Synthesis and Thermal Analysis of the Strontium and Iron-doped Lanthanum Cobaltite Nano-powder Precursors

Abstract

Powders of perovskite-type oxides, with the general formula La 0.8 Sr 0.2 Co 1 x Fe x O 3 0.0 x 1.0 , were synthesized by the amorphous citrate method, and chemical reactions in such a synthesis process were systematically investigated via thermal analysis. A series of decompositions of citric acid derivatives occurred at 575-750 K, and the subsequent oxidation of metal-organic amorphous compounds to perovskite-type oxides occurred at 650-850 K. The apparent activation energies for those processes in La 0.8 Sr 0.2 Co 0.5 Fe 0.5 O 3 x 0.5 were determined to be 101-105 and 45-49 kJmol, respectively, using a non-isothermal technique based on the Kissinger approach. The exothermic peaks of those reactions were temperature-dependent on Fe content x , and they increased with increasing x, reaching a maximum at x 0.7-0.8, and then decreased. An X-ray diffraction analysis of samples heat-treated at 873 K for 2 h revealed that they have a single-phase perovskite structure for all compositions, with their unit cell volume increasing with Fe content x . The obtained oxides were nanoparticles with diameters of 10 to 20 nm, which increased with Fe content x . The amorphous citrate route was found to give excellent starting gel precursors for the low-temperature synthesis of La 0.8 Sr 0.2 Co 1 x Fe x O 3 nanoparticles.

Modified Pechini Synthesis of Oxide Powders and Thin Films

“…The typical cation precursors for these perovskites are nitrates (Magnone et al 2007), occasionally prepared by dissolving the parent oxide in HNO3 (da Conceição et al 2009), although sometimes carbonates are used for the more basic cations (Fan and Liu 2009). Gupta and Whang also did a series of experiments where they changed between nitrates and acetates as precursors for the preparation of La0.9Sr0.1Cr0.85Fe0.05Co0.05Ni0.05O3−δ (Gupta and Whang 2007).…”

“…Phase-pure LSCF has been prepared by the amorphous citrate synthesis, without the use of EG (Magnone et al 2007;Fan and Liu 2009). On the other hand, Kakihana et al demonstrated that the polymerization was crucial in order to avoid secondary phases during the synthesis of lanthanum manganite ).…”

Some structural considerations on the perovskite‐type A1‐ySryCo1‐xFexO3‐δ solid solution series

“…In both case these results suggest that both Sm-Sr (y) and Co-Fe substitutions (x) has a strongly effect on crystallographic parameters of Sm 1-y Sr y Co 1-x Fe x O 3-δ solid solution series. In addition, the normalized pseudo-cubic lattice parameter composition-dependence of A 0.8 Sr 0.2 Co 1-x Fe x O 3-δ (RE=La and Pr) and Ba 0.5 Sr 0.5 Co 1-x Fe x O 3-δ solid solution series obtained from our measurments [11][12][13] O 3+δ end-members, but has probably solubility limit between x=0.2 and 0.1 [16].…”

“…In analogy with our earlier studies, where we have investigated the crystalline structure of A 1-y Sr y Co 1-x Fe x O 3-δ solid solution series for A=La [11], Pr [12], and Ba [13] in an attempt to understand the correlations between structure and and electrochemical properties of the materials, here we report the chemical synthesis and structural characterization of the Sm 0.8 Sr 0.2 Co 1-x Fe x O 3-δ solid solution series.…”

“…Sm 0.8 Sr 0.2 Co 1-x Fe x O 3-δ solid solution series (0.0≤x≤1.0) was prepared by one-step combustion synthesis based on the reaction of cations activated by an organic mixture as reported in [11][12][13]. The Sm 0.8 Sr 0.2 Co 1-x Fe x O 3-δ gel mixture was ignited at about 200-300 °C on a preheated hot-plate.…”