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1.
SONAL SINGHAL SHEENU JAUHAR KAILASH CHANDRA SANDEEP BANSAL 《Bulletin of Materials Science》2013,36(1):107-114
Synthesis of non-collinear (spin canted) ferrites having the formula, CoCd x Fe2???x O 4 (x?= 0·0, 0·2, 0·4, 0·6, 0·8 and 1·0), has been carried out using the sol–gel auto combustion method. The ferrite samples show an interesting magnetic transition from Neel to Yafet–Kittel configuration, as the Cd2?+? concentration is increased beyond x?= 0·4. The FT–IR spectra confirm the formation of the metal oxide bond as they exhibit two frequency bands in the range of ~595 cm???1 and ~450 cm???1, corresponding to the tetrahedral and the octahedral stretching vibrations of the metal oxide, respectively. The structural evolutions of the nanophase investigated using powder X-ray diffraction (XRD) technique show that the average crystallite size is ~ 35 nm. The magnetic studies reveal that the saturation magnetization, M s , increases up to x?= 0·4 and decreases when the value of x is >0·4. It is proposed that the incorporation of Cd2?+? ion takes place into the tetrahedral sites and up to x?= 0·4, Neel’s model is followed. But for x?> 0·4, canting of spins occurs, as explained by Yafet–Kittel (Y–K) model. The d.c. resistivity decreases as a function of temperature, indicating semiconducting nature of the ferrites and the positive value of Seebeck coefficient establishes p-type conduction behaviour for all the ferrite samples. 相似文献
2.
Conic Ba0·5Sr0·5Co0·8Fe0·2O3−δ (BSCF) functional composite oxide was synthesized via a simple in situ templating process. The treatment of the solid precursor with concentrated nitric acid resulted in the mismatch of ionic
radius at A-site and B-site of the ABO3 perovskite, due to the oxidation of cobalt/iron ions, and the formation of Ba0·5Sr0·5(NO3)2 solid solution. Therefore, instead of the direct formation of BSCF oxide, an intermediate phase of Ba0·5Sr0·5CoO3 (BSC) in hexagonal lattice structure and with conic particle shape was preferentially formed during calcination at low temperature.
BSCF perovskite was then produced by the in situ templating of BSC with iron diffusing into the BSC lattice during calcination at high temperature. Well-crystallized BSCF
particles in conic shape were obtained by the calcination of the nitric acid treated precursor at 900°C. 相似文献
3.
L. P. Lyashenko L. G. Shcherbakova D. A. Belov E. I. Knerel��man N. N. Dremova 《Inorganic Materials》2013,49(1):70-75
We have studied the detailed structure and electrical properties of single-crystal and polycrystalline fluorite-like R2 + x TiO5 + 1.5x (R = Y, Er; 0 ?? x ?? 1) materials and found the first evidence for the formation of nanodomains ? 40?C1000 nm in size, which are coherent with the matrix and have various degrees of structural order. The formation of the nanodomains is driven by internal stress. Using impedance spectroscopy, we have determined the electrical conductivity of the materials in air at temperatures from 300 to 1000°C. The 1000°C electrical conductivity of Y2TiO5 (Er2TiO5) and Y2.44TiO5.67 (Er2.44TiO5.67) is 1.86 × 10?3 (1.35 × 10?3) and 9.98 × 10?4 (8.13 × 10?4) S/cm, respectively. The effective activation energy for electrical conduction in Y2TiO5 (Er2TiO5) and Y2.44TiO5.67 (Er2.44TiO5.67) is 1.16 (1.21) and 1.25 (1.21) eV, respectively. 相似文献
4.
Saket Asthana 《Bulletin of Materials Science》2011,34(2):279-282
The magnetic and transport properties of the compounds Nd0·5Sr0·5Mn1-x_{{\rm 1}-{x}}Cox_{{x}}O3 (x = 0·1, 0·3 and 0·5), synthesized by citrate–gel route have been investigated. The spin transition in cobaltates at low temperatures
affects the magnetic as well as transport properties. The irreversibility behaviour between the zero-field cooled (ZFC) and
field cooled (FC) magnetization as a function of temperature becomes stronger with increasing Co content. This is understood
on the basis of glassy behaviour, which becomes more robust with increasing Co substitution. The non-saturating M–H behaviour
indicates strong magnetic inhomogeneities which may cause the magnetic phase separation at the nanoscopic length scale. The
double exchange interaction is stronger between Mn3 + –O2 − –Mn4 + as compared to Co3 + –O2 − –Co4 + pairs. Co-substitution suppresses the double exchange which will lead to cluster/spin glass like behaviour as well as semiconducting
features due to localization of charge carriers (mobile eg{e}_{\rm g} electrons). 相似文献
5.
Feng Gao Jing Zhang Hongzhang Song Zhen Qin Delin Yang Xing Hu 《Journal of Materials Science: Materials in Electronics》2013,24(8):3095-3100
The influence of Fe doping on the lattice structure and thermoelectric properties of GdBaCo2?x Fe x O5+δ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) ceramics was studied from room temperature to 525 K. The results show that presence of Fe will increase both electrical resistivity and Seebeck coefficients of the samples. Due to the lattice misfit and carrier concentration reduction caused by Fe, the thermal conductivity of the sample decreases. The activation energy of conductivity is larger than that of thermopower calculated in the semiconductive region, which means that the conduction mechanism may be determined as a small polaron hopping model. The optimum Fe doping amount is x = 0.6, which results in a ZT value 0.02 at 373 K. 相似文献
6.
TAIMIN NOH JINSEONG KIM YONGTAE KIM HO HWAN CHUN MIN-SEOK JEON HEESOO LEE 《Bulletin of Materials Science》2013,36(7):1261-1266
Cu-free and Cu-doped LSM system, La0·8Sr0·2Mn1???x Cu x O3???δ (x?=?0, 0·2), with perovskite structure were prepared using an EDTA combined citrate process and the effects of Cu ion at B-site were investigated. Electrical conductivity and polarization resistance of the Cu-doped LSM were 210 S·cm???1 at 750 °C, and 2·54 Ω · cm2 at 800 °C, respectively which were better than those of the Cu-free LSM. This indicated that the electrode performance of LSM was improved by the addition of Cu. The oxidation state of Mn ions increased with addition of Cu. The increase in the oxidation state of Mn ions was due to the formation of Mn4?+? ions and oxygen vacancies. The addition of Cu ions to LSM systems could lead to enhanced electrode performance for oxygen reduction reactions originating from the change in valence of Mn ions. 相似文献
7.
XIAO-MING LIU YI-JING GU ZHAN-GUO LIU JIA-HU OUYANG FU-YAO YAN YAN JUN XIANG 《Bulletin of Materials Science》2013,36(3):395-401
BaCe0·8???x A x Gd0·2O3???δ (A = In, Zr, Ta; x?=?0, 0·1) ceramics were synthesized by solid-state reaction method. Microstructure and electrical properties of BaCe0·8???x A x Gd0·2O3???δ ceramics were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance analysis at intermediate temperatures of 573–1073 K in different atmospheres. BaCe0·8Gd0·2O3???δ , BaCe0·7In0·1Gd0·2O3???δ and BaCe0·7Zr0·1Gd0·2O3???δ ceramics exhibit a single cubic perovskite structure. BaCe0·7In0·1Gd0·2O3???δ ceramic has the highest conductivity of 4·6 × 10???2 S·cm???1 in air at 1073 K. BaCe0·7In0·1Gd0·2O3???δ and BaCe0·7Zr0·1Gd0·2O3???δ ceramics exhibit an excellent chemical stability against boiling water. Indium is a suitable doping element to promote the sintering densification and to enhance both electrical conductivity and chemical stability of Gd-doped BaCeO3 at operating temperatures. 相似文献
8.
SHILPI BANERJEE ANINDYA DATTA ASIM BHAUMIK DIPANKAR CHAKRAVORTY 《Bulletin of Materials Science》2012,35(6):919-924
Nanoporous Ni0·5Zn0·5Fe2O4 particles of diameter, ~ 9·5 nm, were synthesized by citric acid assisted thermal decomposition in an autoclave. The BET surface area measured was 80 m2 g???1 and the average pore diameter was 2·5 nm. By soaking the particles in a suitable precursor solution and then subjecting them to a heat treatment at 923 K for 3 h, Pb(Zr0·52Ti0·48)O3 was grown within the nanopores. X-ray and electron diffraction studies confirmed the presence of both these phases. The nanocomposites showed ferromagnetic behaviour over the temperature range 2–300 K. No ferroelectric hysteresis loop could be found which was consistent with the earlier theoretical prediction of loss of ferroelectricity below a critical thickness of 2·4 nm. Good magneto-dielectric response of the order of 7% at a magnetic field of 9 kOe was recorded for the present system. This is believed to arise due to a negative magnetostriction coefficient of Ni0·5Zn0·5Fe2O4 which exerted a compressive strain on Pb(Zr0·52Ti0·48)O3 thereby lowering the tetragonality in its crystal structure. 相似文献
9.
Ba0·5Sr0·5Ti0·6Zr0·4O3 ceramic has been prepared through solid state reaction route. X-ray diffraction shows that the sample has cubic perovskite
structure with space group Pm-3m at room temperature. Temperature dependent dielectric study of the ceramic has been investigated in the frequency range 50
Hz-1 MHz. The density of the sample is determined using Archimedes’ principle and is found to be ∼99% of X-ray density. The
dielectric study revealed diffuse phase transition of second order. A broad dielectric anomaly coupled with the shift of dielectric
maxima toward a higher temperature with increasing frequency indicates the relaxor-type behaviour in the ceramics. The index
of relaxation (γ) and the broadening parameter (Δ) were estimated from a linear fit of the modified Curie-Weiss law. The value of γ ∼ 1·72 indicates the strong relaxor nature of the ceramic. A remarkably good fit to the Vogel-Fulcher relation further supports
such a relaxor nature. 相似文献
10.
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
11.
The thermal properties (glass transformation, T
g, and softening, T
s, temperatures), the crystalline phases formed during heating in a differential thermal analysis (DTA) apparatus, the kinetic parameters and the mechanism of the devitrification process, of glasses of the system diopside-wollastonite were investigated. The substitution of CaO by MgO induces an increase in T
g and the crystal growth activation energy, E
c; this is probably linked to the greater coordination number of Caz+ ions with respect to the Mg2+ ions. The substitution of CaO by MgO lowers the nucleation rates of the diopside phase; wollastonite solid solution nuclei form whose growth appears to leave a glassy matrix in which diopside formation is inhibited. Only surface nucleation was observed, but, in finely powdered samples, which soften and efficiently sinter before devitrifying, surface nuclei behave as bulk nuclei. When bulk crystallization occurs, the Avrami parameter m was found to be 2 for all glasses, except the diopside one, for which m=3. 相似文献
12.
S. Kurogi K. Kudo T. Noji Y. Koike T. Nishizaki N. Kobayashi 《Journal of Low Temperature Physics》2003,131(3-4):353-357
We have investigated the spin state of the one-dimensional edge-sharing chain system Ca2+x
Y2–x
Cu5O10 with 0x1.667 by means of the magnetic susceptibility and specific heat measurements, using the large-size single-crystals. It has been found that the magnetic ground state is an antiferromagnetically ordered state for 0x1.0, while a spin-gap state seems to be formed for x1.5. Accordingly, it appears that the quantum critical point is located between x=1.0 and 1.5 in Ca2+x
Y2–x
Cu5O10. 相似文献
13.
S. M. Ramay Murtaza Saleem S. Atiq Saadat A. Siddiqi S. Naseem M. Sabieh Anwar 《Bulletin of Materials Science》2011,34(7):1415-1419
Co0·5Mn0·5Fe2O4 ferrites have been synthesized using a single-step sol-gel auto-combustion method in which the metal nitrate (MN)-to-citric acid (CA) ratio was adjusted to 0.5: 1 and pH to 7, respectively. The structural and magnetic properties of as-burnt and annealed samples were studied as a function of temperature. The inverse spinel structure was confirmed by X-ray diffraction (XRD) and crystallite size was estimated by the most intense peak (311) using Scherrer’s formula. Contrary to earlier studies reported in the literature, both as-burnt and annealed samples exhibit crystalline behaviour. Room temperature magnetic properties were studied using vibrating sample magnetometer (VSM) with field strengths up to ±10 kOe. Lattice constant and crystallite size increased as the annealing temperature was increased. However, the coercivity (H c) initially increased and then decreased with the increase of crystallite size. The variation in coercivity is ascribed to the transition from a multi-domain to a single-domain configuration. 相似文献
14.
The perovskite Yb-doped strontium cerate–zirconate material, SrCe0·4Zr0·4Yb0·2O2·9, was prepared by solid-state reaction and the structure was characterized by X-ray diffraction. The calcination process of the powder was investigated by thermogravimetric/differential thermal analysis (TG–DTA). The high temperature conductivities were measured by d.c. four-probe technique in the temperature range from 500 to 950°C in wet hydrogen and effect of temperature on conductivity was investigated. The conductivity increased with the elevation of temperature from 500 to 950°C. The highest conductivity of 4·4 × 10???2 S· cm???1 was observed for SrCe0·4Zr0·4Yb0·2O2·9 at 950°C. The current–voltage (I–V) and current–power (I–P) characteristics of the single cell (H2, Pt/SrCe0·4Zr0·4Yb0·2O2·9/Pt, O2) at temperature range from 600 to 850°C were tested. With the temperature increasing from 600 to 850°C, the open circuit voltage (OCV) decreased from 1·164 to 1·073 V and the ionic transfer number decreased from 0·996 to 0·946. At 850°C, the maximum power density of 25·2 mW· cm???2 was observed. 相似文献
15.
Polycrystalline thermistor ceramics with the stoichiometric formula, Sr x Ba1???x Fe0·6Sn0·4O3???ε (0·2 ≤ x ≤ 0·8), had been prepared by a standard solid state reaction route. X-ray diffraction analysis indicates that the ceramic system remains cubic perovskite structure with a very small lattice change. The electrical properties of Sr x Ba1???x Fe0·6Sn0·4O3???ε thermistors were studied using a digital thermometer over a wide range of 298–400 K. The thermistors showed an excellent negative temperature coefficient (NTC) thermistor behaviour. The values of resistivity at 298 K (ρ 298), thermistor constant (B 298/358) and activation energy (E a) of the Sr x Ba1???x Fe0·6Sn0·4O3???ε thermistors, decreasing with the increase of Sr content, were in the range of 0·37–11·0 kΩ ·cm, 2466–3703 K and 0·212–0·319 eV, respectively. For the thermistors with the compositions x?= 0·2 and 0·4, the fitting equivalent circuit was composed of three RCPE elements corresponding to grain, grain boundary and ceramic–electrode interface, respectively. From the impedance plots, it was found that the fitting data showed good agreement with the experimental data. The extracted grain boundary resistance exhibited a NTC thermistor behaviour. 相似文献
16.
Gergana I. Drandova Troy C. Messina Jae-Hyuk Choi Javier F. Hernandez John T. Markert 《Journal of Low Temperature Physics》2003,131(3-4):305-309
We report NMR lineshape, spin-lattice relaxation time T
1, and spin-spin relaxation time T
2 data at 17 MHz (8.07 T) for 89Y in the copper-oxide spin-chain compound Ca2+x
Y2–x
Cu5O10. For x=0, a broad, asymmetric line with width 90 kHz is observed for T=250–300 K. The spectra exhibit an appreciable average shift (H/H+0.7%) and sharpen at lower temperature, possibly due to increasing intrachain ferromagnetic correlations. T
1 and T
2 decrease with decreasing temperature. The Tl data imply a short correlation-time limit, with e=3–5×10–11 s. The T
2 data apparently include a contribution from dipolar interactions with copper nuclei. Relaxation time data for a doped (x=0.5) compound surprisingly show more rapid relaxation. 相似文献
17.
《Materials Science & Technology》2013,29(6):504-509
AbstractThe creep of a Pb–2·5Sb–0·2Sn alloy has been studied at stresses up to 6·5 MN m?2 in the temperature range 318–348 K (0·53–0·58Tm) using helical specimens. At 333 K, a transition in the stress exponent from ~1 to 3 occurred at ~3 MN m?2. The observed good agreements below the transition stress, both for experimental dE/do and predictions for Coble diffusional creep of lead, and for measured activation energy for creep and the activation energy for grain boundary self-diffusion in lead, suggest that grain boundary diffusional creep is the dominant mechanism. at low stresses. The presence of antimony does not seem to affect the magnitude of dE/do appreciably, and the results suggest that the grain boundary self-diffusivity of lead is not influenced by the presence of segregated antimony on the grain boundaries. The diffusional creep occurred above a threshold stress of magnitude ~0·5 MN m?2, and its temperature dependence was characterised by an activation energy of ~20 kJ mol?1, similar to the value of 23 ± 7 kJ mol?1 typical of pure metals in the temperature range investigated. The stress exponent of ~3 observed for the power law regime suggests control by viscous glide of dislocations constrained by dragging of solute atmospheres. Preliminary tests on sagging beam specimens of as-worked material at an applied stress of 2·5 MN m?2 and a test temperature of 333 K has provided the first direct evidence that anisotropic grain shape affects Coble creep. The specimen with the longest grain dimension along the stress axis underwent slower creep than the specimen with the longest grain dimension perpendicular to the stress axis. This observation is in qualitative agreement with theoretical predictions.MST/1139 相似文献
18.
《Materials Science & Technology》2013,29(7):677-685
AbstractMany high–temperature creep tests are performed on low–chromium, ferritic steels in an uncontrolled atmosphere. Examination of creep rupture specimens of 0·5Cr–0·5Mo–0·25V steel tested in air has shown that decarburization accompanies oxidation and is an important factor in accelerating the failure of creep tests in air. Similarly, pre-aging in air reduces the creep life more than pre-aging in a capsule. There is also evidence that decarburization is accelerated during straining. Measurements of surface carbon contents in 10 mm thick blocks heat treated in air at 600–700°C have given an apparent activation energy for decarburization of about 250 kJ mol?1, at least twice that for carbon diffusing in ferrite. However, this value is still below that for creep, so the influence of decarburization on creep life is expected to increase at lower temperatures. Structural observations are discussed in relation to loss of carbon and are related to creep behaviour. Secondary precipitation was observed after low-temperature treatments in aged encapsulated specimens, but not in specimens aged in air. This is attributed to the loss of carbon in the air aged specimens, which also showed a decrease in the M3C content. The iron content of M3C particles depends on carbon content as well as aging time.MST/40 相似文献
19.
本文研究了E_3~1系统,x=-y+δx+mxy+ny~2+a_1x~3+a_3xy~2,y=x的极限环,其中m≠0,a_1≠0,a_3≠0,利用Dulac函数法及地形系法得到了一系列无环性条件,并证明了系统在一定条件下至少可以存在一个及两个极限环,同时通过构造Poinear'e—Bendixson环域得到了系统存在大范围的极限环的条件。 相似文献
20.
采用低温燃烧合成法,在柠檬酸-硝酸盐体系中合成出Ce1-xNdxO2-x/2(0≤x≤0.6)固溶体纳米粉体。X射线衍射(XRD)结果表明,Nd^3+取代Ce^4+进入晶格内部,形成具有单相立方萤石结构的固溶体,其晶格常数随Nd^3+掺杂浓度的增大而线性增加,晶粒尺寸在15-24nm之间。透射电镜(TEM)结果表明,粉体颗粒尺寸在20-40nm之间,分散性较好,具有较高的烧结活性。拉曼光谱(Raman Spectrum)结果表明,F2g宽化峰的出现与掺杂后固溶体中产生的氧空位有关,并且随着掺杂浓度的增加,氧空位数量也再增加。 相似文献