BiCrO3 and BiCr0.9Sc0.1O3: low temperature phase transition studies


BiCrO3 is a multiferroic metastable perovskite with a reversible phase transition from the monoclinic C2/c phase (resultant from high-pressure synthesis) to the non-polar orthorhombic Pnma phase above ~410 K. In the BiCrO3- based solid solutions reported so far, the B-site substituting cation is very similar in size to Cr3+. A considerable size difference is suggested to induce new phases that are not observed in the end members. We report on synthesis of perovskite phases of the BiCr1-xScxO3 series and detailed studies of their crystal structures and physical properties as a function of the relative amount of scandium in the materials. The compositions BiCrO3 and BiCr0.9Sc0.1O3 were synthesized under high-pressure and characterized using in-situ x-ray diffraction (XRD), scanning electron microscopy and energy dispersive x-ray spectroscopy (SEM-EDS), atomic and piezoresponse force microscopy (AFM-PFM), SQUID magnetometry, and dielectric spectroscopy. From the preliminary AFM-PFM measurements, some changes in the microstructure resulted from a low-temperature annealing (below 473 K) were suggested. Afterwards a sample (with no post-treatment after high pressure synthesis) was analyzed ex situ, through SEM and XRD after 2-h annealing at 373, 423, 448 and 473 K. The microstructure was checked after each treatment. The SEM images presented on Figure 1 show visible cracks on the grain boundaries that grew with the annealing temperature. These result from the stress relief associated with the drop of the unit cell volume at the reversible phase transition observed at ~410 K and given the high density of the compact cracks arise to relief the stress (as confirmed by the reduction in FWHM, from ex situ XRD).


J.P. Cardoso, V. Paukšta, D. Delmonte, E. Gilioli, E.L. Fertman, A.V. Fedorchenko, V.V. Shvartsman, R. Grigalaitis, J. Banys, J.M. Vieira, A.N. Salak

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