Piezoelectric properties of nonstoichiometric Sr1−xBi2+2x∕3Ta2O9 ceramics

Abstract

The effect of poling on the structural, dielectric, and piezoelectric properties has been investigated for sol-gel-derived strontium bismuth tantalate (SBT) [Sr1−xBi2+2x∕3Ta2O9] ceramics with x=0.0,0.15,0.30,0.45. The dielectric and ferroelectric properties are found to improve with increase in x up to 0.3. Beyond x>0.3 the properties are found to degrade due to the limited solid solubility and the presence of a mixed phase of bismuth tantalate (BiTaO4) is detected with x=0.45. Poling treatment reduces the dielectric dispersion and dielectric loss in the frequency range (0.1–100kHz). The resonance and antiresonance frequencies increase with increase in x (x=0–0.30), and the corresponding minimum impedance decreases. The measured coupling coefficients (kp) are small (0.0967–0.1) for x=0–0.30, and the electromechanical quality factor (Qm=915) is a maximum for the Sr0.7Bi2.2Ta2O9 composition (x=0.30). The estimated piezoelectric charge coefficient (d31) and piezoelectric voltage coefficient (g31) are 5.2pC∕N and 5.8×10−3Vm∕N, respectively. The positive values of d31 and g31 and the low dielectric permittivity of SBT yield a high value for the hydrostatic coefficients, despite the low charge coefficient of d33=24pC∕N. The maximum values of charge coefficient (dh=34pC∕N) and voltage coefficient (gh=39×10−3Vm∕N) are obtained for Sr0.7Bi2.2Ta2O9 composition, and the estimated hydrostatic figure of merit (dhgh×10−15=1215m2/N) is high.