resumo
Some compositions with the general chemical formula ABO3, which do not exist as single phases at normal pressure or crystallize into less compact structural polymorphs, can be stabilized in perovskite structure under high pressure and high temperature and then quenched to ambient conditions. A number of perovskite phases with new configurations of properties have been produced using high-pressure synthesis. Among those, perovskite-multiferroics i.e., phases that combine at least two of the three phenomena, ferroelectricity, ferroelasticity and/or ferromagnetism are particularly interesting. Perovskite bismuth chromate (BiCrO3) is a notable case. Since the first reported high-pressure synthesis in 19681, BiCrO3 continues to be attractive for studies of the crystal structure and magnetic behaviour2,3. BiCrO3 exhibits a reversible phase transition from the monoclinic C2/c phase (resultant from high-pressure synthesis) to the nonpolar orthorhombic Pnma phase upon annealing above ~410 K4,5. Here we report on a comparative study of this phase transition in BiCrO3 and BiCr0.9Sc0.1O3. The interest in the BiCr1-xScxO3 system has arisen from the recent studies of BiFeO3-BiScO3 solid solutions, where the metastable perovskite phases were obtained using the high-pressure synthesis method6,7. Temperature-induced reversible and irreversible transitions between the metastable phases have been revealed. Annealing-stimulated irreversible transformation known as conversion polymorphism7 is believed to occur on other ABO3 systems. Due to a considerable size difference between Cr3+ by Sc3+, 10 mol% substitution of chromium by scandium was expected to result in structural changes without destroying the long-range magnetic order.
autores
J.P. Cardoso, D. Delmonte, E. Gilioli, V.V. Shvartsman, J.M. Vieira, A.N. Salak
nossos autores
