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1.
Temperature dependence of d.c. conductivity is studied ina- Se75In25-x
Pb
x
thin films wherex is varied from 0–10. From these measurements, the values of the pre-exponential factor (σ0) and activation energy (ΔE) are calculated for each glassy alloy. An approximate linear dependence of ln σ0 on AE is observed in this glassy system with good agreement between the expected and calculated σ0 values using Meyer-Neldel rule. Linear dependence of ln σ0 on ΔE in case of amorphous materials indicates that the conduction band tails a finite energy distance towards the valence band
and Fermi level is controlled by fixed dominant hole levels deeper in the gap. 相似文献
2.
The superconducting properties of iodine-intercalated high-temperature superconducting Bi2Sr2Ca2Cu3O10+x
phase (Bi-2223) were systematically studied. It was found that for samples containing a significant amount of Bi2Sr2CaCu2O8+x
, iodine intercalation results in the dramatic decrease of the inter-granular critical current density, as well as a significant
decrease of the critical temperature (T
c), the critical current density in the grains (J
cg), and of the amount of Bi-2223. For samples with a large amount of Bi-2223, T
c changes insignificantly, whereas J
cg can even increase. We argue that the different behavior of the superconducting parameters is the result of various oxygen
concentrations, and we explain the effect of iodine intercalation based on the parabolic dependence between T
c and the number of holes per CuO2 layer. The H(T) curves (determined from the peak position in the loss signal of ac susceptibility) for intercalated samples deviate significantly
from the quasi 2D-like behavior, pointing toward an enhancement of the 3D fluctuations of vortices. For the change in the
values and dimensionality of the flux pinning in the process of the intercalation, we attempted a qualitative explanation
based on the models proposed in literature. 相似文献
3.
Pellets of ceramic Na1−xKxNbO3 (x = 0, 0.2 and 0.5), were prepared by conventional solid-state reaction method. Prepared samples were characterized using
XRD and SEM. The frequency and temperature variation of dielectric constant, loss tangent and dielectric conductivity of prepared
samples were measured in the frequency range from 10 KHz-1 MHz, and in the temperature range from 50–250°C for x = 0.2 and
0.5, and between 50 and 480°C for x = 0 compositions. It was observed that the dielectric constant and loss tangent decrease,
and conductivity increases with increasing frequency. Near the transition temperature the material shows anomalous behaviour
for the observed properties, and the peaks of dielectric constant and loss tangent were observed shifting towards lower temperature
with increasing frequency. 相似文献
4.
The formation mechanisms of Li x Na1 ?x Ta y Nb1 ? y O3 perovskite solid solutions in the Li2CO3-Na2CO3-Nb2O5-Ta2O5 system have been studied by x-ray diffraction, differential thermal analysis, thermogravimetry, IR spectroscopy, and mass spectrometry at temperatures from 300 to 1100°C. The results indicate that the synthesis of Li x Na1 ? x Ta y Nb1 ? y O3 solid solutions involves a complex sequence of consecutive and parallel solid-state reactions. An optimized synthesis procedure for Li x Na1 ? x Ta y Nb1 ? y O3 solid solutions is proposed. 相似文献
5.
This review describes the principles of semiconductor spintronics, represents the physicochemical properties of materials
based on manganese-alloyed AIIBIVC2V compounds, considers the results from theoretical simulation of magnetic properties of AIIBIVC2V alloyed with 3d metals, summarizes the basic approaches to explanation of ferromagnetism with Curie points above room temperature
arising in AIIBIVC2V:Mn, and indicates promising ways to synthesize and study magnetic semiconductors based on chalcopyrites AIIBIVC2V in order to produce a suitable material for spintronic devices. 相似文献
6.
K. F. Eid O. Maksimov M. B. Stone P. Schiffer N. Samarth 《Journal of Superconductivity and Novel Magnetism》2005,18(3):421-426
We discuss the annealing-dependence of exchange bias in Ga1−
x
Mn
x
As epilayers that are overgrown with Mn. Although pure Mn is a known antiferromagnet, we find that the as-grown Mn overlayer
does not produce any exchange coupling with Ga1−
x
Mn
x
As. Rather, our studies indicate that annealing in air is essential for creating the standard signatures of exchange bias
(a clear shift in the magnetization hysteresis loop and an increased coercive field). We use X-ray photoelectron spectroscopy
to characterize the compositional depth profile of both as-grown and rapid thermal annealed samples. These studies demonstrate
that the cleanest exchange bias arises when the Mn overlayer is completely converted into MnO. 相似文献
7.
New potassium ion conducting solid electrolytes based on potassium monoferrite have been prepared through partial substitution
of the divalent cation Cd2+ on the potassium site, and their properties have been investigated. The introduction of cadmium cations sharply increases
the electrical conductivity of KFeO2 over the entire temperature range studied. In addition to the maximum in conductivity at the boundary of the K1 − 2x
Cd
x
FeO2 solid solution, there is a maximum at a higher cadmium content (x = 0.30–0.35). The possible origins of this maximum are discussed. 相似文献
8.
G. V. Tikhonov 《Radiochemistry》2009,51(3):256-261
The effect of the synthesis conditions on the properties of inorganic laser-active liquids POCl3-SbCl5-235UO 2 2+ -Nd3+ is considered. The kinetic dependences of the U(IV) content and decay time of the Nd3+ luminescence in POCl3-SbCl5-235UO 2 2+ -Nd3+ solutions for various synthesis procedures at 380 K have been obtained. In POCl3-SbCl5-235UO 2 2+ -Nd3+ solutions, nonradiative energy transfer Nd3+ → U4+ is observed, and quenching of the Nd3+ luminescence is described by the Stern-Volmer law: k q = (6.4 ± 0.6) × 105 l mol?1 s?1. Laser liquids POCl3-SbCl5-235UO 2 2+ -Nd3+ with neodymium concentration of up to 0.7 M, uranyl concentration of up to 0.1 M, and decay time of the Nd3+ luminescence of up to 220 μs have been prepared for the first time. 相似文献
9.
A. S. Antsyshkina G. G. Sadikov T. I. Koneshova V. S. Sergienko 《Inorganic Materials》2004,40(12):1259-1263
The structure of three compounds in the Cu2Se-In2Se3-Cr2Se3 system near CuInCr2Se5 is determined by single-crystal x-ray diffraction: CuInCr4Se8 (I), Cu2In2Se4 (II), and Cu0.5In0.5Se (III). I has a cubic (spinel type) structure: a = 10.606(4) Å, Z = 4, sp. gr. F43m. II has a pseudotetragonal (sphalerite type) structure: a = 5.774(2) Å, c = 11.617(6) Å. The structure of II was solved in a reduced unit cell with a = 5.774(2) Å, b = 5.774(2) Å, c = 7.095(6) Å, = 113.95(5)°, = 113.95(5)°, = 90.00(4)°, Z = 1, sp. gr. P1. III has a triclinic cell (disordered structure of II): a = 4.088(1) Å, b = 4.091(2) Å, c = 4.101(1) Å, = 60.05(1)°, = 60.08(1)°, = 89.98(4)°, Z = 1, sp. gr. P1. The Cu and In atoms in I sit in inequivalent tetrahedral sites, and the Cr atoms reside in octahedral interstices of the close packing of Se atoms. The bond lengths are In–Se = 2.538(6), Cr(1)–Se(1) = 2.514(7), Cr(1)–Se(2) = 2.576(8), and Cu–Se = 2.437(5) Å. In II, all of the atoms sit in tetrahedral sites; the mean bond lengths are In–Se = 2.578(6) and Cu–Se = 2.44(1) Å. In III, the Cu and In atoms are fully disordered in the same tetrahedral site; the mean Cu(In)–Se bond length is 2.508(6) Å.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1435–1439.Original Russian Text Copyright © 2004 by Antsyshkina, Sadikov, Koneshova, Sergienko. 相似文献
10.
Anuj Kumar Shiva Kumar Monika Mudgel H. Kishan V. P. S. Awana 《Journal of Superconductivity and Novel Magnetism》2008,21(4):259-264
We report synthesis and magnetic characterization of variously processed magneto-superconducting (Rutheno-cuprates) RuSr2Eu1.5Ce0.5Cu2O10−δ
. The compound crystallizes in I4/mmm tetragonal structure. Magnetization measurements showed bulk magnetic ordering and superconductivity
at around 100 K and 30 K, respectively. Further, the careful examination of the low field magnetic susceptibility reveals
two minor magnetic transitions at around 135 K and 200 K, in addition to the major transition at 100 K. When the samples are
processed in different environments of air, O2 and slightly pressurized O2, the nature of magnetic transitions and the superconductivity changes dramatically. The highest superconducting transition
is achieved for the high pressure O2 annealed samples and the lowest for the air annealed one. On the other hand, the minor magnetic transitions are more prominent
in air-annealed samples. Though the minor magnetic transitions are intrinsic to all variously processed samples, they are
not clearly seen for higher O2 content samples. Basically, the Ru spins order antiferro magnetically at around 200 K (first minor transition), and reorients
themselves at 125 K (second minor transition) before finally ordering in canted ferromagnetic state or a spin glass structure.
These results can be explained on the basis of fluctuating valance of Ru4+/Ru5+.
相似文献
11.
E. V. Dudnik V. V. Tsukrenko A. V. Shevchenko A. K. Ruban L. M. Lopato 《Inorganic Materials》2011,47(10):1107-1110
We have studied the properties of nanocrystalline ZrO2-Y2O3-CeO2-CoO-Al2O3 powders prepared via hydrothermal treatment of a mixture of coprecipitated hydroxides at 210°C. A number of general trends
are identified in the variation of the properties of the synthesized powders during heat treatment at temperatures from 500
to 1200°C. Our results demonstrate that the addition of 0.3 mol % CoO to nanocrystalline ZrO2-based powders containing 1 to 5 mol % Al2O3 allows one to obtain composites with good sinterability at a reduced temperature (1200°C). 相似文献
12.
Ana Cristina F. M. Costa Márcio R. Morelli Ruth H. G. A. Kiminami 《Journal of Materials Science》2007,42(3):779-783
An investigation was made of samples having a chemical formula of Ni1−x
Zn
x
Fe2O4, where x = 0.3, 0.5 and 0.7. The samples were prepared by the reaction combustion synthesis method and sintered at 1,200 °C/2 h in
a static air atmosphere. The influence of the Zn concentration on the relative density, microstructure and magnetic properties
of the samples was studied. X-ray diffraction, scanning electron microscopy and magnetic hysteresis loop tracer were used
to analyze the compositions. The samples were found to have a spinel cubic structure, sintered density of 92.9%–98.8% of the
corresponding X-ray density, homogeneous microstructure with grain size ranging from 1.37 to 3.36 μm, maximum flux density
of 0.16–0.35 T, field coercivity ranging from 17 to 168 A/m, and loss hysteresis of 1.5–105 W/kg. Increased grain growth,
with fine pores inside the grains, was found to occur as the Zn concentration increased. The overall findings are discussed
here in light of the existing understanding of these systems. 相似文献
13.
14.
Y2O3 + Nd2O3 co-stabilized ZrO2-based composites with 40 vol% WC were fully densified by pulsed electric current sintering (PECS) at 1350 °C and 1450 °C.
The influence of the PECS temperature and Nd2O3 co-stabilizer content on the densification, hardness, fracture toughness and bending strength of the composites was investigated.
The best combination of properties was obtained for a 1 mol% Y2O3 and 0.75 mol% Nd2O3 co-stabilized composite densified for 2 min at 1450 °C under a pressure of 62 MPa, resulting in a hardness of 15.5 ± 0.2
GPa, an excellent toughness of 9.6 ± 0.4 MPa.m0.5 and an impressive 3-point bending strength of 2.04 ± 0.08 GPa. The hydrothermal stability of the 1 mol% Y2O3 + 1 mol% Nd2O3 co-stabilized ZrO2-WC (60/40) composites was compared with that of the equivalent 2 mol% Y2O3 stabilized ceramic. The double stabilized composite did not degrade in 1.5 MPa steam at 200 °C after 4000 min, whereas the
yttria stabilized composite degraded after less than 2000 min. Moreover, the (1Y,1Nd) ZrO2-WC composites have a substantially higher toughness (~9 MPa.m0.5) than their 2Y stabilized equivalents (~7 MPa.m0.5). 相似文献
15.
16.
Perovskite structure based ceramic precursors have a characteristic property of substitution in the “A” site of the ABO3 structure. This makes them a potential material for nuclear waste management in synthetic rock (SYNROC) technology. In order
to simulate the mechanism of rare earth fixation in perovskite, Lax Ca1−xTiO3 (wherex = 0.05) has been synthesized through ceramic route by taking calculated quantities of oxides of Ca, Ti and La as starting
materials. Solid state synthesis has been carried out by repeated pelletizing and sintering the finely powdered oxide mixture
in a muffle furnace at 1050°C. The ceramic phase has been characterized by its powder diffraction pattern. Step analysis data
has been used to determine the structure of solid solution of lanthanum substituted calcium titanate. The SEM and EDAX analyses
also confirm that the CaTiO3 can act as a host for lanthanum. X-ray data has been interpreted using CRYSFIRE and POWDERCELL softwares. Theh, k, l values for different lattice planes have been generated from the experimental data. The lanthanum substituted perovskite
crystallizes in orthorhombic symmetry with space groupP n m a (#62). Following unit cell parameters have been calculated:a = 5.410,b = 7.631,c = 5.382. The calculated and observed values of corresponding intensities, 2θ, and density show good agreement. GSAS based
calculation for bond distances Ti-O, Ca-O, La-O and bond angles Ti-O-Ca, Ca-O-Ca, La-O-Ti have been reported. 相似文献
17.
John D. Dow Dale R. Harshman Anthony T. Fiory 《Journal of Superconductivity and Novel Magnetism》2010,23(5):641-644
The superconducting hole condensate of YBa2Cu3O7 resides in its BaO layers, and involves s-wave paired holes. This picture differs from the currently widespread opinion that the superconductivity at the surface and
in the bulk is d-like, and resides in the CuO2 planes: it is the main reason why high-temperature superconductivity has been unsolved. 相似文献
18.
Shanxing Huang Hongwei Qin Peng Song Xing Liu Lun Li Rui Zhang Jifan Hu Hongdan Yan Minhua Jiang 《Journal of Materials Science》2007,42(24):9973-9977
Rare earth oxides LaFe1-x
Zn
x
O3 were synthesized by sol–gel method. The X-ray diffraction patterns (XRD) showed that LaFe1-x
Zn
x
O3oxides are single phase with orthorhombic perovskite structure, they all show p-type semiconducting properties. Among nanocrystalline
LaFe1-x
Zn
x
O3 oxides, LaFe0.77Zn0.23O3 exhibits the highest sensitivity of 44.5 to 100 ppm formaldehyde. The optimal working temperature was found to be around
240 °C. Moreover the LaFe0.77Zn0.23O3 exhibites short response and recovery time to 100 ppm formaldehyde. The lattice parameter doesn’t agree with Vegard’s law
with the increasing Zn content, and the relative density was 70–80%. 相似文献
19.
Basavaraj Angadi V. M. Jali M. T. Lagare N. S. Kini A. M. Umarji 《Bulletin of Materials Science》2002,25(3):191-196
The low thermal expansion ceramic system, Ca1-xSr{x}Zr4P6O24, for the compositions with x = 0, 0.25, 0.50, 0.75 and 1 was synthesized by solid-state reaction. The sintering characteristics
were ascertained by bulk density measurements. The fracture surface microstructure examined by scanning electron microscopy
showed the average grain size of 2.47 μm for all the compositions. The thermal expansion data for these ceramic systems over
the temperature range 25–800°C is reported. The sinterability of various solid solutions and the hysteresis in dilatometric
behaviour are shown to be related to the crystallographic thermal expansion anisotropy. A steady increase in the amount of
porosity and critical grain size with increase in x is suggested to explain the observed decrease in the hysteresis. 相似文献