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1.
This paper investigates the crystal structure, thermal expansion, and electrical conductivity of two series of perovskites
(LaMn0.25−x
Co0.75−x
Cu2x
O3−δ and LaMn0.75−x
Co0.25−x
Cu2x
O3−δ with x = 0, 0.025, 0.05, 0.1, 0.15, 0.2, and 0.25) in the quasi-ternary system LaMnO3–LaCoO3–“LaCuO3”. The Mn/Co ratio was found to have a stronger influence on these properties than the Cu content. In comparison to the Co-rich
series (LaMn0.25−x
Co0.75−x
Cu2x
O3−δ), the Mn-rich series (LaMn0.75−x
Co0.25−x
Cu2x
O3−δ) showed a much higher Cu solubility. All compositions in this series were single-phase materials after calcination at 1100 °C.
The Co-rich series showed higher thermal expansion coefficients (αmax = 19.6 × 10−6 K−1) and electrical conductivity (σmax = 730 S/cm at 800 °C) than the Mn-rich series (αmax = 10.6 × 10−6 K−1, σmax = 94 S/cm at 800 °C). Irregularities in the thermal expansion curves indicated phase transitions at 150–350 °C for the Mn-rich
series, while partial melting occurred at 980–1000 °C for the Co-rich series with x > 0.15.
I. Arul Raj—on leave from Central Electrochemical Research Institute, Karaikudi, 630006 India. 相似文献
2.
New NASICON type materials of composition, Li3−2x
Al2−x
Sb
x
(PO4)3 (x = 0·6 to 1·4), have been prepared and characterized by powder XRD and IR. D.C. conductivities were measured in the temperature
range 300–573 K by a two-probe method. Impedance studies were carried out in the frequency region 102−106 Hz as a function of temperature (300–573 K). An Arrhenius behaviour is observed for all compositions by d.c. conductivity
and the Cole-Cole plots obtained from impedance data do not show any spikes on the lower frequency side indicating negligible
electrode effects. A maximum conductivity of 4·5 × 10−6 S cm−1 at 573 K was obtained for x = 0·8 of the Li3−2x
Al2−x
Sb
x
(PO4)3 system. 相似文献
3.
H. Khelifi A. Aydi N. Abdelmoula A. Simon A. Maalej H. Khemakhem M. Maglione 《Journal of Materials Science》2012,47(4):1943-1949
Lead-free (1 − x)NaNbO3/xBa(Ti0.5Sn0.5)O3 (x = 0.1, 0.125, 0.15, 0.175, 0.2, and 0.3) ceramics were elaborated by the conventional ceramic technique. Sintering has been
made at 1523 K for 2 h. The crystal structure was investigated by X-ray diffraction with CuKα radiation at room temperature.
As a function of composition, these compounds crystallize with tetragonal or cubic symmetry. Dielectric measurements show
that the materials have a classical ferroelectric behavior for compositions in the range 0.10 ≤ x ≤ 0.15 and relaxor one for compositions in the range 0.15 < x ≤ 0.30. Temperatures T
C or T
m decrease as x content increases. The ferroelectric behavior has been confirmed by hysteresis characterization. For x = 0.1, a piezoelectric coefficient d
31 of 42.146 pC N−1 was obtained at room temperature. The evolution of the Raman spectra was studied as a function of temperature for x = 0.1. 相似文献
4.
A. I. Svitan’ko S. A. Novikova D. V. Safronov A. B. Yaroslavtsev 《Inorganic Materials》2011,47(12):1391-1395
Li1 + x
Ti2 − x
Cr
x
(PO4)3 NASICON-type materials have been prepared and characterized by X-ray diffraction, scanning electron microscopy, and impedance
spectroscopy. The results demonstrate that Cr3+ doping increases the ionic conductivity of LiTi2(PO4)3 within the single-phase region of the doped material, which extends to x = 0.7. From temperature-dependent ionic conductivity data, the activation energy for lithium transport through interstitial
sites and the enthalpy of defect formation in LiTi2(PO4)3 are estimated at 30.0 ± 0.5 and 56 ± 1 kJ/mol, respectively. 相似文献
5.
S. I. Vecherskii S. N. Tabatchikova B. D. Antonov V. A. Biryukov 《Inorganic Materials》2011,47(12):1356-1360
We have studied the effect of Co and Li concentrations on the phase composition and electrical conductivity of LaCo
x
Fe1 − x
O3 − δ and LaLi0.1Co
x
Fe0.9 − x
O3 − δ perovskite-like oxides synthesized in air at 1470 K. Single-phase materials with an orthorhombic crystal structure were obtained
in the range 0 ≤ x ≤ 0.3. The composition dependences of conductivity have a minimum at x
c = 0.1 and 0.2, respectively. In the range x > 0.1, the conductivity of LaCo
x
Fe1 − x
O3 − δ increases with increasing Co concentration for T > 700 K and decreases for T < 600 K. The conductivity of La(Li0.1Co
x
Fe0.9 − x
)O3 − δ in the range 0 ≤ x ≤ 0.1 and for x ≥ 0.2 increases with Co concentration throughout the temperature range studied. 相似文献
6.
I. V. Belen’kaya O. A. Savinskaya M. A. Neklyudova A. P. Nemudry 《Inorganic Materials》2011,47(12):1347-1355
We have synthesized Sr1 − x
Pb
x
FeO3 − δ (x = 0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.5) perovskite-like materials and studied their structure by X-ray diffraction, M?ssbauer
spectroscopy, and electron microscopy. According to the X-ray diffraction data, the Pb solubility limit in the perovskite
structure is x ≈ 0.15. The materials with x = 0.05 and 0.1 contained Pb1.33Sr0.67Fe2O5 inclusions 10–30 nm in size. Using chronopotentiometry and temperature-programmed desorption, we have estimated oxygen mobility
in the materials with x = 0.05 and 0.1. The results demonstrate that Pb doping increases oxygen mobility in the strontium-ferrite-based materials. 相似文献
7.
The solubility of Nd at the Ba sites and the superconductivity of YBa2–x
Nd
x
Cu3O
y
were investigated by X-ray powder diffraction and measurements of the electrical resistance and ac susceptibility. The single Re123 phase was obtained for x0.30. The onset transition temperature
is insensitive to the Nd content x in the region of x0.40. All are higher than 95 K. The zero resistance transition temperatures
, however, exhibits two-step variation with the increase of x. For x0.25,
are all above 92 K. The highest
of 94 K was obtained for x=0.25. For x0.3
drops sharply to about 84 K. Finally
falls to 30 K and
is below 10 K for x=0.5. The two-step variation of T
c might be an indication of the existence of two trap levels for holes. 相似文献
8.
The multicomponent refractory oxide system Zn2 − x
(Ti
a
Zr
b
)1 − x
Fe2x
O4 (a + b = 1; a: b = 1: 5, 1: 4, 1: 3, 1: 2, 1: 1, 2: 1, 3: 1, 4: 1; x = 0–1.0; Δx = 0.05) has been studied by X-ray diffraction, using samples prepared by melting appropriate metal oxide mixtures in a low-temperature
hydrogen-oxygen plasma. Two phases, both with wide homogeneity ranges, have been identified: α-phase, with a cubic inverse
spinel structure, and β-phase, with a tetragonal inverse spinel structure. The phase boundaries in the system have been determined.
Structural data are presented for about 100 solid solutions. 相似文献
9.
Hengwei Liu Aimin Sun Yanzhong Lu Yaotong Ma Jinyuan Ma Guidan Wei Long Zheng 《Journal of Superconductivity and Novel Magnetism》2010,23(8):1525-1528
A series of polycrystalline samples of Mg1−x
Zn
x
(B1−x
C
x
)2 (x=0.00, 0.02, 0.04, 0.06, 0.08, and 0.10) were synthesized by a conventional solid-state reaction method under a background
pressure about 10−3 Pa. Phase identification, crystal structure and superconducting transition temperature (T
c) were studied by means of X-ray diffraction (XRD) and resistivity measurements. The results indicated that the lattice parameters
a and c show no clear trend in their changes with increasing doping level, and it turned out that the dopants had a marked effect
on the crystal-lattice parameters and changed the crystal structure of the samples. The T
c for Mg1−x
Zn
x
(B1−x
C
x
)2 decreased with C and Zn doping, but the rate of decrease was slower than single C-doped. We propose that the suppression
of T
c by doping originates largely from the structural change. 相似文献
10.
S. J. Hao W. T. Jin X. J. Zhang Y. Zhao H. Zhang 《Journal of Superconductivity and Novel Magnetism》2010,23(5):819-822
The co-doped compounds of Y1−x
Ca
x
Ba2Cu3−x
Al
x
O
z
, with x from 0.1 to 0.4, were synthesized through a solid-state reaction method. Structural and superconducting properties have been
investigated by X-ray diffraction, Rietveld refinement, and DC magnetization measurement. The lattice constant a decreases while b increases with the addition of x. The difference between a and b diminishes gradually. Careful study of the crystalline structure shows that the critical temperature (T
c
) changes monotonically with some local structural parameters, such as the difference between Ba and Cu(2) atoms’ Z coordinates,
the bond length of Cu(2)–O(4), and the bond angle of Cu(2)–O(2)–Cu(2), which are all closely related to the interaction between
the perovskite block and the rock salt block in the unit cell. The results indicated that the influence of the crystalline
structure on superconductivity is important and independent of the carrier concentration. 相似文献
11.
V. D. Parvanova S. K. Andreev 《Journal of Materials Science: Materials in Electronics》2005,16(5):249-252
By means of a solid-phase synthesis two types of microwave dielectric materials are obtained as follows: Ba1–xSrx(Zn1/3Ta2/3)0.94Ti0.06O3, where x = 0.20, 0.25, 0.30, 0.35 and 0.40 at sintering temperature TS = 1350, 1400 and 1450 C; Ba(Zn1/3Nb2/3)1–xZrxO3, where x = 0.04, 0.06, 0.08 and 0.10 at TS = 1300, 1350, and 1400 C. The microwave characteristics of the materials are investigated at f = 10 GHz. The composition Ba(Zn1/3Nb2/3)1–xZrxO3 demonstrates r = 38, Q = 6100 and f = +15 ppm C–1 and the composition Ba0.80Sr0.20- (Zn1/3Ta2/3)0.94Ti0.06O3 has r = 42, Q = 8200 and f = –13 ppm C–1. The composition Ba0.75Sr0.25(Zn1/3Ta2/3)0.94Ti0.06O3 has r = 40, Q = 6500 and low f = –13 C–1 ppm. This composition could be used successfully for realisation of dielectric microwave resonators for the satellite television. 相似文献
12.
A series of oxidized La2–x
Sr
x
CuO4+y
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
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 x0.15, 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
13.
R. Awad A. I. Abou-Aly S. A. Mahmoud M. ME. Barakat 《Journal of Superconductivity and Novel Magnetism》2011,24(8):2227-2236
Bulk superconducting samples of type GdBa2Cu3−x
Ru
x
O7−δ
, Gd-123, with x=0.0–0.3 were prepared by the conventional solid-state reaction technique. X-ray powder diffraction (XRD), scanning electron
microscope (SEM), electron dispersive X-ray (EDX) and electrical-resistivity measurements were performed in order to investigate
the effect of Ru4+ ions substitution on Gd-123 phase. Enhancement of both phase formation and the superconducting transition temperature T
c for GdBa2Cu3−x
Ru
x
O7−δ
phase up to x=0.05 was observed from XRD and electrical-resistivity measurement, respectively. This enhancement was confirmed with the
calculated relative volume fraction. For x>0.05, suppression of both phase formation and T
c was obtained and the superconductivity was completely destroyed around x=0.3. The normal-state electrical resistivity was analyzed by the two- and three-dimensional variable range hopping (2D-VRH
and 3D-VRH) and Coulomb gap CG. The results showed that the dominant mechanism was CG for x≤0.075, while was 3D-VRH for x≥0.15. 相似文献
14.
A. A. Pandit A. R. Shitre D. R. Shengule K. M. Jadhav 《Journal of Materials Science》2005,40(2):423-428
Ferrites with the general formula Mg1+xMnxFe2–2xO4(where x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9) were prepared by the standard ceramic technique and studied by means of X-ray diffraction, magnetization, a.c. susceptibility and dielectric constant measurements. The X-ray analysis confirmed the single-phase formation of the samples. The lattice parameter is found to increase up to x = 0.3 and thereafter it decreases as x increases. The cation distribution has been studied by X-ray analysis and magnetization. Magnetization results exhibit collinear ferrimagnetic structure for x 0.3 and thereafter structure changes into non-collinear for x > 0.3. Curie temperature (TC) obtained from a.c. susceptibility data decreases with increasing x. The dielectric constant (), loss tangent (tan ) show strong frequency dependence. 相似文献
15.
S. Balamurugan 《Journal of Superconductivity and Novel Magnetism》2010,23(4):507-515
In this article, the magneto-transport features of 57Fe isotope (1%) doped SrCoO3 (referred to as SrCo0.99
57Fe0.01O3) perovskite compound have been investigated. The compound crystallized in cubic symmetry undergoes ferromagnetic transition
around ∼270 K. The isothermal magnetization data collected at low temperature (1.8 K) indicates a characteristic of soft ferromagnet
with saturation moment, M
s∼1.81 μ
B/Co. Interestingly, the electrical resistivity, ρ(T), measurements indicate semiconducting properties while metallic nature is seen for the pristine compound. The SrCo0.99
57Fe0.01O3 sample shows temperature and field dependence of magnetoresistance, MR, around 1.5%, which is rather smaller than of the pristine perovskite. The second part of the present work reports the attempt
to dope Cd on Sr-site in the perovskite structure, Sr1−x
Cd
x
CoO3, under extreme conditions. A minimum amount of about x=0.05, 0.1 is tested for solid solution in the Sr1−x
Cd
x
CoO3 structure. However, the structural data indicate that Cd is not fully doped in the matrix for x=0.05, 0.1 samples; some of the CdO is intact as an impurity and it did not show major impact on the physical properties of
the samples. The ρ(T) data reveal metallic nature for both x=0.05 and 0.1 samples with relatively low resistivity at low temperature regions, and they exhibit −MR ∼4% around ∼250 K. For x=0.05 the molar magnetic susceptibility of the sample shows ferromagnetic transition at T
c=244 K, whereas x=0.1 sample exhibits ferromagnetism at T
c=264 K. The effective Bohr magnetron parameter, p
eff, determined for x=0.05 and 0.1 samples is found to be 3.10 μ
B/Co and 3.25 μ
B/Co, respectively, and these data suggest intermediate spin state for Co4+ ion for both the samples. The M(H) data for both the samples reveal soft ferromagnetism. The M
s of x=0.05 reaches 1.9 μ
B/Co and of x=0.1 reaches 1.86 μ
B/Co at 1.8 K and 70 kOe conditions. 相似文献
16.
M. B. Maple C. C. Almasan C. L. Seaman S. H. Han K. Yoshiara M. Buchgeister L. M. Paulius B. W. Lee D. A. Gajewski R. F. Jardim et al. 《Journal of Superconductivity》1994,7(1):97-106
Investigations of Y1–x
M
x
Ba2Cu3O7–
(M=Ce, Th)c-axis oriented thin film specimens show that the rate of depression ofT
c
withx is larger for M=Th, than for M=Ce and Pr, and suggest that Ce, like Th, is tetravalent in this compound. Hall effect measurements on Y1–x
Pr
x
Ba2Cu3O7–
single crystals reveal aT
2 dependence of the cotangent of the Hall angle in the normal state and a negative Hall anomaly belowT
c
in the superconducting state, in agreement with recent reports. Our research shows that the depth, , of the negative Hall signal scales withT/T
c
and that the maximum value of decreases linearly withx and vanishes atx0.24. Magnetoresistance measurements on Y1–x
Pr
x
Ba2Cu3O7–
single crystals indicate that the irreversibility lineH(T
*) obeys a universal scaling relation characterized by anm=3/2 power law nearT
c, with a crossover to a more rapid temperature dependence of belowT/T
c
0.6, similar to that observed for polycrystalline specimens. 相似文献
17.
S. M. Hasnain M. Mumtaz Nawazish A. Khan 《Journal of Superconductivity and Novel Magnetism》2011,24(5):1653-1657
The effect of synthesis temperature on the superconducting properties of (Cu1−x
Tl
x
)Ba2Ca3Cu4O12−δ
(CuTl-1234) samples has been explored. Almost all the superconducting parameters studied in this research work are observed
to be suppressed with the increase of synthesis temperature beyond 880 °C, which may be due to impurities caused by the volatility
of some constituents such as thallium and oxygen deficiencies as well in the final compound. The Fluctuation Induced Conductivity
(FIC) analysis has shown a decrease in the cross-over temperature (T
0) and the shift of three-dimensional (3D) Aslamasov–Larkin (AL) regions to the lower temperature with the increase of synthesis
temperature beyond 880 °C. A direct correlation between the cross-over temperature (T
0), the zero temperature coherence length {ξ
c
(0)}, the zero resistivity critical temperature {T
c
(R=0)} as well as carrier concentration has also been observed. 相似文献
18.
19.
P. A. Popov P. P. Fedorov E. A. Garibin A. N. Smirnov P. E. Gusev M. A. Krutov 《Inorganic Materials》2012,48(8):857-860
The thermal conductivity of Ca1 − x Ho x F2 + x (x ≤ 0.03) optical ceramics has been studied experimentally in the temperature range 50–300 K. With increasing holmium content, the thermal conductivity of the ceramics decreases, especially at low temperatures: from 10.2 to 2.3 W/(m K) at 300 K and from 250 to 4.5 W/(m K) at 50 K. 相似文献
20.
N. P. Stepanov V. Yu. Nalivkin L. D. Ivanova Yu. V. Granatkina 《Inorganic Materials》2012,48(3):234-237
The magnetic susceptibility (χ) of crystals of (Bi2 − x
Sb
x
)Te3 (0 < x < 1) solid solutions has been measured at temperatures from 2 to 400 K. The χ of the crystals containing 10 and 25 mol %
Sb2Te3 increases with temperature in the range 50 to 220 K, where the Hall coefficient of Bi2Te3 increases anomalously. The increase in diamagnetic susceptibility and Hall coefficient with temperature is shown to be caused
by a reduction in light-hole concentration, accompanied by a decrease in light-hole effective mass. With increasing Sb2Te3 content, the shape of the χ(T) curve changes as a consequence of changes in band structure, which increase the influence of heavy, paramagnetic holes. 相似文献