The search for electroceramic materials with enhanced ferro-pyro-piezoelectric properties and revealing the perovskite type structure has been the objective of a significant number of manuscripts reported in the literature. This has been usually carried out by proposing the synthesis and processing of new compounds and solid solution series. In this work, several methods to obtain ferro-pyro-piezoelectric families of materials featuring the well-known ABO₃ perovskite structure (or related) such as BaTiO₃, Ba_1–xCa_xTi_1–yZr_yO₃, (Bi_0.5Na_0.5)TiO₃, (K_0.5Na_0.5)NbO₃ and their solid solutions with different cations either in the A or B positions, are presented. For this kind of materials, the challenge for obtaining a single phase compound with a specific grain size and morphology and, most importantly, with the adequate stoichiometry, will also be discussed. The results reviewed herein will be discussed in terms of the tendency of working with softer conditions, i.e., lower temperature and shorter reaction times, also referred to as soft-chemistry.

The attention on piezoelectric devices has been moved in the past decade to lead-free ceramics, especially on (Ba,Ca)(Ti,Zr)O₃-based materials, due to growing environmental concerns. Here we report a systematic evaluation of the effect that electric field application has on the structure, microstructure and electrical properties of Ba_0.9Ca_0.1Ti_0.9Zr_0.1O₃ (BCTZ) lead-free ceramics. Powders were prepared by Pechini method. Dense ceramic samples were sintered at 1275 °C for 5 h. As observed by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS), the ceramics are single perovskite-type structure phases and they are homogeneous both at global and local scales. Rietveld analysis of the diffraction patterns for the non-poled sample is consistent with a coexistence of ferroelectric tetragonal P4mm and rhombohedral R3m symmetries. It is shown that the electric field induces changes in rhombohedral–tetragonal relative content that facilitates the polarization process of the system. Ceramics exhibit a significantly high piezoelectric response with a d₃₃ value as high as ∼390 pC N⁻¹, which is comparable to soft Pb(Zr_1−xTi_x)O₃ (PZTs). Scanning Electron Microscopy (SEM) analysis showed an average grain size of 20 μm and complex ferroelectric domains. A confocal Raman spectroscopy and imaging study carried out on both types of samples reveals that, upon application of an electric field, the E(LO₃) + A₁(LO₂) + E(TO₄) mode of the Raman spectra shifts to lower frequencies, indicating a reduction of the bonding force between the ions at the B-site of the perovskite (Ti⁴⁺, Zr⁴⁺) and the oxygen ions of the octahedron for the poled samples. Besides, the mentioned spatially resolved mode of the Raman spectra shows a narrower distribution in the poled sample, monitoring the polarization alignment effect in the direction of the field. These characteristics are related to the complex ferroelectric domain distribution. The polar structure changes are revealed after the application of the electric field, as well by the changes on the dielectric permittivity curves as a function of the temperature. Ceramics also display a high ferroelectric remnant polarization (P_r = 15.3 μC cm⁻²) and low coercive field (E_C = 1.5 kV cm⁻¹) at room temperature.

Ba_1−xCa_xTi_0.9Zr_0.1O₃ (x = 0.10, 0.15, 0.18) solid solutions were synthesized by the conventional solid-state method. A perovskite-type structure was determined using the X-ray diffraction (XRD) technique. The addition of Ca²⁺ reduced the grain size (22.6, 17.9 and 13.3 μm, respectively) for all well-sintered ceramics (≈98%). Moreover, the stability temperature ranges for the tetragonal phase were promoted by displacing the ferroelectric-ferroelectric phase’s transition temperatures while T_C was maintained (86 °C). The electrical performance of the material improved as the stoichiometric composition was positioned near the morphotropic phase boundary (x = 0.15): ε_r ≈ 16,500 (T_C) at 1 kHz. For T > T_C, a thermally activated relaxation process occurred. In addition, the bulk and grain boundary processes were responsible for the conduction mechanisms. The composition x = 0.15 showed an activation energy of Ea = 1.49 eV with a maximum conductivity of σ_max = 2.48 × 10⁻² S·cm⁻¹ at 580 °C. Systematic studies at high temperature for dielectric properties were accomplished for analyzing electrical inhomogeneities associated with the grain, grain boundaries or surfaces, which are important for device design and a fundamental electrical characterization.

The solid-state synthesis of Ba _{1− x} Ca _x Ti _0.9 Zr _0.1 O ₃ ( x = 0.10, 0.15) (BCTZ) powder and the processing method of ceramics, by the use of reduced synthesis time and temperature (1250 °C for 2 h), are reported. Homogeneous and dense (≥95%) ceramic microstructures with sub-10 μm grain size were obtained under all sintering conditions. A comparative study of their ferro-piezoelectric properties as a function of sintering temperatures is presented. The study shows the role of the grain size effect for improving both piezoelectric and ferroelectric properties of these materials. With an increase of the sintering temperature, grain growth was promoted; therefore, higher ferro-piezoelectric values were obtained (at 1400 °C, for x = 0.10: d ₃₃ = 300 pC/N, k _p = 48%; for x = 0.15: d ₃₃ = 410 pC/N, d ₃₁ =–154 pC/N, k _p = 50%). In addition, a diffuse phase transition is observed in these BCTZ ceramics with a Curie temperature near 100 °C at 1 kHz.