A New Low-Temperature Preparetion Method of Highly Homogeneous Mixed Oxides from d-f Heteronuclear Complex Precursors

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The purpose of this work is to propose a new preparation method of mixed oxides from the heteronuclear complexes, mainly using the d-f heteronuclear systems. Homogeneous mixed oxides in an atomic level with high specific area are expected by this method.Single phase of perovskite-type oxide LaCoO_3 was formed by the thermal decomposition of La[Co(CN)_6]・5H_2O and La[Co(ox)_3]・8.5H_2O at 600℃, where these complexes have a three dimensional network structure constructed by the cyanide and oxalate bridges, respectively, between La and Co ions. This formation temperature is much lower than that (1000℃) for the conventional ceramic method. The EPMA results showed that the LaCoO_3 prepared from the heteronuclear complexes was highly homogeneous.Decomposition of Bi_<0.5>La_<0.5>[Fe(CN)_6]・4H_2O and [La_2Cu(C_4O_4)(H_2O)_<16>]・2H_2O led to the formation of Bi_<0.5>La_<0.5>FeO_3 and La_2CuO_4 at 500 and 700℃, respectively, where H_2C_4O_4 is squaric acid.Perovskite-type oxide LaNiO_3 was formed by the decomposition of heterodinuclear complex LaNi(dhbaen)(NO_3)(H_2O)_2 in the range of 600 to 900℃, where H_4dhbaen is N,N'-bis(3-hydroxysalicylidene)ethylenediamine. However, LaNiO_3 was not obtained even at 1000℃ when the (1:2) mixture of La_2O_3 and NiO was calcined.Thus, heteronuclear complexes were found to be very superior as precursors of mixed oxides.