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.     

Electric conduction properties of boron-doped ceria

In the present study, the effect of the addition of boron on the electrical conduction properties of nanocrystalline cerium oxide (CeO₂) was investigated. Pellets consisting of pure CeO₂ and a mixture of CeO₂ and 10 mol.% of boron oxide (B-CeO₂ samples) were sintered at 800 °C as well as 1100 °C and their electrical conduction properties investigated by impedance spectroscopy at different temperatures and oxygen partial pressures. The nanocrystalline B-CeO₂ samples exhibit a higher electronic grain boundary conductivity and higher activation energy compared to a pure CeO₂ sample (1.41 eV for B-CeO₂ vs. 1.21 eV for pure CeO₂). According to electron energy-loss spectroscopy analysis, (i) boron can be detected only at the grain boundaries and (ii) cerium cations are lightly reduced at the grain boundaries. The results are consistent with both the formation of a space charge layer with a positive space charge potential but also with conduction along a glassy cerium-boron-oxide phase.     

Anomalous conductivity and microstructure in gadolinium doped ceria prepared from nano-sized powder

The temperature and the oxygen partial pressure dependences of the electron and hole conductivities were measured by the dc polarization method using a Hebb–Wagner's ion blocking cell for Gd_0.2Ce_0.8O_1.9 polycrystalline bodies with grain size of 0.5 μm prepared by sintering of nano-sized powder. A significant enrichment of gadolinium was observed in the vicinity of the grain boundary by TEM/EDS analyses. The electron conductivity were comparable with those of conventional Gd_0.2Ce_0.8O_1.9 polycrystalline body with grain size of 2 μm, and it followed p(O₂)^− 1/4 dependence at temperatures T = 973–1273 K. However, the observed hole conductivity was higher than that of conventional Gd_0.2Ce_0.8O_1.9, and it did not follow p(O₂)^1/4 dependence. This anomalous p(O₂) dependence disappeared after the sample was treated at T = 1773 K for 38 h and grain size was enlarged to 2–10 μm.     

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⁺.     

Magnetic properties of silicon doped with gadolinium

The magnetic semiconductor Gd_xSi_1-x was prepared by low-energy dual ion-beam epitaxy. Gd_xSi_1-x shows excellent magnetic properties at room temperature. A high magnetic moment of 10 _B per Gd atom is observed. The high atomic magnetic moment is interpreted as being a result of the RKKY mechanism. The indirect exchange interaction between ions is strong at large distances due to the low state density of the carriers in the magnetic semiconductor. PACS 81.05.Zx; 81.15.Hi; 75.50.Pp; 75.70.-i; 61.72.Tt     

Electrical properties of nanocrystalline Sm-doped ceria ceramics

Electrical properties of nanocrystalline materials are usually different than that of microcrystalline. This phenomenon is not fully understood and therefore it is of continuous interest in the scientific community. In this paper, the results of investigation of nanocrystalline Sm-doped ceria prepared by a net shape technology are presented. The net shape technology is a relatively new ceramic preparation method, which combine powder and polymer precursor methods. The ceramics prepared in this way can be dense and nanocrystalline. Net-shaped prepared Sm-doped ceria was fabricated in the form of bulk ceramics and film on platinum foil. Their electrical properties were investigated and compared with the results obtained from microcrystalline sample.     

Dielectric and optical properties of gadolinium doped bismuth ferrite

Polycrystalline samples of a Gd _x Bi_1?x FeO₃ system are prepared by a conventional ceramic technology. Temperature and frequency dependences of a component of permittivity in the range of radio- and ultra-high frequencies are investigated. Features of the behavior of the reflectance spectra and spectra of the components of the dielectric and optical functions in the region of lattice and electronic resonances are investigated.     

Si被注入Gd后的磁性及其整流特性的研究

采用离子束技术，在n型硅基片中注入稀土元素钆，制备了磁性-非磁性p-n结.磁性层Gd_xSi_1-x表现出优良的磁学性能，高居里温度，高原子磁矩(利用RKKY模 型 可以得到解释)，低矫顽力，并保持着半导体的属性，磁性-非磁性p-n结具有整流特性，但 没有观察到明显的磁电阻效应. 关键词： 磁性半导体 磁性p-n结 钆的硅化物 离子束外延     

Dielectric properties of titanium and gadolinium doped MgO single crystals

The dielectric properties of titanium doped magnesium oxide (Ti/MgO) and gadolinium doped magnesium oxide (Gd/MgO) single crystals have been measured at room temperature over the frequency range 500 Hz to 50 kHz. For both the crystals, the dielectric constant is found to be independent of frequency and the ac conductivity Re{_ae} agrees well with the relation Re{_ae} ⁿ , being the angular frequency with n=0.84±0.05 for Ti/MgO andn=0.81±0.03 for Gd/MgO. The data fits well with the relation ^n–1(n<1), being the dielectric loss factor. An explanation may be found on the basis of the hopping phenomenon.     

Electrical transport properties of gadolinium scandium gallium garnet

Electrical conductivity and thermoelectric power are measured on a single crystal of Gd_3.0Sc_1.8Ga_3.2O₁₂ (GSGG) between 1273 and 1673 K. The measurements are made both in air and in controlled atmospheres, and P_O2 varies from 10^?1.68 to 10^?5.6 MPa. The data indicate GSGG may well be a mixed conductor in this temperature and P_O2 range, with n-type electronic conductivity and ionic transport on the oxygen sublattice. Changes in temperature induce long-lived disequilibrium in electrical conductivity of GSGG (over 30 h at T < 1373 K) that can be explained by temperature dependent cation redistribution. The effective activation energy for equilibrium electrical conductivity is E_a = 2.40 ± 0.05 eV, as opposed to values of E_a between 1.8 and 2.2 eV during actual temperature changes. An additional contribution in the equilibrium E_a, due to thermally activated cation redistribution, can account for the higher value seen.     

Electrical properties of n-type Si layers doped with proton bombardment induced shallow donors

Sheet Hall coefficients and resistivities of n-type Si layers doped with shallow donors produced by proton bombardment have been measured between 35 and 300°K. The donor ionization energy is (26 ± 1) meV. The donor concentration profile has been determined.     

Electrical properties of heterovalently doped apatite-like oxosilicates

Oxygen-ion-conductive apatite-like oxosilicate and silicophosphate ceramics has been prepared by sintering sol-gel synthesis products at temperatures 200°C below those of solid-phase synthesis. The electrical properties of the ceramics obtained have been studied by impedance spectroscopy in the range 400–1000°C. A positive effect of heterovalent substitutions in the silicon sublattice on the bulk and intergrain conductivities is established. The increase in the oxygen-ion conductivity in La_9.6Si_5.7Mg_0.3O_26.1 in comparison with the other studied oxosilicates by more than two orders of magnitude is related to the formation of additional interstitial positions for oxygen ions as a result of partial substitution of the silicon ion, tetrahedrally coordinated by oxygen, with the Mg ion having a characteristic octahedral coordinatio     

Electrical properties of cadmium and zinc doped CuInS2

The electrical resistivity and mobility of Cd and Zn doped CuInS₂ single crystals grown by a Bridgman technique have been investigated. Crystals annealed in Cd or Zn vapor at high temperatures (～ 800°C) exhibit degenerate behaviour while those crystals annealed at more moderate temperatures (～650°C) show ionized impurity conduction with a shallow activation energy on the order of 0.004 eV. Resistivities as low as 0.15 Ω-cm and mobilities as high as 90 cm²/v-sec have been observed.     

Transport properties and stability of cobalt doped proton conducting oxides

Cobalt doping between 2 and 10 at.% was utilized to lower the required sintering temperature of materials in the series BaCe_0.5Zr_0.4(Y,Yb)_0.1 ? yCo_yO_3 ? δ to between 1373 and 1698 K. The required sintering temperature decreased with increasing Co content; however, significant electronic conductivity was observed in both oxidizing and reducing environments for materials with 10 at.% Co. This was accompanied by a loss of chemical stability in H₂O/H₂ and CO₂ environments. BaCe_0.5Zr_0.4Yb_0.07Co_0.03O_3 ? δ was stable in these environments and provided the highest proton conductivity of the materials tested, 1.98 × 10^? 3 S/cm at 923 K in humidified H₂. Measurements in a hydrogen concentration cell indicated that the total ionic transference number for this material was between 0.86 and 1.00 with proton transference number between 0.84 and 0.75 at 773 and 973 K respectively. Under oxidizing conditions, the ionic transference number decreased to below 0.10. The grain boundary resistance dominated the total conductivity at low temperatures but was found to decrease with increased sintering temperature due to grain growth.     

Spectral and luminescence properties of gadolinium gallium garnet epitaxial films doped with terbium

Gadolinium gallium garnet single-crystal films containing terbium are grown through liquid-phase epitaxy from a supercooled solution melt in the PbO-B₂O₃ system. The optical absorption spectra in the wavelength range 0.2–10.0 μm and the luminescence spectra excited by synchrotron radiation with energies in the range 3.5–30.0 eV are investigated at temperatures of 10 and 300 K. It is revealed that the optical absorption spectra contain an absorption band with the maximum at a wavelength λ ≈0.260 μm, which corresponds to the spin-allowed electric dipole transition between the electronic configurations 4f ⁸(⁷ F ₆) → 4f ⁷(⁸ S)5d of the Tb³⁺ ions. The narrow low-intensity absorption bands attributed to the 4f → 4f transitions from the ⁷ F ₆ ground level to the ⁷ F _0–5 multiplet levels of the Tb³⁺ ions are observed in the wavelength range 1.7–10.0 μm. In the luminescence spectra measured at a temperature of 10 K, the highest intensity is observed for a band with the maximum at a wavelength λ ≈ 0.544 μm, which is associated with the ⁵ D ₄ → ⁷ F ₅ radiative transition in the Tb³⁺ ion.     

Electrical properties of doped single crystals of ZnSb

The conductivity , thermo-emf , and Hall constant R are reported for the range 100 °-490 ° K for ZnSb crystals doped with Ag, Au, Ga, In, Sn, Pb, and Te. Ag, Au, sn, and Pb act as acceptors, while In and Te increase the hole concentration, increase , and leduce . This occuis at relatively high concentrations by foimation of InSb and ZnTe molecules. Ga in ZnSb acts as a donor (compensating) component.     

铂掺杂扶手椅型石墨烯纳米带的电学特性研究

本文采用基于密度泛函理论(DFT)的第一性原理计算了铂原子填充扶手椅型石墨烯纳米带(AGNR)中双空位结构的电学性能.计算结果表明: 通过控制铂原子的掺杂位置, 可以实现纳米带循环经历小带隙半导体—金属—大带隙半导体的相变过程; 纳米带边缘位置是铂原子掺杂的最稳定位置, 边缘掺杂纳米带的带隙值随宽度的变化与本征AGNR一样可用三簇曲线表示, 但在较大宽度时简并成两条曲线, 一定程度上抑制了带隙值的振荡; 并且铂原子边缘掺杂导致宽度系数N_a = 3p和3p + 1(p是一个整数)的几个较窄纳米带的带隙中出现杂质能级, 有效地降低了其过大的带隙值. 此外, 铂掺杂AGNR的能带结构对掺杂浓度不是很敏感, 从而降低了对实验精度的挑战. 本文的计算有利于推动石墨烯纳米带在纳米电子学方面的应用.     

Electrical conductivity and dielectric properties of sulfamic acid doped polyaniline

The temperature and frequency dependence of dielectric constant (ε′) and dielectric loss (ε″) is studied for different samples of polyaniline (PANI), doped with different concentration of sulfamic acid in the frequency range (10–100 kHz) and temperature range (300–400 K). The dc conductivity has also been measured to see the effect of sulfamic acid and the conduction mechanism has been explained by the propagation of polaron through a conjugated polymer chain due to shifting of double bonds (alternation), which gives rise to electrical conduction.     

Electrical and optical properties of chlorine doped SnO2 coatings

Pure and chlorine doped SnO₂ coatings are prepared using spray pyrolysis technique. The effect of chlorine doping on the electrical and optical properties of SnO₂ are studied and compared with other types of doping. The absorption coefficient data vs photon energy are analysed and interpreted in terms of direct and indirect allowed transitions. The electrical resistivity is minimum and the figure of merit is maximum for SnO₂ coatings doped with 0.4 wt% Cl.