The effect of polarizability of cation dopants on oxygen diffusion in δ-Bi2O3 is determined using molecular-dynamics simulation in which the polarizability of the ions is treated within the shell model.
It is found that the magnitude of the oxygen polarizability has no affect on diffusion. However, the high cation polarizability,
associated with the lone pair of electrons in Bi, is found to be the key to achieving sustained oxygen diffusion. Consistent
with earlier experimental results, the oxygen diffusion path is found to be between oxygen equilibrium sites, which are displaced
from the 8c oxygen sites of the fluorite lattice. 相似文献
Luminescence photoexcitation spectra of α-Bi2O3 ceramics are investigated. Luminescence spectra were deconvoluted into fundamental components using the Alentsev-Fok method.
It is established that the luminescence spectra of α-Bi2O3 ceramics consist of three fundamental bands with maxima at 2.75, 2.40, and 1.97 eV. A comparison of the results with those
from an investigation of luminescence of various modifications of bismuth oxide and bismuth germanates suggests that luminescence
of these compounds is caused by radiation processes that occur in structural complexes that contain the bismuth ion in a nearest
oxygen environment.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 672–676, September–October, 2008. 相似文献
Samples of high-temperature superconducting oxide EuBa2Cu3O6 + δ (Eu-123) with total cationic composition Eu: Ba: Cu = 1: 2: 3 are investigated by means of local X-ray microanalysis and high-resolution transmission electron microscopy. The cationic nonstoichiometry of Eu-123 oxide is revealed. The particles of the studied samples are inhomogeneous in structure on the nanoscale, with two types of inhomogeneities: one with typical sizes of one to several nanometers, and one with typical sizes of 10 to 20 nm, respectively. 相似文献
An in-situ photoreduction strategy is applied to coat Ag nanowires (NWs) directly onto the surface of one-dimensional (1D) α-Fe2O3 nanotube arrays (NTAs) fabricated by anodization treatment, and their chemical composition, morphologies, optical properties, and stability are systematically characterized. Structural characterization results manifest that Ag NWs are successfully anchored on α-Fe2O3 NTAs with the average nanotube diameter of 80 nm and confirm the formation of Ag/α-Fe2O3 NTA heterostructure. An apparent red shift in absorption edges of Ag/α-Fe2O3 NTAs is observed. Particularly, the 30-min Ag/α-Fe2O3 NTAs with Ag NW’s average length of 100 nm display the best photocatalytic ability for photocatalytic degradation of methylene blue (MB) dye under visible light illumination, owing to the synergistic effect of the localized surface plasmon resonance (LSPR) on Ag NWs as well as the synergistic effect on the electron delivery and effective separation of photogenerated carriers between Ag NWs and α-Fe2O3 NTAs. In addition, the photogenerated holes (h+) and superoxide radicals (O2·?) played crucial roles during the photocatalytic process.
Graphical abstract Schematic illustration of the synergistic effect between Ag NWs and α-Fe2O3 NTA combined with conjectural photocatalytic degradation MB mechanism.
A method has been developed for fabricating nanoporous matrices based on anodic aluminum oxide for the deposition of ferromagnetic nanoparticles in them. The modes of deposition of strontium ferromolybdate thin films prepared by the ion-plasma method have been worked out, and the magnetic and magnetoresistive properties, structure, and composition of the films have been investigated. It has been revealed that the microstructure and properties of the strontium ferromolybdate films deposited by ionplasma sputtering depend on the deposition rate and the temperature of the substrate. Based on the measurement of the electrical resistivity of nanoheterostructures in a magnetic field, it has been found that the magnetoresistance reaches 14% at T = 15 K and B = 8 T, which is due to the manifestation of tunneling magnetoresistance. 相似文献
Hysteresis of the magnetoresistance of ceramic YBa2Cu3O~6.95 HTSC samples is studied at T = 77.3 K in an external magnetic field Hext changing in 0 → Hmax → 0 cycles, where Hmax is the maximum magnitude of Hext. Information is obtained about the dependences of the critical fields of Josephson weak links Hc2J, the lower critical fields of superconducting grains Hc1A, and the critical fields HBG-VG of the Bragg glass-vortex glass phase transition in the vortex matter on transport current I, magnetic field, and the mutual orientation of I and Hext. It is found that the magnetoresistance δρ+/ρ273 K measured with increasing Hext is significantly higher than Δρ?/ρ273 K and that Hc2J+ < Hc2J?, Hc1A+ < Hc1A?, and HBG-VG+ < HBG-VG?. 相似文献
Novel β-Bi2O3 crystals with nanoring and nanoplate surperstructures, which are composed of porous nanoparticles with mean pore diameter
of 8 nm, were produced via a facile soft chemistry route of solvent refluxing technique. Most of the rings have the average
inner diameter of 200 nm and the mean rim thickness of 20 nm. Photoluminescence spectra of the nanorings at room temperature
were investigated, which demonstrated that the rings presented excellent optical properties. The influence of aging time on
the morphology and structure of β-Bi2O3 superstructures was also studied, indicating that the nanoring superstructures transformed into nanoplates after a long aging
time. The formation mechanism of the β-Bi2O3 superstructures was also explored. This approach will be further extended to solvent-controlled fabrication of related oxides
with novel complex superstructures. 相似文献
Differential scanning calorimetry has been used to study the influence of temperature on the heat capacity of synthesized vanadates Zn2V2O7, (Cu0.56Zn1.44)V2O7, and (Cu1.0Zn1.0)V2O7. It is found that dependences Cp = f(T) have extremes. The thermodynamic properties of Zn2V2O7 have been determined. 相似文献
A series of glasses [(TeO2)x(B2O3)1−x]1−y[Ag2O]y with x = 70 and y = 10, 15, 20, 25 and 30 mol% were synthesised by rapid quenching. Longitudinal and shear ultrasonic velocity were measured
at room temperature and at 5 MHz frequency. Elastic properties, Poisson's ratio, microhardness, softening temperature and
Debye temperature have been calculated from the measured density and ultrasonic velocity at room temperature. The experimental
results indicate that the elastic constants depend upon the composition of the glasses and the role of the Ag2O inside the glass network is discussed. Estimated parameters based on Makishima–Mackenzie theory and bond compression model
were calculated in order to analyse the experimental elastic moduli. Comparison between the experimental elastic moduli data
obtained in the study and the calculated theoretically by the mentioned above models has been discussed. 相似文献
Experimental evidence for the existence of chain paramagnetic Curie-type contributions to the temperature dependence of static magnetic susceptibility χ(T) in the normal (nonsuperconducting) state is obtained for a series of pure YBa2Cu3O6 + δ high temperature superconductors with different oxygen contents (0.6 < δ ≤ 1). It is shown that the chain contribution is obvious on χ(T) curves only in the T < 150K range of temperatures, grows along with the number of oxygen vacancies in Cu1–O4 chains, and depends on the ordering of these vacancies. 相似文献
The influence of interaction between anisotropic γ-Fe2O3 nanoparticles on their coercive force Hc is studied. In samples where the degree of homogenization of anisotropic γ-Fe2O3 nanoparticles is high owing to mechanical, ultrasonic, and magnetic dispersion with subsequent filtering of resulting suspensions,
Hc is almost independent of volume concentration η of the particles when η varies between 4 × 10−4 and 10−1. In samples homogenized only mechanically, the Hc versus logη dependence is linear. 相似文献
Features of the formation of lead-ferroniobate compounds in the xBaCO3–(1 – x)PbO–Fe2O3–Nb2O5 system by solid-phase synthesis are investigated. For perovskite-type lead-ferroniobate solid solution, a single-phase concentration region is revealed at 1233 K. The crystalline structures of the synthesized compounds are refined using Rietveld analysis and the Pm3?m and R3m space groups. Ceramic samples of lead ferroniobate are studied by scanning electron microscopy. 相似文献
High field electrical switching on blown films of MoO3(60%)–P2O5(40%), MoO3(50%)–WO3(10%)–P2O5(40%), and MoO3(45%)–WO3(15%)–P2O5(40%) having different thicknesses was studied and compared. Switching was observed using two terminal samples. S-type current–voltage
characteristic (current-controlled negative resistance—CCNR) with memory was observed in molybdenum–phosphate glasses, but
N-type characteristic (voltage-controlled negative resistance—VCNR) with threshold in tungsten–molybdenum–phosphate glasses
was observed. The important observation was that with the addition of WO3 to binary MoO3–P2O5 led to a change of I–V characteristic from CCNR with memory to VCNR with threshold. The measurements of density and molar volume showed linear relation
between MoO3 content and density which decreased with the increase of MoO3 content. The samples’ thickness had no significant effect on threshold voltage. The attained results also indicated that
the electrode material had no effect on switching property of devices. The switching behavior of the devices did not show
any dependence on the polarity of the applied voltage. In terms of the effect of heat on the switching behavior of molybdenum–phosphate
glasses, it was found that threshold voltage decreases with increasing of temperature. Finally, the switching phenomenon was
explained by thermal (formation of crystalline filaments) and electronic models. 相似文献
Using time-resolved photoelectron spectroscopy, the decay channels of AuO2− and Au2O2− following photoexcitation with 3.1-eV photons have been studied. For AuO2−, a state with a rather long lifetime of 30 ps has been identified. Its decay path could not be determined but photodesorption
can be excluded. For Au2O2−, the spectra indicate O2 desorption after 3.1-eV photoexcitation on a time scale of 1 ps. While comparing these results on AunO2− with analogous data on AgnO2− clusters, a discernible pattern emerges: for dissociatively bound O2(AuO2−, Ag3O2−), there are long-living excited states which do not decay by oxygen desorption, while for molecular chemisorption (Au2O2−, Ag2O2−, Ag4O2−, Ag8O2−), the 3.1-eV photoexcitation triggers fast O2 desorption with a high quantum yield. 相似文献
The temperature dependence of the heat capacity of the HTSC YBa2Cu3O6 + δ is measured in the temperature range 1.8–300 K and the doping range 0.70 < δ < 0.86. The results obtained suggest that the
transition from the 60-K to the 90-K phase in YBa2Cu3O6 + δ has a percolation nature and that the underdoped 60-K phase represents a heterophase structure in which numerous superconducting
clusters are embedded into an insulating matrix. 相似文献
The magnetoresistance of ceramic YBa2Cu3O~6.5 HTSC samples is studied as a function of the mutual orientation of the current I and external magnetic field Hext at T = 77.3 K in magnetic fields of up to ~500 Oe. It is found that, if the demagnetization factor D is taken into account, the effective critical field of complete penetration of Josephson vortices into weak links Hc2Jeff does not depend on the mutual orientation of I and Hext. The lower critical field Hc1Aeff associated with the beginning of penetration of Abrikosov vortices into superconducting grains increases substantially with the angle between I and Hext. The strongest variation with the mutual orientation of I and Hext is exhibited by the critical field of the Bragg glass-vortex glass first-order phase transition HBG-VGeff and by the magnetoresistance jump at this phase transition. 相似文献
A comparative μSR study of ceramic samples of the EuMn2O5 and Eu0.8Ce0.2Mn2O5 multiferroics is performed in the temperature range from 15 to 300 K. It is found that the Ce doping of the EuMn2O5 sample slightly reduces the temperature of the magnetic phase transition from TN = 45 K for the EuMn2O5 sample to TN = 42.5 K for the Eu0.8Ce0.2Mn2O5 sample. Below the temperature TN for both samples, there are two types of localization of a thermalized muon with different temperature dependences of the precession frequency of the magnetic moment of the muon in an internal magnetic field. The higher frequency in both samples refers to the initial antiferromagnetic matrix. The behavior of this frequency in Eu0.8Ce0.2Mn2O5 follows the Curie–Weiss law with the exponent β = 0.29 ± 0.02, which differs from the value β = 0.39 standard for 3D Heisenberg magnetics and is observed in EuMn2O5, because of the strong frustration of the doped sample. The temperature-independent low frequency is due to the presence of Mn3+–Mn4+ ferromagnetic pairs located along the b axis of the antiferromagnetic matrix and in the regions of phase separation, which contain such ion pairs and eg electrons recharging them. In both samples, polarization losses are the same (about 20%) and are associated with the formation of Mn4+–Mn4+ + Mu complexes near Mn3+–Mn4+ ferromagnetic pairs. In the temperature interval from 25 to 45 K, the separation of the Eu0.8Ce0.2Mn2O5 structure into two fractions where the relaxation rates of polarization of muons differ by an order of magnitude is revealed. This effect is due to a change in the state of regions of phase separation (1D superlattices) at the indicated temperatures. Such effect in EuMn2O5 is significantly weaker. 相似文献
The synthesis procedure of the Li3Fe2(PO4)3?+?Fe2O3 composite is presented. The monoclinic (A type) and hematite phases were detected by X-ray diffraction after the synthesis of the composite. The structural α–β (at a temperature of 460 K) and β–γ (at a temperature of 523 K) phase transitions in the composite were indicated by the anomalies of the electrical conductivity, dielectric permittivity, and changes of activation energies of conductivity. Two phase transitions have been detected in the Li3Fe2(PO4)3?+?Fe2O3 composite by 57Fe Mössbauer spectroscopy: the phase transition in Li3Fe2(PO4)3 from the paramagnetic to antiferromagnetic phase at temperature TN?=?29.5 K and the Morin phase transition in Fe2O3 at temperature TM?=?235 K. 相似文献
The dependence of the magnetization relaxation rate S = ?d lnM/dlnt on temperature T is measured in YBa2Cu3O7 ? δ samples with various oxygen concentrations. It is found that the S(T) curve changes qualitatively when oxygen deficit δ exceeds the threshold value δth = 0.37. For δ < δth (Tc > 60 K, where Tc is the superconducting transition temperature), function S(T) has the well-known peak at T/Tc = 0.4. For δ > δth (at Tc < 51 K), this peak transforms into a plateau and a new sharp peak appears at T/Tc = 0.1. The threshold value δth of the oxygen deficit corresponds to the transition of the sample from the disordered state into the ordered state of oxygen vacancies. We consider the change in the shape of the S(T) curve as a macroscopic manifestation of this transition. 相似文献
Composite solid electrolytes in the system (1???x)Li2CO3–xAl2O3, with x?=?0.0–0.5 (mole), were synthesized by a sol–gel method. The synthesis carried out at low temperature resulted in voluminous and fluffy products. The obtained materials were characterized by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy/energy-dispersive X-ray, Fourier transform infrared spectroscopy and AC impedance spectroscopy. Structural analysis of the samples showed an amorphous feature of Li2CO3 and traces of α-LiAlO2, γ-LiAlO2 and LiAl5O8. The prepared composite samples possess high ionic conductivities at 130–180 °C on account of the presence of lithium aluminates as well as the formation of a high concentration of an amorphous phase of Li2CO3 via this sol–gel preparative technique. 相似文献