Low‐Temperature Synthesis and Properties of LaMnO_3±d and La_0.67R_0.33MnO_3±d (R = Ca, Sr, Ba) from Citrate Precursors

Abstract

LaMn1−y3+Mny4+O3±d and La0.67R0.33Mn1−y3+Mny4+O3±d (R = Ca, Sr, Ba) phases were synthesized at 350°C by using very reactive, amorphous precursors obtained from the stoichiometric citrate solutions. The chemical process was optimized with respect to the solution concentration, pH, and additives. The precursor reactions were investigated as a function of the cation stoichiometry and the additive by simultaneous thermal and thermogravimetric analysis and X‐ray diffraction. The reaction pathway was found to be independent of the cation stoichiometry, but related to the acid or base additive. The annealing temperature was systematically increased in the 350–1200°C interval and the La0.67Sr0.33MnO3±d properties (i.e., crystal sizes, Mn average valence, Curie temperature, magnetization, magnetic susceptibility) were measured and found to vary consistently as a function of it.

Effect of water content in powder mixture on mechanochemical reaction of LaMnO3 fine powder

“…6 shows the XRD patterns of the powder mixture with the water content of 8% mass fraction that have been milled for various time periods: 0, 10, 20 and 30 min. The peaks intensity of La(OH) 3 and Mn 3 O 4 decreased with increasing milling time. Although the peak of LaMnO 3 was detected after the milling for 30 min, the peaks of La(OH) 3 and Mn 3 O 4 considerably remained.…”

“…The peaks intensity of La(OH) 3 and Mn 3 O 4 decreased with increasing milling time. Although the peak of LaMnO 3 was detected after the milling for 30 min, the peaks of La(OH) 3 and Mn 3 O 4 considerably remained. Fig.…”

“…La(OH) 3 phase was detected in the powder mixture with the water content of 2% mass fraction. When the water content was 8% mass fraction, the XRD peaks were identified as only those of La(OH) 3 and Mn 3 O 4 . It is noted that La 2 O 3 is hygroscopic oxide.…”

“…1 The liquid-phase reactions have provided possibility for fine and homogeneous LaMnO 3 powders. [2][3][4] However, liquid-phase reaction seems to be more troublesome than solid-state reaction because liquid-phase process requires some delicate techniques and/or the development of sintering process for the obtained LaMnO 3 powder.…”

Nano-structured composite cathodes for intermediate-temperature solid oxide fuel cells via an infiltration/impregnation technique

“…The traditional cathode fabrication process is a ceramic mixing process that can be represented as a "powder to structure" process involving the deposition of the cathode powder on the electrolyte surface and a subsequent firing step. Very fine powder with high specific surface area and high catalytic activity can be synthesized using wet chemical routes such as sol-gel [38][39][40][41], combustion [42][43][44][45][46], and spray-pyrolysis methods [47,48]. However, the fine powder is coarsened by the following firing process at high temperature, which is necessary to achieve a good bonding between the electrode and electrolyte, good connectivity of particles that allowing effective conduction of charge carriers, and a robust cell structure.…”