Elastic response of (1 − x)Ba(Ti0.8Zr0.2)O3 – x(Ba0.7Ca0.3)TiO3 (x = 0.45–0.55) and the role of the intermediate orthorhombic phase in enhancing the piezoelectric coupling

Abstract

The elastic response of (Ba,Ca)(Ti,Zr)O3 at compositions where the piezoelectric effect is maximized has been measured by different methods between 1 Hz and 250 kHz and compared with that of PZT at the middle of its morphotropic phase boundary. In all cases, the compliance is peaked at the border between the tetragonal (T) and the orthorhombic (O) phases, intermediate between the T and the low-temperature rhombohedral phase. The anomalies do not exhibit dependence on frequency and their relative amplitude is 200–300 times larger than the losses, demonstrating that they are intrinsic rather than due to the domain wall motion. This also demonstrates the role of an intermediate O or monoclinic phase in enhancing the transverse instability and piezoelectric coupling at a (morphotropic) phase boundary between R and T phases.

Strain Mechanisms in Lead-Free Ferroelectrics for Actuators

“…The triple point was called a tricritical point, although no proof on the critically was reported. 194 Recent reports indicate unambiguously the presence of two PPBs on the system 318,322,325,331,333,341 , similarly as found in other BT-based materials. 196,342 Despite the agreement of an interleaving region between R and T phases, further clearance is still required especially in the convergence region (yellow blurred shaded area), as well as the interleaving region between R and T phases.…”

“…For the R phase, increasing temperature leads to higher 33 , which indicates the typical elastic softening expected in ferroelectrics 42 and was previously reported by different experimental techniques in BZT-BCT. 318,349 Interestingly, compositions with x > 0.40 in the temperature range where the T phase is stable feature decreasing 33 values with temperature, which indicates elastic hardening. The BZT-0.60BCT displays a weak temperature dependence and relatively low 33 values, which are typical properties for hard ferroelectric materials.…”

“…342 Moreover, the O to T PPB is more elastic than the R to T PPB ( Figure 3.3 (c)), and displays similar elasticity as the convergence region. 318,341,349 Li et al 350 reported that the electrostrictive coefficients of BZT-BCT are ~ 0.04 m 4 /C 2 and remain relatively constant with composition and temperature. It was demonstrated that switching determines to a great extent small 323 and large 329 signal properties.…”

“…156 Recent reports also highlighted the importance of studying elastic properties of the system, as they couple with piezoelectric properties. 318,341,349 Figure 3.6 displays (a) ´ and (b) 33 as a function of composition. 322 It is observed that ´ and 33 values at the O to T PPB are higher than at the R to O PPB, similarly as reported in other BT-based materials.…”

“…The intrinsic ionic and orientational polarization contributions are enhanced due to either the transverse or longitudinal instability of , while the extrinsic domain contribution is normally maximized due to elastic softening as reported for BZT-BCT. 318,348 Therefore, the maxima observed in the temperature profiles of ´ are considered to indicate phase transitions. 42 Since the extrinsic contributions are inherently lossy 393,394 , the local maxima of ´ are correlated to the local maxima of ´´.…”