Abstract
(Bi0.5Na0.5)0.94Ba0.06TiO3 dense ceramics were obtained from autocombustion sol-gel synthesized nanopowders and sintered at 1050 °C for 1–2 h for the study of the electromechanical anisotropy. Measurement of the complex impedance spectrum was carried out on thin ceramic disks, thickness-poled, as a function of the temperature from 16 °C up to the vanishing of the electromechanical resonances at the ferroelectric to relaxor transition near 100 °C. The spectrum comprises the fundamental radial extensional mode and three overtones of this, together with the fundamental thickness extensional mode, coupled with other complex modes. Thermal evolution of the spectrum shows anisotropic behavior. Piezoelectric, elastic, and dielectric material coefficients, including all losses, were determined from iterative analysis of the complex impedance curves at the planar, thickness, and shear virtually monomodal resonances of disks and shear plates, thickness-poled. d33 was measured quasi-statically at 100 Hz. This set of data was used as the initial condition for the optimization of the numerical calculation by finite elements of the full spectrum of the disk, from 100 kHz to 1.9 MHz, to determine the thermal evolution of the material coefficients. An appropriate measurement strategy to study electromechanical anisotropy of piezoelectric ceramics has been developed.
Highlights
Lead-free ceramics with composition at the solid solution system of (1 − x)(Bi0.5 Na0.5 )TiO3 xBaTiO3 (BNBT100x) with x = 0.06 have been widely studied in recent years due to their complex crystal structure, exhibiting a field induced phase transition at the nano-scale between short-range ordered and ferroelectric, long-range ordered, polar states [1,2]
Thin sintered ceramic disks and plates were electroded at the major faces with silver paste, sintered at 400 ◦ C, and poled in silicon oil bath from 120 ◦ C to 50 ◦ C, cooling with an applied field of 30 KV·cm−1, for 30 min
These peaks are used for the determination of the frequencies of interest for the iterative analysis
Summary
Lead-free ceramics with composition at the solid solution system of (1 − x)(Bi0.5 Na0.5 )TiO3 xBaTiO3 (BNBT100x) with x = 0.06 have been widely studied in recent years due to their complex crystal structure, exhibiting a field induced phase transition at the nano-scale between short-range ordered and ferroelectric, long-range ordered, polar states [1,2]. The thermal depolarization accompanied by the inhibition of the piezoelectric activity [1] has a multiple origin [3,4]. There is a thermal randomization of the polarization at the ferroelectric domains. There is a thermally stimulated and non-abrupt transition, without macroscopic symmetry breaking, from the long-range ordered ferroelectric structure induced by the field to an ergodic relaxor at ~100 ◦ C, well below the transition to the non-polar paraelectric phase.
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