Erbium upconversion luminescence from sol–gel derived multilayer porous inorganic perovskite film

Erbium-doped barium titanate (BaTiO3:Er) xerogel film with a thickness of about 500 nm was formed on the porous strontium titanate (SrTiO[Formula: see text] xerogel film on Si substrate after annealing at 800[Formula: see text]C or 900[Formula: see text]C. The elaborated structures show room temperature upconversion luminescence under 980 nm excitation with the photoluminescence (PL) bands at 523, 546, 658, 800 and 830 nm corresponding to 2H[Formula: see text]4I[Formula: see text], 4S[Formula: see text]I[Formula: see text], 4F[Formula: see text]I[Formula: see text] and 4I[Formula: see text]4I[Formula: see text] transitions of trivalent erbium. Raman and X-ray diffraction (XRD) analysis of BaTiO3:Er\porous SrTiO3\Si structure showed the presence of perovskite phases. Its excellent up-conversion optical performance will greatly broaden its applications in perovskite solar cells and high-end anti-counterfeiting technologies.

Hydrothermal synthesis of ABi2Ta2O9Aurivillius phase: A comparative study of A-site cation size on structure, dielectric, optical properties

In this study, the double-layered Aurivillius phases CaBi2Ta2O9 (CBT) and PbBi2Ta2O9 (PBT) were prepared through a hydrothermal route with NaOH as a mineralizer. XRD analysis confirmed that the CBT and PBT compounds were successfully formed and adopted an orthorhombic crystal structure with an [Formula: see text]21am symmetry. Le Bail refinements of XRD data indicated that the unit cell volume of CBT was smaller than PBT and is associated with the smaller ionic radius of Ca[Formula: see text] compared to Pb[Formula: see text]. The surface morphology of both samples, as determined using SEM, demonstrated plate-like grains with anisotropic grain growth. It was found that the different ionic radii of [Formula: see text]-site cations (Ca[Formula: see text] and Pb[Formula: see text] strongly affected the structural, optical and electrical properties of the Aurivillius phase. The occupation of smaller Ca[Formula: see text] cations induced a higher structural distortion, which resulted in higher bandgap ([Formula: see text] energy and ferroelectric transition temperature ([Formula: see text] of CBT, compared to those of PBT.

Photocatalytic degradations of JWS-type kinetics

Photocatalytic degradation kinetics of Jurlewicz–Weron–Stanislavsky (JWS) type has been identified. Experimental data are taken from previous published works, and fitted with the JWS relaxation function as well as that of the Havriliak–Negami (HN) model. All experimental data can fit with either model fairly good. From the fitting parameters, the Jonscher indices are calculated and Jonscher diagram is plotted for the chemical kinetics of photocatalytic degradations. This work suggests that material parameters of photocatalysts can be well defined in the sense of fractional calculus.

Effect of sintering temperature on structural, magnetic, dielectric and optical properties of Ni–Mn–Zn ferrites

Spinel ferrite Ni[Formula: see text]Mn[Formula: see text]Zn[Formula: see text]Fe2O4 was prepared by a conventional ceramic process followed by sintering at three different temperatures (1050[Formula: see text]C, 1100[Formula: see text]C and 1150[Formula: see text]C). X-ray diffraction (XRD) investigations stated the single-phase cubic spinel structure and the FTIR spectra revealed two prominent bands within the wavenumber region from 600 cm[Formula: see text] to 400 cm[Formula: see text]. Surface morphology showed highly crystalline grain development with sizes ranging from 0.27 [Formula: see text]m to 0.88 [Formula: see text]m. The magnetic hysteresis curve at ambient temperature revealed a significant effect of sintering temperature on both coercivity ([Formula: see text] and saturation magnetization ([Formula: see text]. Temperature caused a decrease in DC electrical resistivity, while the electron transport increased, suggesting the semiconducting nature of all samples and that they well followed the Arrhenius law from which their activation energies were determined. The values of Curie temperature ([Formula: see text] and activation energy were influenced by the sintering temperature. Frequency-dependent dielectric behavior (100 Hz–1 MHz) was also analyzed, which may be interpreted by the Maxwell–Wagner-type polarization. The UV–vis–NIR reflectance curve was analyzed to calculate the bandgap of ferrites, which showed a decreasing trend with increasing sintering temperature.

Electrical transport properties of V2O5-added Ni–Co–Zn ferrites

Frequency-dependent dielectric constant, dielectric loss, AC conductivity values and complex impedance spectra of V2O5-added Ni–Co–Zn ferrites (Ni[Formula: see text]Co[Formula: see text]Zn[Formula: see text]Fe2O4 + [Formula: see text]V2O5, where [Formula: see text] = 0, 0.5, 1 and 1.5 wt.%) have been investigated at room temperature. The dielectric properties of the samples follow the Maxwell–Wagner polarization model. An inverse relationship was found between dielectric constant and AC electrical resistivity for all the samples. The dielectric constants decreased with the addition of V2O5, while the electrical resistivities of V2O5-added Ni–Co–Zn ferrites are found to be larger than that of pure Ni–Co–Zn ferrite. The AC conductivity was reduced with the addition of V2O5 to Ni–Co–Zn ferrite at lower-frequency region. However, AC conductivity shows a sharp increase at higher-frequency region, which could be attributed to the enhancement of electron hopping between the Fe[Formula: see text] and Fe[Formula: see text] ions in the ferrite matrix due to the activity of the grains. The complex impedance spectroscopy results through Cole–Cole/Nyquist plot have demonstrated a single semicircular arc. It indicates that conduction mechanism takes place predominantly through the grain/bulk property, which could be ascribed to the larger grain size of V2O5-added Ni–Co–Zn ferrites.

Pyroelectric properties of 91.5Na0.5Bi0.5TiO3–8.5K0.5Bi0.5TiO3 lead-free single crystal

The dielectric and pyroelectric performances of 91.5Na[Formula: see text]Bi[Formula: see text]TiO3–8.5K[Formula: see text]Bi[Formula: see text]TiO3 lead-free single crystal were investigated. The depolarization temperature of the crystal is about 153[Formula: see text]C. Among the [Formula: see text]001[Formula: see text], [Formula: see text]110[Formula: see text], and [Formula: see text]111[Formula: see text] crystallographic orientations, the [Formula: see text]111[Formula: see text]-oriented crystal possesses the highest pyroelectric coefficient and the largest figures of merit, and the values of [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]are 5.63× 10[Formula: see text] C/m2 ⋅ K, 0.06 m2/C, and 21.5 [Formula: see text]Pa[Formula: see text] for the [Formula: see text]111[Formula: see text]-oriented crystal at room temperature. The [Formula: see text]and [Formula: see text]exhibit weak frequency dependence in the range of 100–300 Hz. With the increase of the temperature, the value of [Formula: see text]increases, while the [Formula: see text] value of [Formula: see text] decreases from 18[Formula: see text]C to 103 [Formula: see text]C.

Synthesis of ZnO nanorods for piezoelectric resonators and sensors

Efficiency of the piezoelectric chemisensors may be considerably enhanced by use of zinc oxide nanorods as sensing elements. ZnO nanorod arrays being good piezoelectric materials possess large surface area, which provides extra benefits for chemisorption and photodetection. Highly oriented nanorod arrays are typically prepared onto highly crystalline substrates, whereas the nanorods growth onto metal contacts meets significant technological difficulties. In this paper, we report on carbothermal, electrochemical, and hydrothermal techniques of ZnO nanorod arrays synthesis on metal contacts. The optical and structural properties of the obtained nanorods were studied using scanning electron microscopy, X-ray diffraction (XRD), Raman spectroscopy, and luminescence spectroscopy. A reliable technique was developed for obtaining ohmic contact with the grown nanorods. I–U curves of prepared contact were studied. Carbothermal synthesis made it possible to obtain the most crystallinely perfect, homogeneous, and dense arrays of nanorods and control the concentration of point defects by changing the synthesis parameters over a wide range. The electrochemical synthesis demonstrated excellent results for synthesis of ZnO nanorods on the surface of resonator electrodes.

Effect of lithium carbonate modification on the ferroelectric phase transition diffusion in lead ferroniobate ceramics

The paper discusses the features of the effect of modification with lithium carbonate on the dielectric dispersion of lead ferroniobate ceramics. The modifier has been previously shown to change the ways of the recrystallization sintering and therefore reduce the sintering temperature of the ceramics, increase their average grain size, and improve their dielectric and piezoelectric properties. In this study, the emphasis is placed on the analysis of the diffusion effects of the ferroelectric phase transition upon such modification considered from the standpoint of the chemical specifics of the modifier and its location in the structure of the parent compound.