In the search of lead-free piezoelectric materials, ceramic processing techniques offer potential tools to increase the piezoelectric and ferroelectric properties in addition to new chemical compositions. Powders of pure BNKT16 (Bi_0.5(Na_0.84K_0.16)_0.5TiO₃) phase were synthesized by sol-gel method with a low crystallization temperature (750 °C). Ceramic samples were sintered by pressureless sintering (PLS), sinter-forging (SF), and spark plasma sintering (SPS) techniques. Structural, morphological, and chemical characterizations were performed by XRD, Raman, EDS, and SEM. Sintered samples by PLS and SF exhibit rod-like grains associated to bismuth volatility. The highest remanent polarization (11.05 µC/cm²), coercive field (26.2 kV/mm), and piezoelectric coefficient (165 pC/N) were obtained for SF sample. The piezoresponse force microscopy (PFM) analysis shows that the crystallites at the nanoscale exhibit piezoelectric phenomenon and the highest piezoelectric response is reported for PLS sample. The presence of the rhombohedral phase, the increase in grain and crystallite size, and the oriented rod-like inclusions favoring the crystallographic texture are facts that enhance the piezoelectric coefficient for BNKT16 piezoceramics.

Results from the analysis of the variation of structural defects, such as oxygen vacancies indicate that by adjusting the thickness of the WO₃ films, fabricated by DC reactive sputtering, it is possible to modulate the oxygen vacancies concentration. This has a tremendous influence on the applications of these semiconductor materials. The thicknesses analyzed here are 42, 66, and 131 nm. After the annealing process at 500 °C, films were directly transformed to a stable γ-monoclinic crystal structure with P2₁/n space group, with a preferential orientation in the (200) plane. Atomic force microscopy exhibits nanometer range particle size with the highest roughness and higher surface area for the thinner film. FTIR analysis shows the presence of characteristic bands of the double bond stretching vibrational modes (W=O) and stretching vibrations of the γ(W-O-W) bonds corresponding to the monoclinic WO₃. Raman bands located at 345, and 435 cm⁻¹ are ascribed to the presence of W⁵⁺ species that induces the formation of oxygen vacancies VO. The thinner film shows a decrease in the optical indirect band gap attributed to the formation of oxygen vacancies in combination with W⁵⁺ species that induce the formation of energy states within the forbidden band gap range.

The complex permeability dispersions: relaxation and resonance are investigated in the ${\text{Ni}}_{0.7}{\text{Zn}}_{0.3}{\text{Fe}}_2{\text{O}}_4$ ferrites doped with ${\text{V}}_2{\text{O}}_3$ at different weight percent. The complex permeability was measured at frequencies in the 30 kHz to 6 GHz range. The intragranular porosity plays an important role to distinguish between relaxation and resonant dispersion. The results obtained show that a tight grain size distribution leads to a resonant character, while a wide grain size distribution results in a mixed dispersion. The complex permeability results were modeled with the resonant $RCL$ equivalent circuit formed by a series $RL$ arrangement in parallel with a capacitor $C$ . The experimental results and the model are in agreement.