All alkoxide route to manganate and coboltate perovskite films and powders: effects of processing parameters

Manganate and cobaltate perovskites having the general formula ABO 3 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 (La 0.67 Ca 0.33 MnO 3 ), LSMO (La 0.75 Sr 0.25 MnO 3 ), LNCMO (La 0.33 Nd 0.33 Ca 0.33 MnO 3 ), LBSMO (La 0.75 Ba 0.125 Sr 0.125 MnO 3 ) and LSCO (La 0.50 Sr 0.50 CoO 3 ). The Mn and Co (oxo) methoxy-ethoxide precursors were prepared by reaction of MnCl 2 or CoCl 2 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 H 2 O in the range 20–300 °C, decomposition of carbonate groups into oxide and CO 2 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/SiO 2 /TiO 2 /Pt substrates with all compositions and high quality epitaxial films were prepared of LCMO (on 100 LaAlO 3 ) and LSCO (on 100 SrTiO 3 ). 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-Al 2 O 3 , respectively).