Polymorphism of the iron doped strontium aluminate SrAl{sub 1.5}Fe{sub 0.5}O{sub 4}

Journal Article · Wed Jul 15 00:00:00 EDT 2009 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2009.04.013· OSTI ID:21370487

Desmoulins, H ^[1]; Malo, S ^[1]; Boudin, S; Caignaert, V; Hervieu, M ^[1]

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1. Laboratoire CRISMAT-ENSICAEN, Bd du Marechal Juin-14050 CAEN, Cedex (France)

The partial substitution of Al by Fe atoms in SrAl{sub 2}O{sub 4} allowed to stabilize four stuffed tridymite derivative structures SrAl{sub 1.5}Fe{sub 0.5}O{sub 4}. The different phases have been characterized by TEM and XRPD techniques. Two are isotypes of those observed for the undoped oxides, namely the hexagonal phase with sq root(3)Axsq root(3)AxC (with A and C being the tridymite unit cell parameters) and space group P6{sub 3} and the monoclinic one with Axsq root(3)AxC, {beta}{approx}93{sup o} and space group P2{sub 1}, with a synthesis temperature lower than the one required for SrAl{sub 2}O{sub 4}. By annealing, two original phases, denoted O{sub 1} and O{sub 2}, are obtained; they are metrically similar (3Axsq root(3)AxC and {beta}{approx}90{sup o}) and only differ by their space groups. The TEM study showed that the transitions between the different phases follow topotactic mechanisms, through the formation of twinning boundaries, antiphase boundaries and planar defects. The annealed sample exhibits a mesomorph state and a reversible transition from this semi-ordered state to a crystalline phase. This dynamic transition takes place over a very wide temperature range from 620 to 1120 deg. C. The reversibility of the transition has been studied by DSC measurements. The crystallization energy of the orthorhombic phases is of the order of 10 J/g, at T{approx}622 deg. C as T decreases. The variation of the peak height observed as the annealing temperature increases is explained by the complex microstructures, which create an ill-defined energy barrier. Structural models related to the stuffed tridymite derivative structures are proposed for the new forms of the ferri-aluminate. - Graphical abstract: Four tridymite derivative structures SrAl{sub 1.5}Fe{sub 0.5}O{sub 4} have been characterized. Two phases are isotypes of those observed for SrAl{sub 2}O{sub 4}. Two 'orthorhombic' original phases are characterized by superstructures. The transitions between the different phases follow topotactic mechanisms. The transition LT->HT takes place from 620 to 1120 deg. C, explained by complex microstructures, creating ill-defined energy barriers.

• OSTI ID: 21370487
• Journal Information: Journal of Solid State Chemistry, Vol. 182, Issue 7; Other Information: DOI: 10.1016/j.jssc.2009.04.013; PII: S0022-4596(09)00168-6; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINATES
ANNEALING
CALORIMETRY
CRYSTAL DEFECTS
CRYSTALLIZATION
DOPED MATERIALS
HEXAGONAL LATTICES
IRON COMPOUNDS
MICROSTRUCTURE
MONOCLINIC LATTICES
ORTHORHOMBIC LATTICES
SPACE GROUPS
STRONTIUM COMPOUNDS
STRUCTURAL MODELS
SYNTHESIS
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
THERMAL ANALYSIS
TRANSMISSION ELECTRON MICROSCOPY
TWINNING
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
CRYSTAL LATTICES
CRYSTAL STRUCTURE
ELECTRON MICROSCOPY
HEAT TREATMENTS
MATERIALS
MICROSCOPY
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
SYMMETRY GROUPS
TEMPERATURE RANGE
TRANSITION ELEMENT COMPOUNDS