Linking large piezoelectric coefficients to highly flexible polarization of lead free BaTiO3-CaTiO3-BaZrO3 ceramics

Abstract

We report a large d 31 piezoelectric coefficient and corresponding electromechanical coupling factor, K p , of 0.5Ba(Zr 0.2 Ti 0.8 )O 3 -0.5(Ba 0.7 Ca 0.3 )TiO 3 (BCTZ50) and 0.68Ba(Zr 0.2 Ti 0.8 )O 3 -0.32 (Ba 0.7 Ca 0.3 )TiO 3 (BCTZ32) lead-free piezoceramics. The piezoelectric coefficient, d 31 , reaches a high value of 200 pC/N for BCTZ50 at room temperature which is comparable to the one of the soft PZT. This confirms the previously reported d 33 for the same material. A useful way to achieve such performances at the expense of a smaller thermal budget is suggested, enabling better control of the ceramics composition and microstructure. Based on pyroelectric and ferroelectric hysteresis loops measurements, we show that such outstanding properties are likely due to the high flexibility of polarization under thermal and electric stresses. V

Revised structural phase diagram of (Ba0.7Ca0.3TiO3)-(BaZr0.2Ti0.8O3)

“…We note that no extra reflections consistent with octahedral tilting are observed in any pattern in the current study. We therefore conclude that despite the introduction of the small Ca 2+ cation, no long-range octahedral tilts are introduced to the structure.To confirm the succession of 3 phase transitions for compositions beyond BCTZ32, we reconsidered the published dielectric data for BCTZ32 and BCTZ50 (ref 16 ) and we undertook further investigations of BCTZ20 and BCTZ40. In our earlier work 16 In order to confirm the suggested phase sequences and to assign a space group to the individual phase, full Rietveld refinements were performed on powder patterns collected for significantly longer times.…”

“…To confirm the succession of 3 phase transitions for compositions beyond BCTZ32, we reconsidered the published dielectric data for BCTZ32 and BCTZ50 (ref 16 ) and we undertook further investigations of BCTZ20 and BCTZ40. In our earlier work 16 In order to confirm the suggested phase sequences and to assign a space group to the individual phase, full Rietveld refinements were performed on powder patterns collected for significantly longer times.…”

“…As a consequence, there is an increasing interest in the development of lead-free piezoelectric materials [8][9][10][11][12][13] with the main challenge to develop materials with an equivalent or even -on both ceramics and thin film samples (e.g. [15][16][17][18][19][20] ). The first structural phase diagram of BCTZ has been reported 14 and the different phase sequences with increasing temperature can be summarized as follows: (i) x ≤ 0.32: a single phase transition is observed from the low temperature R-phase to the high-temperature prototype cubic ̅ structure (C), (ii) 0.32 < x < 0.8 : presence of two phase transitions through a R-T-C phase sequence and (iii) x > 0.8: a single phase transition from a T-phase to the C-phase.…”

Polarization dynamics across the morphotropic phase boundary in Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 ferroelectrics

“…9 At room temperature, this boundary is at x $0.5 between a rhombohedral (R) and a tetragonal (T) phase, although the exact phase diagram in BCZT100x is still controversial. 9,[12][13][14][15][16][17][18] For example, a recent study 18 suggested that an intermediate orthorhombic (O) phase and a phase convergence region where four phases (R, O, T, and cubic (C)) may occur in a narrow temperature and compositional range. Thereby, the existence of such polymorphic regions seems to be a key to achieving the outstanding piezoelectric performance.…”

Strain Mechanisms in Lead-Free Ferroelectrics for Actuators

“…325 In general, the system susceptibility to external parameters was considered to be a result of its high elastic softness that enables an easy polarization rotation along different crystallographic orientations. 332 This was mentioned as crucial for the development of enhanced electromechanical properties. High temperature poling was proved to be quite beneficial for attaining maximized properties.…”