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1.
A. H. Qureshi M. Arshad S. K. Durrani H. Waqas 《Journal of Thermal Analysis and Calorimetry》2008,94(1):175-180
Sol-gel process was employed to synthesize the Pb-BSCCO system having general composition Bi2−xPbxSr2Ca2Cu3O10−δ, where x=0.2, 0.4 and 0.8. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), dilatometry and vibrating sample
magnetometer (VSM) were employed to study the materials produced at different stages. Two-stage heating firstly at 300 and
then 800°C was adopted in order to avoid the burning of the materials and formation of carbonates. The carbonate formation
was avoided by heating the materials firstly at 300°C for 2 h and without intermediate cooling moved to the furnace having
temperature 800°C and hold for 2 h. The sintering behaviour of samples was studied by dilatometry and the results revealed
that the sample having x=0.4 was stabled up to a temperature of 700°C while samples having x=0.2 and 0.8 to a temperature of 625°C. The maximum shrinkage was observed at 850°C in all the samples. On the basis of dilatometry
results, the samples were sintered at 845°C for 60 h to observe the superconducting phases. The highest volume fraction of
high superconducting phase (2223) was noticed in the sample containing x=0.4 having onset T
c=110 K. 相似文献
2.
The high TC
superconducting phase Bi2Sr2Ca2Cu3Ox
(2223) in the Pb-BSCCO system has been produced by EDTA-gel processing
using nitrate solutions. The precursor has heated in two stages, at 300 and
800°C each for 2 h, to avoid the burning of the important species involved
in the final product. The effects of time (6 to 48 h) and temperature (845
and 855°C) on the formation of the 2223 phase have been studied by sintering
the samples in air. Thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning
electron microscopy (SEM) and a vibrating sample magnetometer (VSM) have been
employed to investigate the powder produced at different stages of decomposition,
oxidation and formation of sintered materials from the powders. The volume-fraction
of the 2223 phase at 845°C increases with time, the maximum value of the
2223 phase was obtained at 120 h. It has been observed that the formation
of the high TC phase
is remarkably enhanced at the temperature of the endothermic peak of the DTA
curve. The best result has been obtained in the sample sintered for 24 h at
the temperature 855°C (endothermic peak). This also indicated that at
855°C, the large volume-fraction of 2223 phase with TC
113 K grew in short time and as the sintering time increased, it decomposed
into the Bi2Sr2CaCu2Ox
(2212) phase and other phases. 相似文献
3.
J. Plewa S Cherepov D. Kohler J. F. Löns H. Altenburg 《Journal of Thermal Analysis and Calorimetry》1995,45(3):395-403
The glassy precursors were fabricated by quenching the melted materials with copper plates. In the case of heating the properties of the quenched samples were changed, because as a result of solid-state reactions formation of cuprate occurs. The amorphous samples were annealed in air and transformed to the crystalline state. This process can be seen by DTA and electric resistivity behaviours. The microscopic observation of the polished surfaces show the growth of the superconducting phase Bi2Sr2CaCu2O8+x (for composition Bi-2212) and Bi2Sr2CaCu2O8+x with Bi2Sr2Ca2Cu3O10+x (for composition Bi-2223 and Bi-2234), respectively. 相似文献
4.
Paola Benzi Elena Bottizzo Chiara Demaria Nicoletta Rizzi 《Journal of Chemical Sciences》2007,119(6):631-635
YBa2Cu3Ox (Y-123) and Bi2Sr2Ca1Cu2Ox (Bi-2212) films on various substrates have been prepared by Metal-Organic Deposition starting from different metallorganic
fluorine-free compounds and using a very simple instrumentation. The processing conditions include a rapid pyrolysis step
in air and an annealing step in oxygen for Y-123 and in air for Bi-2212. The films obtained have been characterized by X-ray
diffraction (XRD) and the formation of a superconducting phase of Y-123 or Bi-2212 was confirmed measuring the critical temperature
(T
c) with Ac-susceptibility and resistive measurements. Microstructure and final cationic ratios have been studied by scanning
electron microscopy (SEM) and energy dispersive spectroscopy (EDS). 相似文献
5.
The benzene-mediated iodine intercalation into the pseudo-layered superconductor Bi2Sr1.8Ca1.2Cu2Ox (2212) is an efficient way to prepare an intercalate with nominal composition IBi2Sr1.8Ca1.2 Cu 2Ox. Expansion by 22 percent along the crystallographic c-axis was observed but both a-and b-axes of the intercalates remained unchanged. The superconducting temperature (Tc) of 2212 phase decreased 10 K upon iodine intercalation. We report the First solvent-mediated intercalation reaction and preliminary characterizations of a presumably stage-1 phase IBi2Sr1.8Ca1.2Cu2Ox. 相似文献
6.
Jun-Gang Hou Yuan-Fang Qu Wei-Bing Ma Qing-Chi Sun 《Journal of Sol-Gel Science and Technology》2007,44(1):15-20
A sol–gel auto-combustion method was investigated to incorporate small amounts of additives of Cu and Bi uniformly into soft
magnetic MnZn-ferrite nanoparticles, which were prepared by Fe(NO3)3·9H2O, Mn(NO3)2 and Zn(NO3)2·6H2O dissolved in water and citric acid. The powder was characterized by the X-ray diffraction analysis and transmission electron
microscope method. The effects of nano-particle sized powders in microstructure development and adding CuO–Bi2O3 into MnZn-ferrite on phase formation, densification process as well as magnetic properties were studied by scanning electron
microscope and vibrating sample magnetometer techniques. The sample without additive can be sintered well at 930 °C, while
the samples with a small amount of the additive can be sintered at less than 900 °C. Obviously, the micron-sized powders exhibited
high sintering activity. It was also found that CuO–Bi2O3 additive promoted the growth of grains and improved magnetic properties. The permeability and the saturation magnetization
were improved substantially by adding CuO–Bi2O3 into MnZn-ferrite and the sintering temperature was lowered to 875 °C, which may be associated with the redistribution of
cations on the tetrahedral (A) sites and octahedral (B) sites within the spinel lattice. 相似文献
7.
Y. Akishige H. Shigematsu T. Tojo H. Kawaji T. Atake 《Journal of Thermal Analysis and Calorimetry》2005,81(3):537-540
Summary Specific heats on the single crystals of Sr2Nb2O7, Sr2Ta2O7 and (Sr1-xBax)2Nb2O7 were measured in a wide temperature range of 2-600 K. Heat anomalies of a λ-type were observed at the incommensurate phase transition of TINC (=495 K) on Sr2Nb2O7 and at the super-lattice phase transition of TSL (=443 K) on Sr2Ta2O7; the transition enthalpies and the transition entropies were estimated. Furthermore, a small heat anomaly was observed at the low temperature ferroelectric phase transition of TLOW (=95 K) on Sr2Nb2O7. The transition temperature TLOW decreases with increasing Ba content x and it vanishes for samples of x>2%. 相似文献
8.
E. S. Buyanova O. S. Kaimieva A. N. Shatokhina M. V. Morozova Yu. V. Emel’yanova S. A. Petrova 《Russian Journal of Inorganic Chemistry》2016,61(4):470-476
Solid solutions Bi3Nb1–yWyO7 ± δ, Bi3Nb1–yVyO7 ± δ, Bi3Nb1–yFeyO7 ± δ (y = 0.1–0.5; Δy = 0.1), and Bi3–xYxNb1–yWyO7 ± δ (x = 0.05, 0.1; y = 0–0.3; Δy = 0.1) have been studied. The homogeneity ranges of the solid solutions and crystal-chemical parameters have been determined by means of X-ray powder diffraction. The electrical conductivity of sintered samples has been studied by impedance spectroscopy. The joint introduction of yttrium and tungsten into the niobium sublattice does not lead to an increase in the conductivity of solid solutions, and the change of the dopant type has no noticeable effect on this conductivity. 相似文献
9.
Summary We have fabricated glasses in the Bi-2223 HTc superconductor system with Bi2Sr2Ca2Cu3-xErxO10+ δ nominal composition, where x=0.5 and 1.0, by the glass-ceramic technique. Using an analysis developed for non-isothermal crystallization studies, information on some aspects of crystallization temperature and thermal properties has been obtained. The crystallization studies were made using DTA with several uniform rates. The calculations of crystallization activation energies, Ea, and the Avrami parameters, n, were made based on the non-isothermal kinetic theory of Kissinger and the Ozawa’s equations. The DTA data of the samples showed that the first crystallization temperature, Tx1, increases and the second crystallization temperature, Tx2, decreases by increasing the Er concentration. This suggests that the Er substitution had significant effect on the glassification of the BSCCO material due to change on the surface nucleation and increased ionic activities at high temperature region. The activation energy for crystallization, Ea, of the samples was also showed an increase at high Er concentration case. However, the Avrami parameter, n, decreased from 2.5 to 1.7 for x=0.5 and 1.0 samples, respectively. This suggests that the growth mechanism is diffusion-controlled and three-dimensional parabolic growth takes place near the first crystallization temperature. The oxidization rates and the activation barrier for oxygen out-diffusion process, E, was calculated using the TG data. It was found that the total mass gain in the x=0.5 sample is comparably smaller than that of the x=1.0 sample. This shows that the oxygen absorption of the x=1.0 sample is faster than the x=0.5 sample, leading to increase in the oxidization rate in the x=1.0 material. 相似文献
10.
Ca3Co4O9 powder was prepared by a polyacrylamide gel route in this paper. The effect of the processing on microstructure and thermoelectric
properties of Ca3Co4O9 ceramics via spark plasma sintering were investigated. Electrical measurement shows that the Seebeck coefficient and conductivity
are 170 μV/K and 128 S/cm, respectively, at 700 °C, yielding a power factor value of 3.70 × 10−4 W m−1 K−2 at 700 °C, which is larger than that of Ca3Co4O9 ceramics via solid-state reaction processing. The polyacrylamide gel processing is a fast, cheap, reproducible and easily
scaled up chemical route to improve the thermoelectric properties of Ca3Co4O9 ceramics by preparing the homogeneous and pure Ca3Co4O9 phase. 相似文献
11.
A continuous solid solution LaMn1?y Cr y O3 with an orthorhombic structure is found to exist in the range of 0.0 ≤ y ≤ 1.0. An orthorhombic solid solution La1?x Sr x CrO3 exists in the range of 0.0 ≤ x ≤ 0.1. The stability boundaries are determined for the perovskite phase La1?x Sr x Mn1?y Cr y O3. An isobaric-isothermal section LaMnO3-SrMnO3-SrCrO4-LaCrO3 of the system La2O3-SrO-Mn3O4-Cr2O3 in air at 1100°C is designed. 相似文献
12.
G. Nenartaviciene K. Tõnsuaadu D. Jasaitis A. Beganskiene A. Kareiva 《Journal of Thermal Analysis and Calorimetry》2007,90(1):173-178
In this study the formation of chromium substituted YBa2Cu4O8 (Y-124) superconductors has been investigated by TG/DTA measurements. The YBa2(Cu1−xCrx)4O8 ceramics with nominal compositions of x=0.01, 0.03, 0.05, 0.10 and 0.20 have been prepared by an aqueous sol-gel method using aqueous mixtures of the corresponding
metal acetates and nitrates. Homogeneous precursor gels were obtained by complexing metal ions with tartaric acid. To assist
the interpretation of the results obtained the synthesis products were additionally characterized by X-ray powder diffraction
(XRD) and resistivity measurements. It was determined that doping the YBa2Cu4O8 phase with chromium has a strong effect on the phase purity and superconducting properties of the synthesis products. 相似文献
13.
Substitution of rare earths of various size (i.e., La and Yb) in the superconducting 2212 phase Bi2Sr2Ca1−yLnyCu2O8+x+y/2 (0 ≤ y ≤ 1) shows: (i) the larger La atoms substitute preferentially on the Sr site while the small Yb atoms occupy the Ca site; (ii) the superconductive property disappears when y reaches 0.5; (iii) as the Yb-doped phase approaches y = 0.5 the oxygen layers sandwiched between the Bi layers rearrange; an effect which may be associated with the observed variation of the modulation vector of the superstructure and, subsequently, with the phenomenon of superconductivity. Various phases corresponding to y = 0.1, 0.2, 0.3, 0.4, and 0.5 have been identified as separate through powder and single crystal diffraction, X-ray techniques, and electron microscopy investigations and their superconductivity properties checked by four probe resistivity measurements. 相似文献
14.
Z. Branković K. Đuriš A. Radojković S. Bernik Z. Jagličić M. Jagodič K. Vojisavljevic G. Branković 《Journal of Sol-Gel Science and Technology》2010,55(3):311-316
Substituted lanthanum manganites with the general formula A1−x
B
x
MnO3 (A = La, B = Ca, Sr…) have attracted a lot of attention due to their exceptional electric and magnetic properties. In this
work, pure and Ca2+, Sr2+-doped LaMnO3 (LMO) with the concentrations of dopants 30% Ca2+ (LCMO), 30% Sr2+ (LSMO) and 15% Ca2+ + 15% Sr2+ (LCSMO) (in mol. %) were synthesized by polymerizable complex method. Bulk samples were prepared by sintering at 1300 °C
for 4 h in oxygen atmosphere. It was found that sintering in oxygen atmosphere enables preparation of single phase ceramics
with rhombohedral crystal structure. Chemically prepared fine, submicronic precursor powders provided uniform microstructure
and grain size distribution in final ceramics. As a result, pure and doped LMO ceramics with excellent microstructural and
magnetic properties were obtained. Depending on the composition, magnetic measurements showed high saturation magnetizations
(up to 93 emu/g), with values of the Curie temperature in the range 180–390 K and magnetoresistance up to 67%. 相似文献
15.
S. K. Durrani A. H. Qureshi S. Qayyum M. Arif 《Journal of Thermal Analysis and Calorimetry》2009,95(1):87-91
The effects of barium substitution for Bi or Sr sites on the growth of superconducting phases have been studied. The sol spray
process has been used to synthesis the Bi-Sr-Ca-Cu-O (BSCCO) and Ba-BSCCO homogeneous ceramic powders. Thermogravimetric (TG),
differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) techniques were employed
to characterize the synthesized materials. The electrical resistance was measured by classical d.c. fourprobe technique. It
has been observed that sol spray process has affected the physico-chemical properties of the materials and also avoid the
use of chelating agent as in the case of sol gel process. In addition to the Bi2Sr2CaCu2O8 (2212) phase Ba doped specimens also contained Bi2Sr2Ca2Cu3O10 (2223), BaBiO3, BaCuO2 and CuO phases.
The results revealed that the specific effect of barium-doping on either sites (Bi or Sr) seems to avoid the formation of
higher volume fraction of the low T
c phase and promoting the formation of BiBaO3, BaCuO2 and CuO along with formation of a high T
c 2223 phase. The substitution of Ba on either sites (Bi or Sr) lower the sintering temperature for the formation of high T
c (small volume fraction) however, the Ba doped specimens also contained non-superconducting phases. 相似文献
16.
T. I. Krasnenko M. V. Rotermel’ S. A. Petrova R. G. Zakharov O. V. Sivtsova A. N. Chvanova 《Russian Journal of Inorganic Chemistry》2008,53(10):1641-1647
Phase relations in the Zn2V2O7-Cu2V2O7 system were studied by high-temperature X-ray diffraction and differential thermal analysis. The major phase constituents
of the system are solid solutions based on Zn2V2O7 and Cu2V2O7 polymorphs and their coexistence regions. The generation of α-Zn2 − 2x
Cu2x
V2O7 solid solution, where 0 ≤ x ≤ 0.30, leaves almost unchanged the stabilization temperature of the high-temperature zinc pyrovanadate phase. The α-Cu2 − 2x
Zn2x
V2O7 homogeneity range is 5 mol % Zn2V2O7. In the range 0.050 ≤ x ≤ 0.09 from 20 to ∼ 620°C, there is the two-phase field of α-Cu2V2O7 and β-Cu2V2O7 base solid solutions. At still higher temperatures, β-Zn2 − 2x
Cu2x
V2O7 and α-Cu2 − 2x
Zn2x
V2O7 coexist in the mixed-phase region. β-Zn2 − 2x
Cu2x
V2O7 solid solution, where 0 ≤ x ≤ 0.30, exists above 610 ± 5°C. The extent of the β′-Cu2V2O7-base solid solution is 9 to 65 mol % Zn2V2O7 at 615 ± 5°C, expanding to 0 mol % Zn2V2O7 with rising temperature.
Original Russian Text ¢ T.I. Krasnenko, M.V. Rotermel’, S.A. Petrova, R.G. Zakharov, O.V. Sivtsova, A.N. Chvanova, 2008, published
in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 10, pp. 1755–1762. 相似文献
17.
Z. A. Mikhailovskaya E. S. Buyanova S. A. Petrova M. V. Morozova R. G. Zakharov V. M. Zhukovskii 《Russian Journal of Inorganic Chemistry》2013,58(6):695-700
The existence boundaries, structures, and transport parameters of Bi1 ? x Co x [Bi12O14]Mo5O20 ± δ and Bi[Bi12O14]Mo5 ? y Co y O20 ± δ solid solutions, which have a unique columnar structure, were studied. Electrical conductivity in these solid solutions was studied by impedance spectroscopy. 相似文献
18.
Optimization of the Sintering Process by DSC for the Preparation of High-Temperature Superconductors
M. Ochsenkühn-Petropulu P. Tarantilis R. Argyropulu G. Parissakis 《Journal of Thermal Analysis and Calorimetry》1998,52(3):903-914
The optimum calcination and sintering conditions for the preparation of the desired phases with the proper stoichiometry of
the bulk high-temperature superconductors YBa2Cu3O7-x (YBCO) and Bi2Sr2CaCu2Oy> (BSCCO) were investigated by differential scanning calorimetry. DSC analysis on the corresponding superconducting coatings,
electrophoretically deposited, indicated that the sintering and annealing procedure was suitable for the production of stable,
strong and adherent coatings. X-ray diffraction analysis, Raman spectroscopy and magnetic measurements confirmed the improved
properties of the superconducting powders and coatings obtained.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
Thermal behaviour of the glass series (100-x)[50ZnO-10B2O3-40P2O5]·xSb2O3 (x=0-42 mol%) and (100-y)[60ZnO-10B2O3-30P2O5]·ySb2O3 (y=0-28 mol%) was investigated by DSC and TMA. The addition of Sb2O3 results in a decrease of the glass transition temperature and crystallization temperature in both compositional series. All
glasses crystallize on heating in the temperature range of 522–632°C. Thermal expansion coefficient of the glasses monotonously
increases with increasing Sb2O3 content in both series and varies within the range of 6.6–11.7 ppm °C−1. From changes of thermal capacity within the glass transition region it was concluded that with increasing Sb2O3 content the ‘fragility’ of the studied glasses increases. 相似文献
20.
M. Boča V. Danielik Z. Ivanová E. Mikšíková B. Kubíková 《Journal of Thermal Analysis and Calorimetry》2007,90(1):159-165
The phase diagrams of the systems KF-K2TaF7 and KF-Ta2O5 were determined using the thermal analysis method. The phase diagrams were described by suitable thermodynamic model. In
the system KF-K2TaF7 eutectic points at x
KF=0.716 and t=725.4°C and at x
KF=0.214 and t=712.2°C has been calculated. It was suggested that K2TaF7 melts incongruently at around 743°C forming two immiscible liquids. The system KF-Ta2O5 have been measured up to 8 mol% of Ta2O5. The eutectic point was estimated to be at x
KF∼0.9 and t∼816°C. The formation of KTaO3 and K3TaO2F4 compounds has been observed in the solidified samples. 相似文献