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Owing to the confinement of ZnO in the photocatalytic application: the wide bandgap, the rapid photogenerated carriers recombination, and the expensive cost for the catalyst separation from the wastewater, the p-n heterojunction of NiFe2O4 magnetic phase and ZnO is considered to improve the photocatalytic efficiency and the catalyst separation by the external magnetic. The NiFe2O4/ZnO composites with 0–12 wt% of NiFe2O4 were prepared by an ordinary process and characterized using XRD, Raman, SEM, EDS, TEM, HRTEM, UV–Vis spectroscopy, and PL techniques. The Raman spectra confirm the crystallinity of ZnO and NiFe2O4, including their defects. As increasing NiFe2O4 incorporation, the crystallite size of ZnO phase depicts a lower value with changing from 53.14 to 40.49 nm, whereas NiFe2O4 phase reveals a greater value of 60.61–141.55 nm. The dislocation density, lattice constants, and atomic coordinates are also discussed in terms of ion diffusion. The morphology analysis reveals ZnO particles on the surface of NiFe2O4 microcrystals, confirming the p-n heterojunction formation. The energy bandgap of the as-synthesized samples is in the range of 1.52–2.85 eV, suggesting to the visible light photocatalysis. The prominent PL spectrum indices the forming of Zn interstitial defect state. Under the visible light irradiation, the dye degradation was investigated as a result of the photoreduction percentage and catalyst dosage. With prepared by a facile process, 12 wt% NiFe2O4-loaded ZnO displayed the high methylene blue degradation of 96.96 % within 150 min under visible light irradiation, confirming an excellent photocatalyst. Due to the microstructural composite, the active surface site and the p-n heterojunction were elucidated as the principal mechanism for the difference in reaction time. The dye degradation was discussed in association with the structural constants, morphology, and defects. [ABSTRACT FROM AUTHOR]

The intrinsic defect of ZnO depicts a crucial role in the charge transfer owing to the suppression of the exciton recombination, exhibiting superior semiconducting performance. In this study, the intrinsic defect of ZnO nanostructures prepared by direct thermal activation of 300–900 °C was investigated. X-ray diffraction (XRD) was employed to analyze phase, crystallite size, Zn–O bond length, and dislocation density. The relation of Williamson–Hall (W–H) was used to calculate crystallite size and micro-strain. The atomic coordination was approximated through the Rietveld method. Morphology and crystal growth investigation was carried on by scanning electron microscope (SEM) and tunneling electron microscope (TEM), exhibiting rod-like nanostructures transform to oval shape particle with high residual strain when increasing calcination temperature, exhibiting the crystal growth direction of (101). Specific surface and pore analysis reveals a significant value corresponding to SEM analysis. Fourier transform infrared spectroscopy (FT-IR) detected Zn–O stretching vibration bands, presenting a notable increase in the intensity when heat at 600 °C. Relating to the thermal regime, energy bandgap (Eg) was found to be 3.41–3.50 eV as increasing heat treatment temperatures. Photoluminescence (PL) was applied to determine intrinsic defects through emissive spectra. The surface charge was determined through the zeta potential measurement. The photo-induced dye degradation was measured to understand the effect of the defect in semiconductors. The X-ray photoelectron spectroscopy (XPS) confirms the wurtzite structure appearance, including the intrinsic defects. The observed intrinsic defects are discussed, associating with the structural constants, emissive spectra, cationic dye degradation, and binding energy. [ABSTRACT FROM AUTHOR]

Barium titanate (BaTiO3) has been recognized as an important perovskite ceramic since its discovery due to its excellent dielectric, ferroelectric and piezoelectric properties. Its modifications have been studied in many perspectives depending on applications. In this review, the basic principles of BaTiO3 were described, then followed by the explanation on the recent modifications of BaTiO3 to improve the dielectric properties. Relaxor ferroelectric behavior of BaTiO3 was revealed by combining BaTiO3 with other Bi-based perovskites. These modified- BaTiO3 opened the opportunities for emerging energy storage applications. Next, the modifications for ferroelectric and ferromagnetic aspects were further discussed. BaTiO3 can also be doped by other ions to enhance such properties. Solid solution between Bi-based perovskites such as BiFeO3, (Bi0.5K0.5)TiO3, or Bi(Zn0.5Ti0.5)O3 and BaTiO3 can also improve ferroelectric and ferromagnetic properties. Therefore, these details of recent BaTiO3 modifications may provide guidance for the next BaTiO3 investigations in order to gain the maximum benefits from BaTiO3. [ABSTRACT FROM AUTHOR]

Multiferroic (1-x)PbTiO3−(x)Fe2O3 composite materials, when x = 0.1, 0.3, 0.5, 0.7 and 0.9, were prepared by solid-state reaction technique. PbTiO3 powder was synthesized with a calcination temperature of 900 °C in air. Phase formation, densification, morphology and magnetic properties of (1-x)PbTiO3−(x)Fe2O3 composites were investigated and discussed. The XRD technique was used to analyze the phase formation behavior of all specimens which shown the Fe2O3 accumulate phase with increasing Fe2O3 content. Densities of the sintered ceramics trend to decrease, possibly caused by an anomaly morphology of the specimens that related to particle packing. Also besides, the superparamagnetic behaviors were observed using a Vibrating Sample Magnetometer (VSM), which reached the maximum value at x = 0.7. In conclusion, Fe2O3 addition has been found to affect the phase formation, microstructure and magnetic properties of PbTiO3 ceramics. [ABSTRACT FROM AUTHOR]

The double perovskite Sr(Ni1/2Mo1/2)O3 has been prepared with solid-state reaction and was characterized by x-ray diffraction technique. It has been indicated that the single phase is formed at 1300 °C in air. The compound undergoes a phase transition at 280 °C, where the structure of the ordered perovskite type changes from tetragonal (I4/m) to cubic (Fm3m). Dielectric constant ([variant_greek_epsilon]r) and dielectric loss (tan δ) are observed at the transition point. The conductivity of the sample has been studied, and the slope of dc conductivity versus the inverse of temperature corresponds to an Arrhenius activation energy in the range of 0.34–0.46 eV. This range of activation is nearly double ionized oxygen vacancies VO·· in the resistivity transition of other perovskite oxides. [ABSTRACT FROM AUTHOR]

X-ray diffraction method is used for characterizing the double perovskite Sr([Ni.sub.1/2][Mo.sub.1/2])[O.sub.3] prepared with solid-state reaction. The compound has undergone a phase transition where the structure of the ordered perovskite type has changed from tetragonal to cubic and the dielectric constant and dielectric loss are observed at the transition point.

Effects of compressive stress applied perpendicular to electric field on dielectric properties of (1-x)Pb(Zr1/2Ti1/2)O3-(x)Pb(Zn1/3Nb2/3)O3 (x = 0.1-0.5) ceramics were investigated. The results showed that the superimposed compression stress had pronounced effects on the dielectric properties of PZT-PZN ceramics. With increasing compressive stress the dielectric constant of the ceramics decreased, while the dielectric loss tangent increased. The observations were mainly interpreted in terms of competing influences of the domain switching through non-180° domain walls, clamping of domain walls, and de-aging mechanisms. Interestingly, the observed changes of the dielectric properties with the perpendicular compressive stress were generally similar to those under the parallel stress. [ABSTRACT FROM AUTHOR]

The influences of compressive stress on the dielectric properties of (1-x)Pb(Zr1/2Ti1/2)O3-(x)Pb(Co1/3Nb2/3)O3 (x = 0.1-0.5) ceramics were investigated in this study. The dielectric properties were measured under compressive stress applied parallel and perpendicular to an electric field direction. The results clearly showed that the superimposed compression stress had pronounced effects on the dielectric properties of PZT-PCN ceramics. In general, with increasing compressive stress (applied parallel with the electric field direction) the dielectric constant of the ceramics increased, while the dielectric loss tangent decreased. Interestingly, the observed changes of the dielectric properties with the perpendicular compressive stress were opposite to those under the parallel stress. [ABSTRACT FROM AUTHOR]