Synthesis of Various LaMO₃Perovskites in Molten Carbonates

Abstract

Lanthanum-containing perovskites, LaMO 3 (M 5 Al, Sc, Cr, Mn, Fe, Co, Ni, Ga, and In), have been synthesized in molten carbonates from a mixture of lanthanum carbonate and an Mcontaining oxide or an acetate, or from a co-precipitation mixture of metal (M) and lanthanum. Metal aluminum, chromium, and iron, immersed in a mixture of molten (Li 0.52 Na 0.48 ) 2 CO 3 and lanthanum carbonate at 923 K, were covered, respectively, with LaAlO 3 , LaCrO 3 , and LaFeO 3 . Ceramic and single-crystal a-Al 2 O 3 , immersed in molten (Li 0.52 Na 0.48 ) 2 CO 3 mixed with lanthanum carbonate, were also covered with LaAlO 3 . In situ X-ray diffractometry revealed that La 2 O 2 CO 3 reacted with a-LiAlO 2 to yield LaAlO 3 ; the reaction proceeded faster under N 2 than under a CO 2 atmosphere.(2) LaMO 3 Production on the Metal and Ceramic Surfaces The following substrates were placed in a Au-Pd (80:20 wt%) crucible containing the mixture of (Li 0.52 Na 0.48 ) 2 CO 3 and La 2 (CO 3 ) 3 Á 8H 2 O (1:1 by weight): the metals aluminum (Nilaco Corp., Tokyo, Japan, 99.999%, 20 mm  20 mm  0.1 mm), chromium (Nilaco, 99.9%, 20 mm  5 mm  5 mm), iron (Nilaco, 99.98%, 20 mm  20 mm  0.5 mm), cobalt (Nilaco, 99.98%, 20 mm  20 mm  0.5 mm), and nickel (Nilaco, 99.7%, 20 mm  20 mm  0.5 mm), and a-Al 2 O 3 ceramics J ournal

Synthesis of LaMO3 (M=Fe, Co, Ni) using nitrate or nitrite molten salts

“…Previously, LaFeO 3 was successfully obtained in molten NaOH at 450 • C for 2 h [32], molten NaNO 2 at 450 • C for 2 h [33] and molten carbonates at 650 • C for 16 h or 550 • C for 12 h in CO 2 atmosphere [34], respectively, using La(NO 3 ) 3 ·6H 2 O and Fe(NO 3 ) 3 ·9H 2 O as reactants.…”

“…Rare earth orthoferrites of the general formula LnFeO 3 (Ln = La, Pr and Nd) phases were synthesized in molten NaOH flux at 673 K [32]. As far as we know, however, there are quite a few reports on the synthesis of LaMO 3 perovskites using molten nitrates [33,34]. In this paper, we systematically investigate the effect of salt medium, annealing temperatures (mainly 450-850 • C) and basicity of the melt (NaNO 2 , NaNO 3 -KNO 3 and NaNO 3 -KNO 3 with Na 2 O 2 ) on morphology, composition, size and shape of the product in the synthesis of crystalline LaMO 3 (M = Fe, Co, Ni) perovskite particles.…”

Markedly enhancing the visible-light photocatalytic activity of LaFeO3 by post-treatment in molten salt

“…Performance of photocatalyst It is well known that photocatalytic oxidation of organic pollutants follows Langmuir-Hinshelwood kinetics [11]. This kind of reaction can be represented as: kt = ln(C 0 /C).…”

“…Furthermore, most of the perovskite photocatalysts are still prepared by conventional solid state reactions where particles are typically on a micron scale [10], which limits their commercial applications due to lower light absorption in the visible region and short lifetimes of the excited states. As an alternative route, the molten salt reaction method has been reported to prepare crystals of various mixed oxides from corresponding single oxides, in which molten alkali metal fluorides, chlorides, hydroxides or nitrates were used [11]. Recently, lanthanum-based perovskites were obtained in molten nitrates and nitrites [12].…”

Molten salts synthesis and electrical properties of Sr- and/or Mg-doped perovskite-type LaAlO3 powders

“…Then, the synthesis of the target material can be completed within a very short time without the limitations associated to slow diffusion kinetics in the solid state. Following this procedure polycrystalline LaAlO 3 has been obtained by MSS but only after long reaction times and using complex salts of high melting points (C650°C), such as KF/KCl or alkali metal carbonate eutectics, as reaction media [24,25]; furthermore, because of La's high reactivity toward atmospheric CO 2 , the as-prepared samples were contaminated with lanthanum hydroxy and/or oxycarbonates and/or unreacted metal oxides, and thus, required of a final purification step using concentrated HCl to yield single phase products. Since no previous reports were found in the literature on the synthesis of the title series or any Al-containing complex oxide in molten nitrates following the general MSS procedure, some preliminary experiments were run to analyze the reactivity of Al-and La-hydrated nitrates toward producing LaAlO 3 powders in molten NaNO 3 .…”