Ni_1−xZn_xFe₂O₄ (x = 0.5, 0.6, 0.7) nanoparticles were synthesized by a thermal decomposition method. The synthesized particles were identified as pure spinel ferrite structures by X-ray diffraction analysis, and they were calculated to be 46–51 nm in diameter by the Scherrer equation, depending on the composition. In the FE-SEM image, the ferrite nanoparticles have spherical shapes with slight agglomeration, and the particle size is about 50 nm, which was consistent with the value obtained by the Scherrer equation. The lattice parameter of the ferrite nanoparticles monotonically increased from 8.34 to 8.358 Å as the Zn concentration increased from 0.5 to 0.7. Initially, the saturation magnetization value slowly decreases from 81.44 to 83.97 emu/g, then quickly decreases to 71.84 emu/g as the zinc content increases from x = 0.5, through 0.6, to 0.7. Ni_1−xZn_xFe₂O₄ toroidal samples were prepared by sintering ferrite nanoparticles at 1250 °C and exhibited faceted grain morphologies in the FE-SEM images with their grain sizes being around 5 µm regardless of the Zinc content. The real magnetic permeability (μ′) of the toroidal samples measured at 5 MHz was monotonically increased from 106, through 150, to 217 with increasing the Zinc content from x = 0.5, through 0.6, to 0.7. The cutoff frequency of the ferrite toroidal samples was estimated to be about 20 MHz from the broad maximum point in the plot of imaginary magnetic permeability (μ″) vs. frequencies, which seemed to be associated with domain wall resonance.

Three types of In₂O₃ nanoparticles decorated with Au, Pd and Pt nanoparticles, respectively, were synthesized by thermal decomposition method, and the effects of metal nanoparticles on their phase, microstructure, chemical state, carrier types were investigated with XRD, SEM/TEM, and XPS. Additionally, sensing properties to CO gas, such as sensitivity, etc., were examined with sensing apparatus. Au-decorated In₂O₃ nanoparticles exhibited the highest sensitivity to CO gas, with S = 5.59 at a 10 ppm CO gas concentration at 50 °C compared to Pd or Pt-decorated In₂O₃ nanoparticles. This can be interpreted as a much higher adsorption of oxygen molecules on the In₂O₃ surface due to the high oxygen vacancies in the In₂O₃ lattice, which generates an electron depletion region in the outer layer of In₂O₃ to sharply increase the resistance or the spill-over effect due to Au nanoparticles on In₂O₃. Au nanoparticles were observed in the TEM images and confirmed by XPS analysis.

We prepared Li0.04(K0.5Na0.5)x(NbySb0.06)O3 ceramics using the conventional solid-state sintering method and investigated the non-stoichiometric effect on sintering behavior and electrical properties in these material systems. The deficiency of B-site ions gave rise to poor densities, while the densification was improved by adding excess Nb2O5. As the vacancy concentration in the A-site of the perovskite structure increased, the diffuse phase transition was enhanced and the transition temperature (To–t) was lowered. Furthermore, high deficiency in the A-site with x=0.90 and y=0.98 promoted a second phase formation. An increase of alkali cation vacancies led to large remnant polarization and enhanced a pinched hysteresis loop, while the remnant polarization decreased due to a second phase formation. The electro-mechanical coupling factors were significantly influenced by density and second phase formation, not non-stoichiometry, while dielectric constants were influenced by non-stoichiometry, not second phase formation.