High-temperature behavior of calcium substituted layered neodymium nickelates

• Published in: Journal of alloys and compounds 2019-09, Vol.801, p.558-567
• Main Authors: Pikalov, S.M., Vedmid’, L.B., Filonova, E.A., Pikalova, E. Yu, Lyagaeva, J.G., Danilov, N.A., Murashkina, A.A.
• Format: Article
• Language: English
• Subjects: Ca-doping; Calcium; Ceramic membrane; Dependence; Dilatometry; Doping; Electrical properties; Electrical resistivity; Electrode materials; Electrolytes; High temperature; High-temperature behavior; Molten salt electrolytes; Nd2NiO4; Neodymium; Oxygen; Oxygen content; Oxygen electrode; Ruddlesden-Popper phase; Solid electrolytes; Stoichiometry; Thermal expansion; Thermomechanical properties
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2019.05.349

Layered lanthanide nickelates of the first order with a K2NiF4-type structure, including Nd2NiO4, are considered as prospective oxygen electrode materials for different high-temperature electrochemical devices, membrane materials and catalysts. The presence of highly-mobile over-stoichiometric oxygen in their structure, the content of which depends on the synthesis and ambient conditions, strongly influences their functional properties. In this study, the materials of the Nd2-xCaxNiO4+δ (x = 0–1.0) series were obtained via a citrate-nitrate method. The Ca substitution limit was found to be equal to 30 mol %. The high-temperature structural, thermo-mechanical and electrical properties of the materials obtained were investigated in close relation with their oxygen over-stoichiometry. It was found that the absolute oxygen content decreased with Ca doping, which resulted in a transition from an orthorhombic structure (Fmmm sp. gr.) at x = 0, 0.1 to a tetragonal structure (I4/mmm sp. gr.) at x = 0.2, 0.3 and then, with further increase in Ca doping, to an orthorhombic structure (Bmab sp. gr.). Dilatometric curves for all the samples possessed high-temperature breaks corresponding to the structural changes caused by oxygen release upon heating, which was revealed in the HT-XRD and TGA-DSC experiments. There was a tendency for the thermal expansion coefficient to decrease both in the low and high temperature range with Ca doping. The minimum average TEC values were found for the samples with x = 0.4 (12.1 × 10−6 K−1) and with x = 0.6 (11.8 × 10−6 K−1) according to the HT-XRD and dilatometry data, respectively. There was a maximum at x = 0.4 (135 S cm−1) on the concentration dependence of the total conductivity obtained in the dc four-probe measurements. Materials with a medium Ca content (0.3–0.4), possessing moderate CTE values (∼12 × 10−6 K−1), close to those of the majority of solid-state electrolytes, and showing a high level of total conductivity, can be recommended as promising materials for various electrochemical applications. [Display omitted] •Nd2-xCaxNiO4 (x = 0–1) were obtained by a citrate-nitrate combustion method.•Solubility limit was found to be equal to 30 mol % of Ca.•High-temperature structural, thermo-mechanical and electrical properties were studied.•Materials with medium Ca content are promising for electrochemical applications.