Search

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). [ABSTRACT FROM AUTHOR]

Abstract The synthesis, structure and properties of Na2Zn(OEt)4(HOEt)5, having the right Na:Zn ratio for sol–gel synthesis of the highly Na-ion conducting ceramic Na1.8Zn0.9Si1.1O4, is described. It was synthesised in high yield by a metathesis reaction of ZnCl2 and 4NaOEt in ethanol or ethanol/toluene solvent. The structure was determined by single-crystal X-ray methods and consists of two symmetry related polymeric strands with the metal sequence ...–Zn–Na–Na–Zn–.... Extensive hydrogen bonding is present within each chain. Further characterization was made with IR- and Raman-spectroscopy and thermo-calorimetry, showing that the compound is stable to 65°C. [ABSTRACT FROM AUTHOR]

Abstract The molecular alkoxide, ErNb2(OPri)13 was prepared by metathesis with 2KNb(OPri)6, KOPri and ErCl3, and structurally determined by single-crystal X-ray diffraction techniques. Each molecule contains a central Er3+-ion coordinated by six OPri groups of which one is terminal. On each side is an Nb5+-ion coordinated by six OPri groups placed, one via a double alkoxo-bridge and the other via a triple alkoxo-bridge. It is isostructural with LaNb2(OPri)13, in spite of the large difference in ionic radius between Er3+ and La3+ (16%). The compound was characterized by its IR- and UV-vis-NIR-spectroscopic fine structures, and found to be structurally intact in hexane:isopropanol solution. [ABSTRACT FROM AUTHOR]