AC conduction mechanism of the zinc potassium diphosphate

Zinc potassium pyrophosphate K₂ZnP₂O₇ was synthesized using the conventional solid-state reaction. X-ray powder diffraction analysis proves the formation of a pure phase which crystallizes in the tetragonal system. The electrical conductivity and modulus characteristics of the system have been investigated in the temperature and the frequency range 614–718 K and 200 Hz–1 MHz, respectively, by means of impedance spectroscopy. The alternating current (AC) conductivity for grain contribution follows the universal Jonscher’s power law. The frequency exponent s is temperature independent and equal to 0.8. The QMT model was proposed to be the most suitable model to characterize the electrical conduction mechanism in the titled sample. Dielectric data were analyzed using complex electrical modulus M* at various temperatures. The bulk relaxation time was found from the peaks position of the above spectra and the thermodynamic parameters were also found using the Eyring theory.     

Electrical conduction in sodium nitrate crystals

The need for study of electrical transport in non-alkali halide ionic crystals is emphasized. Non-cubic systems with less simple structure present interesting anisotropic properties and problems of spacial hindrance. Our experience in this direction is summarized with detailed reference to the results on sodium nitrate crystal which is being investigated in our laboratory in some detail.     

The electrical conduction mechanism in the semiconducting sodium niobate

The electric resistivity, Hall coefficient and thermoelectric power of the semiconducting NaNbO₃ were measured between 70 and 300K. Data indicate that this material behaves as a non-degenerate seniconductor. Oxygen defects which act as donors create a level at 0.12 eV below the conduction band. The phonon drag effect was observed below 230K.     

极性分子型电流变液导电机理研究

极性分子型电流变液是一种新型的电流变材料.其介电颗粒上吸附极性分子,极性分子在颗粒间强局域电场作用下发生取向是产生巨电流变效应的关键.通过对Ca—Ti—O(CTO)体系极性分子型电流变液电流密度的测量发现,其导电行为遵从Poole-Frenkel效应的规律,这是极性分子型电流变液的重要特征之一.而500 ℃处理过的CTO粉体不含极性分子,所配制的电流变液无巨电流变效应,其电流密度随外电场强度近似地呈线性关系,显示出传统电流变液特性.     

Electrical properties and conduction mechanism of an organic-modified Au/NiPc/n-InP Schottky barrier diode

The effect of nickel phthalocyanine (NiPc) organic interlayer on the electronic parameters of Au/n-InP Schottky contacts has been investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements. Measurements showed that the barrier heights and ideality factors are 0.58 eV (I–V), 0.69 eV(C–V) and 1.32 for Au/n-InP Schottky contact and 0.80 eV (I–V), 1.12 eV (C–V) and 1.73 for Au/NiPc/n-InP Schottky contact, respectively. Experimental results show that the interfacial layer of NiPc increases the effective barrier height by the influence of the space charge region of the Au/n-InP Schottky junction. Further, Cheung’s and modified Norde functions are used to extract the barrier height, series resistance and ideality factors. The discrepancy between barrier heights estimated from I–V to C–V methods is also explained. Moreover, the energy distribution of interface state density is determined from the forward bias I–V data. Results show that the interface states and series resistance play an important role on electrical properties of the structures studied. The reverse leakage current conduction mechanism is investigated. Results reveal that the Schottky conduction mechanism is found to be dominant in the Au/n-InP Schottky contact. However, in the case of Au/NiPc/n-InP Schottky contact, the Schottky conduction mechanism is found to be dominant in the higher bias region, while Poole–Frenkel conduction is found to be dominant in the lower bias region.     

Electrical transport properties of polycrystalline nickel vanadate

Investigations on a.c. and d.c. electrical conductivities, thermoelectric power and dielectric constant of nickel vanadate (NiV₂O₆) are reported in the temperature range from 300 to 800 K. The compound has been found to be ap-type semiconductor with an energy gap of 2.92 eV. Electrical conduction mechanism for this compound is discussed in terms of polaron theory.     

Electrical properties and proton conduction of gadolinium doped ceria

The electrical properties and proton conduction of Gd_0.1Ce_0.9O_1.95 (10GCO) were investigated via impedance spectroscopy in different atmospheres and various gas concentration cells. In oxygen atmosphere, GCO is nearly a pure oxygen ionic conductor, while in hydrogen GCO behaves as a mixed conductor of oxygen ions, electrons and protons. Depending on the temperature, the total conductivity is usually enhanced by one to two orders of magnitude in hydrogen than in air/oxygen due to mixed conduction. By examining ionic transport properties of oxygen ions and protons using gas concentration cells we have discovered that the ionic transport properties depend largely on the gas atmospheres and change from one type to the other. Proton conduction generally exists in GCOs, and becomes significant in hydrogen atmospheres, which normally results in a contribution between 5 to 10 % of the total conductivity for 10 GCO. A maximum value of 17 % of the contribution by protons has been observed. The reduction of Ce⁴⁺ to Ce³⁺ of the sample in reduced atmospheres causes the formation of additional oxygen vacancies and electrons, associated also with the creation of protons. All these charge carriers are responsible for the electrical and transport properties of the investigated GCO materials. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Electrical conduction mechanism in nanocrystalline CdTe (nc-CdTe) thin films

The present paper reports the electrical characterization of nc-CdTe thin films in different temperature ranges. Thin films of nc-CdTe are deposited on the glass substrates by Physical Vapor Deposition (PVD) using the Inert Gas Condensation (IGC) method. The Transmission Electron Microscopy (TEM) studies are made on the CdTe nanocrystals. The surface morphology and structure of the thin films are studied by the Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD) measurements. Dark conductivity measurements are made on the nc-CdTe thin films in the temperature range 110–370 K in order to identify the conduction mechanism in this temperature range. The obtained results reveal three distinct regions at high, low, and sufficiently low temperature regions with decreasing activation energies. The analysis of the high temperature conductivity data is based on the Seto’s model of thermionic emission. At very low temperatures, dc conductivity (σ _d) obeys the law: lnσT ^1/2∝T ^?1/4, indicating variable-range hopping in localized states near the Fermi level. The density of the localized states N(E _F) and various other Mott’s parameters like the degree of disorder (T _O), hopping distance (R), and hopping energy (W) near the Fermi level are calculated using dc conductivity measurements at low temperatures. Carrier type, carrier concentration, and mobility are determined from the Hall measurements. The transient photoconductivity decay measurements are performed on the nc-CdTe thin films at different intensities in order to know the nature of the decay process.     

Electrical properties of calcia-doped ceria with oxygen ion conduction

The electrical conductivity of sintered specimens of (CeO₂)_1−x(CaO)_x was investigated by employing a standard four-probe dc technique as a function of temperature between 400°C and 900°C, composition from 0.10x0.80, and oxygen partial pressure from 10⁻¹⁸ to 1 atm. The temperature and composition dependence of the emf have been carried out with a concentration cell. X-ray diffraction studies indicated that a cubic fluorite crystal remained in all specimens studied, although the solubility limit of CaO in CeO₂ was assumed to lie close to 23 mol% from the change of the lattice constant. The magnitude of the conductivity decreased slightly with increase of the dopant concentrations up to x=0.50. The conductivity of these specimens was about 100 times larger than that of calcia-stabilized zirconia at 600°C with a smaller activation energies of 0.83–0.89 eV. With further increasing dopant concentrations, the magnitude of the conductivity was found to decrease remarkably. With an increase in the dopant concentration, the domain of primarily ionic conduction extended to a lower partial pressure. The conductivity of (CeO₂)_0.50(CaO)_0.50 was found to be primarily ionic down to 10⁻¹² atm even at 900°C. These results indicate that CaO-doped CeO₂ may be more an attractive candidate for fuel cells and other applications.     

Electrical conduction properties of rare earth orthophosphates under reducing conditions

Electrical conduction properties of Sr-doped PrPO₄, NdPO₄ and SmPO₄ with the monazite structure were investigated at 500–925 °C under H₂/H₂O reducing conditions. From H/D isotope effects and p(H₂)-dependencies of the conductivities, it was found that the materials dominantly conducted protons under the wet reducing conditions although the materials slightly showed n-type electronic conduction at higher temperatures. Based on p(H₂O) and p(H₂)-dependencies of the conductivities, defect structures of the materials under the reducing conditions were discussed. As a result, it was considered that major positive defects were oxygen deficits at higher temperatures and protons at lower temperatures.     

Electrical properties and recombination activity of copper, nickel and cobalt in silicon

This article combines an extensive literature review of new experimental data on properties of Cu, Ni and Co and their precipitates in silicon with a discussion of experimental data recently obtained by the authors. Special attention is paid to the recombination activity of these metals. It is shown that the recombination activity of Cu, Ni, Co and their complexes is low in p-type Si, compared to that of other transition metals such as iron. However, it increases markedly upon formation of precipitates or decoration of existing lattice defects. This is explained by the formation of a precipitate-related defect band and of an attractive potential for minority charge carriers by the charged precipitates. The role of Cu, Ni and Co in the degradation of multicrystalline solar cells efficiency is discussed in a separate section. It is suggested that recently reported intragranular microdefects, which decrease the lifetime of solar cells, may be microprecipitates of these metals. Received: 18 September 1997/Accepted: 25 September 1997     

Electrical conduction in copper vanadate

A.C. and d.c. electrical conductivities, thermoelectric power and dielectric constant of copper vanadate (CuV₂O₆) have been measured in the temperature range 300–1000 K in order to discuss the electrical conduction in the compound. The extrinsic conduction, which takes place below 500 K, has been explained by small polaron hopping mechanism while intrinsic conduction, which takes place above 500 K, has been explained by large polaron band mechanism in view of the values of activation energy and charge carrier mobility in the temperature ranges 300–500 K and 500–1000 K.     

Electrical conduction and dielectric properties of vanadium phosphate glasses doped with lithium

AC conductivity and dielectric studies on vanadium phosphate glasses doped with lithium have been carried out in the frequency range 0.2-100 kHz and temperature range 290-493 K. The frequency dependence of the conductivity at higher frequencies in glasses obeys a power relationship, σ_ac=Aω^s. The obtained values of the power s lie in the range 0.5≤s≤1 for both undoped and doped with low lithium content which confirms the electron hopping between V⁴⁺ and V⁵⁺ ions. For doped glasses with high lithium content, the values of s≤0.5 which confirm the domination of ionic conductivity. The study of frequency dependence of both dielectric constant and dielectric loss showed a decrease with increasing frequency while they increase with increasing temperature. The results have been explained on the basis of frequency assistance of electron hopping besides the ionic polarization of the glasses. The bulk conductivity increases with increasing temperature whereas decreases with increasing lithium content which means a reduction of the V⁵⁺.     

Electrical conduction in manganese tungstate

The a.c. and d.c. electrical conductivity and thermoelectric power of a single crystal of MnWO₄ are reported in the temperature range 300–1200 K. It has been found that the dominant charge carriers are holes over the entire temperature range studied. A break in the log σ-($\text{1}\text{T}$) curve occurs around 600 K. The activation energies below and above this break temperature have been estimated as 0.53 and 0.57 eV. The charge carrier mobilities have also been estimated. The data have been analysed using the polaronic concept of electrical conduction.     

Anisotropic properties and conduction mechanism of TlInSe2 chain semiconductor

TlInSe₂ chain crystals were prepared using the modification of the Bridgman technique. The grown crystals were identified by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), and X-ray diffraction (XRD). We investigate the anisotropy of transport properties for the first time for TlInSe₂ crystals. Temperature dependence of the dc electrical conductivity, Hall coefficient, Hall mobility, and charge carrier concentration were investigated in the temperature range 184–455 K. The conduction mechanism of TlInSe₂ crystals was studied, and measurements revealed that the dc behavior of the grown crystals can be described by Mott’s variable range hopping (VRH) model in the low temperature range, while it is due to thermoionic emission of charge carriers over the chain boundaries above 369 K. The Mott temperature, the density of states at the Fermi level, and the average hopping distance are estimated in the two crystallographic directions. The temperature dependence of the ac conductivity and the frequency exponent, s, is reasonably well interpreted in terms of the correlated barrier-hopping CBH model.     

Electrical and magnetic properties of mercury selenide doped with nickel and chromium

The electrical properties of mercury selenide single-crystals doped with nickel and chromium are studied over the temperature range 80–400 K in magnetic fields of 0–8 kOe. It is established that in the mercury selenide lattice the impurity Ni is electrically and magnetically inactive. With growth in Cr concentration the paramagnetism of mercury selenide specimens increases. Results of a study of magnetic susceptibility are compared to theoretical calculations for a point model and a point model with consideration of covalence effects.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 44–47, November, 1990.     

Electrical conduction and thermodynamic properties of K2NiP2O7

The pyrophosphate K₂NiP₂O₇ has been synthesized by the classic ceramic method and characterized by X-ray diffraction, solid-state ³¹P magic angle spinning (MAS) NMR, and IR and electrical impedance spectroscopy. The solid-state ³¹P MAS NMR, performed at 121.49 MHz, shows two isotropic resonances at ?17.66 and ?19.94 ppm, revealing the existence of two phosphorus environments in the structure. The electrical conductivity and dielectric properties have been investigated in the frequency and the temperature range of 200 Hz–1 MHz and 603–728 K, respectively. The frequency dependence of the conductivity is interpreted using the augmented Jonscher relation. The close values of activation energies obtained from the analysis of hopping frequency and dc conductivity imply that the transport is through ion hopping mechanism. The charge carrier concentration in the investigated sample has been evaluated using the Almond–West formalism and shown to be independent of temperature. Thermodynamic parameters such as the free energy of activation ΔF, the enthalpy ΔH, and the change in entropy ΔS have been calculated.     

Electrical conduction in ordered defect compounds

A comparative study of the temperature dependence of electrical resistivity, carrier concentration and carrier mobility of the Ordered Defect Compounds (ODCs) CuIn₃Se₅, CuIn₃Te₅, and CuIn₅Te₈ with their corresponding normal 1:1:2 phase is reported. Relatively lower carrier concentration and higher activation energy observed in ODCs is explained on the basis that shallow acceptor or donor levels observed in 1:1:2 phase are partially annihilated in these compounds due to attractive interaction between V_Cu⁻¹ and In_Cu⁺² defect pair. In the activation regime, the mobility is explained by taking into account a scattering mechanism of the charge carriers with donor–acceptor defect pairs. The electrical data at lower temperatures is explained with the existing theoretical expression for the nearest neighbor hopping conduction mechanism.