Confocal Raman Microscopy, Synchrotron X-ray Diffraction, and Photoacoustic Study of Ba_0.85Ca_0.15Ti_0.90Zr_0.10O₃: Understanding Structural and Microstructural Response to the Electric Field

Abstract

The synergetic role of the phase transitions taking place between long-range, polar ordered, ferroelectric phases in lead-free ceramics with Ba 0.85 Ca 0.15 Ti 0.90 Zr 0.10 O 3 composition on their electromechanical behavior has been analyzed. Synchrotron X-ray diffraction (XRD) and Rietveld analysis revealed a room temperature coexistence of rhombohedral (R), tetragonal (T), and orthorhombic (O) phases. The proportions of these phases in the investigated samples vary from the order of 42R-45T-13O in the nonpolarized condition to an estimated 65R-26T-9O in the polarized, significantly textured sample. These characteristics are related to the complex ferroelectric domain distribution that electron scanning microscopy exposes, which favors domain wall mobility and provides a large extrinsic contribution to the electromechanical response of the material. A confocal Raman spectroscopy and imaging study was carried out on both unpoled and poled samples and reveals that, under the action of the electric field, the E(LO 3 ) + A 1 (LO 2 ) + E(TO 4 ) mode of the Raman spectra shifts from 517.8 to 516.4 cm −1 , indicating the lengthening of the distance between B 5+ type ions and their coordinated oxygens for the poled samples. Besides, the mentioned spatially resolved model of the Raman spectra shows a narrower distribution in the poled sample, compatible with the strong texture revealed by XRD. Photoacoustic signal evolution with the temperature, in agreement with the dielectric permittivity curve, reveals the diffusive character of the phase transition taking place at 40 °C between the long-range polar ordered phase at low temperature and the high temperature one, which influences the phase coexistence at room temperature. Moreover, an evaluation of the resultant complex piezoelectric, dielectric, and elastic coefficients at resonance, including all losses, is presented. The obtained results indicate the remarkable electromechanical activity, its anisotropy, and the soft character of this ferro-piezo-electric type ceramic.

Chemical-Composition Tuning-Enabled Optimization of Structure, Properties, and Performance of Lead-Free (1 – x)BaZr0.05Ti0.95O3–(x)Ba0.92Ca0.08TiO3 Electroceramics

“…The absence of any other peaks (i.e., the peaks corresponding to the possible CaTiO 3 impurity phase) other than the expected ferroelectric phase of (1 − x)BZT5−(x)BCT8 materials is an indication of the fact that the substitution of Ca 2+ takes place for the Ba 2+ site in the perovskite lattice. 12 Further, from Figure 5, it is evident that the A 1 (TO 2 ) mode observed at ∼263 cm −1 has the maximum scattering efficiency 66,67 and this peak is observed for all the samples. 26 Figure 6 presents a comprehensive Raman spectroscopic study with temperature spanning from −193 to 227 °C for all the samples under investigation.…”

Ferroelectric, Dielectric and Electromechanical Performance of Ba0.92Ca0.08Ti0.95Zr0.05O3 Ceramics with an Enhanced Curie Temperature

“…When compared with the data available for BCZT1010 [ 24 ] and BCZT1510 [ 25 ], it is evident that BCZT8-5 was slightly more compliant, while the mechanical losses were similar. Furthermore, all the ceramics were high-sensitivity piezoelectric, while BCZT8-5 had lower permittivity and slightly higher dielectric losses at resonance.…”

“…The calculated dielectric permittivity and losses of the non-poled BCTZ8-5 ceramic (at different frequencies) are shown in Figure 2 a. Two-phase transitions corresponding to the Rhombohedral-Tetragonal (~35 °C) and Tetragonal-Cubic (~104 °C) were observed [ 12 , 23 , 24 , 25 ]. This confirmed the probable coexistence of polymorphs at room temperature revealed by XRD ( Figure 1 a).…”

“…Ba 0.92 Ca 0.08 Ti 0.95 Zr 0.05 O 3 (BCZT8-5) ceramic materials have been scarcely studied [ 23 ] as a lead-free piezo/ferroelectric, despite their enhanced Curie temperature (>100 °C) with respect to most studied BCZT compositions, namely BCZT1010 [ 24 ] and BCZT1510 [ 25 ]. In this work, Ba 0.92 Ca 0.08 Ti 0.95 Zr 0.05 O 3 (BCZT8-5) ceramics were fabricated using a conventional mixed oxide route using a moderate synthesis schedule.…”

Feasible Way to Achieve Multifunctional (K, Na)NbO3-Based Ceramics: Controlling Long-Range Ferroelectric Ordering

“…Thus, ε ″ – T curves of unpoled samples are still unable to distinguish T R–O and T O–T because of their diffuseness and/or overlap . Interestingly, ε ″ – T curves of poled samples make T R–O and T O–T more distinguishable (see the black dashed lines in Figure b), indicating that the low-temperature dielectric anomaly peak is strengthened after poling, which might be ascribed to the reinforced R phase after poling and the domain reorientation and the possible electric-induced phase transition. − Note that although T R–O is observed at x = 0–0.05, it gradually becomes diffused with increasing x , which may be one of the reasons why it can hardly be observed in unpoled samples. Then, only one dielectric anomaly peak is still observed at x = 0.06–0.08 below T C , illustrating that T R–O and T O–T completely converge into one (defined as T R–O&O–T ).…”