Abstract
This paper reports the first structure refinement of natural wangdaodeite, LiNbO3-type FeTiO3 from the Ries impact structure. Wangdaodeite occurs together with recrystallized ilmenite clasts in shock melt veins which have experienced peak shock pressures of between 17 and 22 GPa. Comparison of natural and synthetic wangdaodeite points toward a correlation between the distortion of ferrate- and titanate-polyhedra and the c/a ratio of the unit cell. The Raman spectrum of wangdaodeite is calculated based on the refined structure. Comparison to the reported spectrum of the type-material shows that the Raman peak at 738–740 cm−1 is indicative for this phase, whereas other features in type-wangdaodeite are tentatively assigned to disordered ilmenite.
Highlights
FeTiO3 is trimorph with ilmenite stable at ambient pressure; liuite [1], a GdFeO3 -type perovskite, stable above ~15–20 GPa [2,3,4,5]; and wangdaodeite, a LiNbO3 -type perovskite as intermediary phase [3,4,6,7]
We used the structure of synthetic LiNbO3 -type FeTiO3 as the starting model [19]
We present the first structure analysis of wangdaodeite, natural FeTiO3 in the LiNbO3 -type structure
Summary
FeTiO3 is trimorph with ilmenite stable at ambient pressure; liuite [1], a GdFeO3 -type perovskite, stable above ~15–20 GPa [2,3,4,5]; and wangdaodeite, a LiNbO3 -type perovskite as intermediary phase [3,4,6,7]. The high-pressure phase transition of ilmenite to an intermediate structure prior to the formation of the GdFeO3 -type perovskite was first reported by Syono et al [8] and Ito and Matsui [9]. These authors proposed this phase to assume the corundum-structure. Later, this phase was identified as LiNbO3 -type FeTiO3 [3]. LiNbO3 -type FeTiO3 can be conserved at ambient pressure and has found attention in solid state physics because of its multiferroic behavior [11] Assessment of phase boundaries through calorimetric data [10] and compression-decompression cycling [4,5] show that at least pure LiNbO3 -type FeTiO3 has no stability field.
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