Presence Of More Oxygen Vacancies Research Articles

Bipolar resistive switching behavior of bilayer β-Ga2O3/WO3 thin film memristor device

This article investigates the bipolar resistive switching behavior of bilayer Au/β-Ga2O3/WO3 thin film (TF)/Ag heterostructure memristor device deposited using an electron beam evaporation technique. The purity of the deposited sample was confirmed by the XRD and FESEM with EDS characterizations. The root mean square roughness(RRMS) of single layer WO3 TF and heterolayer of Ga2O3/WO3 TF were obtained from the AFM analysis as 4.56nm and 2.20nm, respectively. The presence of more oxygen vacancies in WO3 sample was also confirmed by the XPS analysis. The optical measurement of the sample also revealed a bandgap of ~ 4.35eV for β-Ga2O3 TF and ~ 3.66eV for WO3 TF. Moreover, the bilayer Au/β-Ga2O3/WO3 TF/Ag heterostructure memristor device demonstrated bipolar resistive switching behavior with a good resistance ratio of ~ 182, an endurance of 300 cycles, and a data retention of 103s at room temperature. The device also yielded a low SET power of 1.17mW (at 1.74mA, +0.67V) and a low RESET power of 2.50mW (at 7.16mA, – 0.35V). The logarithmic current-voltage (I-V) relationship revealed that the switching behavior of the memristor device is mainly dominated by Ohmic conduction in LRS as well as Child’s square law, TCLC and Ohmic conductions in HRS. With the above parameters, the Au/β-Ga2O3/WO3 TF/Ag memristor device has the potential for future RRAM applications.

Effects of CeO2 doping on the mechanical, infrared radiative, and thermophysical properties of Pr2Zr2O7 ceramics for potential thermal protective coatings

A series of Ce4+-doped Pr2Zr2O7 ceramics were produced using a solid reaction method to utilize novel ceramic materials as potential candidates for thermally protective coatings. The effects of Ce4+ doping on the phase composition and mechanical, infrared radiative, and thermophysical properties were studied in detail. The results indicated the good phase stability and sintering resistance of the Pr2(Zr1−xCex)2O7 ceramics. Moreover, Ce4+-doped Pr2Zr2O7 bulk materials exhibited higher infrared emissivity (0.904) at wavelengths of 3–5 μm and 1000 °C for Pr2(Zr0.5Ce0.5)2O7) owing to the introduction of impurity energy levels. Pr2(Zr0.7Ce0.3)2O7 exhibited an appropriate average coefficient of thermal expansion of 12.4 × 10−6 K−1 and a low thermal conductivity of 1.14 W m−1 K−1 at 1000 °C, owing to the reduction of lattice energy and the presence of more oxygen vacancies and substitution atoms.

Exploring the Impact of Oxygen Vacancies in Co/Pr-CeO2 Catalysts on H2 Production via the Water-Gas Shift Reaction.

In this study, we utilized various Pr-doped CeO2 catalysts (Pr=5, 10, 20, and 30 wt.%) as a support medium for the dispersion of cobalt (Co) nanoparticles, aiming to investigate the impact of oxygen vacancies on the water-gas shift (WGS) reaction. Different characterization techniques were employed to understand the insights into the structure-activity relationship governing the performance of Pr doped ceria supported Co catalysts towards WGS reaction. Our findings reveal that Co/Pr-CeO2 catalysts at optimum Pr loading (10 wt.%) exhibit a superior CO conversion (88 %) facilitated by the presence of more oxygen vacancies induced by Pr doping into the CeO2 lattice, as opposed to the performance of the pure Co/CeO2 catalytic system. It was also found that the highest activity was obtained at increased intrinsic oxygen vacancies and strong synergy between Co and Pr/CeO2 support, fostering more favorable CO activation at the interfacial sites, thus accounting for the observed enhanced activity.

Improvement in ammonia gas sensing properties of La doped MoO3 thin films fabricated by nebulizer spray pyrolysis method

In the present work, different doping concentration (0, 1, 2, 3, 4 and 5 wt%) of Lanthanum (La) doped Molybdenum trioxide (MoO3) thin films were prepared using low cost Nebulizer spray pyrolysis (NSP)technique. The crystalline, morphology, optical and gas sensing properties of thin films were investigated. The presence of monoclinic MoO3 structure was confirmed through the XRD investigation for all the samples with highest crystallite of 61 nm was observed for 2 wt% La doped MoO3 thin film. The surface morphology of the produced thin films exhibits a reticulate nanofibrous mesh shape with increased particle size and porosity on addition of 2% La dopants in MoO3.The UV–Vis results showed the band gap values for the prepared thin films in the range 3.12–3.26 eV and the minimum bandgap was observed for the 2 wt% of La doped MoO3 thin film. Also the PL results confirmed the presence of more oxygen vacancies for the 2 wt% of La doped MoO3 thin film. The NH3 gas sensing study was conducted for the prepared films at room temperature, the 2 wt% of La doped MoO3thin film exhibits a maximum sensor response of 900, faster response times (28 s and 2.9s) compared to other fabricated devices. The results suggest that the 2% La doping in MoO3 could be an optimum doping concentration for the preparation of commercial NH3 gas sensors.

Au-Deposited Ce0.5Zr0.5O2 Nanostructures for Photocatalytic H2 Production under Visible Light

Pure Ce0.5Zr0.5O2 and Au (0.1–1.0 wt.%)-deposited Ce0.5Zr0.5O2 nanomaterials were synthesized via hydrothermal and non-aqueous precipitation methods using gold acetate as a chloride-free Au precursor. The synthesized nanostructures exhibited enhanced photocatalytic activity for hydrogen production via aqueous bioethanol photoreforming under visible light. Different characterization tools such as powder XRD, HRTEM, FT-IR, DR UV-vis, XPS and N2 gas adsorption were used to analyze the physicochemical properties of the synthesized photocatalysts. The band gap value was lowered from 3.25 eV to 2.86 eV after Au nanoparticles were deposited on the surface of Ce0.5Zr0.5O2. The 1.0 wt.% Au-deposited Ce0.5Zr0.5O2 sample exhibited the highest photocatalytic activity for H2 production (3210 μmol g−1) due to its low band gap, the presence of more oxygen vacancies and its porous character. The EIS results reveal that the deposition of 1.0 wt.% Au nanoparticles is responsible for the highest charge separation efficiency with an increased lifetime of photogenerated e−/h+ species compared to the other samples. In addition, the presence of plasmonic Au is responsible for the effectiveness of the electron trap in improving the rate of H2 formation.

Engineering oxygen vacancies in perovskite oxides by in-situ electrochemical activation for highly efficient nitrate reduction

Perovskite oxides have emerged as a new category of catalysts for NO3RR, yet their low intrinsic catalytic activity results in unsatisfactory performance. Oxygen vacancy engineering has recently been found to be effective for improving the NO3RR performance of perovskite oxides. Herein, a novel and efficient strategy of electrochemical activation for in-situ oxygen vacancies (OVs) creation in perovskite oxide La0.9FeO3-δ was reported. The results showed that the NO3−-N removal rate increased 2.6-fold on activated La0.9FeO3-δ in comparison to pristine La0.9FeO3-δ. The enhanced NO3RR performance was attributed to the presence of more OVs, which served to increase the adsorption energy of NO3− while also promoting atomic H* formation for NO3−-N hydrogenation. Furthermore, a continuous experiment lasting 240 h found the activated La0.9FeO3-δ exhibited extremely high stability. Additionally, we demonstrated that the electrochemical activation method was applicable to other typical perovskite oxides, such as LaCoO3, indicating its generalizability. This study provides a simple and scalable approach for the preparation of a high-performance perovskite oxide-type electrocatalysts for NO3RR.

High porosity and oxygen vacancy enriched WO3-x thin films for room temperature hydrogen gas sensors

Due to the increase in demand for hydrogen in several fields, sensors that detect the presence of hydrogen gas more precisely even at room temperature (30 °C) are required for its safe use. In this work, we report the hydrogen gas sensing performance of the WO3-x thin film deposited at different oxygen partial pressures (10%, 15%, and 20%) onto SiO2/Si substrate using a radio frequency (RF) magnetron sputtering technique. To study the hydrogen gas sensing performance, Ag/WO3-x/Ag test-device is fabricated by depositing interdigitated Ag electrodes onto the WO3-x gas sensing layer via thermal evaporation. The performance of the obtained sensors is investigated at different hydrogen concentrations (100 ppm–300 ppm) and different operating temperatures (30°C–300 °C). WO3-x thin films deposited at 10% of pO2 show a maximum response of 3.40% for 100 ppm of H2 gas even at room temperature, which is due to the high crystallinity, high porosity, and the presence of more oxygen vacancies. The oxygen vacancies that are created during the reactive magnetron sputtering would enhance the hydrogen adsorption and hence superior hydrogen sensing results achieved. Herein, the response and recovery times are measured in most of the sensing conditions and the sensing mechanism has been discussed.

Ce-doped indium oxide nanozymes with peroxidase-like activity induced by cerium–indium synergy for colourimetric detection of H2O2

InCex has a higher catalytic efficiency due to the presence of more oxygen vacancies and higher Ce3+ content, which can provide a wide range of binding sites for TMB, and also can accelerate the electron transfer rate.

Photophysical investigation of the formation of defect levels in P doped ZnO thin films

Zinc oxide (ZnO) offers a major disadvantage of asymmetry doping in terms of reliability, stability, and reproducibility of p-type doping, which is the main hindrance in realization of optoelectronic devices. The problem is even more complicated due to formation of various native defects in unintentionally doped n-type ZnO. The realization of p-type conductivity in doped ZnO requires an in-depth understanding of the formation of an effective shallow acceptor, as well as donor-acceptor compensation. Photophysical properties such as photoconductivity along with photoluminescence (PL) studies have unprecedentedly and effectively been utilized in this work to monitor the evolution of various in-gap defects. Phosphorus (P) doped ZnO thin films have been grown by RF magnetron sputtering under various Ar to O2 gas ratios to investigate the effect of O2 on the donor-acceptor compensation by comprehensive photoconductivity measurements supported by the PL studies. Initial elemental analyses indicate presence of abundant zinc vacancies (VZn) in O-rich ambience. The results predict that P sits in the zinc (Zn) site rather than the oxygen (O) site causing the formation of PZn–2VZn acceptor-like defects, which compensates the donor defects in P doped ZnO films. Photocurrent spectra uniquely reveal presence of more oxygen vacancies (VO) defects states in lower O2 flow, which gets compensated with an increase in the O2 flow. Successive photocurrent transients indicate probable presence of more VO in the films grown with lower O2 flow and more VZn in higher O2 flow. Overall the photosensitivity measurements clearly present that O-rich ambience expedites the formation of acceptor defects which are compensated, thereby lowering the dark current and enhancing the ultraviolet photosensitivity.

Transformation of phase and heterojunction type by using HAc-adsorbed Bi(NO3)3 as a Bi source

Generally, preparing high-efficiency heterojunction photocatalysts via a facile room-temperature route is attractive from the perspective of energy and labor saving. Herein, by using dried and glacial acetic acid (HAc)-adsorbed bismuth nitrate, instead of Bi(NO3)3·5H2O, as a Bi source, a β-Bi2O3/Bi5O7I heterojunction with well dispersed flowery hierarchical architecture was synthesized, which endows it with high surface area, open channels and good light harvest. More importantly, the change of the precursor achieved a successful transformation for both of phase and heterojunction type, i.e. from type-Ⅰ BiOI/[Bi6O5(OH)3](NO3)5·3H2O (labeled as BiOI/BBN) to Z-scheme β-Bi2O3/Bi5O7I heterojunction. Since both β-Bi2O3 and Bi5O7I are visible light responsive, β-Bi2O3/Bi5O7I exhibited improved visible-light photocatalytic activity for the degradation of tetracycline (TC) and malachite green (MG) with apparent reactant rate (kapp) values about 10 and 11 times higher than those of BiOI/BBN. Besides, the presence of more oxygen vacancies also contributed to the enhancement in photocatalytic performance.

HCHO Catalytic Oxidation Performance over Cerium Containing MCM-41 Type Mesoporous Materials Supported Ag Catalysts

Understanding the effects of cerium in the formaldehyde (HCHO) catalytic oxidation performance over Ag/MCM-41 catalysts, cerium modified MCM-41 mesoporous materials (Ce-MCM-41) with different ratios were synthesized by one-step hydrothermal method. The activity test results showed that Ag/Ce-MCM-41 with the ratio of Si:Ce = 1:1 catalysts could reach complete HCHO oxidation above 130 °C. These Ag/Ce-MCM-41 catalysts with different Si:Ce ratios were characterized by IR, SXRD, XRD, TEM, UV–Vis, Raman, XPS and H2-TPR. The results show that the interactions between Ag and Ce, between Ce and SiO2 in our Ag/Ce-MCM-41 are enhanced due to adding Ce to MCM-41. The presence of Ce-SiO2 interaction dramatically enhances the reducibility of surface-capping oxygen of CeO2, promotes the bulk oxygen migration to the surface and creates oxygen vacancies in the bulk region of CeO2 and the presence of more oxygen vacancies can facilitate the anchoring and dispersing of Ag particles, which lastly improves the interaction between Ag and Ce. In addition, the amount of formed oxygen vacancy is the highest when the Si:Ce = 1:1. The activation of surface oxygen is closely related to oxygen vacancy, O2 may be transformed into the highly active O2−. The high active O2− in surface adsorbed oxygen promotes the activation of oxygen molecules and enhanced the catalytic oxidation of HCHO.

Defect controlled adsorption/desorption kinetics of ZnO nanorods for UV-activated NO2 gas sensing at room temperature

In this work, the adsorption/desorption kinetics of ZnO nanorods with two different levels of defects for UV-activated NO2 gas sensing at room temperature is investigated. It is found that the pristine ZnO has higher sensitivity than the thermally annealed ZnO and the consequence can be attributed to the presence of more oxygen vacancies that act as adsorption sites. Based on the Langmuir adsorption model, the adsorption and desorption constants are determined to be 2.7 × 10–5 ppb−1 s−1 and 3.2 × 10–3 s−1, respectively, for the pristine ZnO; and 1.5 × 10–5 ppb−1 s−1 and 2.1 × 10–3 s−1, respectively, for the annealed ZnO. Both kinetic constants for the pristine ZnO are higher, which manifests its higher sensitivity. The determination of kinetic constants could provide valuable information for better understanding of nanomaterials based gas sensors.

Preferential oxidation of carbon monoxide in a hydrogen-rich gas stream over supported gold catalysts: the effect of a mixed ceria–zirconia support composition

The effect of the ceria–zirconia (CeO2–ZrO2) support composition of a gold (Au) catalyst (Au/Ce1−xZrxO2, where x is the molar ratio), prepared by deposition–precipitation, on its catalytic activity was investigated in the preferential carbon monoxide (CO) oxidation. A maximum CO conversion level of 94% was obtained with 1% by weight Au/Ce0.75Zr0.25O2 at 50 °C, while the presence of water and carbon dioxide in the feed stream had only a slight effect on the catalytic activity. Catalyst characterizations were performed to investigate the effect of the Ce:Zr molar ratios on the redox properties and physicochemical properties of the obtained Au/CeO2–ZrO2 catalysts. It was found that a certain amount of Ce in the Au/CeO2–ZrO2 catalyst promoted solid solution formation and facilitated the activity of Au3+ and Au0 nanoparticles with a small crystallite size. The enhanced catalytic activity of Au/Ce0.75Zr0.25O2 was attributed to the presence of more oxygen vacancies, easier reducibility, and appropriate amount of Au3+ species, as confirmed by Fourier transform Raman spectroscopy and hydrogen-temperature-programme reduction analyses, respectively. The catalytic activity showed a high stability for a long period of time (28 h).

Bi3+ engineered black anatase titania coupled with graphene for effective tobramycin photoelectrochemical detection

Photoelectrochemical (PEC) sensing is an efficient method for trace tobramycin (TOB) detection, which poses a serious threat to public health. Therefore, this work developed a photoelectric nanohybrid, Bi3+ doped black anatase titania that was decorated with reduced graphene oxide (Bi3+/B-TiO2/rGO), which exhibited excellent PEC activity. Compared with pristine TiO2, B-TiO2, and B-TiO2/rGO, the PEC response of as-prepared Bi3+/B-TiO2/rGO was respectively 40.0-fold, 4.0-fold and 2.4-fold higher under visible light illumination. The photocurrent of B-TiO2 was enhanced compared with TiO2 due to the existence of oxygen vacancies (OVs), while the increased photocurrent of Bi3+/B-TiO2/rGO was ascribed to the presence of more OVs and an improved charge transfer rate. The proposed PEC aptasensor for the sensitive detection of TOB was constructed by combining Bi3+/B-TiO2/rGO with a specific aptamer. Under the optimal experimental conditions, the Bi3+/B-TiO2/rGO-based aptasensor exhibited a low detection limit of 0.33 pg/mL (S/N = 3) with a wide linear response range from 0.001 ng/mL to 50 ng/mL. The prepared Bi3+/B-TiO2/rGO may find potential applications as a photoactive material in PEC aptasensors.

Room-temperature synthesis of yellow TiO2 nanoparticles with enhanced photocatalytic properties

Anatase titanium dioxide (TiO2) nanoparticles have been successfully synthesized through a simple approach at low temperature. Particularly yellow TiO2 is well obtained at room temperature (25 °C). TiO2 samples are characterized by XRD, Raman, XPS, TEM, BET, UV–Vis, and Zeta Potential. The zeta potential value of TiO2 samples can be tuned from −26.8 to +13.6 mV by different reaction temperature. The yellow TiO2 has more oxygen vacancies and Ti3+ compared with other samples, which reduces the band gap from 3.1 to 2.9 eV and made the conduction band positively shift about 0.2 eV. Electrochemical impedance spectroscopy and Mott-Schottky plots reveal that the yellow TiO2 nanocrystals had higher carrier density and better conductivity for electron transfer. According to the XPS analysis, the Ti3+ content in different samples is 8.1%, 7.8%, 6%, 1%, and zero, respectively. The decomposition rate of Rhodamine B under UV light and visible light was 99.7% and 70.0%, and the NO removal efficiency in 5 min is 84.8% for yellow TiO2, respectively. The enhanced photocatalytic performance can be attributed to the presence of more oxygen vacancies in yellow TiO2 that can act as traps to reduce the recombination of e−/h+ pairs.

X-ray photoelectron spectroscopic studies of CeO2 thin films deposited on Ni-W (100), c-Al2O3 (0001) and Si (100) substrates

The oxidation states of CeO2 films, deposited on biaxially textured Ni-W(100), c-Al2O3(0001) and Si(100) substrates, were investigated by using X-ray photoelectron spectroscopy (XPS). The CeO2 films were deposited by RF magnetron sputtering under same deposition conditions. X-ray diffraction (XRD) studies of the films revealed that preferred (200) orientation of CeO2 was observed in case of Ni-W substrate while (111) orientation on Al2O3 and Si substrates. The O1s and Ce3d spectra reveal that the films mostly consist of Ce4+ oxidation states with ∼72.6%, 74.7% and 74.9% on Ni-W, Al2O3 and Si substrates, respectively. The less Ce4+ content in case of Ni-W substrate has been attributed to the migration of oxygen atoms from film to the metallic substrate. The decrease of O2p states in the valence band spectra also in support with the presence of more oxygen vacancies in CeO2/Ni-W compared to that in other substrates. Further, the position of valance band maxima is almost identical (∼2.6 eV) for all the deposited films indicating that all films are n-type in nature.

Manganese doped CeO2-ZrO2 catalyst for elemental mercury oxidation at low temperature

To develop an efficient catalyst used for elemental mercury (Hg0) oxidation at low temperature in coal-fired power plant, Mn doped CeO2-ZrO2 catalysts were synthesized and studied concerning their performance on Hg0 oxidation. Under the atmosphere of simulated coal-fired flue gas, Ce0.47Zr0.23Mn0.3O2 (CZM0.3) exhibited the best activity at 150°C. It was found that Hg0 oxidation performance over CZM0.3 was determined by the flue gas compositions. Gaseous O2 was important for the oxidation process, because it regenerated the lattice oxygen and replenished the chemisorbed oxygen, which boosted Hg0 oxidation. HCl and NO could improve the Hg0 oxidation efficiency slightly, respectively. In N2+HCl+O2 atmosphere, the Hg0 oxidation efficiency observed was significantly higher than those in N2+O2 or N2+HCl atmosphere. Compared with the effects of HCl on the Hg0 oxidation activity, the similar results were obtained for effects of NO on the performance Hg0 oxidation. NO could facilitate the Hg0 oxidation activity, especially in the presence of O2. In N2+SO2 atmosphere, SO2 inhibited Hg0 oxidation. In N2+O2+SO2 atmosphere, SO2 promoted Hg0 oxidation probably due to the generation of SO3. Water vapor inhibited Hg0 oxidation, because it diminished the HCl and Hg0 adsorption. The characterization of the CZM0.3 indicated that the higher activity of the catalyst was most likely attributed to the presence of more oxygen vacancies, enhanced Mn4+/(Mn4++Mn3+) ratio and more surface adsorbed oxygen on the catalyst surface.

One Dimensional Manganese Oxides As Cathode Materials in Li-Ion Batteries: The Impact of Physicochemical Properties on Electrochemical Performance

Hollandites(OMS-2) are an intriguing class of energy storage materials with a tunnel structure permitting one-dimensional insertion and deinsertion of ions and small molecules along the c direction. Previous research demonstrated the ability to control crystal size of AgxMn8O16 by manipulation of Ag content over a range of 1.0 ≤ x ≤ 1.8 where lower Ag content was accompanied by small crystallite size and higher silver content demonstrated large crystallite size (Figure 1a-c) Notably, we recently observed a seven-fold increase in delivered capacity for Li/AgxMn8O16 electrochemical cells (160 versus 23 mAh/g) upon a seemingly small change in silver content (x ~1.1(L-Ag-OMS-2) and 1.6(H-Ag-OMS-2)) (Figure 1f). This led us to characterize the structure and defects of the silver hollandite nanorods through the combined use of local (atomic imaging, nanodiffraction, electron energy-loss spectroscopy) and bulk (synchrotron based x-ray diffraction, thermogravimetric analysis) techniques. Selected area diffraction and high resolution transmission electron microscopy show a structure consistent with that refined by synchrotron based XRD (NSLS II), however the Ag occupancy varies significantly even within neighboring channels. Both local (EELS) and bulk measurements (TGA) indicate a greater quantity of oxygen vacancies in L-Ag-OMS-2, resulting in lower average Mn valence relative to H-Ag-OMS-2. Electron energy loss spectroscopy shows a lower Mn oxidation state on the surface relative to the interior of the nanorods (Figure 1d, e). Considering Ag occupancy and oxygen vacancies, the average Mn valence can be estimated to be about Mn3.7+ for H-Ag-OMS-2 and Mn3.5+ for L-Ag-OMS-2 nanorods, respectively. The significance of the oxygen vacancies can be best understood through consideration of the crystallographic structure of silver hollandite. Silver hollandite has a body-centered tetragonal structure where the Ag is surrounded by eight MnO6 octahedra, forming a tunnel with a dimension of ~0.51 nm in the ab plane which extends along the [001] direction. Though there is a small gap (less than 0.06 nm) in the a or b direction, in the ab plane all directions are basically closed by MnO6 octahedra. Therefore, if the nanorod has no defects, the diffusion of Li ions in ab plane would be limited. The oxygen vacancies and MnO6 octahedra distortion may open the MnO6 octahedra walls, facilitating Li ion diffusion in the ab plane (Figure 1g, h). Thus, the higher capacity of the L-Ag-OMS-2 samples may be due to not only to the smaller crystallite size but also to the presence of more oxygen vacancies as compared to the H-Ag-OMS-2 samples. Thus the oxygen vacancies and MnO6 octahedra distortion are assumed to open the MnO6 octahedra walls, facilitating Li diffusion in the ab plane. In-situ transmission electron microscopy was used to probe lithium transport and phase evolution in silver hollandite, Ag1.63Mn8O16, nanowires by nanoscale imaging, diffraction and EELS spectroscopy. Additionally, the findings were further rationalized through density functional theory (DFT). These results indicate both crystallite size and surface defects are significant factors affecting battery performance. Figure 1 caption: Typical TEM bright field images from (a) H-Ag-OMS-2 and (b) L-Ag-OMS-2. (c) HRTEM image of L-Ag-OMS-2 nanorod. (d) Relative composition map calculated from EELS spectrum across L-Ag-OMS-2 nanorod. (e) HAADF of H-Ag-OMS-2 along [001], Ag (red) and Mn (green) indicated. (f) Discharge curves of Li/AgxMn8O16 (L-Ag-OMS-2, H-Ag-OMS-2) batteries. (g) Conceptual perspective along [001], with Ag (red), Mn (green), O (yellow), (h) with oxygen vacancy facilitating ab plane diffusion. Figure 1

Characterization of B site codoped LaFeO3 nanoparticles prepared via co-precipitation route

LaFe1−x−y Co x Pd y O3 [(x, y) = (0, 0), (0.40, 0), (0.38, 0.05)] nanoparticles were synthesized via a co-precipitation route using ammonium hydroxide, sodium hydroxide and ammonium carbonate as the precipitant and calcination at different temperatures to study the compositional driven structural changes in lanthanum ferrites. Analysis of X-ray diffraction (XRD) patterns confirms the formation of single-phase perovskite structure and existence of orthorhombic Pnma symmetry for calcined powders. Field emission scanning electron microscope (FESEM) observations show that Pd-doped powders yield finer particles along with narrower particle size distribution compared with LaFeO3 and LaFe0.6Co0.4O3. Moreover, using ammonia as the precipitant leads to a smaller mean particle size of powders compared to NaOH, as well as significant difference in morphology of the particles. Raman analysis reveals that both Co and Pd atoms substitute Fe site in perovskite structure with shifting of phonon modes. Comparing Raman spectra demonstrates the presence of more oxygen vacancies in Pd-doped perovskites. It can be concluded from the results that Pd is successfully incorporated into the perovskite structure by co-precipitation method.

High electrical conductivity in oxygen deficient BaSnO3 films

BaSnO3(BSO) films were grown epitaxially on MgO substrate under a wide range of pressures (from 20 to 0.03 Pa) by pulsed laser deposition. The structural, electrical, and optical properties of films were investigated. X-ray diffraction characterization reveals that the film unit cell volume increases gradually with decreasing the growth oxygen pressure while preserving the perovskite structure. The transport property measurement suggests that the film resistivity was tuned with variation from nearly insulator to metallic conductor by controlling the grown oxygen pressure, which was attributed to the presence of more oxygen vacancies in films during deposition. Remarkably, the lowest room-temperature resistivity of 8.07 × 10−4 Ω cm was obtained in film grown in 0.3 Pa without any dopant, with the carrier concentration and mobility of 7.60 × 1020 cm−3 and 10.81 cm2/V respectively. All the BSO films have high transmittance of more than 80% in the visible range regardless of the oxygen pressure, whereas the optical band gaps increase from 3.49 to 3.70 eV, which was explained by the Burstein-Moss effect.