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Conversion polymorphism: preparation of new materials

1minút, 13sekúnd

Many solid phases, which are at equilibrium under high pressure and high temperature, can be quenched to ambient conditions, where they remain kinetically stable (usually referred to as the metastable phases). Very often, these phases represent new structural polymorphs with useful and unique properties.

In the present work, we systematically studied the transformation of perovskite phases and their magnetic properties in the whole BiFe1-yScyO3 series. For the compositions with y ≥ 0.2, the perovskite phases can only be stabilized under high-pressure conditions and the metastable phases were subject to post-synthesis thermal treatment. As a result, we observed a set of annealing-stimulated irreversible phase transformations between the different metastable perovskite phases. This remarkable behaviour allowed us to obtain these perovskites at ambient conditions in different polymorphs, which represent novel structures with interesting magnetic properties. In particular, a new orthorhombic modification of BiScO3 has been obtained and a novel magnetic phase transition from an unusual collinear magnetic ground state to a cycloidal structure has been found in the converted polar R3c modification of the BiFe0.7Sc0.3O3 composition.

We refer to the annealing-stimulated irreversible transformations as ‘‘conversion polymorphism’’ and demonstrate that this is a rather general phenomenon, which has been likely overlooked in many other metastable phases. The results of our study were published in the prestigious journal Chemical Communications [D.D. Khalyavin et al., Chem. Commn. 55 (2019) 4683-4686] with impact factor of 6.164, which is included in Nature index.

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