Metal Oxides

The charge trapping properties of HfO2 thin films for application in charge trap memories are investigated as a function of high-temperature post-deposition annealing (PDA) and oxide thickness in the TaN/Al2O3/HfO2/SiO2/Si structure. The trap density (NT) in HfO2, extracted by simulating the programming transient, is in the 1019–1020 cm
3 range, and it is related to film thickness and PDA temperature. Diffusion
phenomena in the stack play a significant role in modifying NT in HfO2 and the insulating properties of the Al2O3 layer. The memory performances for 1030 C PDA are promising with respect to standard stacks featuring Si3N4.

— A surge arrester is used to protect the equipment of transmission and distribution systems from the effects of lightning and switching overvoltage. They are very reliable devices that are able to offer decades of service without causing any problems, if only they are properly designed and configured. This paper examines the effects of lightning strokes in an electrical network and attempts to analyze two different frequency dependent (FD) models of metal oxide surge arrester following the IEEE standards. The main objective of this paper is to create a suitable model of tower which considers propagation of surge, airgap leaders of two types and footing resistance phenomenon. It is found that with the identification of overvoltage, the rate of failure of substation can be determined. This is done through a comprehensive study that used different strategies. It was found that all of the strategies generated the similar transient overvoltage. It is concluded that the range of values obtained are considered to comply with the standards.

This study provides an in-depth investigation into low-cost and no-cost substrate release mechanisms that allow gas metal arc weld 3-D printed ER4043 aluminum and ER70S-6 steel parts to be removed from a reusable print substrate with minimal energy. Aluminum oxide, boron nitride, and titanium nitride coatings were evaluated as possible substrate release agents for aluminum printing. Additionally, the in situ formation of substrate release agents such as intermetallics and oxides were tested for both aluminum and steel printing. Testing was performed with a modified Charpy impact tester to remove 3-D printed metal parts from an 1100 aluminum or A36 low carbon steel print substrate to assess the impact energy required for removal. Specimen porosity was measured prior to sectioning and microstructural analysis, hardness traverses were measured across the specimens, and the elastic and shear moduli of the parts were analyzed via ultrasonic methods. All of the employed substrate release mechanisms minimized weld penetration and, in some instances, formed a brittle phase with the print substrate that allowed the specimens to be removed with minimal impact energy. These results thus provide methods with the removal of metal 3-D printed parts from print substrates with no specialized tooling or equipment conducive to distributed manufacturing.

Never before electricity has been generated out of metal oxides without using any light (UV/IR), acid or alkali but it has been achieved by adding few drops of water on nano porous metal oxide based Hydroelectric cell (HEC) at room temperature. Electricity generation has been validated and unified for six different metal oxides based on the principle of water dissociation at oxygen deficient nonporous pellet. Presence of oxygen vacancies at the surface of all metal oxide samples has been confirmed by Raman and Photoluminescence spectroscopy.  Oxide based HEC delivers maximum power ~16.6 mW in 4.48 cm2 area of SnO2 cell with peak current 22.2 mA, approximately 2.075 times higher than reported 8 mA current in ferrite based HEC. Water chemidissociation at metal oxide surface was found to be reinforced predominantly by electronegativity of metal cations and defect structures at nanoporous surface. Divergent peak current values ranging from 22.2 mA to 1.1 mA were obtained depending on internal resistance, grain boundary nature, water molecule dissociation capability and nanopores connectivity of different oxides. Slow diffusion of ions in certain metal oxides pertaining to highly impeding grain boundaries have reduced current that confirmed by dielectric and impedance spectroscopy. Metal oxide HEC provides an ecofriendly, cost effective and portable green energy source with almost no running cost.

We report the results of the studies on crystal structure, electronic structure and dielectric properties of Er 1-x La x FeO 3 (ELFO) (x ¼ 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) orthoferrites synthesized by co-precipitation method. Rietveld refinement of the XRD data confirms the orthorhombic crystal structure for all the samples. The study of Fe L 3,2-edge X-ray Absorption spectroscopy shows the presence of Fe-ions in 3 þ valence state in all the samples. Investigations on the dielectric behavior of ELFO samples over the wide frequency range of 20 Hz to 5 MHz show the increment in the dielectric constant with La-doping. ErFeO 3 has the lowest value of dielectric constant whereas LaFeO 3 has the highest value of dielectric constant among all the samples. Effect of grain and grain boundary contribution on the dielectric behavior is studied using complex dielectric permittivity. The observed colossal dielectric behavior in LaFeO 3 is attributed to the combined contribution from the intrinsic dielectric constant of the material and that due to the modification in the microstructure.

Metal oxides (MOs) nanostructures, as visible light active photocatalysts, are widely used in applications such as solar energy conversion, biocidal coating, and environmental remediation. This dissertation investigates the morphological, structural, optical, and photocatalytic properties of some visible light active MO photocatalysts, WO3, CuxO (x = 1, 2), and α-Fe2O3 nanostructures fabricated by the dynamic shadowing growth for above mentioned applications.
Dye adsorption and photodegradation property of WO3 nanorods (NRs) has first been studied. The porous and amorphous WO3 NRs are observed to exhibit superior methylene blue (MB) adsorption capability in aqueous solution due to its large specific surface area and active surface functionality. The adsorption of MB on the surface of WO3 NRs are well described by Langmuir isotherm behavior. Photocatalytic MB degradation with WO3 NRs under UV irradiation is observed to be relatively higher than that under visible light.
The solar water splitting reaction in a photoelectrochemical (PEC) cell and photocatalytic dye degradation behavior of CuxO (x=1,2) NR arrays have been studied under visible light irradiation. Both single phase Cu2O and CuO, and mixed phase Cu2O/CuO polycrystalline NRs are observed to exhibit excellent visible light induced photocatalytic activity for both cationic (MB) and anionic (methyl orange) dye degradation. When used as a photocathode, they also show good PEC performance, especially for the mixed phase Cu2O/CuO NRs. The maximum stable photocurrent density is observed to be -0.24 mA/cm2 under a simulated solar light (AM 1.5G) at an applied bias potential of -0.5 V (versus Ag/AgCl reference electrode). About 20% and 44% incident photon-to-current conversion efficiency are obtained at incident light wavelengths λ = 500 nm and 400 nm respectively.
Finally, both MB degradation and bactericidal activities are studied for the α-Fe2O3 NR arrays and films under the ambient light conditions. The α-Fe2O3 NR arrays annealed at 350 °C exhibit an enhanced bactericidal performance in inactivating E. coli O157:H7, when compared to α-Fe2O3 film. Mathematical models are used to correlate the observed photocatalytic activities.

Ferrite spinels are metal oxides used in a wide variety of applications, many of which are controlled by the diffusion of metal cations through the metal oxide lattice. In this work, we used density functional theory (DFT) to examine the diffusion of Fe, Co, and Ni cations through the Fe3O4 , CoFe2O4 , and NiFe2O4 ferrite spinels. We apply DFT and crystal field theory to uncover the principles that govern cation diffusion in ferrite spinels. We found that a migrating cation hops from its initial octahedral site to a neighboring octahedral vacancy via a tetrahedral metastable intermediate separated from octahedral sites by a trigonal planar transition state (TS). The cations hop with relative activation energies of Co ≈< Fe < Ni; the ordering of the diffusion barriers is controlled by the crystal field splitting of the diffusing cation. Specifically, the barriers depend on the orbital splitting and number of electrons which must be promoted into the higher energy t2g orbitals of the tetrahedral metastable intermediate as the cations move along the minimum energy pathway of hopping. Additionally, for each diffusing cation, the barriers are inversely proportional to the spinel lattice parameter, leading to relative barriers for cation diffusion of Fe3O4 < CoFe2O4 < NiFe2O4. This results from the shorter cation-O bonds at the TS for spinels with smaller lattices, which inherently possess shorter bond lengths, and consequently higher system energies at their more constricted TS geometries.

Potassium sodium niobate (KNN) is a potential candidate to replace lead zirconate titanate in sensor and ac-tuator applications but there are many fundamental science and materials processing issues to be understood before it can be used commercially, including the influence of composition and processing atmosphere on the conduction mechanisms and functional properties. Consequently, KNN pellets with different K/Na ratios were sintered to 95% relative density in air and N 2 using a conventional mixed oxide route. Oxygen vacancies (V O ••) played a major role in the semi-conduction mechanism in low p(O 2) for all compositions. Impedance spectro-scopy and thermo-power data confirmed KNN to be n-type in low p(O 2) in contradiction to previous reports of p-type behaviour. The best piezoelectric properties were observed for air-rather than N 2-sintered samples with d 33 = 125 pC/N and k p = 0.38 obtained for K 0.51 Na 0.49 NbO 3 .

Theoretical and experimental data on the synthesis,
structure, properties, and applications of phosphate tungsten
bronzes accumulated to date are systematized. Attention is
focussed on interrelations between structural features and electro-
physical properties of these compounds. Prospects for practical
applications of phosphate tungsten bronzes are discussed. The
bibliography includes 138 references.

The effect of surface Fe-doping on the structural, photocatalytic, optical properties of polydisperse anatase and rutile TiO2 has been comprehensively studied. The TiO2 surface has been modified by Fe3+ ions through the adsorption from the diluted FeCl3 aqueous solutions. The prepared powders were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area analysis, temperature programmed desorption techniques (TPD), Raman and UV-vis spectroscopy. With the adsorption isotherms of Fe3+ ions from FeCl3 aqueous solutions, it was found that adsorption of Fe3+ ions on the anatase surface is twice more efficient compared to that one on the rutile. The XRD and Raman spectroscopy measurements confirmed the monophase structure of the Fe-doped TiO2 with a subtle change in the lattice parameters and O/Ti ratio compared to the undoped counterparts. The red shift of the UV absorption edge has been registered for the Fe-doped anatase resulting in a significant decrease of its bandgap from 3.2 to 2.7 eV. The photocatalytic destruction of organic dye Safranin-T over the prepared Fe-doped TiO2 under UV irradiation has been investigated. The influence of various energetically nonequivalent active sites on the surfaces of anatase and rutile on their photoactivity is considered.

This paper demonstrates fabrication and characterization of thin-film Ti-TiO 2-Pd based
Metal-Insulator-Metal (MIM) diodes on flexible substrates. MIM diodes with contact areas of 9 μm 2 and 48 μm 2 were fabricated, and a comparison is made for their DC and RF performances. The current-voltage characteristics of the fabricated diodes show strong non-linearity. The diodes are also tested for microwave circuit applications such as detection, frequency multiplication and mixing over a frequency range of 1-18 GHz. The devices show strong second harmonic frequency multiplication for fundamental frequencies of 1-10 GHz. Details of DC characteristics, RF rectification, mixing and multiplication using MIM diodes are presented.

Free-standing two-dimensional (2D) nanomaterials have attracted extensive and growing research interest owing to their exotic physical and mechanical properties, which have enabled their applications in electronics, optoelectronics, electrochemical and biomedical devices. Current synthesis strategies rely largely on top-down approaches such as etching and exfoliation. Among bottom-up approaches in literature, there lacks a systematic understanding of the mechanisms of 2D crystal growth, unlike one-dimensional nanomaterials whose growth mechanisms have been well documented. To date, the growth design of free-standing 2D nanomaterials has remained a case-by-case practice. This review focuses on the bottom-up solution synthesis of free-standing 2D nanomaterials and summarizes the general mechanisms and empirical methodologies that can lead to 2D crystal growth. A brief outlook on the development of synthesis and application of solution-grown 2D nanomaterials is also presented.

In this study, MgO nanoparticles are applied to
control the initial burst release by modification of matrix
structure, thereby affecting the release mechanism. The
effects of MgO nanofiller loading on the in vitro release of
a model drug are investigated. Surface topography and
release kinetics of hydrogel nanocomposites are also
studied in order to have better insight into the release
mechanism. It was found that the incorporation of MgO
nanofillers can significantly decrease the initial burst
release. The effect of genipin (GN) on burst release was
also compared with MgO nanoparticles, and it was found
that the impact of MgO on burst release reduction is more
obvious than GN; however, GN cross-linking caused
greater final release compared to blanks and nanocomposites.
To confirm the capability of nanocomposite
hydrogels to reduce burst release, the release of b-carotene
in Simulated Gastric Fluid and Simulated Intestinal Fluid
was also carried out. Thus, the application of MgO nanoparticles
seems to be a promising strategy to control burst
release.

This study aims to observe the changes in the structural characterization and physical properties of calcium-praseodymium-cobalt oxide thermoelectric materials with graphene doping. Structural characterizations were examined via X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), and Fourier Transformed Infrared Spectroscopy (FTIR) measurements. Temperature-dependent thermal conductivity and Seebeck coefficient were measured by Physical Properties Measurement System (PPMS). In the SEM images, the samples were observed to be crystalline and showed enhanced fusion with graphene doping. There were no impurities in the samples according to the EDX results and all sample components were observed in these results. The properties and structures of the bonds in the XRD results were also visible in the FTIR results. According to the PPMS results, it was determined by measurements and graphs that graphene doping provided a significant and changeable effect to the thermoelectric materials. Published by the AVS.

Journal of Vacuum Science & Technology A 37, 061201 (2019); https://avs.scitation.org/doi/pdf/10.1116/1.5121253?class=pdf

<<< Final published version for free until October 27th:  https://authors.elsevier.com/a/1XhJP3IQMPAqsP  >>>
Monitoring of hazardous gases is nowadays very important, since the urbanized environment is more subject to this kind of pollutants. Therefore, a capillary network of small gas sensors capable to check the quality of the environment is necessary. Metal oxide gas nanosensors are small economic devices that can be easily integrated in any context, however they unfortunately lack of selectivity. We present an approach using hydrothermally grown nickel oxide nanowires working at different temperatures and creating a virtual sensors array, thus exploiting the thermal fingerprints (sensor response as a function of temperature) of the gases. Using only one nanostructured material (nickel oxide) and different machine learning techniques, the system can easily discriminate any of 7 harmful gases (C 2 H 5 OH, H 2 , CO, LPG, CO 2 , NH 3 and H 2 S, all of them reducing gases) with an accuracy of 100%. Furthermore, the nanosensor also evaluates the gas concentration with an average error lower than 15%. Our results show that, exploiting thermal fingerprints from a temperature gradient, single metal oxide resistive nanosensors can efficiently discriminate specific hazardous gases.

Zinc oxide (ZnO, n-type) and copper oxide (CuO, p-type) nanowires have been synthesized and preliminarily investigated as inno- vative materials for the fabrication of a proof-of-concept thermoelectric device. The Seebeck coefficients, electrical conductivity and thermoelectric power factors (TPF) of both semiconductor materials have been determined independently using a custom experimental set-up, leading to results in agreement with available literature with potential improvement. Combining bundles of ZnO and CuO nanowires in a series of five thermocouples on alumina leads to a macroscopic prototype of a planar thermoelectric
generator (TEG) unit. This demonstrates the possibility of further electric devices.

Metal oxides are of great technological importance in environmental remediation and electronics because of their capability to generate charge carriers when stimulated with required amount of energy. The promising arrangement of electronic structure, light absorption properties, and charge transport characteristics of most of the metal oxides has made possible its application as photocatalyst. In this article definition of metal oxides as photocatalyst, structural characteristics, requirements of the photocatalyst, classification of photocatalysts and the mechanism of the photocatalytic process are discussed.

Concrete has been used as a construction material for building roads and housing structures since early as 6500 BC. It has been modified from the volcanic ash compound used in the early ages to the compound using in the modern era a mixture with cement, aggregates, additives, accelerators and retarders. The aim of this study is to investigate the effect of chemically modified concrete with titanium dioxide (TiO2) and zinc oxide (ZnO) micro particles on compressive strength, tensile strength and workability. The particle sizes used are 0.22-0.23 μm titanium dioxide (TiO2) particles and 1-8 μm zinc oxide (ZnO). The ratios for M25 concrete is 1: 1: 2 the metal oxides are added in 1%, 2%, and 5% in respective to the cement weight to test its properties. Test cubes are casted to test the compressive strength from 7 days curing and 28 days curing. Experiments reveal that the compressive strength of the chemically enhanced M25 concrete is much higher than conventional M25 concrete is much ...

A unique metal oxide semiconductor sensor (MOS) array detector with eight sensors was designed and fabricated in
a PTFE chamber as an interface for coupling with multicapillary gas chromatography. This design consists of eight transfer lines with
equal length between the multicapillary columns (MCC) and sensors. The deactivated capillary columns were passed through each
transfer line and homemade flow splitter to distribute the same gas flow on each sensor. Using eight ports flow splitter design helps
us to equal the length of carrier gas path and flow for each sensor, minimizing the dead volume of the sensor’s chamber and increasing
chromatographic resolution. In addition to coupling of MCC to MOS array detector and other consideration in hardware design,
modulation of MOS temperature was used to increase sensitivity and selectivity and data analysis was enhanced with adapted Gaussian
apodization factor analysis (GAFA) as a multivariate curve resolution algorithm. Continues air sampling and injecting system
(CASI) design provides fast and easily applied method for continues injection of air sample with no additional sample preparation.
Analysis cycle time required for each run is less than 300 sec. The high sample load and sharp injection with the fast separation by
MCC decrease the peak widths, and improve detection limits. This homemade customized instrument is an alternative to other time
consuming and expensive technologies for continuous monitoring of outgassing in air samples.

Micro-nanorod structures of zinc oxide (ZnO) have been successfully synthesized via a simple and low-cost hydrothermal method. ZnO solutions with different concentrations of 0.05 and 0.1 M were prepared using zinc nitrate tetrahydrate and hexamethylenetetramine precursors. They were dissolved in aquades and stirred before the hydrothermal process at 95 C for 4 hours in an oven. Extensive characterizations using scanning electron microscope (SEM) and X-ray diffraction (XRD) were conducted on ZnO powder samples. SEM results showed that hexagonally shaped ZnO micro-nanorods were formed with diameters ranging from hundreds of nanometers to several micrometers. The ZnO sample synthesized at 0.05 M was observed to have a better surface morphological structure than the 0.1 M sample. In addition, XRD measurements confirmed that samples exhibited a hexagonal crystal structure of ZnO. Moreover, the calculated crystallite sizes of ZnO using the Debye-Scherrer equation using the full-width half maxima of the XRD peaks were 25.153 nm for the 0.05 M sample and 28.707 nm for the 0.1 M sample. The most prominent growth of ZnO had 101 plane orientation or nonpolar a-plane followed by nonpolar 100 m-plane and 002 polar c-plane orientations. This study offers a simple and low-cost route to produce high-quality ZnO micro-nanorods for use in various electrical and optical devices. Abstrak Kajian Morfologi dan Struktural Batang Mikro-nano ZnO Disintesis Menggunakan Metode Hidrotermal dengan Biaya Rendah. Struktur batang mikro-nano seng oksida (ZnO) berhasil disintesis menggunakan metode hidrotermal sederhana dan dengan biaya yang rendah. Larutan ZnO dengan konsentrasi berbeda yaitu 0,05 dan 0,1 M disiapkan menggunakan prekursor seng nitrat tetrahidrat dan heksamethilentetramin. Prekursor tersebut dilarutkan di dalam akuades dan diaduk sebelum proses hidrotermal berlangsung pada suhu 95 C selama 4 jam di dalam oven. Sampel serbuk ZnO dikarakterisasi secara ekstensif menggunakan mikroskop elektron (SEM) dan difraksi sinar-x (XRD). Hasil analisis SEM menunjukkan bahwa batang mikro-nano ZnO berbentuk heksagonal dihasilkan dengan rentang diameter dari ratusan nanometer hingga beberapa mikrometer. Sampel ZnO yang disintesis dengan konsentrasi 0,05 M teramati memiliki struktur morfologi yang lebih baik dibandingkan sampel 0,1 M. Pengukuran XRD mengkonfirmasi bahwa sampel sesuai dengan ZnO dengan struktur kristal heksagonal. Lebih lanjut, perhitungan estimasi rata-rata ukuran kristal ZnO menggunakan persamaan Debye-Scherrer dengan puncak XRD lebar penuh pada setengah maksimum didapat yaitu sebesar 25,153 nm untuk sampel 0,05 M dan 28,707 nm untuk sampel 0,1 M. Pertumbuhan ZnO paling dominan yaitu pada orientasi bidang 101 atau bidang nonpolar a diikuti orientasi bidang nonpolar m 100 dan bidang polar c 002. Kajian ini menawarkan metode yang simpel dan dengan biaya rendah untuk menghasilkan batang mikro-nano ZnO yang memiliki potensi untuk diaplikasikan dalam berbagai peralatan elektronik dan optik.

A B S T R A C T TiO 2 nanofibers (TNF) are prepared by electrospinning method and they are decorated over the surface of Li[Ni 0.8 Co 0.15 Al 0.05 ]O 2 (LNCA) cathodes at three different ratios. The structural, electrochemical, and thermal characteristics of TNF-decorated LNCAs are compared with pristine LNCA. The TNF-decorated LNCA electrodes demonstrate better cycleability and specific capacity than those of the pristine LNCA. Under the current density of a C/10 rate, 1 wt% TNF-decorated LNCA delivers 89.2% and 81.4% of capacity retention at room temperature and elevated temperature, respectively. The onset temperature of thermal decomposition is also shifted towards higher temperature for TNF-decorated LNCA electrodes than pristine LNCA electrodes.

The composition dependence of oxygen vacancy formation energies (EV) in the complex perovskite SrxLa1−xMnyAl1−yO3, a material system demonstrated to significantly outperform ceria for solar thermochemical (STC) fuel production, was investigated using a combination of ab initio and experimental
techniques. Density functional theory calculations predict that EV as a function of composition spans a large range from near 0 to over 3 eV under standard conditions and exhibits trends consistent with equilibrium oxygen nonstoichiometries we
determined using thermogravimetric analysis. Our findings show that the strong sensitivity of EV to composition arises from the composition dependence of the Fermi energy relative to the O 2p band center. From these results, we identify the
range of EV particularly suited for STC cycles for a given set of reduction and oxidation reaction conditions and present a materials design strategy for the optimization of EV through compositional tuning.