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Piezoceramics with composition (1–z) [Bi0.5(Na0.84K0.16)0.5TiO3]0.96–0.04SrTiO3–zLiTaO3 (z = 0.00–0.030) were formulated by ordinary firing process following by rapid quenching treatment. Effect of LiTaO3 on the structural, electrical and energy-storage properties were analyzed. For the composition with molar ratio 0.025, room temperature large-field piezoelectric coefficient (Smax/Emax = d33*) of 885 pm/V at 3.6 kV/mm was recorded. Furthermore, for compositions z = 0.025 and 0.030, broad temperature stable dielectric constants and low losses from ~135 to 350 °C with a small variation of ± 15% was observed. Additionally, the energy density for z = 0.025 was ~0.60 J/cm3 in the broader temperature range of 75–125 °C, along with the energy-storage efficiency of greater than 70%. These observations suggest that the studied piezo-material compositions are promising for the ceramic actuators and capacitor applications.

In this study, pure cobalt ferrite (CoFe2O4) nanoparticles and europium doped CoFe2O4 (CoFe2−xEuxO4; x = 0.1, 0.2, 0.3) nanoparticles were synthesized by the precipitation and hydrothermal approach. The impact of replacing trivalent iron (Fe3+) ions by trivalent rare earth europium (RE-Eu3+) ions on the microstructure, optical and magnetic properties of the produced CoFe2O4 nanoparticles was studied. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra exposed the consistency of a single cubic phase with the evidence of Eu2O3 phases for x ≥ 0.2. FTIR transmittance spectra showed that, the all investigated samples have three characteristic metal-oxygen bond vibrations corresponding to octahedral B-site (υ1 and υ2) and tetrahedral A-site (υ3) around 415 cm−1, 470 cm−1 and 600 cm−1 respectively. XRD and energy dispersive X-ray spectroscopy studies affirmed the integration of RE-Eu3+ ions within CoFe2O4 host lattice and decrease of average crystals size from 13.7 nm to 4.7 nm. Transmission electron microscopy (TEM) analysis showed the crucial role played by RE-Eu3+ added to CoFe2O4 in reducing the particle size below 5 nm in agreement with XRD analysis. High resolution-TEM (HR-TEM) analysis showed that the as-synthesized spinel ferrite, i.e., CoFe2−xEuxO4, nanoparticles are single-crystalline with no visible defects. In addition, the HR-TEM results showed that pure and doped CoFe2O4 have well-resolved lattice fringes and their interplanar spacings matches that obtained by XRD analysis. Magnetic properties investigated by the vibrating sample magnetometer technique illustrated transformation of magnetic state from ferromagnetic to superparamagnetic at 300 K resulting in introducing RE-Eu3+ in CoFe2O4 lattice. At low temperature (~5 K) the magnetic order was ferromagnetic for both pure and doped CoFe2O4 samples. Substitution of Fe3+ ions in CoFe2O4 nanoparticles with RE-Eu3+ ions optimizes the sample nanocrystals size, cation distribution and magnetic properties for many applications.

In the present work, we investigate the effect of Ni doping on the crystallite size (Dhkl), optical band gap ($$E_{\text{g}}^{\text{opt}}$$), Photoluminescence emission (PL) behavior, as well as the photocatalytic degradation efficiency of methylene blue (MB) by ZnS nanoparticles (NPs) catalyst. Undoped and Ni-doped ZnS NPs at Ni concentrations of 2, 4, 6, 8, and 10% are successfully synthesized with average Dhkl from 2.75 to 3.76 nm by the sonochemical technique. X-ray diffraction (XRD) patterns and high-resolution transmission electron microscope (HRTEM) images of all samples exhibit pure zinc-blende type of ZnS cubic structure. The increase in Ni content up to 4% results in an increase in the Dhkl and unit cell volume (V) accompanied by a decrease in $$E_{\text{g}}^{\text{opt}}$$. Meanwhile, a further increase in Ni content above 4% leads to a decrease in Dhkl and V and an increase in $$E_{\text{g}}^{\text{opt}}$$. The deconvoluted PL emission spectrum of the undoped sample at the excitation wavelength (λex) of 325 nm reveals emission bands centered at 3.41, 3.16, 2.89, and 2.26 eV, which are red-shifted with increasing λex to 370 nm. It is observed that the PL emission intensity is quenched with increasing Ni content without any noticeable change in the PL peak position. Ni-doped ZnS catalyst with 2% Ni exhibits maximum photo-degradation efficiency of 52.23% with a rate constant of 0.00396 min−1. The obtained results demonstrate that Ni doping can tune the optical band gap and photocatalytic efficiency of ZnS NPs that make it applicable for many optoelectronic applications.

Charge carrier modulation of graphene-based field effect transistors (GFETs) is the key factor to utilize and enhance its fascinating properties for technological applicability. Here, we have demonstrated the gate-dependent tweaking of electrical properties of graphene devices by application of honey as a top gate dielectric. Electrical characterization of dual-gated GFET is elucidated at different top and back-gate voltages. A charge neutrality point is fine-tuned by varying the top gate voltage (Vtg) from + 3 to − 4 V. The change in carrier density is clearly observed from 3.66 × 1012 to 2.15 × 1011 cm−2 at + 3 to − 4 Vtg. The charge carrier mobility of gel-gated GFET is increased significantly to 5376 cm2/V ⋅ sec by increasing top-gate voltages up to − 4 V. Result demonstrates a cost-effective, facile and rapid fabrication of top-gated devices and suggest natural dielectric materials as good candidate to replace conventionally available gate dielectrics in FET technology.

This paper reports the microstrcure, optical and electrical characteristics of undoped and Cu doped CdTe nanostructured thin films prepared on glass substrates by electron beam evaporation technique. The Crystallographic study of X-ray diffraction shows that CdTe and Cu doped CdTe films crystallize in the form of a cubic zinc blende structure. Microstructure analysis reveals that as the Cu doping level increases, the average crystallite size increases, while the microstrian decreases due to the improvement of the crystallinty, thereby reducing defects. XRD and AFM investigations confirmed the nanostructure characteristic of undoped and Cu doped films. It was found that the optical band gap energy increases from 1.485 eV to 1.683 eV as the Cu concentration increases from 0 wt. % to 10 wt. %, which may be related to the Burstein-Moss effect. The refractive index is calculated from the Swanepoel envelope method and found to decrease with the increase of the Cu doping due to the decrease in the prolizability. Similarly, the extinction coefficient decreases with the increase of Cu in CdTe matrix. The dc electrical conductivity is found to increase with increasing Cu doping, which is attributed to the increase in the grain size, thereby reducing the scattering of the grain boundary. Furthermore, two conduction mechanisms of the carrier transport in nanostrcutured undoped and Cu doped CdTe films were observed. The low temperature dependence of the conductivity of undoped and Cu doped CdTe nanostructured films is explained based on Mott’s variable range hopping conduction mechanism model (VRH). Interestingly, the calculated values of hopping distance R, the hopping energy W and the the density of states at the Fermi level N(EF) are consistent with the Mott's VRH. Finally, Hall effect measurements show that all the films have p- type conduction behavior. Besides, the results show that as Cu doping level increases, the carrier concentration and the Hall mobility increase due to the decrease in grain boundary scattering with the increase in grain size. Accordingly, it can be concluded that by increasing the Cu doping level in the CdTe film, the conductivity is increased, thereby improving the performance of the CdTe absorber layer in the solar cell structure.

Cadmium telluride (CdTe) thin films were deposited by thermal evaporation method under base pressure 2 × 10−5 mbar on corning glass substrate. In this work, we study the effect of cadmium chloride (CdCl2) heat treatment in argon and oxygen (Ar + O2) atmosphere on the structural, morphological and optical properties of CdTe thin films to achieve high quality thin film absorber layer for solar cells applications. The structural characteristics were studied by X-ray diffraction (XRD). The microstructure parameters of the films such as average grain size (Davg), average lattice strain (eavg) and dislocation density (ρD) have been calculated via XRD line broadening analysis. XRD investigation revealed that, the samples show polycrystalline nature pronounced with cubic zinc blende structure with a strong preferentially (1 1 1) texture orientation. It has been found that the crystallinity of the films enhanced during (Ar + O2) annealing and CdCl2 heat treatment. The surface morphology of CdTe thin films was investigated by field emission scanning electron microscope (FE-SEM). XRD and FE-SEM results of CdCl2 treated films showed recrystallization and progressive increase in grain size. The optical properties of all samples were estimated using UV–vis–near-infrared (NIR) spectrophotometer. The Swanepoel envelope method has been employed to evaluate the various optical parameters of CdTe films such as refractive index and film thickness. The as-deposited films have a relatively high value of refractive index of 2.54, in contrast the CdCl2 treated films have a relatively low value of 2.1 in the whole wavelength range. The optical energy gap values slightly decrease from 1.56 eV for as-deposited films up to 1.54 eV for CdCl2 heat treated films. CdCl2 heat treatment in (Ar + O2) atmosphere is found to be a promising method to improve the physical properties of CdTe thin film solar cells.

In the present work, we synthesized CoxZn1-xFe2O4 spinel ferrite nanoparticles (x= 0, 0.1, 0.2, 0.3 and 0.4) via the precipitation and hydrothermal-joint method. Structural parameters were cross-verified using X-ray powder diffraction (XRPD) and electron microscopy-based techniques. The magnetic parameters were determined by means of vibrating sample magnetometry. The as-synthesized CoxZn1-xFe2O4 nanoparticles exhibit high phase purity with a single-phase cubic spinel-type structure of Zn-ferrite. The microstructural parameters of the samples were estimated by XRD line profile analysis using the Williamson–Hall approach. The calculated grain sizes from XRPD analysis for the synthesized samples ranged from 8.3 to 11.4 nm. The electron microscopy analysis revealed that the constituents of all powder samples are spherical nanoparticles with proportions highly dependent on the Co doping ratio. The CoxZn1-xFe2O4 spinel ferrite system exhibits paramagnetic, superparamagnetic and weak ferromagnetic behavior at room temperature depending on the Co2+ doping ratio, while ferromagnetic ordering with a clear hysteresis loop is observed at low temperatures (5K). We concluded that replacing Zn2+ ions with Co2+ ions changes both the structural and magnetic properties of ZnFe2O4 nanoparticles., This research was funded by Spanish “Ministerio de Economía y Competitividad” (MAT2016-78155-C2-1-R, MAT2013-40950-R, MAT2011-27573-C04-02 and FPI grant BES-2011-046948 to MSM.A.), “Gobierno del Principado de Asturias” (GRUPIN14-060) and FEDER.

The current work focused on studying the optical and structural properties of (CdS)1-x (ZnS)x thin films fabricated by thermal vacuum evaporation approach. The evaporation was implemented at room temperature from bulk samples synthesis by sintering approach. The energy gap, index of refraction, extinction coefficient and absorption coefficient were estimated from the experiment and employed in our theoretical model to estimate quantitatively the solar cell efficiency and short-circuit current density of CdS:ZnS/CdTe structure. The calculations of cell efficiency as well as short-circuit current density were computed on the bases of the optical losses caused by reflection at interfaces and absorption process occurred in the frontal charge-collecting and window layers and the recombination losses at front and back surface of CdTe. The XRD analysis showed that the intensity and position of predominant peak of CdS gradually changes with increasing the ZnS content indicating a success of forming CdS:ZnS alloy. The films exhibited direct band-to-band transitions and the optical energy gap increased from 2.40 eV to 3.10 eV with increasing of ZnS content up to x = 0.50. The short-circuit current density increased from 16.50 mA/cm2 to 21 mA/cm2 and the cell efficiency increased from 13.10% to 17.10% due to the increase of the ZnS content from x = 0 to x = 0.50.

In this study, low-dimensional (LD) MgO nanostructured thin films with three different morphologies, namely, nanowires (NWs), nanotubes (NTs) and nanoparticles (NPs) were fabricated by a vapor transport method on quartz and silicon substrates under optimum growth conditions. It was found that the deposition parameters have great influences on the morphology, optical, photoluminescent, electrical, gas sensing and magnetic behavior of the resulting products. X-ray diffraction analysis illustrated that all three LD MgO nanostructures have five expected Bragg peaks of cubic MgO phase purity with well crystalline nature. The morphology and diameter of LD MgO nanostructures were probed by scanning electron and transmission electron-microscopes. The optical band gap values for LD MgO nanostructure films varies between 3.65 eV and 3.95 eV depending on growth conditions. It was found that all MgO films exhibit two distinguishing PL peaks related to the near band edge luminescence of LD MgO nanostructures and defect levels produced by oxygen vacancies, respectively. It was found that the dependence of electrical conductivity on film morphology can be attributed to the defect levels produced by O2- ion vacancies during the synthesis process. NH3 gas sensing efficiency of LD MgO nanostructures with various morphologies were carried out at different operating temperatures from 25 °C to 300 °C. The MgO film with NWs structure has the highest sensor response value of 27 at 100 °C and the film with NPs structure has the lowest response value of 12 at 150 °C. Ferromagnetic order has been recorded for all morphologies at room temperature with clear hysteresis loop and different magnetic parameters depending on growth conditions. Thus, our results present a direct route for the growth of high-quality and diverse LD MgO nanostructures developed via vapor transport for many technological applications.

The low-temperature softening of the TO1 phonon of SrTiO3 (STO), which determines its incipient ferroelectricity, is known to be partially hindered either in the bulk under strong electric fields, or in thin STO films. Here we show, by terahertz (THz) reflectivity measurements, that a similar effect is produced in bulk STO and at zero static field by ultrathin metallic films on its surface, like a 10-nm-thick film of SrRuO3 (SRO), or the two-dimensional electron system (2DES) present at the interface with LaAlO3. In SRO/STO, the observed hardening is well explained by the depolarizing action of the SRO free electrons which follow adiabatically the ion motion. In LAO/STO, a weaker TO1 hardening could be detected by patterning the 2DES in the form of microstripes and using a polarized THz field parallel (E-) or orthogonal (E-) to the stripes. At 10 K, when TO1 is excited together with the free electrons by E-, its absorbance is harder by about 7 cm-1 than that measured when TO1 is coupled to the plasmon-polariton confined within the stripes, being excited by E-.

Cadmium sulphide (CdS) thin films have been grown on corning glass substrate by thermal evaporation technique under base pressure 2 × 105 mbar. In this study we investigate the influence of Cadmium chloride (CdCl2) heat treatment and argon and oxygen (Ar + O2) annealing on the structural, morphological optical and electrical properties of CdS thin films to achieve high quality thin films for solar cells applications. X-ray diffraction (XRD), Field Emission scanning electron microscope (FE-SEM) and UV–Vis-NIR spectrophotometer were used to confirm and investigate the different physical properties of CdS films. The quality of CdS thin films crystallinity including the average grain size (D avg), the average lattice strain (e ls) and the dislocation density (ρ D) were extracted via XRD line broadening analysis. XRD analysis revealed that the samples are polycrystalline in nature with a mixed (hexagonal + cubic) structure and the crystallinity of the films increases with both (Ar + O2) annealing and CdCl2 heat treatment. After (Ar + O2) annealing and CdCl2 heat treatment processes the mean values of the grain size indicating the grain growth of CdS films. The surface morphology of the CdS films was examined by (FE-SEM) analysis; which confirmed the nano-crystalline nature of the CdS films with uniform coverage of the substrate surface; The optical properties of as-deposited, (Ar + O2) annealed and CdCl2 treated CdS films were discussed in detail. The optical energy gap was calculated using Tauc plot extrapolation. It was found to be increased from 2.43 eV for as-deposited film to 2.45 for CdCl2 treated CdS film. Swanepoel method was employed to estimate the thicknesses and extract the refractive index of the CdS films. The Room temperature resistivity decreased from 13.4 Ω cm for as-deposited CdS film to 2 and 0.8 Ω cm for (Ar + O2) annealed and CdCl2 treated CdS films respectively. The CdCl2 treated CdS film has the highest figure of merit value of 29 × 10−4 Ω−1. The obtained results confirm that the CdCl2 heat treatment process in (Ar + O2) atmosphere can enhance the physical properties of CdS thin films as a promising window layer or buffer layer material for CdS/CdTe and Cu(In,Ga)Se2 solar cells.