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1.
E. Arushanov S. Levcenko G. Fuchs B. Holzapfel S. L. Drechsler L. Schultz 《Journal of Superconductivity and Novel Magnetism》2011,24(8):2285-2292
We show that the temperature-dependent resistivity ρ(T), Hall number n
H(T) and the cotangent of the Hall angle cot θ
H(T) of Ba(Fe1−x
Co
x
)As2 (x=0.0–0.2) can be scaled using a recently proposed model-independent scaling method (Luo et al. in Phys. Rev. B 77:014529,
2008). The zero field normal-state resistivity above T
c can be reproduced by the expresion
r(T) = r0 +cTexp(- \frac2\varDelta T )\rho(T) = \rho_{0} +cT\exp(- \frac{2\varDelta }{T} ) and scaled using the energy scale Δ, c and the residual resistivity ρ
0 as scaling parameters. The scaling parameters have been calculated and the compositional variation of 2Δ and ρ
0 has been determined. The 2Δ(x) dependence show almost linear decreasing in underdoped regime, minimum corresponding to the T
c maximum and increasing in overdoped regime. The latter is different from that reported for cuprates. The existence of a universal
metallic ρ(T) curve which, however, is restricted for the underdoped compounds to temperatures above a structural and antiferromagnetic
transition is interpreted as an indication of a single mechanism which dominates the scattering of the charge carriers in
Ba(Fe1−x
Co
x
)As2 (x=0.0–0.2). 相似文献
2.
A. B. Bodade Minaz Alvi A. V. Kadu G. N. Chaudhari 《Journal of Materials Science》2010,45(19):5264-5270
Nanocrystalline La1−x
Co
x
Mn1−y
Ni
y
O3 (x = 0.2 and 0.4; y = 0.1, 0.3, and 0.5) thick films sensors prepared by sol–gel method were studied for their H2S gas sensitivity. The structural and morphological properties have been carried out by X-ray diffraction (XRD) and transmission
electron microscopy (TEM). Average particle size estimated from XRD and TEM analyses was observed to be 30–35 nm. The gas
response characteristics were found to depend on the dopants concentration and operating temperature. The maximum H2S gas response of pure LaMnO3 was found to be at 300 °C. In order to improve the gas response, material doped with transition metals Co and Ni on A- and
B-site, respectively. The La0.6Co0.4Mn0.5Ni0.5O3 shows high response towards H2S gas at an operating temperature 250 °C. The Pd-doped La0.6Co0.4Mn0.5Ni0.5O3 sensor was found to be highly sensitive to H2S at an operating temperature 200 °C. The gas response, selectivity, response time and recovery time were studied and discussed. 相似文献
3.
T. Tamegai T. Taen Y. Tsuchiya Y. Nakajima S. Okayasu M. Sasase 《Journal of Superconductivity and Novel Magnetism》2010,23(5):605-608
Superconducting properties are evaluated for high-quality single crystals of Ba(Fe1−x
Co
x
)2As2 in a wide range of doping levels. The critical current density, J
c
, in an optimally-doped crystal (T
c
∼24 K) shows a fishtail effect with its value over 105 A/cm2 even at 5 T below 10 K. Magneto-optical imaging has clarified rather homogeneous supercurrent flow in the crystal, in spite
of a large amount of impurities. In the heavy-ion irradiated sample, the presence of columnar defects are confirmed and J
c
has been enhanced by a factor of five at low temperatures, reaching 6×106 A/cm2 at 2 K under zero field. Flux creep rate in the heavy-ion irradiated sample has been reduced in accordance with the enhancement
of J
c
. 相似文献
4.
G. D. Nipan V. A. Ketsko A. I. Stognij A. V. Trukhanov T. N. Kol’tsova M. A. Kop’eva L. V. Elesina N. T. Kuznetsov 《Inorganic Materials》2010,46(4):429-433
Using pyrohydrolytic synthesis, we have obtained a continuous series of Mg(Fe1 − x
Ga
x
)2O4 + δ solid solutions, as checked by X-ray diffraction. The magnetization and coercivity of the samples have been determined from
field dependences in applied magnetic fields of ±5 T, and their conductivity has been assessed using current-voltage measurements
at 300 K in electric fields from −200 to +200 V. The effective band gap of the solid solutions has been evaluated from their
absorption spectra obtained by diffuse reflectance measurements. The optimal composition for spintronic applications is Mg(Fe0.8Ga0.2)2O4 + δ. 相似文献
5.
xBaTiO3 + (1 − x)Ni0.93Co0.02Cu0.05Fe2O4 (x = 0.5, 0.6, 0.7, 0.8) composites with ferroelectric–ferromagnetic characteristics were synthesized by the ceramic sintering
technique. The presence of constituent phases in the composites was confirmed by X-ray diffraction studies. The average grain
size was calculated by using a scanning electron micrograph. The dielectric characteristics were studied in the 100 kHz to
15 MHz. The dielectric constant changed higher with ferroelectric content increasing; and it was constant in this frequency
range. The relation of dielectric constant with temperature was researched at 1, 10, 100 kHz. The Curie temperature would
be higher with frequency increasing. The hysteresis behavior was studied to understand the magnetic properties such as saturation
magnetization (M
s). The composites were a typical soft magnetic character with low coercive force. Both the ferroelectric and ferromagnetic
phases preserve their basic properties in the bulk composite, thus these composites are good candidates as magnetoelectric
materials. 相似文献
6.
Biao Dong Hua Yang Lianxiang Yu Yuming Cui Weiqun Jin Shouhua Feng 《Journal of Materials Science》2007,42(13):5003-5006
Sm
x
BiY2–x
Fe5O12 (x = 0, 0.1, 0.2, 0.4, 0.6, 0.8) nanocrystals were fabricated by sol–gel method. Samples were characterized by powder X-ray
diffraction (XRD), thermal gravity analysis (TGA) and differential thermal analysis (DTA), transmission electron microscopy
(TEM), vibrating sample magnetometer(VSM). The samples were calcined at 850 °C and 1000 °C and the average size of the particles
were determined by Scherrer’s formula . In this paper, we discussed the effect of Sm3+ substitution for Y3+ on magnetic properties of BiY2Fe5O12. The magnetic properties of Sm
x
BiY2−x Fe5O12 are decreased with increasing content of Sm ion. 相似文献
7.
K. M. Reddy A. Punnoose 《Journal of Materials Science: Materials in Electronics》2007,18(11):1137-1142
We report the development of ferromagnetism in ∼30 nm sized well-characterized Ti1−x
Co
x
O2 powders with x = 0.00015–0.006 and its absence for x > 0.006. In addition, these studies show the effect of Co doping on the structural stability and anatase to rutile phase
transformation. X-ray diffraction data of samples synthesized by a wet chemical method and annealed at 450 °C indicate a limited
solubility of ∼1.2% for Co in the anatase TiO2 matrix, and with further increase, the CoTiO3 phase is formed along with increased presence of rutile TiO2. The bandgap (∼3.23 eV) of the anatase TiO2 remained almost unchanged for x < 0.006, but decreased rapidly for x ≥ 0.006 approaching 2.8 eV for x = 0.03. The magnetic data from Ti1−x
Co
x
O2 samples with x = 0.006 showed a coercivity H
c ∼ 150 Oe and a weak magnetic moment of 0.2 μB/ion at 300 K. The ferromagnetism of Ti0.994Co0.006O2 with open hysteresis loops continue up to a high superparamagnetic blocking temperature T
B ∼ 675 K, above which a superparamagnetic behavior was observed. Systematic changes in the structural, magnetic and optical
properties suggest that Co doping is an excellent method to tailor the physical properties of TiO2 nanoparticles. 相似文献
8.
Jian Wang Hong Zhang Yiyu Li Zhicheng Li 《Journal of Materials Science: Materials in Electronics》2010,21(8):811-816
BaTi1−x
Co
x
O3−δ (0.01 ≤ x ≤ 0.4) ceramics were prepared by a wet chemical process polymerized with polyvinyl alcohol. The phases and related electrical
properties of the ceramics were investigated. The phase component of the ceramics changes from a tetragonal phase to a hexagonal
one with the Co concentration increase. A pure hexagonal phase formed in the ceramic with x = 0.2. The measurement of the temperature dependence of resistances revealed that the ceramic resistivities increase with
temperature rising at the temperatures (T) lower than half of the related Debye temperature (ΘD), and the ceramics show a negative temperature coefficient (NTC) effect at T > ΘD/2. The material constants B
50/120 of the BaTi1−x
Co
x
O3−δ NTC thermistors were calculated to be 3,187, 2,968 and 2,648 K for x = 0.2, 0.3 and 0.4, respectively. Narrow-band conduction and non-adiabatic hopping models are proposed for the conduction
mechanisms at T < ΘD/2 and T > ΘD/2, respectively. 相似文献
9.
The thermoelectric power and d.c electrical conductivity of x V2O5⋅40CaO⋅(60−x)P2O5 (10 ≤ x ≤ 30) glasses were measured. The Seebeck coefficient (Q) varied from +88 μ V K−1 to −93 μV K−1 as a function of V2O5 mol%. Glasses with 10 and 15 mol% V2O5 exhibited p-type conduction and glasses with 25 and 30 mol% V2O5 exhibited n-type conduction. The majority charge carrier reversal occurred at x = 20 mol% V2O5. The variation of Q was interpreted in terms of the variation in vanadium ion ratio (V5 +/V4 +). d.c electrical conduction in x V2O5⋅40CaO⋅(60−x)P2O5 (10 ≤ x ≤ 30) glasses was studied in the temperature range of 150 to 480 K. All the glass compositions exhibited a cross over from
small polaron hopping (SPH) to variable range hopping (VRH) conduction mechanism. Mott parameter analysis of the low temperature
data gave values for the density of states at Fermi level N (EF) between 1.7 × 1026 and 3.9 × 1026 m−3 eV−1 at 230 K and hopping distance for VRH (RVRH) between 3.8 × 10−9m to 3.4 × 10−9 m. The disorder energy was found to vary between 0.02 and 0.03 eV. N (EF) and RVRH exhibit an interesting composition dependence. 相似文献
10.
Fe
x
Pt100−x
(70.1 ≤ x ≤ 83.4) thin films with ordered Fe3Pt phase were grown successfully onto MgO(110) substrates by electron beam evaporation. The unit cell of ordered Fe3Pt phase is elongated along c-axis direction and the thin films become more chemically ordered with decreasing Fe content. The magnetization of thin films
shows a decrease when Fe content is around 79 at.%. The relationship between magnetic anisotropy and structural parameters
suggests that the change of magnetic anisotropy in ordered Fe3Pt thin films with different compositions most likely stems from the magnetocrystalline origin. 相似文献
11.
Xiang Dong Haiqing Wang Zhongqiu Hua Shujie Peng Liang Dong Yu Wang 《Journal of Materials Science: Materials in Electronics》2012,23(6):1210-1214
Tungsten trioxide (WO3) doped with cobalt sesquioxide (Co2O3) was prepared by a conventional mixed oxide processing route and the thermoelectric properties were studied from 300 up to
1,000 K. The addition of Co2O3 to WO3 resulted in an increase in both the grain size and porosity, indicating that Co2O3 promotes the grain grown of WO3. The magnitude of the electrical conductivity (σ) and the absolute value of the Seebeck coefficient (|S|) depended strongly on the Co2O3 content. As for the power factor (σS
2
), the 5.0 mol% sample has the maximum value of the power factor which is 0.12 μWm−1K−2 at 873 K. 相似文献
12.
S. A. Lokare R. S. Devan D. R. Patil Y. D. Kolekar K. K. Patankar B. K. Chougule 《Journal of Materials Science》2007,42(24):10250-10253
Polycrystalline samples of mixed composites of Ni0.93Co0.02Mn0.05Fe2O4 + BaTiO3 were prepared by conventional double sintering ceramic method. The phase analysis was carried out by using X-ray diffraction
technique. Variation of dc resistivity and thermo emf was studied as a function of temperature. AC conductivity (σac) was investigated in the frequency range 100 Hz–1 MHz. The loss tangent (tan δ) measurements conclude that the conduction
mechanism in these samples is due to small polaron hopping. The magnetoelectric conversion factor, i.e. dc(ME)
H
was studied as a function of intensity of magnetic field and the maximum value 407 μV/cm/Oe was observed at a field of 0.8 kOe
in a composite with 85% BaTiO3 and 15% Ni0.93Co0.02Mn0.05Fe2O4 phase. 相似文献
13.
Hong-Tie Soong Cheng-Hsing Hsu Cheng-Liang Huang Ming-Ta Kuo 《Journal of Materials Science》2007,42(7):2393-2398
The microwave dielectric properties and the microstructures of Sm(Co1/2Ti1/2)O3 ceramics with B2O3 additions (0.25 and 0.5 wt%) prepared by conventional solid-state route have been investigated. The prepared Sm(Co1/2Ti1/2)O3 exhibited a mixture of Co and Ti showing 1:1 order in the B-site. Doping with B2O3 (up to 0.5 wt%) can effectively promote the densification of Sm(Co1/2Ti1/2)O3 ceramics with low sintering temperature. It is found that Sm(Co1/2Ti1/2)O3 ceramics can be sintered at 1,260 °C due to the grain boundary phase effect of B2O3 addition. At 1,290 °C, Sm(Co1/2Ti1/2)O3 ceramics with 0.5 wt% B2O3 addition possess a dielectric constant (ε
r) of 27.7, a Q × f value of 33,600 (at 9 GHz) and a temperature coefficient of resonant frequency (τf) of −11.4 ppm/ °C. The B2O3-doped Sm(Co1/2Ti1/2)O3 ceramics can find applications in microwave devices requiring low sintering temperature. 相似文献
14.
R. N. P. Choudhary Dillip K. Pradhan C. M. Tirado G. E. Bonilla R. S. Katiyar 《Journal of Materials Science》2007,42(17):7423-7432
The nanocrystalline fine powders (∼80 nm) of (Ba1−x
La
x
)(Fe2/3W1/3)1−x/4O3, (BLFW) (x = 0.0, 0.05, 0.10 and 0.15) were synthesized with a combined mechanical activation and conventional high-temperature solid-state
reaction methods. Preliminary X-ray structural analysis of pellet samples (prepared from fine powders) showed formation of
a single-phase tetragonal system. Detailed studies of dielectric properties (εr and tan δ) exhibit that these parameters are strongly dependent on frequency, temperature and La composition. The La-substitution
increases the dielectric constant and decreases the tan δ up to 10% substitutions of La at the Ba-site, and then reversed
the variation, and hence this composition is considered as a critical composition. This observation was found valid for structure,
microstructures, dielectric constant, electrical conductivity, J–E characteristics and impedance parameters also. Like in other perovskites (PZT, BZT), La substitution plays an important role
in tailoring the properties of Ba(Fe2/3W1/3)O3 ceramics. 相似文献
15.
Josef Jirák Ladislav Koudelka Jaroslav Pospíšil Petr Mošner Lionel Montagne Laurent Delevoye 《Journal of Materials Science》2007,42(20):8592-8598
Glasses of the ternary system ZnO–Bi2O3–P2O5 were prepared and studied in two compositional series 50ZnO–xBi2O3–(50 − x)P2O5 and (50 − y)ZnO–yBi2O3–50P2O5. Two distinct glass-forming regions were found in the 50ZnO–xBi2O3–(50 − x)P2O5 glass series with x = 0–10 and 20–35 mol.% Bi2O3. All prepared Bi2O3-containing glasses reveal a high chemical durability. Small additions of Bi2O3 (∼5 mol.%) improve thermal stability of glasses. All glasses crystallize on heating within the temperature range of 505–583 °C.
Structural studies by Raman and 31P MAS NMR spectroscopies showed the rapid depolymerisation of phosphate chains within the first region with x = 0–15 and the presence of isolated Q0 phosphate units within the second region with x = 20–35. Raman studies showed that bismuth is incorporated in the glass structure in BiO6 units and their vibrational bands were observed within the spectral region of 350–700 cm−1. The evolution of properties and the spectroscopic data are both in accordance with a network former effect of Bi2O3. 相似文献
16.
Hideki Taguchi Sho Matsuoka Masaki Kato Ken Hirota 《Journal of Materials Science》2009,44(21):5732-5736
Perovskite-type (La1−x
Nd
x
)CoO3 was synthesized using citric acid at 700 °C. The Rietveld method indicated that the crystal structure changed from a rhombohedral
to an orthorhombic system at x = 0.4. The Co–O distance of the rhombohedral structure connected continuously with the average Co–O(2) distance of the orthorhombic
structure, and the Co–O–Co angle of the rhombohedral structure and the Co–O(2)–Co angle of the orthorhombic structure were
continuous. The average particle size of the samples was approximately 55 nm. CH4 oxidation started above 300 °C, and the temperature corresponding to the 50% conversion (T
1/2) of CH4 increased linearly with increases in x. It is considered that the amount of adsorbed oxygen decreased in response to the steric hindrance, and that T
1/2 increased as a result. 相似文献
17.
A. V. Semeno A. A. Pronin N. E. Sluchanko N. A. Samarin A. V. Kuznetsov S. V. Demishev 《Journal of Superconductivity and Novel Magnetism》2007,20(2):109-112
Electron spin resonance of a single crystal of CuGeO3 doped with 2% of Co has been studied at f = 99 GHz in temperature range 1.8–50 K. Contributions to ESR absorption from Cu2+ chains and from Co2+ ions were derived. It is found that functions obtained for ESR integrated intensities: Curie-Weiss for Cu2+ (χCu ∼ C
Cu/(T + Θ), with Θ = 92 K) and Curie for Co2+ (χCo ∼ C
Co/T) are well consistent with temperature dependence of static magnetic susceptibility. Strong dependence of ESR absorption on
polarization of oscillating magnetic field was discovered for Co2+ contribution. Polarization effect was studied for magnetic field applied along a, b and c directions. Values of g-factors of resonance lines are presented. 相似文献
18.
We have performed partial HSO4− substitution in CsH2PO4 and studied the associated structural changes and the proton conductivity of the resultant (CsH2PO4)1 − x
(CsHSO4)
x
solid solutions in the range x = 0.01–0.3. The results indicate that, at room temperature, the solid solutions are disordered. In the range x = 0.01–0.1, they are isostructural with the low-temperature phase of CsH2PO4 (sp. gr. P21/m), and their unit-cell parameters increase with x, whereas in the range x = 0.15–0.3 the solid solutions are isostructural with the high-temperature, cubic phase of CsH2PO4 (Pm3m), and their unit-cell parameter decreases. The conductivity of the (CsH2PO4)1 − x
(CsHSO4)
x
solid solutions with x ≤ 0.3 depends significantly on their composition and increases at low temperatures by up to four orders of magnitude, approaching
that of the superionic phase of CsH2PO4 in the range x = 0.15–0.3 because of the hydrogen bond weakening and increased proton mobility. The conductivity of the superionic phase
decreases with increasing x by no more than a factor of 1.5–2, and the superionic phase transition, which occurs at 231°C in CsH2PO4, shifts to lower temperatures and disappears for x ≥ 0.15. The activation energy for low-temperature conduction decreases with increasing x: from 0.9 eV in CsH2PO4 to 0.48 eV at x = 0.1. 相似文献
19.
Ternary perovskite ceramics of Pb[(Zr0.5Ti0.5)0.8−x
(Mg1/3Nb2/3)0.2+x]0.98Nb0.02O3.01 (PZTMN, x = −0.075, −0.05, −0.025, 0, 0.025, 0.05, and 0.075 ), are synthesized via dry–dry method. B-site precursors of PZTMN ([(Zr0.5Ti0.5)0.8−x
(Mg1/3Nb2/3)0.2+x
]0.98Nb0.02O2.01, ZTMN) can be synthesized via a two-step solid state reaction method. The first calcination temperature is 1,300 °C, and
the second is not higher than 1,360 °C. Incorporation of magnesium and niobium ions promotes the formation of the single phase
solid solution with ZrTiO4 structure. Single phase perovskite PZTMN is formed at 780 °C, much lower than that in conventional process. Dense ceramics
can be sintered at about 1,260 °C with dielectric and piezoelectric properties comparable to that of wet–dry method and higher
than that of conventional method. It seems that B-site precursor method is cost effective in preparation of ternary piezoelectric
ceramics. 相似文献
20.
Nb3+-substituted garnet nanoparticles Y3−xNdxFe5O12 (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were fabricated by a sol-gel method and their crystalline structures and magnetic properties
were investigated by using X-ray diffraction (XRD), thermal analysis (DTA/TG), and vibrating sample magnetometer (VSM). The
XRD patterns of Y3−xNdxFe5O12 have only peaks of the garnet structure and the sizes of particles range from 34 to 70 nm. From the results of VSM, it is
shown that when the Nd concentration x ( 1.0, the saturation magnetization of Y3−xNdxFe5O12 increases as the Nd concentration (x) is increased, and gets its maximum at x = 1.0, but when x ( 1.0, the saturation magnetization
decreases with increasing the Nd concentration (x), this may be due to the distortion of the microstructure of Y3−xNdxFe5O12, which leads to the decrease of the effective moment formed by Fe3+. Meanwhile, it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the
particle size is increased. 相似文献