Lorena Pardo

Replacement of the ubiquitous lead titanate zirconate piezoceramics is still a challenge involving sustainable materials and processes. An extended effort has been paid for the optimization of the properties of (K _0.5 Na _0.5 )NbO ₃ (KNN) lead‐free piezoceramics at the expenses of high‐energetic budget. A sustainable solid‐state processing with potential for industrial scaling (knowledge‐based, sustainable, reproducible, and cost‐effective) is still lacking. In this work, an efficient solution is proposed using the well‐known and noncontaminant attrition‐ball‐milling of the mixture of reagents for only 3 h, prior to the synthesis tests at increasing temperatures. After calcination at only 450 °C/2 h, 60 wt% KNN is achieved. Moreover, after 850 °C/2 h the calcined powder becomes a pure KNN. A second ball‐milling of powder calcined at 700850 °C gives place to populations of nanostructured particles (380–40 nm, respectively). The milled powder calcined at 700 °C is pressureless sintered in air for 2 h at 1050 and 1100 °C, leading to coarse grained ceramics. Milled powder calcined at 750 and 850 °C, sintered at the same conditions, produces fine grain homogeneous microstructures. Ceramics show an orthorhombic Amm2 pure KNN perovskite phase, as seen by x‐ray diffraction and Rietveld analysis. The piezoelectric values ( d ₃₃ = 115 pC/N, d ₃₁ = ₋ 22 pC/N, k _p = 20%, k _t = 40%) are exceptional when derived from such a straightforward solid‐state route.

A 3D-printable, ARDUINO-based multipurpose X-ray stage of compact dimensions enabling in situ electric field and temperature-dependent measurements is put into practice and tested here. It can be routinely applied in combination with a technique of structural characterization of materials. Using high-performance X-ray laboratory equipment, two investigations were conducted to illustrate the device’s performance. The lattice characteristics and microstructure evolution of piezoelectric ceramics of barium titanate, BaTiO₃ (BT), and barium calcium zirconate titanate, with compositions of (Ba_0.92Ca_0.08) (Ti_0.95Zr_0.05)O₃ (BC8TZ5), were studied as a function of the applied electric field and temperature. The X-ray stage is amenable as an off-the-shelf device for a diffraction line in a synchrotron. It provides valuable information for poling piezoceramics and subsequent optimization of their performance.

A 3D-printable, ARDUINO-based multipurpose X-ray stage of compact dimensions enabling in-situ electric field and temperature dependent measurements is put into practice and tested here. It can be routinely applied in combination with a technique of structural characterization of materials. Using high-performance X-ray laboratory equipment, two investigations were conducted to illustrate the device performance. The lattice characteristics and microstructure evolution of piezoelectric ceramics of barium titanate, BaTiO3 (BT), and barium calcium zirconate titanate, with compositions of (Ba0.92Ca0.08)(Ti0.95Zr0.05)O3 (BC8TZ5), were studied as a function of the applied electric field and temperature. The stage is amenable as an off-the-shelf device for a diffraction line in a synchrotron. It provides valuable information for poling piezoceramics and subsequent optimization of their performance.

Ba_0.92Ca_0.08Ti_0.95Zr_0.05O₃ (BCZT8-5) ceramic materials have been scarcely studied as lead-free piezo/ferroelectrics despite their enhanced Curie temperature (>100 °C) with respect to most studied BCZT compositions. In this work, homogeneous dense BCZT8-5 ceramics with grain size in the range of 20 μm, and optimum ferroelectric, dielectric, and electromechanical performance, were prepared by the mixed oxides route using moderate synthesis (1250 °C-2 h) and sintering (1400 °C-2 h) conditions. Thickness-poled thin disks and monomodal shear plate resonators were used for the determination of piezoelectric coefficients, coupling factors, elastic, and dielectric permittivity coefficients, including all losses, by iterative analysis of impedance curves at resonance. Furthermore, the thermal evolution of the piezoelectric characteristics at resonance was determined to assess the enhanced working range of the ceramics (≈100 °C). Ferroelectric hysteresis loops and strains vs. electric-field butterfly loops were also measured and showed soft behavior with E_c = 2 kV/cm, P_r = 12 μC/cm² after a maximum applied field of 3 kV was used. The ceramics showed a high endurance of P-E cycles to electrical fatigue up to 10⁷ cycles. Moreover, dielectric properties as a function of temperature were also accomplished and showed nearly normal ferroelectric behavior, characteristic of samples with low crystallographic disorder. Overall, these ceramics showed high sensitivity and higher stability than other currently studied BCZT compositions.

Lead-free (Ba_0.92Ca_0.08) (Ti_0.95 Zr_0.05) O₃ (BCZT) ceramics were prepared by a solid-state route (SSR) using ultra-low synthesis (700 °C/30 min and 700 °C/2 h) and sintering temperatures (from 1150 °C to 1280 °C), due to prior activation and homogenization by attrition milling of the starting high purity raw materials for 6 h before the synthesis and of the calcined powders for 3 h before the sintering. The comparison of the thermal analysis of the mixture of the starting raw materials and the same mixture after 6 h attrition milling allowed to evidence the mechanisms of activation, resulting in a significant decrease of the perovskite formation temperature (from 854 °C down to 582 °C). The secondary phases that limit the functional properties of the ceramic and their evolution with the sintering conditions were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), which allowed the design of a two-step sintering method to eliminate them. A pure tetragonal BCZT perovskite phase (P4mm, c/a = 1.004) and homogeneous ceramic microstructure was obtained for synthesis at 700 °C for 2 h and sintering with the use of a two-step sintering treatment (900 °C for 3 h and 1280 °C for 6 h). The best electromechanical properties achieved were d₃₃ = 455 pC/N, k_p = 35%, Q_m = 155.