Type Semiconductivity Research Articles

Theoretical investigation of CdIn2S4 : A possible substitute for CdS in CuIn1−xGaxSe2 -based photovoltaic devices

Herein we report a theoretical investigation based on density-functional theory (DFT) calculations devoted to the nature of charge carriers in $\mathrm{CdI}{\mathrm{n}}_{2}{\mathrm{S}}_{4}$. Our simulations led to unambiguous results concerning the origin of $n$-type semiconductivity and its magnitude in this material. Namely, the calculated defect formation energies demonstrate that the cadmium substoichiometry is more favorable than the indium one to account for $n$-type conductivity. Moreover, the anionic vacancies would not be the driving force of the occurring processes but a sulfur-poor atmosphere has to be privileged compared to a sulfur-rich one to favor the formation of $\mathrm{CdI}{\mathrm{n}}_{2}{\mathrm{S}}_{4}$ with understoichiometry in Cd(II) and thus achieve a higher concentration of free electrons at room temperature.

Photoelectrochemical properties of CaWO4 synthetized by chemical route. Application to the phenobarbital electro-photocatalysis

Abstract The semiconducting properties of the Scheelite CaWO4, synthesized by nitrate route, were investigated by the photocurrent technique and capacitance measurements in acidic solution (pH ∼ 5). CaWO4 crystallizes in the tetragonal symmetry with a large optical gap (4.88 eV) and a low electrical conductivity (σ300K = 2.63 × 10−5 Ω−1 cm−1). The photo-electrochemical characterization shows n type semi conductivity with a wide depletion length (∼110 nm). The Nyquist representation, measured in the range (10−3–105 Hz), indicates a predominant bulk contribution with a constant phase element which takes its origin from the electrode roughness. The results of CaWO4 are relevant for its applications to electro-photocatalysis. The conversion percentages of Phenobarbital reached respectively 54% and 66% with electro-catalysis and electro-photocatalysis under UV/C irradiation. The oxidation obeys to a first order kinetic with a rate constant of 1.98 × 10−3 min−1 and 2.7 × 10−3 min−1, respectively.

Nonlinear electrical properties and giant dielectric response in Na1/3Ca1/3Y1/3Cu3Ti4O12 ceramic

A new isostructural CaCu3Ti4O12–type perovskite, Na1/3Ca1/3Y1/3Cu3Ti4O12, was successfully synthesized using a solid state reaction method. In this material, Ca–sites in the CaCu3Ti4O12 structure were occupied by Na+, Ca2+, and Y3+ ions, each at a level of ∼33.3 at.%. The dielectric and non –Ohmic properties were investigated. The mean grain sizes of the Na1/3Ca1/3Y1/3Cu3Ti4O12 ceramics sintered at 1100–1110°C for 10–15h were of about ≈15μm. All of the sintered ceramics exhibited high dielectric permittivities (ε′) and low loss tangents (tanδ). By optimizing sintering conditions, a high ε′≈1.2×104 and low tanδ≈0.04 were achieved. Na1/3Ca1/3Y1/3Cu3Ti4O12 ceramics can exhibit nonlinear current-voltage behavior. The existence of Cu+, Cu3+, and Ti3+ ions was confirmed using an X–ray Absorption Near Edge Structure (XANES) and X–ray photoelectron spectroscopic analyses. The n–type semiconductivity inside the grains was primarily caused by the presence of Ti3+ ions, while the existence of Cu+ and Cu3+ may also have an effect on conduction inside the grains. Using impedance and admittance spectroscopy analyses under different conditions (i.e., varying frequency, temperature and DC bias), the giant dielectric response and nonlinear electrical properties could be well explained based on the internal barrier layer capacitor model.

Antiferromagnetism atT>500Kin the layered hexagonal ruthenateSrRu2O6

We report an experimental and computational study of the magnetic and electronic properties of the layered Ru(V) oxide $\mathrm{SrR}{\mathrm{u}}_{2}{\mathrm{O}}_{6}$ (hexagonal, $P\overline{3}1m)$, which shows antiferromagnetic order with a N\'eel temperature of 563(2) K, among the highest for $4d$ oxides. Magnetic order occurs both within edge-shared octahedral sheets and between layers and is accompanied by anisotropic thermal expansivity that implies strong magnetoelastic coupling of Ru(V) centers. Electrical transport measurements using focused-ion-beam--induced deposited contacts on a micron-scale crystallite as a function of temperature show $p$-type semiconductivity. The calculated electronic structure using hybrid density functional theory successfully accounts for the experimentally observed magnetic and electronic structure, and Monte Carlo simulations reveal how strong intralayer as well as weaker interlayer interactions are a defining feature of the high-temperature magnetic order in the material.

Microstructures and properties of low-chromium high corrosion-resistant TiC–VC reinforced Fe-based laser cladding layer

Effects of 3.0wt.%Cr and/or 0.25wt.%CeO2 on microstructures and properties of TiC–VC reinforced Fe-based cladding layer were investigated by using X-ray diffractometry (XRD), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). Passive films formed on cladding layers surface were investigated by using X-ray photoelectron spectroscopy (XPS) and Mott–Schottky analysis. Results showed that phases of cladding layers were α-Fe, γ-Fe, TiC, VC and TiVC2. There were no obvious effects of adding 3.0wt.%Cr and/or 0.25wt.%CeO2 on cladding layers phases. The microstructure of the cladding layer with 3.0wt.%Cr and 0.25wt.%CeO2 was lath martensite and retained austenite. Microhardness of the cladding layer with 0.25wt.%CeO2 decreased slightly. Microhardness and corrosion resistance of the cladding layer with 3.0wt.%Cr and 0.25wt.%CeO2 both increased, the corrosion resistance increased 7.33 times while the EIS Nyquist spectrum transformed into a capacitive arc. The passive film formed on the cladding layer without Cr and CeO2 was Fe3O4 which displayed p type semiconductivity. The passive film formed on the cladding layer with 3.0wt.%Cr and 0.25wt.%CeO2 was composed of Fe(OH)3 and Cr(OH)3, which displayed n and p type semiconductivity respectively.

The Effect of Water Vapor on Thermal Oxide Grown on Inconel 690

Nickel based alloys are well considered materials for uses in high temperature applications. Inconel 690 is the one of outstanding candidate with the superior properties. The aim of this report is to present the influence of water vapor on thermal oxide film. Inconel 690 was oxidized under dry and wet atmosphere at 900°C for 30 hours. The oxidized samples were characterized by SEM/EDS, Raman spectroscopy, and photoelectrochemical technique. The results illustrated that typical thermal oxides grown on alloy composed of Cr, Fe, Ni, in forms of Cr2O3, NiFe2O4, NiCr2O4, Fe2O3, Fe2–xCrxO3and/or solid solution of NiFe2O4−NiCr2O4. The presence of water vapor affected on oxide morphology, its stoichiometry, and also semiconducting behavior. Oxide film grown under water vapor atmosphere show the homogeneity. Water vapor promoted the predominated oxide of Cr2O3with n−type semiconducting. Moreover the characterization revealed the effect of surface orientation on oxidation mechanism in case of sample which oxidized in oxygen atmosphere.

Electronic Structure and Optical Property of Phosphorus Doped Semiconducting Graphene Nanoribbons

The electronic structure and optical property of phosphorus doped semiconducting graphene nanoribbons were calculated by using the density functional theory. Energy band structure and optical spectra were considered to show the special electronic structure of phosphorus doped semiconducting graphene nanoribbons. Our results showed that the Fermi energy of phosphorus doped semiconducting graphene nanoribbons entered in the conduction bands, and that the optical coefficient depend on the width of armchair graphene nanoribbons. It is concluded that the phosphorus doped semiconducting graphene nanoribbons behave p type semiconducting. Therefore, our results have a great significance in developing nanomaterial for fabricating the nanophotovoltaic devices.

Evaluation of metallic and semiconducting single-walled carbon nanotube characteristics

The nature of the mixed electronic type metallic (M-) and semiconducting (S-) single-walled carbon nanotubes (SWNTs) synthesized by current methods has posed a key challenge for the development of high performance SWNT-based electronic devices. The precise measurements of M- to S-SWNT ratio in as-grown or separated samples are of paramount importance for the controlled synthesis, separation and the realization of various applications. The objective of this review is to provide comprehensive overview of the progress achieved so far for measuring the M/S ratio both on individual and collective levels of SWNT states. We begin with a brief introduction of SWNT structures/properties and discussion of the problems and difficulties associated with precise measurement of the M/S ratio, and then introduce the principles for obtaining distinguished signals from M-and S-SWNTs. These techniques are classified into different groups based either on the single/ensemble detection of SWNT samples or on the principles of techniques themselves. We then present the M/S ratio evaluation results of these methods, with emphasis on scanning probe microscopy (SPM)-based detection techniques. Finally, the prospects of precise and large-scale measurement of M/S ratio in achieving controlled synthesis and understanding growth mechanism of SWNTs are discussed.

High-temperature semiconducting cubic phase ofBiFe0.7Mn0.3O3+δ

${\text{BiFe}}_{0.7}{\text{Mn}}_{0.3}{\text{O}}_{3+\ensuremath{\delta}}$ with space group $R3c$ is reported to go through two phase transformations, first to the orthorhombic paraelectric phase $(Pbnm)$ and finally to cubic perovskite structure with space group $Pm\overline{3}m$. A discontinuity in volume and enthalpy shown by thermal analysis revealed that both transitions were first order. Electrical conductivity measurements demonstrated that the material remains semiconducting also in the high-temperature cubic state. The conductivity and the temperature of the two phase transitions were shown to be strongly influenced by the partial pressure of oxygen and a $p$-type semiconductivity was suggested. Finally, oxygen hyperstoichiometry $(\ensuremath{\delta})$ of ${\text{BiFe}}_{0.7}{\text{Mn}}_{0.3}{\text{O}}_{3+\ensuremath{\delta}}$ was demonstrated.

Synthesis, crystal structure, microstructure and electrical behaviour of systems Sr1−xLaxSnO3 and SrSn1−xNixO3 (X ≤ 0·10)

Undoped and donor doped SrSnO3 is used as a humidity sensor. The sensitivity increases with increasing donor substitution. Similarly acceptor doped SrSnO3 has high value of electrical conductivity. In the present investigation, compositions with X ≤ 0·10 were synthesised in the systems Sr1−xLaxSnO3 and SrSn1−xNixO3 by solid state ceramic route to explore the possible applications as a capacitor or sensor materials. All the compositions were found to form solid solutions and have orthorhombic crystal structure. Average grain size is in the range 0·7–1·2 μm. Densities of all the samples are >90% of the theoretical density. The electrical conduction behaviour of these systems was investigated by the measurement of Seebeck coefficient α and DC conductivity in the temperature range 300–1100 K. These materials exhibit p type semiconduction. Conduction occurs by diffusion of doubly positively charged oxygen vacancies. Electrical resistivity of all these three compositions is very high up to 300°C. These materials may be used as capacitor materials over a considerable range of temperature above room temperature.

Preparation of electrodeposited thin films of nickel-iron alloys on mild steel for alkaline water electrolysis. Part I: studies on oxygen evolution

Thin films of electrodeposited nickel-iron alloys containing 15.6–38.5% Fe were obtained on mild steel at 30°C. The films were uniform, porous and p -type semiconducting. Cyclic voltammograms showed the formation of a single quasireversible redox couple, Ni(III)/Ni(II), on each film electrode in the anodic region (0–0.6 V) in 1M KOH. Oxygen evolution studies demonstrated a substantial increase in the electrocatalytic activity of Ni in the presence of 17.9% Fe additive. The Tafel slopes were 40 ± 5 mV decade −1 . The reaction order with respect to OH − ion concentration was observed to be approximately 2. The results suggest that the oxygen evolution reaction occurs on the oxidized Ni(III) sites on the electrode surface with a mechanism involving an electrochemical adsorption of OH − ions in a fast step and their subsequent electrochemical desorption in the slow step.

Physicochemical properties and catalytic behavior of manganese oxides

Two series of manganese oxides have been prepared by the thermal decomposition of manganese carbonate and oxalate under vacuum (300–900°C temperature). The kinetics of aqueous H 2O 2 decomposition on these oxide surfaces have been studied. The reaction was found to be first order with respect to [H 2O 2]. Catalytic activities were found to be decreasing with the increasing temperature of decomposition. X-ray diffraction studies of the powdered samples show that the samples contain mainly two types of structures. NaCl(MnO) and calcinite (Mn 3O 4). Infrared spectra show a characteristic band at 796 cm −1 for the sample obtained by the decomposition of both Mn oxalate and Mn carbonate at 750 and 900°C. Samples prepared at other temperatures show similar characteristic bands, i.e., at 1124, 604, and 484 cm −1, etc. Surface areas vary from 112 to 4 m 2/g. Pores are mainly of cylindrical shape. There is an agglomeration of the particles as the temperature of decomposition is increased. Conductivity measurements indicate that most of the samples show p- type semiconductivity.

Photovoltaic effects of metal–chlorophyll-a–metal sandwich cells

The microcrystalline chlorophyll−a film prepared by the method of electrodeposition is shown to have strong photovoltaic effects. The photovoltaic cell (M1‖Chl‖M2) has lamellar arrangement with the Chl−a film sandwiched between two metal electrodes. With dissimilar electrodes of different work functions, φM, the cell usually exhibits a dark rectification behavior. A large forward bias current is seen when the metal with a lower φM is the negative electrode. The rectification is small when the same metal is used as both electrodes. A blocking contact or Schottky barrier is evidently present at the Chl−a‖metal junction particularly fo the metal having a low φM. A p−type semiconduction in Chl−a is implicated. In the photovoltaic mode, cells such as (Al‖Chl‖Hg) and (Al‖Chl‖Au) have an open circuit voltage ranging from 200−500 mV. The power conversion efficiency for these cells is on the order of 10−3% which is among the highest in photovoltaic cells using organic materials. The direction of the photovoltaic current and the shape of its action spectrum are strongly dependent on the electrode materials. The blocking contact at the Chl−a‖metal junction is primarily responsible for the photovoltaic activity of the cell. When this blocking contact is established at the directly illuminated electrode the action spectrum closely matches the absorption spectrum of the Chl−a film. An inverse type response is found when the blocking contact is at the indirectly illuminated electrode with the Chl−a layer essentially acting as an inner filter. The photocurrent is shown to increase when the cell is reverse biased. A minimum quantum yield for charge generation of about 0.03 is found in (Al‖Chl‖Hg) and (Al‖Chl‖Au) cells.

“n” type semiconductivity in natural single crystals of FeS 2 (pyrite)

Natural single crystals of pyrite from Spanish mines appear to be “ n” type semiconductors. Resistivity, Hall coefficient and Hall mobility have been studied as a function of temperature. An acoustic phonon scattering mechanism is operative in the neighbourhood of room temperature. Results on the influence of the electrical contacts and chemical decomposition of the samples on the intrinsic properties are also included.