Cation order and magnetic behaviour in mixed metal bismuth scheelite Bi3FeMo2O12

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dc.contributor.authorSaura-Múzquiz, Men_AU
dc.contributor.authorMullens, BGen_AU
dc.contributor.authorLiu, Jen_AU
dc.contributor.authorVogt, Ten_AU
dc.contributor.authorMaynard-Casely, HEen_AU
dc.contributor.authorAvdeev, Men_AU
dc.contributor.authorKennedy, BJen_AU
dc.date.accessioned2023-11-28T07:17:42Zen_AU
dc.date.available2023-11-28T07:17:42Zen_AU
dc.date.issued2021-08-14en_AU
dc.date.statistics2023-04-18en_AU
dc.description.abstractThe scheelites are a family of compounds with chemical formula ABO4, and a characteristic crystal structure consisting of AO8 dodecahedra and BO4 tetrahedra. This structure is flexible and can accommodate a large variety of cations with a range of atomic radii and valence combinations. Scheelite-type oxides, such as CaWO4, BiVO4 and NaLa(MoO4)2 have been extensively studied due to their diverse range of physical and electronic properties [1]. In particular, Bi3+ containing molybdates have been found to be efficient photocatalysts due to the strong repulsive force of the 6s2 lone pair of Bi3+, resulting in distortion of the BO4 tetrahedra and alteration of the band gap [2, 3]. In 1974 Bi3FeMo2O12 (BFMO) was reported as the first scheelite-type compound containing trivalent cations on the tetrahedral sites [4]. Interestingly, two different polymorphs of BFMO can be isolated by varying the synthesis conditions [5]. The tetragonal scheelitetype polymorph, described by space group I41/a with a = 5.32106(13) Å and c = 11.656(4) Å, can be prepared by a sol-gel route from aqueous solution of the constituent ionic species and has a disordered arrangement of the Fe and Mo cations. When heated above 500 °C, a 2:1 ordering of the Mo and Fe cations occurs, which lowers the symmetry to monoclinic (C2/c). The corresponding superstructure has a tripling of the a axis (a = 16.9110 (3) Å, b = 11.6489(2) Å, c= 5.25630(9) Å, β = 107.1395(11)°). The two structures are illustrated in Figure 1. In the present study, both polymorphs of BFMO were synthesized and their structure and magnetic properties characterized using a combination of powder diffraction, microscopy and magnetometry techniques. In situ neutron powder diffraction (NPD) measurements of the structural evolution of disordered tetragonal BFMO with increasing temperature showed that no amorphization takes place prior to the formation of the ordered monoclinic phase. The lack of a structural break-down, despite the substantial cation movement required in such a transformation, suggests that a certain degree of local cation order exists in the “disordered” tetragonal phase, facilitating the direct conversion to the fully ordered monoclinic structure. Instead of the expected amorphization and recrystallization, the conversion takes place via a 1st order phase transition, with the tetragonal polymorph exhibiting negative thermal expansion prior to its conversion into the monoclinic structure. Zero-field-cooled/field-cooled and field-dependent magnetization curves of the monoclinic structure revealed the existence of a magnetic transition below 15 K. The long-range nature of the low temperature magnetic structure in the monoclinic polymorph was verified by high-resolution NPD data, which revealed the emergence of an incommensurate magnetic structure. There is no evidence for long-range magnetic order in the tetragonal polymorph. This is, to the best of our knowledge, the first study of the phase transition mechanism and magnetic properties of this complex system and represents a milestone in the structural understanding and targeted design of Bi3+ containing molybdates as efficient photocatalysts. © 2021 The Authorsen_AU
dc.identifier.citationSaura-Múzquiz, M., Mullens, B., Liu, J., Vogt, T., Maynard-Casely, H., Avdeev, M., & Kennedy, B. J. (2021). Cation order and magnetic behaviour in mixed-metal bismuth scheelite Bi3FeMo2O12. Paper presented to the IUCr 2021, 25th Congress of the International Union of Crystallography, 14-22 August 2021, Prague, Czech Republic. In Acta Crystallographica Section A, 77, C154. doi:10.1107/S0108767321095271en_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.journaltitleActa Crystallographica Section Aen_AU
dc.identifier.otherMC-18a-5en_AU
dc.identifier.paginationC154en_AU
dc.identifier.urihttps://doi.org/doi:10.1107/S0108767321095271en_AU
dc.identifier.urihttps://apo.ansto.gov.au/handle/10238/15248en_AU
dc.identifier.volume77en_AU
dc.language.isoenen_AU
dc.publisherInternational Union of Crystallographyen_AU
dc.subjectCationsen_AU
dc.subjectBismuthen_AU
dc.subjectCrystal structureen_AU
dc.subjectBoratesen_AU
dc.subjectMolybdatesen_AU
dc.subjectCalcium tungstatesen_AU
dc.subjectValenceen_AU
dc.subjectPhotocatalysisen_AU
dc.subjectIronen_AU
dc.subjectDiffractionen_AU
dc.titleCation order and magnetic behaviour in mixed metal bismuth scheelite Bi3FeMo2O12en_AU
dc.typeConference Presentationen_AU
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