Grain Orientation and Electrical Properties of Some Bismuth Layer-Structured Ferroelectrics for Lead-Free Piezoelectric Applications

Abstract

The effects of grain orientation for some bismuth layer-structured ferroelectrics (BLSF) systems such as Bi 4 Ti 3−xMxO 12 [BITN-x] or [BITV-x] for M = Nb or V (0 ≦ x ≦ 0.2), Srm−3+xBi 3− x Tim - xTaxO 3 m +3 [SBTTm(x)] (m = 2, x = 1∼2; m = 3, x = 0 ∼ 2), and Sr 2(1− x)Ca 2xBi 4 Ti 5 O 18 [SCBT-x] (0 ≦ x ≦ 1) on electrical properties were studied by the hot-forged (HF) method, comparing them with ordinarily fired (OF) non-oriented ones. The electromechanical coupling factors, k 33 , of BITN-0.08 and BITV-0.02 ceramics were 0.20 and 0.25 for OF samples, and were enhanced to 0.39 and 0.38 for the HF ones. The k 33 and piezoelectric constant, d 33 of the HF SBTT3 (0.3) ceramic were relatively high of k 33 = 0.37 and d 33 = 45.3 pC/N, respectively. The mechanical quality factor, Qm, of the SBTT2 (1.25) ceramic was high of 13500. The k 33 and the d 33 of the HF SCBT-0 were relatively higher values of 0.29 and 51 pC/N, respectively. Temperature coefficients of the resonance frequency, TC-f, in the (33) mode of SCBT-0 (OF) and HF-SCBT-0.5 were –89.2 ppm/°C and −50.0 ppm/°C, respectively. From these results, BITN, BITV, SBTT and SCBT ceramics seem to be a superior candidate for lead-free piezoelectric ceramics for some applications such as piezoelectric resonators or high temperature piezoelectric sensors.