRu2O8) highlights the dramatic effects of the ruthenium valence on the resultant structure. Remarkably, these two structures can be quantitatively interconverted by the appropriate choice of reaction temperature and atmosphere.
Bulk samples of transparent conducting oxides (TCOs) in the Zn-In-Sn and Ga-In-Sn oxide systems were prepared by solid state processing. Phase relations and physical properties were determined and the results compared to similar measurements on thin film materials.
Solid state bulk processing techniques were used to synthesize various transparent conducting oxides (TCO's) with In, Zn, and Sn cations. Optical and electronic properties of resultant phase-pure TCO's were compared to each other and to bulk samples of Sn-doped In2O3 (ITO). Reduction and heat treatment showed significant effects on optical and electronic performance, indicating optimization of processing conditions will be required for industrial applications.
Comparison of optical and electronic properties in the series of compounds: ZnkIn2O3+k, k = 3,4,5,7,11 revealed trends correlated with the materials’ internal structure. These layered compounds showed improvement of optical properties at higher Zn contents and improvement in conductivity at higher In contents. The trends suggest these materials may be useful for applications where tradeoffs between conductivity and transparency are acceptable.
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