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

Abstract

A new series of ferroelectric Aurivillius oxides containing Sc³⁺ in the B site in stoichiometric compositions, Bi₂₊₂xSr_1−2xNb_2−xSc_xO₉ (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 (T_c) obtained from dielectric measurements range from 430–731 °C. Crystal structure refinement on Bi_2.2Sr_0.8Nb_1.9Sc_0.1O₉ (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) ų), at room temperature. I adopts non-polar space group, I4/mmm, at 550 °C (T_c 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 T_c, with tolerance factors are discussed and, with nd⁰ configurations are explored.