共查询到20条相似文献,搜索用时 46 毫秒
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Jwo -Shiun Sun Jon -Jer Yu Jeng -Chei You Chung -Chuang Wei 《Journal of Materials Science》1993,28(8):2163-2168
The dielectric properties of the (1–x)Ba(Zn1/3Nb2/3)O3–xBaSnO3 (0 x 0.32) composition at microwave frequencies were investigated in this study. With the addition of BaSnO3, the dielectric Q(Q
d) value of Ba(Zn1/3Nb2/3)O3 (BZN) can be improved and a small temperature coefficient of resonant frequency (f) can be achieved. When 22.6 mol % of Sn is added to BZN, the characteristics of the Ba(Sn0.226Zn0.258Nb0.516)O3 ceramics sintered at 1500°C are as follows: dielectric constant r = 32, f = + 12 p.p.m.°C1 and high Q
d value of 9700 at 10 GHz. Based on the classical dispersion theory and the logarithmic mixing rule, the effects with additions of substitutional element of BaSnO3 on the microwave dielectric properties of Ba(Zn1/3Nb2/3)O3 can be mostly explained. 相似文献
3.
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
4.
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
5.
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
6.
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
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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
9.
X. S. Wu F. M. Pan X. R. Huang C. Ye X. Jin S. S. Jiang 《Journal of Materials Science》1996,31(23):6113-6117
Co-doped impurity-free YBa2(Cu1–x
Co
x
)3O7–(123Cox) with x=0.03 superconducting samples have been synthesized using conventional solid state reaction techniques. A Rietveld analysis of X-ray diffraction data for these specimens reveals that two structures (one tetragonal represented by T-YBCO, and the other orthorhombic represented by O-YBCO) co-exist at this composition of the cuprate. The use of a single tetragonal or single orthorhombic structure as the model for the refinements does not produce acceptable fits to the X-ray diffraction pattern. The refinements show that the T-YBCO phase at 298 K has tetragonal symmetry (P4/mmm) with a=0.387879(4) nm, c=1.17314(1) nm, and that the O-YBCO phase has at 298 K an orthorhombic symmetry (Pmmm) with a=0.387555(4) nm, b=0.389400(4) nm, c=1.17363(1) nm, respectively. 相似文献
10.
A. S. Saidov É. A. Koshchanov A. Sh. Razzakov Sh. K. Ismailov 《Technical Physics Letters》1999,25(12):986-987
Structures comprising Si-Si1−x
Gex-(Ge2)1−x
(InP)x with an intermediate Si1−x
Gex buffer layer were grown on silicon substrates. Morphological examinations, scanning patterns and diffraction spectra, and
also the electrophysical and luminescence properties of the heterostructures were used to show that the crystal perfection
of these structures depends on the choice of liquid-phase epitaxy conditions.
Pis’ma Zh. Tekh. Fiz. 25, 37–40 (December 26, 1999) 相似文献
11.
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
12.
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
13.
C. Q. Guo C. Y. Zhang J. Yu S. J. Hao W. T. Jin H. Zhang 《Journal of Superconductivity and Novel Magnetism》2013,26(4):891-893
It is found that the samples of x=0.25 and 0.5 in the series samples of Y1?x Pr x Ba2Cu3O7?δ demonstrate some anomalous behavior. First, the changes of T c value of them are a bit different from their neighbor samples. Second, under a small magnetic field, i.e. 5–100 Oe, a little rise in the T c value with the rise of the field is observed. The anomalous behavior is primitively explained by the local structure changes and the magnetic properties. It is attributed to local structural changes, i.e. the chemical bonds in the Cu–O2 plane. 相似文献
14.
The dielectric behaviour of compositions withx=0.01, 0.05, 0.10 and 0.20 in the system Ba1–x
La
x
Ti-1-x
Co
x
O3 was studied in the temperature range 300–473 K. The compositions withx = 0.01 and 0.05 show a diffuse ferroelectric-paraelectric phase transition, while other compositions do not show this transition in this temperature range. The frequency dependence of dielectric constant and dielectric loss in the samples withx0.05 indicates that spacecharge polarization contributes significantly to their observed dielectric parameters. 相似文献
15.
There has been an increasing demand for dielectric resonator materials that operate in the microwave frequency range for applications in microwave communications. (Pb,Ca)ZrO3 ceramics have a dielectric constant (r), high quality factor (Q) and a small temperature coefficient of resonant frequency (f). However, basic properties such as its crystal structure, temperature characteristics and the nature of its phase transformation are not yet fully understood. The temperature coefficient of resonant frequency can be controlled fairly well with the temperature coefficient of the dielectric constant. In this paper, we report the results of investigated crystal structure and the dielectric properties of (Pb1–x
Ca
x
)(Zn1–
y
Sn
y
)O3 ceramics with the objective of elucidating the relationship between the crystal structure and the dielectric properties. The crystal structure refinement was performed by the Rietveld method. The dielectric properties were measured from-150–350 °C. The phase transformation was analysed from high and low temperature XRD data. 相似文献
16.
Detailed magnetic properties of Pr1? x Nd x MnO3 (x = 0.3, 0.5 and 0.7) have been reported. All the samples crystallize in orthorhombic perovskite structure with Pnma space group. Magnetization measurements under field cooled (FC) protocal reveal magnetization reversal at low temperatures and low magnetic field. This indicates clear evidence of two magnetic sublattices aligned opposite to each other. There is a well-defined maximum around 48 K in the x = 0.7 sample (i.e. Pr0.3Nd0.7MnO3) in the χ′ value which is identified as paramagnetic to ferrimagnetic transition. The peak value shifts to higher temperature with decrease of x and width of the maximum broadened. It is also observable that with decrease of Nd, both the value of χ′ and χ″ decrease. An attempt is made to explain the magnetization reversal within the framework of available models. 相似文献
17.
Shaoping Li A. S. Bhalla R. E. Newnham L. E. Cross Chi -Yuen Huang 《Journal of Materials Science》1994,29(5):1290-1294
A simple and direct method has been proposed, which may be used for quantitatively distinguishing the mechanisms of domain reorientation processes in polycrystalline materials. Using this method, the 90 domain reorientation in the Pb(Zr
x
Ti1–x
)O3 ceramic under an electric field was examined through the X-ray diffraction analysis. It was found that polarization switching in the PZT ceramic with a composition near the morphotropic phase boundary, is predominantly controlled by the two successive 90 domain processes rather than only the 180 domain reversal process. Experimental results also indicate that the coercive field of ferroelectric ceramics is related to the cooperative deformation associated with each grain. This cooperative deformation arises from the 90 domain-reversal process. 相似文献
18.
N. Bachar E. Farber M. Roth E. Zhukova B. Gorshunov H. Castro A. Abramovich 《Journal of Low Temperature Physics》2010,158(3-4):647-652
In the current work we have investigated the terahertz response of Ca overdoped YBaCuO thin films using both time and frequency domain spectroscopy methods. For both methods a basic data analysis was performed using the two fluid and a variable dielectric function (VDF) models. The imaginary part of the conductivity was proportional to 1/ω, known from the delta-function response. The real part of conductivity showed a well known frequency and temperature dependence, where it increases below T c and obtains maxima at about 50 K. However, a sharp decrease of the real part of the conductivity was observed at about 10 cm?1. This decrease occurs below T c and becomes dominant as temperature decreases. It was observed on the 5% and 10% Ca doped samples but it was more dominant on the 10% case. Moreover, this sharp decrease in σ 2(ω)at 10 cm?1 was not observed in optimally doped YBCO samples. We would like to stress at this point that these values are much smaller than those obtained by Microwave and Tunneling measurements, arguing for the existence of a complex order parameter in the overdoped regime with an imaginary component of about 1.8 meV. 相似文献
19.
S. Gowrishankar L. Balakrishnan T. Balasubramanian N. Gopalakrishnan 《Materials Science and Engineering: B》2013,178(1):31-38
Ga doped ZnO (GZO) and GaP codoped ZnO (GPZO) thin films of different concentrations (1–4 mol%) have been grown on sapphire substrates by RF sputtering for the fabrication of ZnO homojunction. The grown films have been characterized by X-ray diffraction (XRD), photoluminescence (PL), Hall measurement, energy dispersive spectroscopy (EDS), time-of-flight secondary ion mass spectrometer (ToF-SIMS), UV–Vis–NIR spectroscopy and atomic force microscopy (AFM). Unlike in conventional codoping, here we directly doped (codoped) GaP into ZnO to realize p-ZnO. The Hall measurements indicate that 2 and 4% GPZO films exhibit p-conductivity due to the sufficient amount of phosphorous incorporation while all the monodoped GZO films showed n-conductivity as expected. Among the p-ZnO films, 2% GPZO film shows low resistivity (2.17 Ωcm) and high hole concentration (1.8 × 1018 cm?3) by optimum incorporation of phosphorous due to best codoping. Similarly, among the n-type films, 2% GZO shows low resistivity (1.32 Ωcm) and high electron concentration (2.02 × 1019 cm?3) by optimum amount of Ga incorporation. The blue shift and red shift in NBE emission observed from PL acknowledged the formation of n- and p-conduction in monodoped and codoped films, respectively. The neutral acceptor bound exciton recombination (A0X) observed by low temperature PL for 2% GPZO confirms the p-conductivity. Further, the high concentration of P atoms than Ga observed from ToF-SIMS (2% GPZO) also supports the p-conductivity of the films. The fabricated p–n junction with best codoped p-(ZnO)0.98(GaP)0.02 and best monodoped n-Zn0.98Ga0.02O films showed typical rectification behavior of a diode. The diode parameters have also been estimated for the fabricated homojunction. 相似文献
20.
H. S. Tewari Om Parkash V. B. Tare Devendra Kumar 《Journal of Materials Science》1990,25(4):2181-2184
The dielectric behaviour of the compositions withx0.15 in the system Ca1–x
Y
x
Ti1–x
Co
x
O3 sintered and cooled in air has been studied. Space-charge polarization which arises due to the presence of chemical inhomogeneities at the micro-level contributes significantly to their dielectric constant. The composition with x=0.05 exhibits temperature and frequency-independent dielectric constant and very small dielectric loss. 相似文献