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Dielectric relaxation in ABO3 perovskite oxides can result from many different charge carrier-related phenomena. Despite a strong understanding of dielectric relaxations, a detailed investigation of the relationship between the content of oxygen vacancies (VO) and dielectric relaxation has not been performed in perovskite oxide films. In this work, we report a systematic investigation of the influence of the VO concentration on the dielectric relaxation of Eu0.5Ba0.5TiO3-δ epitaxial thin films. Nuclear resonance backscattering spectrometry was used to directly measure the oxygen concentration in Eu0.5Ba0.5TiO3-δ films. We found that dipolar defects created by VO interact with the off-centered Ti ions, which results in the dielectric relaxation in Eu0.5Ba0.5TiO3-δ films. Activation energy gradually increases with the increasing content of VO. The present work significantly extends our understanding of relaxation properties in oxide films.

We present a critical review that encompasses the fundamentals and state-of-the-art knowledge of barium titanate-based piezoelectrics. First, the essential crystallography, thermodynamic relations, and concepts necessary to understand piezoelectricity and ferroelectricity in barium titanate are discussed. Strategies to optimize piezoelectric properties through microstructure control and chemical modification are also introduced. Thereafter, we systematically review the synthesis, microstructure, and phase diagrams of barium titanate-based piezoelectrics and provide a detailed compilation of their functional and mechanical properties. The most salient materials treated include the (Ba,Ca)(Zr,Ti)O3, (Ba,Ca)(Sn,Ti)O3, and (Ba,Ca)(Hf,Ti)O3 solid solution systems. The technological relevance of barium titanate-based piezoelectrics is also discussed and some potential market indicators are outlined. Finally, perspectives on productive lines of future research and promising areas for the applications of these ma...

The temperature at which the electric field induced long-range ordered ferroelectric state undergoes transition into the short-range ordered relaxor state, TF-R, is commonly defined by the onset of strong dispersion of the dielectric permittivity. However, this combined macroscopic property and structural investigation of the polarization reversal process in the prototypical lead-free relaxor 0.94(Bi1/2Na1/2)TiO3-0.06Ba(Zr0.02Ti0.98)O3 reveals that an applied electric field can trigger depolarization and onset of relaxor-like behavior well below TF-R. The polarization reversal process can as such be described as a combination of (1) ferroelectric domain switching and (2) a reversible phase transition between two polar ferroelectric states mediated by a non-polar relaxor state. Furthermore, the threshold fields of the second, mediated polarization reversal mechanism depend strongly on temperature. These results are concomitant with a continuous ferroelectric to relaxortransition occurring over a broad temperature range, during which mixed behavior is observed. The nature of polarization reversal can be illustrated in electric-field-temperature (E-T) diagrams showing the electric field amplitudes associated with different polarization reversal processes. Such diagrams are useful tools for identifying the best operational temperature regimes for a given composition in actuator applications.

The method of thermally stimulated depolarization currents (TSDC) and polarization switching experiments over a large field, time, and temperature regime are used to refine the controversial phase diagram of Ba(Zr0.2Ti0.8)O3−x(Ba0.7Ca0.3)TiO3 and comprehend its relation to ferroelectric and piezoelectric properties. TSDC results suggest the existence of three ferroelectric phases for the composition range of 0.30 ≤ x ≤ 0.60, which can be assigned to the rhombohedral (R), presumably orthorhombic (O), and tetragonal (T) symmetries. Spontaneous polarization is maximal all over the entire intermediate phase region, where the activation barrier for polarization switching is small, not just at R-O or O-T boundaries as might be deduced from previous observations.

Contributions to the piezoelectric response of (1 − x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 ceramics are quantified by small signal measurements made as functions of bias field and temperature. The highest fraction of intrinsic contributions is observed far from phase boundaries, of extrinsic contributions around phase boundaries, and of irreversible switching in the orthorhombic phase. The largest piezoelectric response, d33 = 475 ± 85 pC/N, is found near the orthorhombic to tetragonal phase boundary due to both reversible and irreversible switching. A peak in reversible switching above the Curie temperature for all compositions suggests a line of critical points associated with first order phase transitions, indicating that concurrence of triple and tricritical points in the zero-field phase diagram is not the responsible mechanism of enhanced piezoelectricity.

The morphotropic phase boundary composition Bi1/2Na1/2TiO3-20 mol. % Bi1/2K1/2TiO3 was chosen as initial material to do selective A-site aliovalent doping replacing Na and K by 1 at. % La, respectively. The materials were studied macroscopically by measuring dielectric and electromechanical properties. The Na-replaced material has a lower freezing temperature Tfr, lower remanent polarization and remanent strain, and thus a higher degree of ergodicity than the K-replaced material. These results are contrasted with local poling experiments and hysteresis loops obtained from piezoresponse force microscopy. The faster relaxation of the tip-induced local polarization and the lower remanent state in bias-on and -off loops confirm the higher degree of ergodicity of the Na-replaced material. The difference in functional properties is attributed to small variations in chemical pressure achieved through selective doping. Raman results support this working hypothesis.

In this work, the lead-free Ba(Zr0.2Ti0.8)O3-0.3(Ba0.7Ca0.3)TiO3 piezoelectric ceramic was investigated in situ under an applied electric field by transmission electron microscopy. Significant changes in domain morphology of the studied material have been observed under an applied electric field. During the poling process, the domain configurations disappeared, forming a single-domain state. This multi- to single-domain state transition occurred with the formation of an intermediate nanodomain state. After removing the electric field, domain configurations reappeared. Selected area electron diffraction during electrical poling gave no indication of any structural changes as for example reflection splitting. Rather, a contribution of the extrinsic effect to the piezoelectric response of the Ba(Zr0.2Ti0.8)O3-0.3(Ba0.7Ca0.3)TiO3 was found to be dominant.

The free strain during unipolar electrical activation and the blocking stress are important figures of merit for actuator applications. The lead-free (1 − x)Ba(Zr0.2Ti0.8)O3−x(Ba0.7Ca0.3)TiO3 (BZT-xBCT) system has been shown to display exceptional unipolar strain at room temperature, making it very attractive as an electroactive material for large displacement, low frequency actuation systems. In this work, the temperature- and composition-dependent blocking stress is measured with the proportional loading method. It was found that BZT-xBCT outperformed Pb(Zr1− x Ti x )O3 and Bi1/2 Na 1/2TiO3–based ceramics for electric fields up to 2 kV/mm.

Analysis of polarization switching dynamics by means of the inhomogeneous field mechanism model allows insight into the microscopic mechanism of reversed polarization domain nucleation. For all chemical compositions studied, two distinct field regions of nucleation are established. In the high-field region, the activation energy barrier is found to be inversely proportional to the local field according to the Merz law. In contrast, the barriers in the low-field region exhibit a linear field dependence with a minimum in the compositional region of phase instability, which can explain the corresponding peak ferroelectric properties.