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- Westin, Gunnar, et al.
(author)
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All alkoxide route to manganate and coboltate perovskite films and powders : effects of processing parameters
- 2008
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In: Journal of Sol-Gel Science and Technology. - : Springer. - 0928-0707 .- 1573-4846. ; 48:1-2, s. 194-202
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Journal article (peer-reviewed)abstract
- Manganate and cobaltate perovskites having the general formula ABO3 have many technologically important applications. Here we present all alkoxide based routes to manganate and coboltate perovskite films and nano-phase powders of the compositions; LCMO (La0.67Ca0.33MnO3), LSMO (La0.75Sr0.25MnO3), LNCMO (La0.33Nd0.33Ca0.33MnO3), LBSMO (La0.75Ba0.125Sr0.125MnO3) and LSCO (La0.50Sr0.50CoO3). The Mn and Co (oxo) methoxy-ethoxide precursors were prepared by reaction of MnCl2 or CoCl2 with 2 Kmoe in methoxy-ethanol-toluene. After hydrolysis of the alkoxide solutions by atmospheric air all systems produced X-ray and electron diffraction amorphous gels of high elemental homogeneity, and the IR spectra showed that they consisted of hydrated oxo-carbonates. Heating in air resulted in similar weight-loss curves for all studied gels passing; loss of H2O in the range 20–300 °C, decomposition of carbonate groups into oxide and CO2 in the temperature range 300–700 °C, and in some cases loss of a small amount of oxygen in the temperature range 700–1,000 °C. The pure perovskites were obtained at 690–770 °C with heat rates of typically 5–20 °C min−1 without annealing. Perovskites could also be obtained at 550 °C by annealing, but these perovskites are prone to be A-site ion inhomogeneous according to the TEM EDS studies, which was not the case for the perovskites heat-treated to at least the carbonate decomposition temperature. This A-site inhomogeneity is ascribed to sequential decomposition of carbonates due to their different thermal stabilities, which is probably a general feature also with other sol–gel precursors and low temperature annealing. High quality polycrystalline films were prepared on Si/SiO2/TiO2/Pt substrates with all compositions and high quality epitaxial films were prepared of LCMO (on 100 LaAlO3) and LSCO (on 100 SrTiO3). The colossal magneto resistance (CMR) of the epitaxial LCMO films of 32% (246 K) is in parity with PLD derived films. The conductivities of the epitaxial and polycrystalline LSCO films were 1.9 mΩcm (on STO) and 1.7 mΩcm (on α-Al2O3, respectively).
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| 3. |
- Westin, Gunnar, et al.
(author)
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Direct processing of porous nano-structured ZnO-CoOx films
- 2007
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In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:20-21, s. 7751-7757
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Journal article (peer-reviewed)abstract
- Highly porous nano-structured films and powders of ZnO:Co (0–5 metal% Co) or ZnO:Co and (Zn,Co)3O4 (10–35% Co) particles were obtained by deposition of mixed Zn- and Co-methoxy-ethoxide precursors on spinning or non-spinning substrates, and heating to 600 °C. The Co- and Zn-methoxy-ethoxide solutions were prepared by metathesis of CoCl2 and potassium methoxy-ethoxide, and reaction of diethylzinc and methoxy-ethanol, respectively. Compositions in the range 0–35% Co were investigated by IR spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and X-ray diffraction. The gels obtained consisted of hydrated amorphous oxo-carbonates and were of good elemental homogeneity in the TEM. Thermogravimetric analysis showed that all residual groups had been removed at 550–600 °C, 5 °C min− 1. The materials heated to 600 °C contained ZnO of the hexagonal modification with cell-edges in close agreement with un-doped ZnO regardless of composition and temperature. TEM-EDS studies showed that the ZnO:Co and (Zn,Co)3O4 spinel particles were well mixed, of similar shape and size, ca 10–25 nm. Heating of the 10% Co sample to 800 °C decomposed the spinel phase and left Co-doped ZnO.
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