The ferroelectric and piezoelectric properties of (1−x)BiFeO3–xPbTiO3 (BF-PT) ceramics were investigated as a function of tetragonal distortion. The latter was adjusted by employing La-doping (0–30 at %) while keeping the material near the morphotropic phase boundary by varying x between 0.35 and 0.46. This allows changing the c/a ratio of tetragonal BF-PT in the range from 1.10–1.01 and consequently alters the level of compatibility stresses. It was found that the c/a ratio has a significant influence on domain switching as inferred from electric field induced polarization, strain hysteresis, and Rayleigh measurements. Specifically, a threshold c/a ratio of about 1.045 was identified below which the electric field induced domain mobility increases sharply.

The piezoelectric coefficient of high temperature piezoelectric ceramics, denoted as Bi(Me)O3‐PbTiO3, (Me = Fe, Sc, (Mg1/2Ti1/2)) was investigated as a function of temperature by using a custom‐designed test frame. Utilizing laser vibrometry, it was possible to assess the piezoelectric coefficient in situ in the range from room temperature to 500°C. The constraints on the sample geometry as they exist in the commonly used resonance/antiresonance technique such as those encountered during poling were circumvented by the use of the converse piezoelectric effect. Comparison with literature data revealed that the current method is a useful alternative for determining the depolarization temperature (Td), defined as the inflection point in a temperature‐dependent d33 plot. Measured Td for each poled specimen was compared with that determined by dielectric permittivity as well as temperature‐dependent X‐ray diffraction data to understand a possible origin of Td. It was also shown that Td matches with the temperature where the dielectric anomaly initiates, and hence Td from the d33 measurement is consistently lower than that from the dielectric permittivity measurement. It is proposed that this discrepancy in the position of Td is due to the fact that the depolarization occurs in two steps.

BiFeO 3 -PbTiO 3 (BF-PT) powders with mixed tetragonal and rhombohedral crystal structure (morphotropic phase boundary: MPB) were modified with lanthanum to provide a wide variation in tetragonal distortion. X-ray diffraction from both the powder and the corresponding bulk ceramic demonstrated that the MPB in the bulk is shifted from 1-5 mol % towards the tetragonal PT as compared to the powder. This shift was correlated with the degree of tetragonal distortion as quantified by c=a ratio.

Articles you may be interested inEffect of tetragonal distortion on ferroelectric domain switching: A case study on La-doped BiFeO 3 -PbTiO 3 ceramics J. Appl. Phys. 108, 014103 (2010) The mechanical stress-induced domain switching and energy dissipation in morphotropic phase boundary (1Àx)(Bi 1 À y La y )FeO 3 -xPbTiO 3 during uniaxial compressive loading have been investigated at three different temperatures. The strain obtained was found to decrease with increasing lanthanum content, although a sharp increase in strain was observed for compositions doped with 7.5 and 10 at. % La. Increased domain switching was found in compositions with decreased tetragonality. This is discussed in terms of the competing influences of the amount of domain switching and the spontaneous strain on the macroscopic behavior under external fields. Comparison of the mechanically and electrically dissipated energy showed significant differences, discussed in terms of the different microscopic interactions of electric field and stress.

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