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The exceptionally large piezoelectric response of the morphotropic-phase-boundary (MPB) composition of the lead-free piezoelectric system (1-x)Ba(Ti0.8Zr0.2)O3-x(Ba0.7Ca0.3)TiO3 has attracted great attention in recent years. Here in this paper we report a detailed investigation of the structural phase transformation behavior of the MPB composition (x=0.50) driven by electric field, stress, and temperature. We show that the system exhibits metastable phases in a wide temperature range, and that the large piezoresponse at room temperature has a significant contribution from the increased fraction of the metastable phases induced by the poling field. Using a "powder poling" technique we also demonstrate the equivalence of stress and electric field with regard to the nature of the structural transformation. The fundamental significance of this interesting observation is discussed. [ABSTRACT FROM AUTHOR]

Pressure-dependent powder x-ray diffraction, Raman spectroscopy, and dielectric constant measurements are performed on 0.65BiFeO3-0.35PbTiO3. Four structural transitions are reported in 0-34 GPa range. The transitions are observed at 0.7(1), 0.8(1), 3.4(1), and 6.1(1) GPa, where the system transformed from ambient tetragonal P4mm to a mixed phase of tetragonal and rhombohedral (P4mm+R3c), followed by transition to rhombohedral R3c, cubic Pm3m and again to rhombohedral R3c structure, respectively. The transformation to the cubic structure coincides with the ferroelectric-paraelectric transition. Higher-pressure cubic-to-rhombohedral transition shows a slight softening of Raman modes along with an enhancement in spontaneous strain. The high-pressure rhombohedral phase shows signatures of another ferroic transition. [ABSTRACT FROM AUTHOR]

Na0.5Bi0.5TiO3- based lead-free piezoelectrics exhibiting giant piezostrain are technologically interesting materials for actuator applications. The lack of clarity with regard to the structure of the nonpolar phase of this system has hindered the understanding of the structural mechanism associated with the giant piezostrain and other related phenomena. In this paper, we have investigated the structure and field-induced phase transformation behavior of a model system (0.94-x)Na0.5Bi0.5TiO3-0.06BaTiO3-xK0.5Na0.5NbO3 (0.0≤x≤0.025). A detailed structural analysis using neutron powder diffraction revealed that the nonpolar phase is neither cubic nor a mixture of rhombohedral (R3c) and tetragonal (P4bm) phases as commonly reported in literature but exhibits a long-period modulated structure, which is most probably of the type √2?√2?n with n=16. Our results suggest that the giant piezoelectric strain is associated with a field-induced phase transformation of the long-period modulated structure to rhombohedral R3c structure above a critical field. We also demonstrate that the giant piezostrain is lost if the system retains a fraction of the field-induced R3c phase. A possible correlation among depolarization temperature, giant piezostrain, and its electrical fatigue behavior has also been indicated. [ABSTRACT FROM AUTHOR]

The complex nature of the structural disorder in the lead-free ferroelectric Na1/2Bi1/2TiO3 has a profound impact on the perceived global structure and polar properties. In this paper, we have investigated the effect of electric field and temperature on the local structure around the Bi and Ti atoms using extended x-ray absorption fine structure. Detailed analysis revealed that poling brings about a noticeable change in the bond distances associated with the Bi-coordination sphere, whereas the Ti coordination remains unaffected. We also observed discontinuity in the Bi-O bond lengths across the depolarization temperature of the poled specimen. These results establish that the disappearance of the monoclinic-like (Cc) global distortion, along with the drastic suppression of the short-ranged in-phase octahedral tilt after poling [B. N. Rao etal., Phys. Rev. B 88, 224103 (2013)] is a result of the readjustment of the A-O bonds by the electric field, so as to be in conformity with the rhombohedral R3e structure. [ABSTRACT FROM AUTHOR]

Although, as part of a general phenomenon, the piezoelectric response of Ba(Ti1-yMy)O3 (M=Zr, Sn, Hf) increases in the vicinity of the orthorhombic (Amm2)-tetragonal (P4mm) and orthorhombic (Amm2)-rhombohedral (R3m) polymorphic phase boundaries, experiments in the last few years have shown that the same phase boundaries show significantly enhanced weak-field piezoproperties in the Ca-modified variants of these ferroelectric alloys, i.e., (Ba,Ca)(Ti,M)O3. So far there is a lack of clarity with regard to the unique feature(s) which Ca modification brings about that enables this significant enhancement. Here, we examine this issue from a structural standpoint with M=Sn as a case study. We carried out a comprehensive comparative structural, ferroelectric, and piezoelectric analysis of the Amm2 phase in the immediate vicinity of the P4mm-Amm2 phase boundaries of (i) Ca-modified Ba(Ti,Sn)O3, as per the nominal formula (1-x)BaTi0.88Sn0.12O3-(x)Ba0.7Ca0.3TiO3 and (ii) without Ca modification, i.e., Ba(Ti1-ySny)O3. We found that the spontaneous lattice strain of the Amm2 phase is noticeably smaller in the Ca-modified counterpart. Interestingly, this happens along with an improved spontaneous polarization by enhancing the covalent character of the Ti-O bond. Our study suggests that the unique role of Ca modification lies in its ability to induce these seemingly contrasting features (reduction in spontaneous lattice strain but increase in polarization). [ABSTRACT FROM AUTHOR]

In general, crystallite size reduction is known to suppress the ferroic order (polarization or magnetization) in ferroelectric and magnetic systems. Using free particles of a giant tetragonality (c/a-1=0.18) ferroelectric alloy BiFeO3-PbTiO3 as the model system, here we show that the intrinsic size effect in ferroelectrics can as well manifest in terms of switching the ground state from one ferroelectric phase (tetragonal with polarization along [001]) to another ferroelectric phase (rhombohedral with polarization along [111]). In this particular case, because of the strong coupling of the magnetic and structural degrees of freedom, a magnetic order also sets in below the critical size, making it a size induced magnetoferroelectric transformation. The driving force for this unusual transformation is argued to be the large depolarizing and domain wall energies in the tetragonal phase. [ABSTRACT FROM AUTHOR]

A comparative study of field-induced domain switching and lattice strain was carried out by in situ electric-field-dependent high-energy synchrotron x-ray diffraction on a morphotropic phase boundary (MPB) and a near-MPB rhombohedral/pseudomonoclinic composition of a high-performance piezoelectric alloy (1-x)PbTiO3-(x)BiScO3. It is demonstrated that the MPB composition showing large d33~425pC/N exhibits significantly reduced propensity of field-induced domain switching as compared to the non-MPB rhombohedral composition (d33~260pC/N). These experimental observations contradict the basic premise of the martensitic-theory-based explanation which emphasizes on enhanced domain wall motion as the primary factor for the anomalous piezoelectric response in MPB piezoelectrics. Our results favor field-induced structural transformation to be the primary mechanism contributing to the large piezoresponse of the critical MPB compositi [ABSTRACT FROM AUTHOR]