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1.
Thermodynamic properties of Ca1 − x
Er
x
F2 + x
and Ca1 − x
Yb
x
F2 + x
heterovalent solid solutions
N. V. Moiseev P. A. Popov P. P. Fedorov E. A. Garibin V. M. Reiterov 《Inorganic Materials》2013,49(3):325-328
The heat capacity of single crystals of the Ca1 ? x Er x F2 + x (x = 0.05, 0.10) and Ca0.95Yb0.05F2.05 fluorite solid solutions was determined by adiabatic calorimetry in the temperature range 55–300 K. The results were used to obtain temperature dependences of the Debye characteristic temperature, entropy, and enthalpy for the solid solutions. 相似文献
2.
A superconductor/semimetal/superconductor (S/SM/S) Josephson junction has been developed. We have used an alloy of Pb1–x
Bi
x
(0x 0.6) as the superconductor and Bi as the semimetal. By irradiating at X-band microwave of 10 GHz, Shapiro steps were observed for various bismuth barrier thicknesses inÅ and bismuth weight ratiosx. Finally, we obtained the empirical relationship for barrier thickness, below which microwaves could be detected for various bismuth weight ratiosx at the temperature of 4.2 K. 相似文献
3.
This paper examines the possibility of producing lattice-matched p-n heterojunctions based on epitaxial n-Pb1 ? x Mn x Se (x = 0.02) and p-PbSe1 ? x S x (x = 0.04) films. The heterojunctions have been grown by molecular beam epitaxy in a single processing cycle, without breaking the vacuum, using a compensating Se vapor source in the growth process. Optimal conditions have been found for the growth of structurally perfect (W 1/2 = 90″-100″) epitaxial films and fabrication of lattice-matched heterojunctions based on such films, photosensitive in the IR spectral region. 相似文献
4.
H. Takahashi H. Okada K. Igawa Y. Kamihara M. Hirano H. Hosono K. Matsubayashi Y. Uwatoko 《Journal of Superconductivity and Novel Magnetism》2009,22(6):595-598
The pressure dependence on the superconducting transition temperature (T
c
) was investigated for the iron-based superconductors LaFeAsO1−x
F
x
and SmFeAsO1−x
F
x
. The T
c
’s increase largely for LaFeAsO1−x
F
x
with a small increase of pressure, while a sharp decrease of T
c
was observed for SmFeAsO1−x
F
x
. The electrical resistivity measurements reveal pressure-induced superconductivity for undoped LaFeAsO and SmFeAsO. These
pressure effects seem to be related to an anisotropic decrease of the lattice constants under high pressure from the x-ray
diffraction measurements up to 10 GPa for the LaFeAsO1−x
F
x
system. 相似文献
5.
Materials of the hollandite structure with the general formulae Kx Alx Ti8–x O16 and Kx Mgx/2 Ti8–x/2 O16 have been synthesized in the composition range 1.6x2.0 and their dielectric properties have been measured in the temperature range 77 to 800 K and the frequency range 10–3 to 106 Hz. The observed response shows a whole range of features characteristic for both charge carrier and dipolar polarization processes and these are seen as being associated with the one-dimensional transport in channels in the hollandite structure. At low temperatures the dominant response is the universal dielectric relation in which the loss follows the law x() n–1, with the exponent n<1 and equal specifically to approximately 0.7. This is followed at 120 to 180 K by a distinct loss peak superimposed on the above law, and finally at higher temperatures by a region of strong dispersion which is associated with strongly interacting many-body processes between charged carriers restricted by defects to move in limited regions of the channels. 相似文献
6.
O. Parkash K. D. Mandal C. C. Christopher M. S. Sastry D. Kumar 《Journal of Materials Science》1996,31(17):4705-4708
The possibility of the formation of a solid solution in the Sr1–x
La
x
Sn1–x
Co
x
O3 system has been explored. Single-phase solid solution forms in the compositions for x0.10. All single-phase solid solution compositions have a cubic structure similar to SrSnO3. The dielectric behaviour of these solid solution compositions has been studied as a function of temperature and frequency. The frequency dependence of dielectric constant and dielectric loss in these materials indicates that space charge polarization contributes significantly to their observed dielectric parameters. Microstructural studies show the presence of well-faceted grains. The average grain size in these samples is small. 相似文献
7.
W. T. Jin S. J. Hao X. J. Zhang Y. Zhao H. Zhang 《Journal of Superconductivity and Novel Magnetism》2010,23(5):847-850
Single-phase samples of a self-compensating Y1?x Ca x Ba2?x La x Cu3O z system were synthesized through a solid-state reaction method with x<0.4. The structure of all samples were characterized by X-ray diffraction and refined by the Rietveld method. Superconducting properties have been investigated by the DC magnetization measurement. The critical temperature (T c ) decreases evidently with the increment of x although the carrier concentration remains constant in the samples for different doping level. Careful study of the chemical bonds in the crystalline lattice demonstrates that the T c is closely correlated to four pairs of bond angles in the unit cell. The analysis indicates that crystalline structure is one of the important factors to high-T c superconductivity, and its influence is independent of the carrier concentration. 相似文献
8.
M. A. Tena G. Monrós J. Carda E. Cordoncillo P. Escribano J. Alarcón 《Journal of Materials Science》1994,29(14):3817-3821
In this study, Cr
x
Ti1–2x
Nb
x
O2 (0 x 0.5) rutile solid solutions have been synthesized from gels built from hydrolysis-condensation of Cr (III) acetylacetonate, NbCl5 and Ti (IV) isopropoxide mixture (polymeric gel). Characterization of these solid solutions was carried out by X-ray diffraction, ultraviolet-visible and infrared spectroscopy, differential thermal and thermogravimetric analysis and CIELAB (Commission Internationale del'Eclairage L*a*b*) parameter measurements. The results obtained by the polymeric gel method were compared with those obtained by traditional ceramic synthesis. This comparison reveals some differences with regard to synthesis temperatures and reaction mechanisms. The formation of Cr
x
Ti1–2x
Nb
x
O2 (0 x 0.5) rutile solid solutions by the ceramic method requires temperatures of about 1200°C and soaking times of several days. These solid solutions are synthesized at 1000°C in 24 h by the polymeric gel method. In ceramic synthesis, the CrNbO4 compound with rutile structure appears as an intermediate compound in the formation of rutile solid solutions. In polymeric gel synthesis, however, the CrNbO4 rutile compound was not detected in the samples. 相似文献
9.
A detailed study of the process of crystallization in amorphous Fe25Sc75, Fe28 Sc72 and Fe25Sc45Zr30 alloys has been carried out using differential scanning calorimetry, X-ray diffraction and Mössbauer spectroscopic techniques. The complex multi-stage transformation process in Fe25Sc75 and Fe28Sc72 is understood in terms of polymorphous formation of an intermediate metastable crystalline phase of orthorhombic structure (a = 0.521 nm, b = 0.648 nm and c = 1.212 nm) and of likely Sc3Fe stoichiometry, before final eutectic crystallization to stable Fe2Sc and -Sc. 相似文献
10.
Makoto Matsuura 《Journal of Materials Science》1986,21(6):2207-2211
The crystallization kinetics of the melt-spun Fe-Zr metallic glasses in the iron-rich region has been investigated by means of DSC and X-ray diffraction. The crystallization mode changes with iron concentration. In the lower iron region, 20 x 25, the Fe
x
Zr100–x glasses crystallize into -Zr and Ti2Ni-type FeZr2 with an accompanying sharp and large exotherm at the first crystallization step and immediately after this step, they transform into orthorhombic FeZr3. On the other hand, the alloys with 35 x 40 exhibit a gradual exotherm which initiates from a temperature far below the definite crystallization temperature (T
x). The Fe-Zr metallic glasses in this concentration region crystallize polymorphously into the oxygenstabilized Ti2Ni-type FeZr2 with accompanying relatively small and composite exotherms. The annealing at a temperature where the gradual exotherm occurs for the alloys with 30 x 40 does not cause any changes of X-ray halo pattern but results in the reduction of the heat of exotherm due to the crystallization. 相似文献
11.
N. Fujiwara S. Matsuishi Y. Kamihara H. Hosono 《Journal of Superconductivity and Novel Magnetism》2013,26(8):2689-2692
In iron-based pnictides, one of the interesting topics is homogeneous coexistence or phase segregation at the boundary between antiferromagnetic (AF) and superconducting (SC) phases. We addressed this problem on a microscopic level by means of 75As NMR measurements in LaFeAsO1?x F x (x=0.026) (La1111), and CaFe1?x Co x AsF (x=0.06) (Ca1111) having an intermediate electronic phase diagram between Ba(Fe1?x Co x )2As2 and the La1111 series. NMR spectra for 6 % Co-doped Ca1111 samples were very similar to those for the undoped samples even below T c , suggesting homogeneous coexistence of the AF and SC states. For 2.6 % F-doped La1111 samples, AF and paramagnetic (PM) domains coexist at ambient pressure, and AF and SC domains coexist at 3.0 GPa. The coexistence of domains is explained by considering a SC dome separated from the AF phase in the phase diagram. The homogeneous coexistence support S ±-wave superconductivity, whereas separation of the AF and SC phases gives credence to S ++-wave superconductivity. 相似文献
12.
Perovskite manganites are interesting because of their colossal magnetoresistance. In this work high resolution thermal diffusivity measurements of La1–x
Sr
x
MnO3 (0 x 0.3) single crystals in the temperature range from 250 to 400 K are presented. A photopyroelectric device in the standard back configuration has been used. The thermal diffusivity through second-order magnetic phase transitions, as well as through first- and second-order structural phase transitions has been measured. The critical parameters of the sample with x = 0.3 at the ferromagnetic-to-paramagnetic transition have been obtained, and are close to the values predicted by the Ising model. 相似文献
13.
Joginder Paul Sumit Bhardwaj Kuldeep Kumar Sharma Ravinder Kumar Kotnala Ravi Kumar 《Journal of Materials Science》2014,49(17):6056-6066
We present the structural, dielectric, ferroelectric, magnetic and magnetoelectric studies of lead free; single phase Bi4?x Sm x Ti3?x Co x O12?δ (0 ≤ x ≤ 0.07) ceramics, synthesized using a standard solid-state reaction technique. Raman spectroscopy analysis reveals the relaxation of distortion in TiO6 octahedron. Field emission scanning electron microscopy confirmed the growth of plate-like grains. It is observed that with the substitution of Sm3+ and Co3+ ions the dielectric constant, loss tangent and ferroelectric transition temperature decreases. Electrical dc resistivity, remnant polarization and magnetization increases with increasing Sm3+ and Co3+ contents. The magnetoelectric coupling co-efficient, α = 0.65 mV cm?1 Oe?1 is realized for Bi4?x Sm x Ti3?x Co x O12?δ (x = 0.07) ceramic sample. Our results clearly demonstrate the lead free, multiferroic nature of Sm/Co-substituted Bi4Ti3O12, which may find useful application in designing cost-effective electromagnetic devices. 相似文献
14.
J. C̀wik T. Palewski K. Nenkov J. Lyubina J. Klamut 《Journal of Low Temperature Physics》2010,159(1-2):37-41
We report magnetic and magnetocaloric properties of the polycrystalline series of Dy1?x Gd x (Co1?x Ni x )2 (x=0.1, 0.2, 0.3, 0.4 and 0.5) solid solutions. The samples were characterized by powder X-ray diffraction patterns taken at room temperature and revealed that all the Dy1?x Gd x (Co1?x Ni x )2 solid solutions consist of the C15 cubic Laves phase MgCu2 type structure and a small amount of DyCo3 and Dy2O3 impurity phases. Magnetic measurements showed that the samples undergoes a second-order type phase transition at T C<130 K, from paramagnetic to ferromagnetic state. Heat capacity measurements have been performed for all solid solutions and allowed us to determine the Debye temperature. The magnetocaloric effect has been studied by means of specific heat measurements in magnetic field 0.42, 1 and 2 T. The GdNi2 substitution effect on magnetic and magnetocaloric properties will be discussed. 相似文献
15.
The system Zn1–x
Co
x
Mn1–x
Fe
x
CrO4 is tetragonal in the range 0.0x0.4 and cubic in the range 0.5x1. Electrical resistivity temperature behaviour obeys Wilson's law for all the compounds and thermoelectric coefficient values vary between 135 to 226V K–1. All compounds exhibit P-type semiconductivity and possess low mobility values (10–9 cm2 V–1 sec–1). The infrared spectra show the presence of two strong absorption bands around 500 and 600 cm–1. The probable ionic configuration for the system is suggested to be Zn
1–x
2+
Fe
x
–y3+
-Co
x
2+
[Mn
1–x
3+
Fe
y
3+
CO
x
–y2+
Cr3+]O4. 相似文献
16.
C. Rial E. Morán M. A. Alario-Franco 《Journal of Superconductivity and Novel Magnetism》1994,7(6):913-916
A series of oxidized La2?x Sr x CuO4+y $(0.05 \preccurlyeq x \preccurlyeq 0.3)$ compounds has been prepared by treating the starting materials with a solution of Br2 in NaOH at room temperature. The structural modifications due to the oxidation of the materials have been studied by X-ray diffraction. Some of the observed changes are: (i) a large increase in the long parameter of the unit cell for samples with Sr content $0.05 \preccurlyeq x \preccurlyeq 0.15$ and (ii) a slight decrease in a along the whole range ofx. Interesting features have been observed regarding the critical temperatures of these materials: transition temperatures are higher for those containing lower Sr amounts (some of them were even nonsuperconducting before the oxidation treatment) in contrast to materials with x?0.15, whoseT c's do not change very much. The influence of both oxygen and strontium contents on the structural modifications and the superconducting properties of the oxidized materials will be discussed. 相似文献
17.
T. G. Aminov N. N. Efimov G. G. Shabunina V. M. Novotortsev 《Inorganic Materials》2012,48(12):1165-1174
We have synthesized Cu1 ? x In1 ? x Fe2x Se2 solid solutions (CuInSe2-FeSe join). The ??-FeSe end-member of the solid-solution system is an antiferromagnet and a superconductor with a superconducting transition temperature of 8 K. The magnetic properties of the solid solutions were studied at temperatures from 5 to 300 K in magnetic fields H = 3.98 and 3184 kA/m. By fitting experimental ??(H) magnetization data with Langevin and Curie equations, we determined the magnetic moment, size, and concentration of the clusters and the concentration of noninteracting Fe2+ ions. The magnetic moment of the Fe2+ ions in the clusters is ??0.8??B at 2x = 0.06 and 0.08, with a tendency to decrease with increasing iron content. This points to antiferromagnetic exchange interaction, which becomes stronger with increasing cluster size. The number of clusters in the materials increases with iron content up to a critical level 2x c < 2x = 0.06. In the range 2x = 0.06 to 0.10, the cluster size increases until a limiting composition determined by the boundary of the solid-solution range is reached. 相似文献
18.
We adopt a t 1-t 2-t 3-J-G model for explanation of x = 1/8 anomaly in La2 ? x Sr x CuO4 family compound. The calculated charge susceptibility shows a maximum near Q = (π, π) at intermediate temperatures and near (π, π/2) as temperature approaches zero, in agreement with neutron scattering experiments. Coulomb repulsion G between the first neighbors turns out to be the source of Charge Density Waves (CDW) in narrow band t eff 1, t eff 2, t eff 3 < G. For physically realistic hopping values we obtain the CDW amplitude e Q = x. The in-phase domain structure as a candidate for “stripe” picture is proposed. 相似文献
19.
We investigated electrical properties of nanostructured La1?x Sr x FeO3 (0 ?? x ?? 1) from 300 K?C400 K. The nanostructured La1?x Sr x FeO3 (0 ?? x ?? 1) was synthesized by citrate gel method requiring no pH control. X-ray diffraction pattern showed that single phase LaFeO3 with an orthorhombic structure was formed. The structure changed into rhombohedral for x = 0.5 and it became cubic for x = 1.0. For x ?? 0.5, our material showed non-linear current-voltage characteristics and for x > 0.5 it showed linear current-voltage characteristics. Poole Frenkel type conduction mechanism was found to be operative in LaFeO3 from 300 K?C400 K. The experimental values of field-lowering coefficient were by 2.56?C6.41 times higher than the predicted value and were attributed to the presence of localized fields. The increase in conductance with Sr content was due to formation of Fe4+ ions in addition to Fe3+ with the increase in Sr content. Impedance spectroscopy and ac conductivity analysis of La1?x Sr x FeO3 (0 ?? x ?? 1) was also carried out in the temperature range from 300 K?C400 K and frequency was varied from 20 Hz - 2 MHz. The ac conduction followed the correlated barrier hopping model in La0.9Sr0.1FeO3. 相似文献
20.
J. F. Barbot G. Rivaud H. Garem C. Blanchard J. C. Desoyer D. Le-Scoul J. L. Dessus A. Durand 《Journal of Materials Science》1990,25(3):1877-1885
Cd
x
Hg1–x
Te (0x1) single crystals were strained by microhardness and by constant strain rate uniaxial compression tests, in the temperature range 300 to 600 K. Hardness curves as function of temperature can be described by empirical relations. Stress-strain curves, relaxation tests and dislocation observations using transmission electron microscopy show that the deformation is controlled by a thermally activated Peierls mechanism. Moreover, dislocations are dissociated with a stacking fault energy which does not depend on thex composition. 相似文献