Activation Energy For Electronic Conduction Research Articles

Effect of Co concentration on the Y0.1Ca0.9Zr1-xCoxO3-δ limiting current dense diffusion barrier oxygen sensor

Y0.1Ca0.9Zr1-xCoxO3-δ (x = 0, 0.1, 0.3, and 0.5) was synthesized by a solid-state reaction. Y0.1Ca0.9Zr1-xCoxO3-δ is orthorhombic perovskite structure. The electronic conductivity and total conductivity increase with increasing Co concentration and temperature. The activation energy of electronic conductivity and total conductivity is lowest when the Co concentration is x = 0.5. A lower activation energy is conducive to the migration of oxygen ions. Using Y0.1Ca0.9Zr0.7Co0.3O3-δ and Y0.1Ca0.9Zr0.5Co0.5O3-δ as dense diffusion barrier and 8YSZ (8 mol% yttria-stabilized zirconia) as a solid electrolyte, the limiting current oxygen sensor was fabricated by the Pt sintered-paste method, and its sensing performance was studied. The oxygen sensor exhibits a limiting current plateau at 760–850 °C. The oxygen measurement range increases with increasing Co concentration. The limiting current is directly proportional to the oxygen concentration, indicating that it shows excellent sensing characteristics at different temperatures. When the test time is more than 75 h, the oxygen sensor has good stability, and the stable limiting current is approximately 4.23 mA. The voltage range of the limiting current plateau has no effect on the increase of the detection time, and its voltage range is 0.75–1.75 V.

Cu co-doping effect on electronic structure and room temperature ferromagnetism of TiO2:V nanoparticles

We have synthesized co-doped Ti0.94−yV0.06CuyO2 (0 ≤ y ≤ 0.02) nanoparticles by sol–gel. Single rutile phase crystal structure has been confirmed from X-ray diffraction patterns. Decreasing trend of bandgap, resistivity and activation energy with increasing Cu co-dopant has been observed in co-doped samples. We found that the ferromagnetism of the V doped TiO2 in the rutile phase is initially strongly suppressed for very low Cu concentration but with increasing Cu content the moment increases very significantly. The non-monotonic changes in the magnetization effects are attributed to the role of Cu in introducing oxygen vacancies, i.e. excess electrons due to its lower valence compared to Ti and V. The role of oxygen vacancies in the formation of magnetic polarons may be the reason of inducing and mediation of the ferromagnetic exchange between the transition metal ions. This interpretation is supported by the resistivity and optical measurements that both reveal the existence of low lying electronic states in the Cu doped systems that lead to lowering of resistivity and the lowering of the activation energy for electronic conduction. Hence it is apparent that variable valence of the dopants and their effects on the oxygen vacancies have an important role in determining the electronic properties of magnetically doped TiO2 semiconductors.

Novel nanocrystalline mixed conductors based on LiFeBO3 glass

Novel nanocrystalline mixed conductors were obtained by thermal nanocrystallisation of lithium–iron–borate glasses (nominally LiFeBO3) prepared via melt-quenching method. After heat treatment, a glass–ceramics consisting of FeBO3 and LiFeBO3 phases was obtained. Grain sizes, estimated using Scherrer formula, were 45–50nm and 70–80nm, respectively. Value of electrical conductivity of the initial glass was estimated as 5.8·10−12Scm−1. After annealing at 475°C, a growth by a factor 2.4·106 was observed, leading to final conductivity value 1.4·10–5Scm−1 at room temperature. The activation energy of electronic conductivity was lowered from 0.81eV for glass to 0.18eV for thermally treated material.

Characterization of Terbium and Samarium Co-Doped Ceria Films as SOFC Electrolyte Prepared by Using Ultrasonic Spray Pyrolysis Method

Because of the high ionic conductivity at intermediate temperatures (500–700 °C), doped ceria oxides are of special interest as the promising electrolyte materials for the intermediate temperature solid oxide fuel cells (IT-SOFC). However, main drawback of the ceria based solid electrolytes is the partial electronic conductivity at reducing conditions resulting in an internal partial short-circuiting of the cell and decreased total efficiency for SOFC. Tb, considered an electron trap, was found to suppress the partial electronic conductivity for microcrystalline ceria electrolyte. The aim of this work is to study the influence of Tb and Sm dopant concentration ratio on the microstructural and electrical properties of Ce0.9Sm0.1-xTbxO2-δ films. Tb and Sm cations binary co-doped ceria films were deposited using the ultrasonic atomizing spray pyrolysis method. The crack-free homogenous films with different dopant concentration were deposited and thereafter annealed at fixed temperatures 900, 1200 and 1300 °C, respectively. It was demonstrated that several microstructural parameters of oxide films are controlled by the sintering temperature. The Ce0.9Sm0.1-xTbxO2-δ films formed were analyzed using X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, atomic force microscopy and four probe dc technique at different pO2 and T values. Based on the SEM analysis the average thickness of Ce0.9Sm0.1-xTbxO2-δ films were 700 nm. The XRD patterns for the Ce0.9Sm0.1-xTbxO2-δ films annealed at 1200 °C indicated the high degree of crystallinity. Tb dopant ions influence the microstructural properties like median diameter of grain, microstrain, lattice parameter and electrical properties like activation energies of ionic and electronic conductivity of the Ce0.9Sm0.1-xTbxO2-δ film. Significantly higher microstrain value for smallest Tb dopant concentration and strong dependence of electrical properties on that was observed. The activation energy of ionic conductivity was lowered in that case, while the activation energy of electronic conductivity was increased. The lower bound of electrolytic domain for Ce0.9Sm0.09Tb0.01O2-δ film was lowered by one order of magnitude toward lower oxygen partial pressures. Further increase of Tb amount increased the activation energy of ionic conductivity, shifting the lower bound of electrolytic domain toward higher oxygen partial pressures.

Pressure-induced conductivity and yellow-to-black piezochromism in a layered Cu-Cl hybrid perovskite.

Pressure-induced changes in the electronic structure of two-dimensional Cu-based materials have been a subject of intense study. In particular, the possibility of suppressing the Jahn-Teller distortion of d(9) Cu centers with applied pressure has been debated over a number of decades. We studied the structural and electronic changes resulting from the application of pressures up to ca. 60 GPa on a two-dimensional copper(II)-chloride perovskite using diamond anvil cells (DACs), through a combination of in situ powder X-ray diffraction, electronic absorption and vibrational spectroscopy, dc resistivity measurements, and optical observations. Our measurements show that compression of this charge-transfer insulator initially yields a first-order structural phase transition at ca. 4 GPa similar to previous reports on other Cu(II)-Cl perovskites, during which the originally translucent yellow solid turns red. Further compression induces a previously unreported phase transition at ca. 8 GPa and dramatic piezochromism from translucent red-orange to opaque black. Two-probe dc resistivity measurements conducted within the DAC show the first instance of appreciable conductivity in Cu(II)-Cl perovskites. The conductivity increases by 5 orders of magnitude between 7 and 50 GPa, with a maximum measured conductivity of 2.9 × 10(-4) S·cm(-1) at 51.4 GPa. Electronic absorption spectroscopy and variable-temperature conductivity measurements indicate that the perovskite behaves as a 1.0 eV band-gap semiconductor at 39.7 GPa and has an activation energy for electronic conduction of 0.232(1) eV at 40.2 GPa. Remarkably, all these changes are reversible: the material reverts to a translucent yellow solid upon decompression, and ambient pressure powder X-ray diffraction data taken before and after compression up to 60 GPa show that the original structure is maintained with minimal hysteresis.

Electronic conductivity of vanadium-tellurite glass-ceramics

In this paper, we investigate the electronic conductivity of 2TeO2–V2O5 glass-ceramics with crystallinity ranging from 0 to 100wt.%, i.e., from entirely amorphous to completely crystalline. The glass is prepared by the melt quenching technique, and the crystal is prepared by subsequent heat treatment thereof. Glass-ceramics are prepared by mixing glass and crystal powder, followed by a sintering procedure. Activation energies for electronic conduction in the glass and in the crystal are determined by fitting the Mott–Austin equation to the electronic conductivity data obtained by impedance spectroscopy. We find similar activation energies for both glass and crystal, implying that they have similar conduction mechanisms, i.e., thermally activated hopping. The electronic conductivity of 2TeO2–V2O5 glass is about one order of magnitude higher than that of the corresponding crystal, and a percolation phenomenon occurs at a glass fraction of 61wt.%, increasing from a lower conductivity in the crystal to a higher conductivity in the glass. We explain the behavior of electronic conduction in the 2TeO2–V2O5 glass-ceramics by considering constriction effects between particles as well as percolation theory. This work implies that, based on its electronic conductivity, vitreous 2TeO2–V2O5 is more suitable as a cathode material in secondary batteries compared to a 2TeO2–V2O5 glass-ceramic.

Electrical conductivity of Gd-doped ceria film fabricated by aerosol deposition method

Gd-doped ceria (GDC) films were deposited on various substrates using aerosol deposition (AD) method in order to determine whether this process is useful for the fabrication of thin (~1μm) electrolyte layers. The AD method is attractive because no vacuum equipment or target material is required. Although the AD method utilizes pre-calcined powder for the deposition of film, the particle size and microstructure of films are largely dependent upon the choice of substrate (sapphire, glass, Si–Pt). The film deposited on sapphire substrate had a relatively dense microstructure and the smallest particle size. Total conductivity of film was measured using either in-plane or across-plane mode depending upon the substrate. Across-plane measurement gave a lower conductivity than in-plane measurement, possibly due to the difficulty of current collection or anisotropic microstructure. The magnitude of in-plane conductivity was comparable to the conductivity of a bulk sample, i.e., ~1.2×10−3S/cm at 450°C for the film deposited on sapphire. The activation energy of electronic conductivity at 300–450°C was also similar, ~2.23eV. However, the activation energy of ionic conductivity differed depending upon the substrates: ~0.71eV for the film on sapphire substrate and 0.93–0.94eV for other films. The Po2 dependence had a −1/4 slope, similar to that of bulk or film form of GDC at higher (>500°C) temperature. Overall, the AD method may be useful for the deposition of thin-film GDC since the conductivity was similar with that of film or bulk samples fabricated by conventional methods.

Stoichiometry dependence of resistance drift phenomena in amorphous GeSnTe phase-change alloys

In phase-change materials, the amorphous state resistivity increases with time following a power law ρ ∝ (t/t0)αRD. This drift in resistivity seriously hampers the potential of multilevel-storage to achieve an increased capacity in phase-change memories. This paper presents the stoichiometric dependence of drift phenomena in amorphous GeSnTe systems (a-GeSnTe) and other known phase-change alloys with the objective to identify low drift materials. The substitution of Ge by Sn results in a systematic decrease of the drift parameter from a-GeTe (αRD = 0.129) to a-Ge2Sn2Te4 (αRD = 0.053). Furthermore, with increasing Sn content a decrease in crystallization temperature, trap state density, optical band gap, and activation energy for electronic conduction is observed. In a-GeSnTe, a-GeSbTe, and a-AgInSbTe alloys as well, the drift parameter αRD correlates to the activation energy for electronic conduction. This study indicates that low drift materials are characterized by low activation energies of electronic conduction. The correlation found between drift and activation energy of electronic conduction manifests a useful criterion for material optimization.

Electronic Conductivity of Scandia-Stabilized Zirconia Doped with 1 mol% CeO2

The electronic conductivity of scandia-stabilized zirconia doped with 1 mol% CeO2 was measured at 1173 - 1273 K in the oxygen partial pressure range (p(O2)) of 10-4 - 10-20 MPa. At 1273 K, the electronic conductivity of 1Ce10ScSZ was in proportion to the 1/4 and -1/4 power of p(O2) due to the hole and electron conductions in higher and lower p(O2) regions (> 10-6 and < 10-17 MPa), respectively. Upper deviation of electronic conductivity was observed at 1273 K in p(O2) range of 10-6 - 10-17 MPa. Such a deviation had the p(O2) dependency similar to the product of Ce3+ and Ce4+ concentrations obtained by thermodynamic calculations. The deviation of electronic conductivity disappeared at 1173 K. This indicates that the activation energy of electronic conduction contributed by 1 mol% Ce dopant was significantly higher than 2.01 eV reported for (CexZr1-xO2)0.8(YO1.5)0.2 with Ce content of x = 0.1.

Effects of metal substitution on the electric and thermoelectric properties in (Ni1−xMx)Mn2O4 (M = Zn and Mg)

The temperature dependence of the electrical resistivity and the thermoelectric power of (Ni1−xMx)Mn2O4 (M=Zn and Mg, x=0, 0.1 and 0.2) are measured. The electric conductivity is described by a small polaron hopping mechanism. The activation energy for electronic conduction is increased above certain temperature. In the low temperature region the absolute value of thermoelectric power is increased by Mg substitution. The thermoelectric powers of all samples are found to change sign from negative to positive with increasing in temperature. This change of sign in the thermoelectric power may take care of the competition between spin-entropy term and hole conduction term caused by the charge transfer from O 2p to transition metal 3d orbitals.

Current-Voltage Characteristics of Platinum Model Electrodes on Yttria-Stabilized Zirconia

In this study, the steady state current-overpotential (I-η) characteristics of the oxygen reduction reaction on the system Pt|yttria-stabilized zirconia (YSZ) were investigated at temperatures between 600 and 720°C. The I-η curve of Pt thin-film model electrodes on YSZ (100) exhibited a quite unexpected behavior, with diffusion limitation at lower and an exponential I-η relationship at high cathodic polarization. This situation was interpreted in terms of two parallel electrochemical oxygen reduction pathways. The diffusion limited path – with an activation energy of the limiting current of 1.57 eV – is attributed to a classical surface path on Pt with diffusion through an impurity phase at the triple phase boundary (TPB) being rate limiting. Stoichiometry polarization is most likely responsible for the exponential part of the I-η curve. In the corresponding second pathway, the oxygen reduction takes place on the YSZ surface with a rate limiting electron supply via the YSZ electrolyte. This interpretation is further supported by good accordance of the obtained activation energy (3.65 eV) with the activation energy of electronic conductivity in YSZ. The data can be used to calculate current contributions in broad temperature and overpotential ranges.

Thermoelectric Properties of Layer-Antiferromagnet CuCrS2

The electrical, thermal conductivity and Seebeck coefficient of the quenched, annealed and slowly cooled phases of the layer compound CuCrS2 have been reported between 15K to 300K. We also confirm the antiferromagnetic transition at 40K in them by our magnetic measurements between 2K and 300K. The crystal flakes show a minimum around 100K in their in-plane resistance behavior. For the polycrystalline pellets the resistivity depends on their flaky texture and it attains at most 10 to 20 times of the room temperature value at the lowest temperature of measurement. The temperature dependence is complex and no definite activation energy of electronic conduction can be discerned. We find that the Seebeck coefficient is between 200-450 microV/K and is unusually large for the observed resistivity values of between 5-100 mOhm-cm at room temperature. The figure of merit ZT for the thermoelectric application is 2.3 for our quenched phases, which is much larger than 1 for useful materials. The thermal conductivity K is mostly due to lattice conduction and is reduced by the disorder in Cu- occupancy in our quenched phase. A dramatic reduction of electrical and thermal conductivity is found as the antiferromagnetic transition is approached from the paramagnetic region, and K subsequently rises in the ordered phase. We discuss the transport properties as being similar to a doped Kondo-insulator.

Hydrogen permeation through terbium doped strontium cerate membranes enabled by presence of reducing gas in the downstream

Hydrogen permeation through SrCe 1− x Tb x O 3− δ ( x = 0.025, 0.05 and 0.10) membranes using various gas streams as the sweep was investigated. Hydrogen impermeable SrCe 1− x Tb x O 3− δ membranes with air or inert gas in the downstream become hydrogen permeable when there is a reducing gas, such carbon monoxide or hydrogen, existing in the downstream. The membrane remains hydrogen permeable after the downstream sweep gas is changed from the reducing gas to the inert gas. This phenomenon is explained by the electronic conductivity of the materials. These results further confirm that SrCe 1− x Tb x O 3− δ (0.025 < x < 0.1) is a mixed proton–electron conducting material in a hydrogen containing atmosphere. The activation energy of hydrogen permeation is close to the activation energy of electronic conduction of the materials, confirming that the hydrogen permeation is determined by the electronic conductivity of the material. For SrCe 0.95Tb 0.05O 3− δ , increasing the downstream CO partial pressure from 0.001 to 0.1 atm leads to a small increase in hydrogen flux from 1.4 × 10 −2 to 1.6 × 10 −2 ml/cm 2 min. The hydrogen flux of SrCe 1− x Tb x O 3− δ increases with upstream hydrogen partial pressure.

Oxidation behavior of metallic interconnects for SOFC in coal syngas

Crofer 22 and Haynes 230 alloys, which are candidates for solid oxide fuel cell (SOFC) interconnects, were exposed at 800 °C to a simulated coal syngas (29.1CO + 28.5H 2 +11.8CO 2 + 27.6H 2O + 2.1N 2 + 0.01CH 4) and air. The samples were characterized by SEM/EDS, XRD and ASR. Results indicated that the compositions of the oxide scales in syngas and in air were similar. For Crofer 22, scales formed in both air and coal syngas were composed of (Cr,Fe) 2O 3, Mn–Cr compounds and Fe 3O 4. For Haynes 230 the main composition was Cr 2O 3. However, it was found that the morphologies of the scales formed in coal syngas were different from those formed in air. Besides, the cross section element distributions of oxide scales formed on Crofer 22 were disparate. In addition, the ASR values of the oxide scales formed in coal syngas and in air were similar at 800 °C but the activation energies for electronic conduction of the oxide scales formed in coal syngas were higher.

Thermal expansion and electrical conductivity of M4 ± x V6O16 ± x (M = K, Rb, Cs) polyvanadates

The thermal expansion coefficient of the M4 ± x V6O16 ± x (M = K, Rb, Cs) polyvanadates is a nonmonotonic function of temperature, with sharp minima at 663, 558, and 713 K, respectively, which are accompanied by no changes in cell symmetry (tetragonal) or a/c axial ratio. The polyvanadates are shown to be ionic-electronic conductors. The activation energy for electronic conduction in the three polyvanadates is 0.43 ± 0.02 eV. In the range 675–740 K, the conductivity of K4.2V6O16.2 shows metallic behavior. Rubidium polyvanadate has a narrower temperature range of unactivated conduction, and Cs3.8V6O15.8 has no such range. The conclusion is made that these phases undergo cation disordering due to deviations from the M4V6O16 stoichiometry.

Defect chemical analysis of the electronic conductivity of strontium-substituted lanthanum ferrite

The electronic conductivity of La 0.4Sr 0.6FeO 3− δ is studied in the oxygen partial pressure range 10 −5≤ pO 2/atm≤1 at temperatures 100≤ T/°C≤900. The oxygen partial pressure dependence of the electronic conductivity in the pO 2 range under investigation shows a predominantly p-type character. Combination of the pO 2 dependences of the oxygen nonstoichiometry δ and the electronic conductivity σ at constant temperatures 600≤ T/°C≤900 indicates a significant decrease of σ with increasing δ. Concentrations of electronic defects are calculated from experimental data of the oxygen nonstoichiometry via a point defect model and applied to modelling of σ as a function of δ. The mobility of holes is estimated from the electronic conductivity and the calculated charge carrier concentrations as a function of oxygen nonstoichiometry. At constant pO 2, the electronic conductivity is thermally activated at T<300 °C, but decreases with further increase of temperature due to desorption of oxygen from the lattice. This effect is especially pronounced in the intermediate pO 2 range 10 −4≤ pO 2/atm≤10 −2 where significant oxygen deficit occurs. The temperature dependence of the electronic conductivity of La 0.4Sr 0.6FeO 3− δ was combined with results of the temperature dependence of the oxygen nonstoichiometry. Thus, activation energies for electronic conduction at constant oxygen content were obtained for the high temperature region ( T>300 °C) which are in agreement with isobaric activation energies of the electronic conductivity at low temperatures ( T<300 °C).

Electrical and magnetic studies of Ba 3Co 2Fe 23−12 xMn 12 xO 41 Z-type hexaferrites

The electromagnetic and dielectric properties of Mn substituted Ba 3Co 2Fe 23−12 x Mn 12 x O 41 (Z-type) hexaferrites where 0≤ x<0.1 were investigated in this study. The ferrite samples behaved as a semiconductor, and DC resistivity as well as activation energy for electronic conduction increased as the amount of Mn substituted for Fe increased, reaching maximum around x=0.02, and then decreased with further substitution. The behavior of dielectric constant was in an opposite manner to that of the activation energy and DC resistivity. Conduction is explained on hopping of electrons between Fe 2+ and Fe 3+. It was inferred that the initial permeability was sensitively controlled by the substitution of Mn because of magnetostriction compensation. Low-temperature sintered Co 2Z hexaferrite with the substitution of Mn for Fe with low dielectric constant and high initial permeability is suitable for very high frequency (VHF; 300–800 MHz) multilayer chip inductors (MLCI) use.

Preparation and Nonstoichiometric Property of wide Compositional Fe(III)-doped TiO2 (anatase)

Fe(III)-doped TiO2 (anatase) was prepared by the oxidation of FexTiS2. Two calcination methods were used to oxidize FexTiS2. In the first, sulfide was calcined in air at a given temperature for 2 h. In the second method, the sulfide was heated in air at a finite heating rate (2.5 K/min) and then held at a constant temperature for 2 h. Fe(III) ions completely dissolved into TiO2 (anatase), forming Fe(III)-doped TiO2 (anatase), in the composition range of 0 ⩽ Fe/Ti ⩽ 0.3 (mole ratio). The properties of the obtained oxide depended on the oxidation method of FexTiS2. The electronic property and the valence stage of the Fe(III)-doped TiO2 (anatase) were examined. The activation energy of electronic conduction decreased with an increase of the doped amount of Fe(III) ions. The x-ray photoelectron spectroscopy result showed that the electron density on the Ti ion in the Fe(III)-doped TiO2 (anatase) was decreased by the Fe(III) doping.

Electrical relaxation in mixed alkali iron pyrophosphate glasses

The electrical relaxation of mixed alkali, sodium and potassium, iron pyrophosphate 20[(1 − x)K 2O– xNa 2O]–20Fe 2O 3–60P 2O 5, (0⩽ x⩽1), glasses has been studied in the frequency range from 0.1 Hz to 10 kHz and over the temperature range from 303 to 423 K. The ac conductivity as a function of the temperature was divided into two domains, one where the absolute magnitude of ac conductivity is close to the dc conductivity, and another where the absolute magnitude of ac conductivity is larger than the dc conductivity. The thermally stimulated polarization current technique was used to study dc conductivity in these iron phosphate glasses. The dc conductivity calculated from thermally stimulated current measurements was in agreement with the dc conductivity obtained from impedance measurements. At the same temperature, the dc conductivity varies slightly in the glasses with different sodium and potassium content. The conductivity was examined on the basis that the activation energy for electronic conduction is lower than that for ionic conduction. The conductivity in these mixed alkali iron phosphate glasses depends upon iron oxide content which suggests electronic conduction.

Nitrogenated amorphous carbon as a semiconductor

At present, hydrogenated amorphous carbon (a-C:H) is a poor electronic material primarily due to the excessive density of defect states in the band gap which act as trapping centres. The ability of nitrogen to improve the semiconducting properties of a-C:H is examined. A reduction in the activation energy for electronic conduction in nitrogenated a-C:H (a-C:H:N) films and the approximately constant optical band gap with increasing N content suggest that N influences the bulk electronic properties of a-C:H. Electron spin resonance shows a reduction of the density of gap states in a-C:H:N with increasing N content. Electron energy loss spectroscopy shows the films to be predominantly sp2 bonded with band edge properties which change significantly as a function of the N content. The C:H:N contents of the films were determined by elastic recoil detection analysis and Rutherford backscattering.