Structural and electrical properties of the 2Bi2O3·3ZrO2 system

Powder mixtures of α-Bi2O3 (bismite) and monoclinic m-ZrO2 (baddeleyite) in the molar ratio 2:3 were mechanochemically and thermally treated with the goal to examine the phases, which may appear during such procedures. The prepared samples were characterized by X-ray powder diffraction, differential scanning calorimetry (DSC), electrical measurements, as well as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mechanochemical reaction leads to the gradual formation of a nanocrystalline phase, which resembles δ-Bi2O3, a high-temperature Bi2O3 polymorph. Isothermal sintering in air at a temperature of 820 °C for 24 h followed by quenching to room temperature yielded a mixture of ZrO2-stabilized β-Bi2O3 and m-ZrO2 phases, whereas in slowly cooled products, the complete separation of the initial α-Bi2O3 and m-ZrO2 constituents was observed. The dielectric permittivity of the sintered samples significantly depended on the temperature. The sintered and quenched samples exhibited a hysteresis dependence of the dielectric shift, showing that the ZrO2-doped β-Bi2O3 phase possess ferroelectric properties, which were detected for the first time. This fact, together with Rietveld refinement of the β-Bi2O3/m-ZrO2 mixture based on neutron powder diffraction data showed that ZrO2-doped β-Bi2O3 has a non-centrosymmetric structure with P4¯21c as the true space group. The ZrO2 content in the doped β-Bi2O3 and the crystal chemical reasons for the stabilization of the β-Bi2O3 phase by the addition of m-ZrO2 are discussed.

Powder mixtures of the 2Bi2O3·3ZrO2 composition were thermally and mechanochemically treated in order to examine the obtained phases, which were characterized by DSC, electrical measurements, SEM, TEM, as well as X-ray and neutron powder diffraction. It is shown that resulting ZrO2-doped β-Bi2O3 phase possess ferroelectric properties.Figure optionsDownload as PowerPoint slide