Evolution of the tetragonal to rhombohedral transition in (1 − x)(Bi_1/2Na_1/2)TiO₃ − xBaTiO₃ (x ≤ 7%)

Abstract

(1 − x)(Bi1/2Na1/2)TiO3 − xBaTiO3 has been the most studied Pb-free piezoelectric material in the last decade; however, puzzles still remain about its phase transitions, especially around the important morphotropic phase boundary (MPB). By introducing the strain glass transition concept from the ferroelastic field, it was found that the phase transition from tetragonal (T, P4bm) to rhombohedral (R, R3c) was affected by a strain glass transition at higher temperature for x ≽ 4%. In these compositions, the T–R transition was delayed or even totally suppressed and displayed huge thermal hysteresis upon cooling and heating. Also, isothermal phase transitions were predicted and realized successfully in the crossover region, where the interaction between the T–R transition and the strain glass transition was strong. Our results revealed the strain glass nature in compositions around the MPB in this important material, and also provide new clues for understanding the transition complexity in other (Bi1/2Na1/2)TiO3-based Pb-free piezoelectric materials.

Polarization alignment, phase transition, and piezoelectricity development in polycrystalline0.5Ba(Zr0.2Ti0.8)O3−Guo1, Voas2, Zhang3 et al. 2014Phys. Rev. BSelf Cite806360View full textAdd to dashboardCite

“…First, the virgin state of this composition at room temperature is a mixture of rhombohedral and tetragonal phases [26]. Second, the orthorhombic phase of this composition has an exceptionally low elastic modulus [5], much lower than those of (Bi 1/2 Na 1/2 )TiO 3 -based and Pb(Zr,Ti)O 3 -based ceramics [28,29]. During electrical poling of polycrystalline ferroelectrics for piezoelectricity, the domain polarization alignment cannot be complete and many domains persist at grain boundary regions even at very high poling fields in order to accommodate the incompatible piezoelectric strain across the grain boundary [30].…”

Elastic Properties and Enhanced Piezoelectric Response at Morphotropic Phase Boundaries

“…It would be tempting to identify the growing maximum at $T_{\mathrm{me}}$ with the transverse instability at the MPB but the situation is more complicated. In fact, a study of this maximum by DMA at varying frequencies and T protocols shows that for $x>0.04$ the maximum at $T_{\mathrm{me}}$ can be interpreted in terms of strain glass transition [174], that prevents the prompt formation of the R phase during normal cooling (hence the absence of the steps) but has little to do with rotational instabilities of the polarization.…”

Unique single-domain state in a polycrystalline ferroelectric ceramic

“…Previous symmetry analysis reveals that the 0.5Ba(Zr 0.2 Ti 0.8 )O 3 -0.5(Ba 0.7 Ca 0.3 )TiO 3 ceramic can exist in rhombohedral, orthorhombic, tetragonal, or any combination of these phases at room temperature [34]. Detailed dynamic mechanical analysis indicates that the intermediate orthorhombic phase displays an elastic storage modulus below 50 GPa [35], which is not only the lowest among all phases in this particular composition, but also much lower than that of (Bi 1/2 Na 1/2 )TiO 3 -based and PbZrO 3 -based ceramics [36,37]. A very recent TEM study with convergent beam electron diffraction analysis shows that the 0.5Ba(Zr 0.2 Ti 0.8 )O 3 -0.5(Ba 0.7 Ca 0.3 )TiO 3 ceramic is a mixture of rhombohedral and tetragonal phases in its virgin state at room temperature [38].…”