Surface structure and quenching effects in BiFeO₃‐BaTiO₃ ceramics

Abstract

The structure and properties of Mn‐doped 0.67BiFeO3‐0.33BaTiO3 ceramics are systematically investigated with respect to the effects of annealing prior to rapid cooling by quenching in air. Air‐quenching induces a change in crystal structure from pseudo‐cubic to rhombohedral, with higher quenching temperatures leading to an increased rhombohedral distortion. These structural changes are correlated with the appearance of more well‐defined ferroelectric domain configurations. It is shown that the surface preparation procedures for XRD measurements can induce significant changes in the peak profiles, indicating differences in crystal structure between the surface and bulk regions. Frequency dispersion in the temperature‐dependent relative permittivity for the as‐sintered sample is significantly reduced after quenching, accompanied by enhancement of the Curie point and improved temperature‐stability of piezoelectric properties. It is proposed that the formation of defect clusters by A‐site cation diffusion during cooling is circumvented by quenching, leading to the observed modification of structural distortion and ferroelectric properties.

Crystal Structure, Magnetic and Photocatalytic Properties of Solid SolutionsBi2‐xLaxFe4O9 (x=0.05, 0.1)

“…However, on X‐ray patterns of Bi 1.95 La 0.05 Fe 4 O 9 and Bi 1.9 La 0.1 Fe 4 O 9 samples the presence of an admixed BiFeO 3 phase was found. It may be due to the fact that in the temperature range (300–1073) K the formation of Bi 2 Fe 4 O 9 and BiFeO 3 from oxides is thermodynamically probable [3,4] . Therefore formation of single‐phase samples Bi 2 Fe 4 O 9 from oxides, in the opinion of a number of authors, is practically unfeasible, equation (1) and (2): $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr {\rm For}\ {\rm reaction}\ {{1}\over{6}}{\rm Bi}{_{2}}{\rm O}{_{3}}+{{1}\over{6}}{\rm Fe}{_{2}}{\rm O}{_{3}}\rightarrow {{1}\over{3}}{\rm BiFeO}{_{3}}{\rm \char44 }\hfill\cr \Delta {\rm G}{^\circ}{_{T}}\ ({\rm kJ})=- 22.2- 0.048\cdot T{\rm \char44 }\hfill\cr}}$$$ $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr {\rm for}\ {\rm reaction}\ {{1}\over{9}}{\rm Bi}{_{2}}{\rm O}{_{3}}+{{2}\over{9}}{\rm Fe}{_{2}}{\rm O}{_{3}}\rightarrow {{1}\over{9}}{\rm Bi}{_{2}}{\rm Fe}{_{4}}{\rm O}{_{9}}{\rm \char44 }\hfill\cr \Delta {\rm G}{^\circ}{_{T}}\ ({\rm kJ})=- 27.5- 0.051\cdot T.\hfill\cr}}$$$ …”

“…It may be due to the fact that in the temperature range (300-1073) K the formation of Bi 2 Fe 4 O 9 and BiFeO 3 from oxides is thermodynamically probable. [3,4] Therefore formation of single-phase samples Bi 2 Fe 4 O 9 from oxides, in the opinion of a number of authors, is practically unfeasible, equation ( 1) and (2):…”

“…As it is known, in the system Bi 2 O 3 -Fe 2 O 3 three bismuth ferrites (BiFeO 3 , Bi 2 Fe 4 O 9, and Bi 25 FeO 39 ) exist. [1][2][3][4] These ferrites attract much attention because of their magnetic, catalytic, photocatalytic, sensing, electric, and scintillating properties. The most investigated compound is BiFeO 3 with a perovskite structure.…”

Influence of temperature-induced A-site cation redistribution on the functional properties of A-site complex polar perovskite K1/2Bi1/2TiO3

“…An enhancement in T d aer rapid cooling to room temperature from temperatures ranging between 700 °C and 1100 °C was also reported for the relaxor Na 1/2 Bi 1/2 TiO 3 -BaTiO 3 and BiFeO 3 -BaTiO 3 . 31,[34][35][36][37] An increase in the defect concentration with quenching, typically understood to be oxygen vacancies, is also considered crucial in stabilizing the FE state. 34 Despite this, an oxygen tracer diffusion study of as-processed and quenched NBT did not reveal any signicant variation in oxygen vacancy concentration due to the quenching.…”