Determination of A-site deficiency in lanthanum manganite by XRD intensity ratio

Zuo, Yanbo; Li, Jianheng; Yi, Jianxin; Wang, Zhongbing; Chen, Chusheng

doi:10.1016/j.jssc.2007.12.033

Cited by 15 publications

(3 citation statements)

References 20 publications

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“…It is apparently the creation of Mn 4+ in addition to Mn 3+ in a mixed valance system that is important in introducing the Mn 3+ /Mn 4+ redox couple. This model is also consistent with the observation that the optimum catalyst has a composition around La 0.85 Mn 0.7 Ni 0.45 O 3– δ : the limit of lattice stability with A-site deficiency has been shown to be around an A-site sub-stoichiometry of about 10 at% 42,44,45…”

Section: Resultssupporting

confidence: 90%

Reversible perovskite electrocatalysts for oxygen reduction/oxygen evolution

et al. 2019

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Section: Resultssupporting

confidence: 90%

Reversible perovskite electrocatalysts for oxygen reduction/oxygen evolution

et al. 2019

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“…Moreover, the ratios of intensities are not affected by the orientations of the sample, thus, it is justified to consider the intensity ratios rather than individual intensities [14]. Structure factors are calculated by using the following equations [13]:…”

Section: (Znmentioning

confidence: 99%

Structural and dielectric studies of Mg2+ substituted Ni–Zn ferrite

Prasad

Babu²,

Prasad

2015

Materials Science-Poland

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Polycrystalline ferrites having the chemical formula Ni 0.65−x Zn 0.35 Mg x Fe 2 O 4 (0 x 0.2) were prepared by solid state reaction route in steps of x = 0.04. The effect of incorporation of diamagnetic divalent magnesium at expense of nickel on the structural properties of these ferrites has been studied. The proposed cation distribution was derived from theoretical X-ray diffraction intensity calculations. These intensity calculations were done by varying the concentration of magnesium ions over two sites in the lattice. For a certain amount of magnesium concentration, the calculated and observed X-ray diffraction intensities were found to be in good agreement. Site occupancy of divalent diamagnetic magnesium was established from this cation distribution. The octahedral environment facilitates magnesium to enter the B-site at about 95 % and the remaining 5 % occupy tetrahedral sites (A-sites). The movements of cations between tetrahedral and octahedral sites as a result of magnesium substitution were discussed in the view of structural parameters, such as tetrahedral and octahedral bond lengths, cation-cation and cation-anion distances, bond angles and hopping lengths, which were calculated using experimental lattice constants and oxygen parameters. All structural parameters showed slight deviations from ideal values. Among all magnesium substituted samples, the ones with x = 0.12 exhibited insignificant variation in view of structural properties. Dielectric measurements were conducted at a standard frequency of 1 kHz. Large values of the recorded dielectric constants displayed typical characteristics of bulk ferrites. Both dielectric constant and loss values showed mixed variations, attributed to the loss of zinc ions during the sintering process.

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“…According to x-ray diffraction studies, the A-site deficiency of 20% Sr-and Ca-substituted LaMnO 3 in air can be as high as 5% 53 or 10% 46 and up to 10% in pure LaMnO 3 . 53,54 While it is currently unknown whether or not B-site deficient acceptor-doped LaMnO 3 powders are stable or not, the extent of B-site deficiency has been reported and quantified for other perovskites, such as pure LaMn 1−y O 3 (3%, 55 6% 56 ), (Ba 0.5 Sr 0.5 )(Co 0.8 Fe 0.2 ) 1−y O 3 (8%), 57 Sr 0.9 La 0.1 Ti 1−y O 3 (6%), 58 Y 0.08 Sr 0.92 Ti 1−y O 3 (5%), 59 Pr 0.5 Ba 0.5 Co 1−y O 3 (>10%), 60 La 0.5 Sr 0.5 Co 1−y O 3 (0.3%), 61 and La 0.85 Sr 0.15 Co 1−y O 3 (>2%). 62 B-site deficiency has also been reported for thin films of SrTiO 3 [63][64][65][66] and La 0.8 Ba 0.2 MnO 3 .…”

Section: Sr Xmentioning

confidence: 99%

Precipitation of dopants on acceptor-doped LaMnO3±δ revealed by defect chemistry from first principles

Heß

Yildiz

2021

The Journal of Chemical Physics

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Perovskite oxides degrade at elevated temperatures while precipitating dopant-rich particles on the surface. A knowledge-based improvement of surface stability requires a fundamental and quantitative understanding of the dopant precipitation mechanism on these materials. We propose that dopant precipitation is a consequence of the variation of dopant solubility between calcination and operating conditions in solid oxide fuel cells (SOFCs) and electrolyzer cells (SOECs). To study dopant precipitation, we use 20% (D = Ca, Sr, Ba)-doped LaMnO 3+δ (LDM20) as a model system. We employ a defect model taking input from density functional theory calculations. The defect model considers the equilibration of LDM20 with a reservoir consisting of dopant oxide (DO), peroxide (DO 2 ), and O 2 in the gas phase. The equilibrated non-stoichiometry of the A-site and B-site as a function of temperature, T, and oxygen partial pressure, p(O 2 ), reveals three regimes for LDM20: A-site deficient (oxidizing conditions), A-site rich (atmospheric conditions), and near-stoichiometric (reducing conditions). Assuming an initial A/B non-stoichiometry, we compute the dopant precipitation boundaries in a p-T phase diagram. Our model predicts precipitation both under reducing (DO) and under highly oxidizing conditions (DO 2 ). We found precipitation under anodic, SOEC conditions to be promoted by large dopant size, while under cathodic, SOFC conditions precipitation is promoted by initial A-site excess. The main driving forces for precipitation are oxygen uptake by the condensed phase under oxidizing conditions and oxygen release assisted by B-site vacancies under reducing conditions. Possible strategies for mitigating dopant precipitation under in electrolytic and fuel cell conditions are discussed.

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Determination of A-site deficiency in lanthanum manganite by XRD intensity ratio

Cited by 15 publications

References 20 publications

Reversible perovskite electrocatalysts for oxygen reduction/oxygen evolution

Reversible perovskite electrocatalysts for oxygen reduction/oxygen evolution

Structural and dielectric studies of Mg2+ substituted Ni–Zn ferrite

Precipitation of dopants on acceptor-doped LaMnO3±δ revealed by defect chemistry from first principles

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