[en] Full text: Texturing in ferroelectric ceramics has played an important role in the enhancement of their piezoelectric properties. Common methods for ceramic texturing are hot pressing and template grain ground; nevertheless, the needed facilities to apply hot pressing and the processing of single crystal make the texture of ceramics expensive and very difficult. In this study, a novel method was investigated to obtain highly textured lead-free ceramics. A (K_0.5Na_0.5)_0.97Li_0.0₃Nb_0.8Ta_0.2 matrix (KNLNT), with CuO excess was sintered between 1070 and 1110 °C following a solid state reaction procedure. The CuO excess promotes liquid phase formation and a partial melting of the material. XRD patterns showed the intensity of (100) family peaks became much stronger with the increasing of sintering temperature and CuO. In addition, Lotgering factor was calculated and exhibited a texture degree between 40 % and 70 % for sintered samples having 13 and 16 wt. % CuO, respectively. These, highly textured ceramics, with adequate cut, can be used as substitutes single crystals for texturing of KNN-based lead-free ceramics. (author)

[en] Full text: In this work, ceramic samples of [(Bi_0.5Na_0.5)_0.94Ba_0.06]₍₁--_x-)La_xTiO₃ (abbreviation: BNT-6BT+xLa), with x=0; 0.001; 0.007; 0.014 and 0.02, were prepared via conventional mixed-oxide method. The powders were calcined in 900 deg C for 3h and conventionally sintered in 1150 deg C for 3h. Structural properties of BNT-6BT+xLa ceramics were investigated by powder method X-ray diffraction (XRD) (Shimazdu, XRD-6000 model). XRD patterns obtained for all sintered samples confirm the formation of complex perovskite structure and showed the absence of spurious phases. In the case of BNT-6BT+0La composition was confirmed, using Rietveld refinement method, that belong to the morphotropic phase boundary (MPB) of the BNT-BT system. On the other hand, for La-doped compositions, changes in the XRD data due increase of lanthanum (shown in diffraction peaks around 46 degrees) suggest the tendency of decrease of the Tetragonal phase, this could mean the Rhombohedral phase stabilization and the leaving of the MPB. In order to analyze the influence of La-doping in BNT-6BT over the anelastic response, elastic energy dissipation (internal friction) and complex elastic modulus, were carried out measurements of these properties as a function of temperature and frequency using a Dynamic Mechanical Analyzer (PerkinElmer, DMA8000 model), in temperature range between room temperature and 600 deg C, and frequencies in a Hz bandwidth. The evolution of the structural phase transition and mechanical relaxation processes exhibited by BNT-6BT+xLa samples were analyzed by mean of anelastic relaxation spectra. (author)

[en] Full text: Bi_0.5Na_0.5TiO₃-Bi_0.5K_0.5TiO₃-BaTiO₃ (BNBK) lead-free piezoelectric ceramic is an ecofriendly candidate to substitution of lead zirconate titanate-based piezoelectric in technological applications. The morphotropic phase boundary (MPB) for BNBK ceramic system is under discussion and it has two controversial proposals [1,2]. With an aim studying the MPB region, in this study, x(Bi_0.5Na_0.5TiO₃) - 0.72(1 - x)Bi_0.5K_0.5TiO₃ - 0.28(1 - x)BaTiO₃ (abbreviated as BNBK100x, with x = 0.82, 0.86, 0.88, 0.91 and 0.93 mol %) piezoelectric ceramics were synthesized by solid state reaction followed by conventional sintering. The crystalline phases evolution of BNBK100x samples were investigated by a combination of the X-ray diffraction (XRD) and Raman spectroscopy techniques, at room temperature. The XRD patterns revealed a complex perovskite structure without spurious phases for all the studied compositions. Rietveld refinements of XRD patterns indicated the BNBK82 sample has a single tetragonal phase (P4mm) and the BNBK91 and BNBK93 samples, single rhombohedral phase (R3c). Raman spectra for all the samples shows wide Raman peaks, denoting a high degree of chemical disorder, as a consequence of four ions (Bi²⁺, Na⁺, K⁺ and Ba²⁺) occupying the same crystallographic A site of the perovskite structure. The deconvolution of the Raman spectra confirmed the results obtained by XRD for the BNBK82, BNBK91 and BNBK93 samples with a single phase of P4mm and R3c symmetries, respectively. For the BNBK86 and BNBK88 samples, the deconvolution of the Raman spectra revealed a mixture of rhombohedral and tetragonal phases, evidencing that these compositions are located in the MPB region of the BNBK system. References: [1] Nagata Hajime, et. al., Jpn. J. Appl. Phys., Vol. 42, N.12, pp. 7401–7403 (2003). [2] Trelcat, Jean-François et. al., Ceramics International, Vol. 38,N. 4,pp.2823 – 2827 (2012). (author)