Ferroelectric phase transitions in new Aurivillius oxides: Bi2+2xSr1−2xNb2−xScxO9

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Abstract
A new series of ferroelectric Aurivillius oxides containing Sc3+ in the B site in stoichiometric compositions, Bi2 + 2xSr1−2xNb2−xScxO9 (x = 0.05, 0.10, 0.15, 0.20), were synthesized by a standard solid state method and characterized by powder X-ray diffraction, dielectric and ferroelectric measurements. The ferroelectric to paraelectric phase transition temperature (Tc) obtained from dielectric measurements range from 430–731 °C. Crystal structure refinement on Bi2.2Sr0.8Nb1.9Sc0.1O9 (I) using powder X-ray diffraction data revealed that I crystallizes in polar space group, A21am (a = 5.5083(4) Å, b = 5.5025 (4) Å, and c = 25.1741(11) Å; V = 763.01 (9) Å3), at room temperature. I adopts non-polar space group, I4/mmm, at 550 °C (Tc from dielectric measurement for I is 528 °C). Polarization vs. electric field measurements on I, showed that the saturation and remanent polarizations are 11.8 μC cm−2 and 7.4 μC cm−2 respectively. In addition, the correlation of Tc, with tolerance factors are discussed and, with nd0 configurations are explored.

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