Polycrystalline La(2)NiMnO(6) thin films are prepared on Pt/Ti/SiO(2)/Si substrates by the sol-gel method. Through controlling the processing parameters, the cation ordering can be tuned. The disordered and ordered thin films exhibit distinct differences for crystal structures as well as properties. The crystal structure at room temperature characterized by X-ray diffraction and Raman spectra is suggested to be monoclinic (P2(1)/n) and orthorhombic (Pbnm) for the ordered and disordered thin films, respectively. The ferromagnetic-paramagnetic transition is 263 K and 60 K for the ordered and disordered samples respectively, whereas the saturation magnetic moment at 5 K is 4.9 μ(B) fu(-1) (fu = formula unit) and 0.9 μ(B) fu(-1). The dielectric constant as well as magnetodielectric effect is higher for the ordered La(2)NiMnO(6) thin films. The magnetodielectric effect for the ordered thin film is dominantly contributed to the intrinsic coupling of electric dipole ordering and fluctuations and magnetic ordering and fluctuations, while it is mainly contributed to Maxwell-Wagner (M-W) effects for the disordered thin film. The successful achievements of ordered and disordered polycrystalline La(2)NiMnO(6) thin films will provide an effective route to fabricate double-perovskite polycrystalline thin films by the sol-gel method.

Transport properties of the good thermoelectric misfit oxide Ca3Co4O9 are examined. In-plane resistivity and Hall resistance measurements were made on epitaxial thin films which were grown on c-cut sapphire substrates using the pulsed laser deposition technique. Interpretation of the in-plane transport experiments relates the substrate-induced strain in the resulting film to single crystals under very high pressure (∼ 5.5 GPa) consistent with a key role of strong electronic correlation. They are confirmed by the measured high temperature maxima in both resistivity and Hall resistance. While hole-like charge carriers are inferred from the Hall effect measurements over the whole investigated temperature range, the Hall resistance reveals a non monotonic behavior at low temperatures that could be interpreted with an anomalous contribution. The resulting unconventional temperature dependence of the Hall resistance seems thus to combine high temperature strongly correlated features above 340 K and anomalous Hall effect at low temperature, below 100 K. Good thermoelectric materials, 1,2 which convert heat into electricity and vice versa, should have high figures of merit (ZT) where ZT= S 2 T/ρκ, so S (the thermoelec-tric power or Seebeck coefficient) should be large while ρ (resistivity) and κ (thermal conductivity) should be small at a temperature T. In addition to these properties , these materials should be physically and chemically robust for high temperature processes such as the generation of energy from waste heat, and therefore, oxides such as Na x CoO 2 and Ca 3 Co 4 O 9 have been received a considerable attention recently. 3,4 Among the oxides Ca 3 Co 4 O 9 is very promising because of its high room temperature (RT) thermopower (125 µV/K), low resistivity (12 mΩ cm), low thermal conductivity (30 mW (cm K) −1), and resistance to humidity. 4,5 Ca 3 Co 4 O 9 is a misfit oxide and can be denoted as [Ca 2 CoO 3 ] RS [CoO 2 ] 1.62 to recognize the incommensu-rate nature of the structure. The structure is composed of alternating layers of a distorted Ca 2 CoO 3 rock salt-like layer (RS) and a CoO 2 cadmium iodide-like layer which are stacked in the c-axis direction. Crystallographically , these two layers have similar a, c, and β lattice parameters but different b lattice parameters. The ratio of the b parameters for the Ca 2 CoO 3 layer to CoO 2 layer is 1.62. The material's anisotropic behavior is easily seen through the comparison of the in-plane and out-of-plane resistivity behavior (metallic versus semiconduct-ing, respectively). 4 Thus, to attain the highest properties in a thermoelectric device, growth along the c-axis would be best to insure uniform properties. The bulk can be magnetically aligned along the c-axis at high temperature, 6,7 but the thin films form provides a more convenient method for manufacturing useful thermoelec-tric devices. For this reason, we have undertaken the synthesis of Ca 3 Co 4 O 9 films on Al 2 O 3 (c-cut sapphire) substrates. 8 The resulting epitaxial film has thermoelec-tric ...

Bi(2)Sr(3)Co(2)O(y) thin films are prepared on SrTiO(3) (100), (110) and (111) single crystal substrates using the sol-gel method. All the thin films are c-axis oriented regardless of the orientation of the substrate suggesting self-assembled c-axis orientation, and X-ray photoelectron spectroscopy results give evidence of coexistence of Co(3+) and Co(2+) ions in the derived films. Transmission electronic microscopy observations reveal that all samples are c-axis oriented with no obvious differences for different samples, and the c-axis lattice constant is determined as ~15 Å suggesting the misfit structure. A phenomenological thermodynamic phase diagram for self-assembled c-axis orientation is established for misfit cobaltate-based films using chemical solution deposition. All samples behave like semiconductors due to the coexistence of Co(3+)/Co(2+) ions, and the resistivity at 350 K is ~47, 39 and 17 mΩ cm for the thin films on SrTiO(3) (100), (110) and (111), respectively, whereas the Seebeck coefficient at 300 K is 97, 89 and 77 μV K(-1). The successful attainment of Bi(2)Sr(3)Co(2)O(y) thin films with self-assembled c-axis orientation will provide an effective prototype for investigation of growth mechanisms in complex oxide thin films with a misfit structure.