Transport properties of n-type ferromagnetic semiconductor HgCr2−xInxSe4(x = 0.100)

Measurements of the electrical conductivity, magnetoresistance, and Hall effect were performed on a n-type ferromagnetic semiconductor HgCr_2?xIn_xSe₄(x = 0.100) single crystal from 6.3 to 296 K in magnetic fields up to 1.19×l0⁶A/m. The conductivity decreases rapidly near the Curie temperatureT_c (≈120 K) as the temperature is raised. A large peak in the magnetoresistance is observed near T_c. The Hall effect measurements indicate that the temperature dependence of the conductivity and the magnetoresistance are due mostly to a change in electron mobility. The electron mobility is 1.2 × 10^?2 m²/V · s at 6.3 K, and decreases rapidly near T_c with the rise in temperature. Then it increases slowly from 5.5 × 10^?4 m²/V · s at 160 K to 7.5 × 10^?4 m²/V · s at 241 K. This temperature dependence of the electron mobility can be explained in terms of the spin-disorder scattering which takes into account the exchange interaction between charge carriers and localized magnetic moments.     

Electrical properties of proton conducting solid biopolymer electrolytes based on starch–chitosan blend

Two systems (salted and plasticized) of starch–chitosan blend-based electrolytes incorporated with ammonium chloride (NH₄Cl) are prepared via solution cast technique. The incorporation of 25 wt% NH₄Cl has maximized the room temperature conductivity of the electrolyte to (6.47?±?1.30)?×?10^?7 S cm^?1. Conductivity is enhanced to (5.11?±?1.60)?×?10^?4 S cm^?1 on addition of 35 wt% glycerol. The temperature dependence of conductivity for all electrolytes is Arrhenian, and the value of activation energy (E _a ) decreases with increasing conductivity. Conductivity is found to be influenced by the number density (n) and mobility (μ) of ions. The complexation between the electrolytes components is proven by Fourier transform infrared analysis. The relaxation time (t _r ) for selected electrolytes is found to decrease with increasing conductivity and temperature. Conduction mechanism for the highest conducting electrolyte in salted and plasticized systems is determined by employing Jonscher’s universal power law.     

Study on factors governing the conductivity performance of acylated chitosan-NaI electrolyte system

Hexanoyl chitosan and lauroyl chitosan were prepared by acyl modification of chitosan. Films of hexanoyl chitosan- and lauroyl chitosan-based polymer electrolytes incorporated with different weight concentrations of sodium iodide (NaI) were prepared using the solution casting technique. FTIR and differential scanning calorimetry (DSC) results suggested that NaI interacted with both hexanoyl chitosan and lauroyl chitosan. Maximum conductivities of 1.3 × 10^?6 and 1.1 × 10^?8 S cm^?1 are achieved for hexanoyl chitosan and lauroyl chitosan, respectively. Higher conductivity in hexanoyl chitosan is attributed to higher ion mobility as supported by DSC results. The dielectric constants of neat hexanoyl chitosan and lauroyl chitosan are 2.7 and 1.9, respectively, estimated from impedance spectroscopy. Higher dielectric constant of hexanoyl chitosan resulted in greater NaI dissociation and hence higher conductivity. Deconvolution of O═C-NHR and OCOR bands of polymer has been carried out to estimate the amount of dissociated Na⁺ ions from NaI. The findings were in good agreement with conductivity results. In order to assess quantitatively, the conductivity, parameter number, n, and mobility, μ, of ions were calculated using impedance spectroscopy. XRD results showed the influence of NaI on the crystalline content of the electrolyte system. Sample with lower crystalline content exhibited higher conductivity.     

Conductivity enhancement in fluorite-structured Ba1−xLaxF2+x solid solutions

The ionic conductivity of single crystals of the fluorite-structured solid solutions Ba_1?xLa_xF_2+x(10^?3 <×<0.45) has been studied as a function of temperature and composition in the range 300–900 K. Three regions can be discerned in the concentration dependence of the ionic conductivity: a dilute concentration region (x<10^?3), where classic relations between solute content and ionic conductivity hold; an intermediate concentration region (10^?3<x?5×10^?2), where large changes occur in the conductivity activation enthalpy and the magnitude of the conductivity; and a concentrated solid solution region (x?5×10^?2) characterized by enhanced ionic motion. In the dilute region the migration enthalpy for interstitial fluoride ions is determined to be 0.714 eV, while a value of 0.39 eV is found for the (La_BaF_i)^X association enthalpy. The defect chemistry in the intermediate concentration region is shown to be controlled by a superlinear increase of the concentration of mobile defects, while in the concentrated solid solution region a composition-independent amount of ≈1 mole% of interstitial fluoride ions with enhanced mobility, carry the current.     

The optical conductivity of free carriers in GaAs

The optical conductivity of free electrons in polar semiconducting compounds has recently been calculated by use of a generalized Boltzmann equation derived from the equation of motion of the quantum density matrix. This reduces to the quasi-classical Boltzmann transport equation in the low frequency limit: the optical conductivity thus obtained spans a spectral range from around 30cm^?1 to 1.2 × 10⁴cm^?1 in GaAs. In this paper, the optical conductivity is calculated for GaAs as a function of carrier concentration in terms of a frequency dependent relaxation time which reduces to the usual relaxation time in the limit of low frequencies and an elastic scattering mechanism. The low frequency limit of the relaxation time is used to estimate the mobility as a function of carrier concentration. The frequency dependent relaxation time is given for GaAs at 298 K over the spectral region from 45 cm^?1 to 2.3 × 10³cm^?1 for carrier concentrations from 3.4 × 10¹⁵cm^?3 to 8.7 × 10¹⁸cm^?3.     

Charge transport in PbMoO<Subscript>4</Subscript> crystals

Dc and ac electrical conductivity of lead molybdate crystals is studied in the temperature range 300–550 K. The electrical conductivity was shown to have electronic (hole) impurity character. The I–V characteristics are typical of a space charge-limited current. The carrier mobility was estimated to be 10^?5 cm² V^?1 sat T=300 K. The results of the study suggest the hopping mechanism of conduction in PbMoO₄ crystals.     

Effect of ethylene carbonate plasticizer on agar-agar: NH<Subscript>4</Subscript>Br-based solid polymer electrolytes

Proton-conducting polymer electrolytes based on biopolymer, agar-agar as the polymer host, ammonium bromide (NH₄Br) as the salt and ethylene carbonate (EC) as the plasticizer have been prepared by solution casting technique with dimethylformamide as solvent. Addition of NH₄Br and EC with the biopolymer resulted in an increase in the ionic conductivity of polymer electrolyte. EC was added to increase the degree of salt dissociation and also ionic mobility. The highest ionic conductivity achieved at room temperature was for 50 wt% agar/50 wt% NH₄Br/0.3% EC with the conductivity 3.73?×?10^?4 S cm^?1. The conductivity of the polymer electrolyte increases with the increase in amount of plasticizer. The frequency-dependent conductivity, dielectric permittivity (ε′) and modulus (M′) studies were carried out.     

The role of anion vacancy migration in lead halide photolysis

From the electrical conductivity of meltgrown Pb₂NaI single crystals for the first time mobility of the iodide ion vacancies along the c-axis is calculated (temperature region 340–540 K). It is shown that the transition from the colour centre mode (CCM) to the print-out mode (POM) of the photolysis of Pb₂ (X = Cl, Br, I) occurs when the anion vacancy mobility in PbCl₂ and PbBr₂ exceeds the value 1.0 × 10^?8cm²V^?1sec^?1, and in PbI₂ the value 8.1 × 10^?8cm²V^?1sec^?1.     

Preparation and properties of co-evaporated bismuth telluride [Bi2Te3] thin films

Thin films of bismuth telluride have been prepared by the reactive evaporation method. Film properties, such as conductivity, Hall effect, and thermoelectric power were studied in the temperature range from liquid nitrogen to 350 K. The films prepared were of n-type with a carrier concentration of 1.25 x 10²⁰ at room temperature. The temperature dependence of the Hall mobility is found to be T^?1.8 indicating lattice scattering.     

Hall effect and magnetoresistance of (SN)x films

Hall effect and electrical conductivity have been investigated between 77 K and 300 K and the magnetoresistance at 4.2 K for a number of (SN)_x films deposited at substrate temperatures between — 10 and 50°C. The small magnitude of the Hall mobility (? 1 cm² Vsec^?1 at 300 K) and its activated temperature dependence are interpreted in terms of a heterogenous model for (SN)_x films with thin depletion layers separating highly conductive islands. The hole concentration in these islands (p ≈ 10²¹ cm^?3, the microscopic mobility (μ ≈ 500 cm² Vsec^?1 at 4.2 K) and the temperatures dependence of μ are found to be close to values for (SN)_x crystals.     

Green electrolytes based on dextran-chitosan blend and the effect of NH<Subscript>4</Subscript>SCN as proton provider on the electrical response studies

Dextran-chitosan blend added with ammonium thiocyanate (NH₄SCN)-based solid polymer electrolytes are prepared by solution cast method. The interaction between the components of the electrolyte is verified by Fourier transform infrared (FTIR) analysis. The blend of 40 wt% dextran-60 wt% chitosan is found to be the most amorphous ratio. The room temperature conductivity of undoped 40 wt% dextran-60 wt% chitosan blend film is identified to be (3.84?±?0.97)?×?10^?10 S cm^?1. The inclusion of 40 wt.% NH₄SCN to the polymer blend has optimized the room temperature conductivity up (1.28?±?0.43)?×?10^?4 S cm^?1. Result from X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analysis shows that the electrolyte with the highest conductivity value has the lowest degree of crystallinity (χ _c) and the glass transition temperature (T _g), respectively. Temperature-dependence of conductivity follows Arrhenius theory. From transport analysis, the conductivity is noticed to be influenced by the mobility (μ) and number density (n) of ions. Conductivity trend is further verified by field emission scanning electron microscopy (FESEM) and dielectric results.     

Structural,electrical, and transport number studies of AgI-doped silver borotellurite fast ion conducting glass system

Silver ion conducting glass system composed of xAgI–(100???x)[0.444 Ag₂SO₄–0.555 (0.4TeO₂–0.6B₂O₃)] has been prepared by melt quenching method for x?=?0 to 80 in step of 10. XRD, DSC, FTIR, and SEM were carried out to understand some structural properties of prepared samples. XRD and DSC studies of the samples with x?≤?60 show predominantly glassy nature. Electrical parameters and activation energies of all the samples were evaluated by complex impedance analysis and Arrhenius plots of DC conductivity, respectively. Carrier concentration, mobility, inter-ionic distance, and ionic conductivity of samples were measured and discussed. It is observed that the conductivity varies with increasing the temperature and composition. The highest conductivity (1.8?×?10^?1 S cm^?1) and ionic current (8.33 μA) is observed for =?50 sample at room temperature; hence, it can be used as best electrolyte material for solid-state battery application.     

Hole mobility in a homogeneous nucleotide chain

The conductivity of molecular DNA-based conductors has been calculated. Charge motion is described by quantum-mechanical equations, and macromolecular vibrations are described by classical equations of motion with dissipation and a source of temperature fluctuations. In a homogeneous sequence of G-C nucleotide pairs, the calculated hole mobility at T=300 K equals ≈2cm² V^?1 s^?1.     

Gelatin-HCl biomembranes with ionic-conducting properties

Gelatin-HCl protonic gel polymer electrolytes were obtained by crosslinking with formaldehyde in the presence of hydrochloric acid and glycerol as plasticizer and characterized in present study. The ionic conductivity measurements revealed the best value of 5.35?×?10^?5 S cm^?1 at room temperature. Factorial design analysis showed that influence of glycerol is more pronounced than influence of acid on ionic conductivity values. Moreover, the 90 % transparent membranes evidenced a linear increase of ionic conductivity values of 5.35?×?10^?5 S cm^?1 at 26.5 °C to 5.77?×?10^?4 S cm^?1 at 82.8 °C following Arrhenius type mechanism of charge mobility.     

Conductivity of β″ and ion rich β alumina.I.H.+(H2O)n compounds

The conductivity and thermal stability of H⁺(H₂O)_n β″ and ion rich β alumina single crystals have been measured by the complex impedance method in the 25–700°C temperature range. Two mechanisms of conductivity were assumed: proton transfer at lower temperatures and H₃O⁺ diffusion in the high-temperature range. Both structures have similar properties, but ion rich β alumina possesses the best stability and the lowest activation energy (β: 0.15 eV, β″: 0.20 eV below 400 and 300°C respectively). The room-temperature conductivity is ≈5×10^?6 Ω^?1 cm^?1. The conducting properties and mechanisms are discussed and compared to other protonic or ionic conductors.     

Lithium ion-poly (ethylene oxide) complexes. I. Effect of anion on conductivity

The ionic conductivities of a series of lithium salt-poly (ethylene oxide) complexes have been studied from ambient temperature to approximately 400 K. Plots of the variation of conductivity with temperature indicate a transition in behaviorr between 330–360 K. The activation energies in the high temperature regime vary from 0.16 eV (LiH₂PO₄) to 1.45 eV (LiNO₃) and in the low temperature regime from 0.86 eV (LiBF₄) to 2.47 eV (LiH₂PO₄). Conductivity values for the salts tested also exhibits wide variation. The lowest measured conductivity was 10^?9 S/cm and the highest was 10^?4 S/cm. The anion plays an important role in the total measured conductivity. Salts with oxygen-containing anions form complexes with an apparent higher conductivity when the sample is vacuum dried. This suggets hydrogen bonding with residual water in the polymer impeding anionic mobility. In one of the salt-complexes (LiBF₄) residual water and thermal history, were shown not to significantly affect conductivity.     

Study on ammonium acetate salt-added polyvinyl alcohol-based solid proton-conducting polymer electrolytes

Polyvinyl alcohol (PVA) complexes with different compositions of ammonium acetate (AA) are prepared by solution cast technique. Polyvinyl alcohol crystallinity decreased with increasing ammonium acetate salt content. Molecular weight and density of polyvinyl alcohol complex increased with the addition of ammonium acetate salt. The ammonium acetate salt addition resulted in plasticization and hence decreased glass transition temperature (T _g) as well as hardness number (HV). 80PVA:20AA presented maximum conductivity (σ?=?1.3?×?10^?7S cm^?1 at 303 K) with minimum activation energy (E _a) 0.151 eV below the T _g. The proton transport number determined using EMF method found ≈0.98 for polymer complex with ammonium acetate content >15 mol%. The complex impedance is measured as a function of frequency, temperature, relative humidity, and hydrogen partial pressure. Enhanced bulk conductivity with increased H₂ partial pressure and relative humidity suggested H⁺ mobility within complex polymer electrolyte.     

a.c. Conduction originated from the atomic two-levels systems in hydrogenated amorphous silicon

The frequency-dependent conductivity of glow-discharge a-Si:H has been measured in the temperature range 90–350 K. The bulk and interfacial relaxations are separated by measurement. The bulk conductivity is well interpreted in terms of hydrogen-related two-level systems (TLS). The density of TLS is estimated to be about 1 × 10²¹cm^?3, which is consistent with the hydrogen content of a-Si:H.     

Electrical properties of the SiC/Si composite and the biomorphic SiC ceramic fabricated from spanish beech wood

A study has been made of the dependences of the electrical resistivity and the Hall coefficient on the temperature and magnetic field for the SiC/Si composite fabricated from spanish beech wood and bio-SiC, a high-porosity material formed by chemical extraction of silicon from this composite. The main charge transport parameters of these materials have been determined and analyzed. It has been shown that electric transport in bio-SiC is effected by n-type carriers with a high concentration of ～10¹⁹ cm^?3 and a low mobility of ～1 cm² V^?1 s^?1. The relations obtained have been analyzed by invoking the theory of quantum corrections to conductivity.     

Effects of doping and preliminary processing on the magnetically stimulated mobility of dislocations in InSb single crystals

The effect of the type of conductivity and the doping level of InSb single crystals on the mobility of fast 60° dislocations in a magnetic field is discovered. It is found that doping of a pure InSb crystal with tellurium (n-type impurity) to 10¹⁸ cm^?3 reduces the mobility of dislocations to the background level. At the same time, in p-type InSb crystals doped with Ge with the same carrier concentration (10¹⁸ cm^?3), the magnetoplastic effect is manifested clearly. It is shown that preliminary mechanical loading and, hence, internal stresses in the crystal affect not only the mean path length of dislocations in a magnetic field but also the magnitude of the threshold magnetic field below which the magnetoplastic effect is not observed. Possible reasons for these phenomena are discussed.