Insight into the structural variations of fergusonite-type structures: combined experimental and computational studies

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dc.contributor.authorMullens, BGen_AU
dc.contributor.authorAvdeev, Men_AU
dc.contributor.authorBrand, HEAen_AU
dc.contributor.authorMondal, Sen_AU
dc.contributor.authorVaitheeswaran, Gen_AU
dc.contributor.authorKennedy, BJen_AU
dc.date.accessioned2024-01-12T00:51:39Zen_AU
dc.date.available2024-01-12T00:51:39Zen_AU
dc.date.issued2021-08-14en_AU
dc.date.statistics2023-04-20en_AU
dc.description.abstractThe development of carbon-neutral energy-generation is critical to combatting climate change. One such technology is the development of next-generation ion conductors for solid-oxide fuel cells (SOFCs). SOFCs offer a much more efficient method to extract energy from hydrogen or hydrocarbon fuels than current combustion engines due to their one-step chemical process. However, a bottleneck to the large-scale uptake of SOFCs is the poor performance of the conducting electrolytes that separate the anode from the cathode. Various lanthanoid fergusonite structures (LnBO4) have recently been proposed as solid electrolyte candidates in solidoxide fuel cells, with increased high-temperature ionic conductivity being measured in chemically doped lanthanum orthoniobates (LaNbO4) [1]. However, a phase transition from I2/a to I41/a within the operational temperature of SOFCs makes these structures nonideal. To understand the effects of chemical doping on the structure and electrochemical properties of these fergusonite structures, several complex fergusonites have been investigated [2-3]. Of interest is the substitution of NbV for TaV on the B-site, which has shown a decrease in the unit cell volume of the structure [4]. This is particularly remarkable, given the two metal cations have the same ionic radius and Ta has an extra 5d valence shell compared to the 4d shell of Nb. Such substitution has further shown to increase the I2/a to I41/a first-order phase transition temperature, highlighting the potential of the properties of these structures to be specifically ‘tailored’ to be used for SOFCs. Various solid-solution series of Ln(Nb1-xTax)O4 (Ln = La-Lu) have been synthesised using conventional solid-state methods. Synchrotron X-ray and neutron powder diffraction methods have been used to investigate their structures, focusing on changes in both their unit cell volumes and the temperature of the I2/a to I41/a phase transitions. Whilst the fergusonite structure is a monoclinic structure derived of the tetragonal scheelite aristotype, its structure is based on BO6 polyhedra as opposed to BO4 scheelite polyhedra. These studies have revealed several anomalies, revealing that different structures can be isolated by controlling the size of the Ln ion and synthetic conditions, and that the volume of the BO6 polyhedra and length of the B–O bonds change depending on its surrounding Ln ion. This data surprisingly implies that the AO8 polyhedra act as a rigid framework in which the BO6 polyhedra respond. The experimental data has been further reinforced by ground state energy calculations performed using density functional theory. This is a landmark accomplishment that has not been previously used in similarly studied structures. These insights can be used in the development and engineering of novel and advanced electrolyte materials for SOFCs. © The Authorsen_AU
dc.identifier.articlenumberC493en_AU
dc.identifier.citationMullens, B. G., Avdeev, M., Brand, H. E. A., Mondal, S., Vaitheeswaran, G., & Kennedy, B. J. (2021). Insight into the structural variations of fergusonite-type structures: combined experimental and computational studies. Paper presented to IUCr 2021, 25th Congress of the International Union of Crystallography, 14-22 August 2021, Prague, Czech Republic. In Acta Crystallographica Section A, 77(a2), C493. doi:10.1107/S0108767321091947en_AU
dc.identifier.conferenceenddate2021-08-22en_AU
dc.identifier.conferencenameIUCr 2021, 25th Congress of the International Union of Crystallographyen_AU
dc.identifier.conferenceplacePrague, Czech Republicen_AU
dc.identifier.conferencestartdate2021-08-14en_AU
dc.identifier.issn2053-2733en_AU
dc.identifier.issuea2en_AU
dc.identifier.journaltitleActa Crystallographica Section Aen_AU
dc.identifier.otherMS-76-3en_AU
dc.identifier.urihttps://doi.org/10.1107/S0108767321091947en_AU
dc.identifier.urihttps://apo.ansto.gov.au/handle/10238/15339en_AU
dc.identifier.volume77en_AU
dc.language.isoenen_AU
dc.publisherInternational Union of Crystallographyen_AU
dc.relation.urihttps://doi.org/10.1107/S0108767321091947en_AU
dc.subjectOrder-disorder modelen_AU
dc.subjectFuel cellsen_AU
dc.subjectDensity functional methoden_AU
dc.subjectClimatic changeen_AU
dc.subjectElectrolytesen_AU
dc.subjectSynchrotronsen_AU
dc.subjectPhase transformationsen_AU
dc.titleInsight into the structural variations of fergusonite-type structures: combined experimental and computational studiesen_AU
dc.typeConference Abstracten_AU
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