Residual tensile stress in robust insulating rhombohedral Bi1−xLaxFe1−yTiyO3 multiferroic ceramics and its ability to pin ferroelectric polarization switching

Robust insulating rhombohedral Bi1−xLaxFe1−yTiyO3 multiferroic ceramics with 0.02 ≤ x ≤ 0.12 and 0.01 ≤ y ≤ 0.08 are prepared by a refined solid-state reaction electroceramic processing. Residual internal tensile stresses existed in the ceramics according to unit cell volume enlargement observed by X-ray diffraction and frequency redshifts of Raman modes related to Bi motion and oxygen octahedral rotation detected by Raman scattering measurements. Residual internal tensile stresses in the ceramics are believed to originate from structural phase transitions through an intermediate paraelectric rhombohedral phase with a negative thermal expansion coefficient in the transformation from paraelectric cubic to ferroelectric rhombohedral phases. All of the rhombohedral Bi1−xLaxFe1−yTiyO3 ceramics exhibited a pinched polarization versus electric field hysteresis loop indicative of ferroelectric subswitching. We argue that the residual internal tensile stresses are responsible for such ferroelectric polarization s...