共查询到20条相似文献,搜索用时 265 毫秒
1.
40CaO–20B 2O 3–40SiO 2 (abbreviate as CBS) glass-doped Sr 0.5Ba 0.5Nb 2O 6 (SBN50) ceramics were fabricated by solid-state ceramic route. The effects of CBS glass addition on the firing, the phase
formation, the microstructure and dielectric characterization of SBN50 ceramics were investigated. Results show that the density
of the samples firstly increase and then slightly decrease with increasing CBS glass content and the highest density achieved
has been 97% of the theoretical density for the sample with 2% (mass fraction) CBS glass. The sintering temperature was significantly
reduced from 1,350 to 1,100 °C. X-ray diffraction analysis shows the single phase tungsten bronze type structure is preserved
up to 2% CBS glass. However, the samples with more than 5% CBS glass are found to have a secondary phase CaNbO 3. The diffuse character and the dielectric constant at room temperature increase as CBS glass content increases. The dielectric
constant of the samples at the Curie temperature ( T
c) firstly increases and then decreases with increasing the content of CSB glass. Interestingly, the grain sizes of SBN phase
are found to obviously increase with increase in CBS glass doping level. 相似文献
2.
The as-sintered Pb(Zn 1/3Nb 2/3) 0.5(Zr 0.47Ti 0.53) 0.5O 3 samples were annealed in oxygen and nitrogen. Both annealed specimens exhibited improved degree of relaxation compared with as-sintered specimens. However, the mechanisms inducing enhancement of relaxation were different in the two kinds of specimens. For the oxygen annealed sample, oxygen vacancies were partially filled, which induced the macro-microdomain transition and resulted in the increase of relaxation degree. Whereas, for the nitrogen annealed specimen, the emergence of pyrochlore phase was inevitable due to the flowing reductive atmosphere, the pyrochlore phase broke the long-range transition invariance of perovskite structure and played a key role in improving the relaxation. 相似文献
3.
The compositional effects on the crystal structure, phase transition, dielectric, ferroelectric and piezoelectric properties
of the (1- x)BaTiO 3- x(Bi 0.5Na 0.5)TiO 3 solid solution ceramics were investigated. After sintering at 1200 °C for 2 h, the ceramics with different content of (Bi 0.5Na 0.5)TiO 3 (BNT) formed single-phase solid solutions with perovskite structure. The lattice constant c/ a ratio of the solid solutions decreased as BNT content increased except that with 20 mol% BNT, which had the largest value
of c/ a ratio for all samples. The second phase transition corresponding to BaTiO 3 (BT) at about 5 °C shifted to low temperature and gradually disappeared as BNT increased. A new secondary phase transition
appeared at 32 °C and 64 °C, respectively, when BNT content was 5 and 14 mol%. The Curie temperature, T
c, shifted in the temperature range between 112 °C and 166 °C, and the remanent polarization, P
r, decreased whereas the coercive field, E
c, increased as the BNT content increased. The relatively high value of piezoelectric coefficient d 33 together with a relatively high Curie temperature and low loss tangent and stable dielectric properties were obtained when
the addition of BNT was 20 mol%. 相似文献
4.
Comparative neutron structural investigations are made on nonsuperconducting (slow-cooled) and superconducting (liquid-nitrogen quenched; T c onset=70 K and R=0 at 20 K) samples of (Bi 0.5Cu 0.5)Sr 2(Y 0.8Cu 0.2)Cu 2O 7 + δ in order to examine the role of excess oxygen on the superconducting behavior of this “1212”-phase compound. Analysis of refined structural parameters shows that the two main factors which influence the superconductivity in (Bi, Cu)-1212 are: (i) the extent of occupancy of excess oxygen at O(5), the 2( e) site located in between the two CuO 2 pyramidal layers, and (ii) the length of the apical Cu(2)-O(2) bond. The (Bi, Cu)-O monolayer plays the role of the “charge reservoir” quite effectively as reflected by the substantial increase in the length of the apical (bridging) Cu(2)-O(2) bond due to depletion of excess oxygen in this layer. Surprisingly, vacancies at as many as 10% of the O(1) site belonging to the CuO 2 planes do not appear to disrupt the flow of current in the Cu(3d)-O(2 p) planar network in the superconducting state. Relevant features of the structure of the (Bi, Cu)-1212 phase, in particular the role of excess oxygen and its occupancy at different sites, are discussed in the light of the available data on the isostructural (Pb, Cu)-1212 phase and the (La, Sr, Ca) 3-Cu 2O 6 + δ phase superconductors. 相似文献
5.
In this study, superconducting samples of type Cu 0.5Tl 0.5Ba 2Ca 2Cu 3O 10??? added by SnO 2 and In 2O 3 in nano-scale were prepared by a solid-state reaction technique. The concentrations of both SnO 2 and In 2O 3 were 0.0, 0.1, 0.2, 0.4, 0.6 and 1.0?wt% of the sample??s total mass. The prepared samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) for phase analysis and microstructure examination. The elemental content of the prepared samples was determined using energy dispersive X-ray (EDX) and particle induced X-ray emission (PIXE). The results of elemental content, determined from EDX and PIXE, were compared and discussed. In addition, The oxygen content of these samples was obtained using non Rutherford backscattering spectroscopy (RBS) at 3 MeV proton beam. It was found that the Oxygen-content of (Cu 0.5Tl 0.5)-1223 phase was not affected by both SnO 2 and In 2O 3 nano-oxides addition. The electrical resistivity of the prepared samples was measured by the conventional four-probe technique from room temperature down to the zero superconducting transition temperature ( T 0). An increase in the superconducting transition temperature T c from 106 to 119 K was observed as x was varied from 0.0 to 0.6?wt% for (SnO 2) x Cu 0.5Tl 0.5Ba 2Ca 2Cu 3O 10??? , followed by a systematic decrease with increasing nano-SnO 2 addition. On the other hand, the T c values for (In 2O 3) x Cu 0.5Tl 0.5Ba 2Ca 2Cu 3O 10??? show a small variation with? x. Moreover, the variation rate of T c with x, for both nano-additions, was found to be directly proportional to the variation of the volume fraction of the prepared samples. 相似文献
6.
Tetragonal CaF 2-related-type t′-/Ce 0.5Zr 0.5)O 2 phase was reduced at 773 K ≤ T red. ≤ 1073 K to prepare precursors with various oxygen compositions: Ce 2Zr 2O 712d /0.111 < δ < 0.379). Metastable tetragonal t ′meta-(Ce 0.5Zr 0.5)O 2 phases were prepared by oxidizing in O 2 at 873 K the precursors, and subjected to evolved oxygen gas analysis by heating the samples at a constant rate. When the precursor was prepared at T red: ? 773 K; i.e. δ ? 0:379; the oxygen release behavior of the tetragonal phase agreed approximately with that of the t ′. For δ < 0.29, distinct features of the t ′meta-(Ce 0.5Zr 0.5)O 2 appeared in the XRD results and Raman spectra. The temperature exhibiting the maximum release rate of oxygen from the t ′meta became lower with decreasing the d value. It could be concluded that the thermodynamic behavior of the t ′meta is related closely to the precursor composition and becomes more unstable with decrease in the δ value. The t ′ and t ′meta phases with disordered arrangement of Ce and Zr ions may belong to the same space group; nevertheless, difference in the random arrays of the Ce and Zr ions was suggested on the basis of the present experimental results. 相似文献
7.
The structures of the B 6O samples prepared by oxidizing boron with ZnO at temperatures of 1350–1500°C in an argon atmosphere have been refined by the Rietveld method. The B 6O samples were found to contain an amorphous phase from their X-ray diffraction profiles in addition to B 6O diffraction peaks. The results indicate that the B 6O samples, space group R¯3 m, no.166, a
hex = 0.5367(1) nm and c
hex = 1.2328(2) nm in the hexagonal unit cell, have oxygen deficiencies with 0.76(6) oxygen occupancy. A radial distribution function method applied to an extracted portion of the amorphous phase, suggests that each amorphous phase has nearly similar short-range order structure to that of the -tetragonal boron type rather than to those of any other related boron phases. 相似文献
8.
We have grown cubic centimeter-size crystals of YBa 2Cu 3O
x
suitable for neutron studies, by a top-seeded melt-growth technique. Growth conditions were optimized with an eye toward maximizing phase purity. It was found that the addition of 2% Y 2BaCuO 5 and 0.5% Pt (by mass) were required to prevent melt loss and to obtain the highest crystallinity. A neutron diffraction study on a mosaic of six such crystals found that the final Y 2BaCuO 5 concentration was 5%, while other impurity phases comprised less than 1% by volume. The oxygen content was set to x = 6.5, the crystals were detwinned, and then carefully annealed to give the well-ordered ortho-II phase. The neutron study determined that 70% of the mosaic's volume was in the majority orthorhomic domain. The neutron (006) and (110) rocking curve widths were 1° per crystal and 2.2° for the mosaic, and the oxygen chain correlation lengths were >100 Å in the a- and b-directions and 50 Å in the c-direction. 相似文献
9.
Comparative neutron structural investigations are made on nonsuperconducting (slow-cooled) and superconducting (liquid-nitrogen quenched; T
c
onset=70 K and R=0 at 20 K) samples of (Bi 0.5Cu 0.5)Sr 2(Y 0.8Cu 0.2)Cu 2O 7 + in order to examine the role of excess oxygen on the superconducting behavior of this 1212-phase compound. Analysis of refined structural parameters shows that the two main factors which influence the superconductivity in (Bi, Cu)-1212 are: (i) the extent of occupancy of excess oxygen at O(5), the 2( e) site located in between the two CuO 2 pyramidal layers, and (ii) the length of the apical Cu(2)-O(2) bond. The (Bi, Cu)-O monolayer plays the role of the charge reservoir quite effectively as reflected by the substantial increase in the length of the apical (bridging) Cu(2)-O(2) bond due to depletion of excess oxygen in this layer. Surprisingly, vacancies at as many as 10% of the O(1) site belonging to the CuO 2 planes do not appear to disrupt the flow of current in the Cu(3d)-O(2 p) planar network in the superconducting state. Relevant features of the structure of the (Bi, Cu)-1212 phase, in particular the role of excess oxygen and its occupancy at different sites, are discussed in the light of the available data on the isostructural (Pb, Cu)-1212 phase and the (La, Sr, Ca) 3-Cu 2O 6 + phase superconductors. 相似文献
10.
The superconducting properties and the irreversibility line of the Tl 0.5Pb 0.5(Sr 2?xBa x)Ca 2Cu 3O 9?δ were studied by ac susceptibility on both ceramic and powdered samples. The samples were prepared by solid state reaction in flowing oxygen at 880°C or in sealed quartz tube at 960°C. The irreversibility lines were measured up to 4 Tesla and were determined by the maximum of the X″ peak, using the same ac field to allow comparison between them. The presence of the 1212 phase as a minor superconducting phase was clearly evidenced in all cases. The case of samples of TlPbl223 with Tl/Pb ratio different from unity was also examined. 相似文献
11.
Superconducting samples of type (Cu 0.5Tl 0.5)-1223 added with nano-Fe 2O 3 ( x=0.0, 0.1, 0.2, 0.4, 0.6 and 1.0 wt.%) were prepared by solid-state reaction technique. The prepared samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) for phase analysis and microstructure examination. The elemental content of the prepared samples was determined using particle induced X-ray emission (PIXE), whereas the Oxygen-content of these samples was obtained using non Rutherford backscattering spectroscopy at 3 MeV proton beam. It was found that the Oxygen-content of (Cu 0.5Tl 0.5)-1223 phase was not affected with the addition of nano-Fe 2O 3. The electrical resistivity measurements showed that the superconducting transition temperature ( T c ) increases up to x=0.2 wt.%, followed by a systematic decrease for x>0.2 wt.%. In addition, room temperature Vickers microhardness ( H v ) measurements were carried out at different applied loads (0.49–2.94 N) to study the performance of the mechanical properties of samples. The experimental results of H v were analyzed using different models such as elastic, energy dissipation, energy balance and modified energy balance models. It has been found that the energy dissipation model is in a good agreement with the microhardness data. 相似文献
12.
Nominally pure and Yb-activated Czochralski-grown (Na 0.5Gd 0.5)WO 4 crystals (scheelite type) were studied by x-ray diffraction (phase analysis, unit-cell parameters, and structure refinement by the Rietveld method and single-crystal techniques). A pseudotetragonal (orthorhombic) superstructure was revealed, which was shown to have doubled unit-cell parameters compared to the scheelite cell. Some of the crystals were found to contain tungsten and oxygen vacancies, which give rise to additional optical absorption. The effects of the growth and heat-treatment conditions and Yb activation on the structure, defect system, and additional absorption spectrum of (Na 0.5Gd 0.5)WO 4 are analyzed. 相似文献
13.
In order to study the relation between the oxygen content and superconductivity samples of Bi 2Sr 2Ca 1–x
K
x
Cu 2O
y
( x=0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) were prepared and treated under different conditions. It was found that the superconducting properties are sensitive to the oxygen concentration and the T
c,zero of Bi 2Sr 2Ca 1–x
K
x
Cu 2O
y
can be shifted over a range of about 22 K by the changing oxygen concentration; no structural difference induced by oxygen were observed. The change in superconducting properties may be the result of a change in Cu average valence state. In addition, the change in superconducting phase with K + concentration is also studied. 相似文献
14.
(Bi0.5Na0.5)0.94Ba0.06Ti1?x(Y0.5Nb0.5)xO3 (abbreviated as BNTBT-100xYN) lead-free relaxor ceramics were designed and prepared using a traditional solid-state sintering technique. The influences of the introduction of (Y0.5Nb0.5)4+ complex ions for the dielectric properties and energy storage performances of BNTBT-100xYN ceramics were systematically studied. All samples exhibited a typical pseudo-cubic symmetry structure and obtained the dense microstructure with the uniform distribution of all elements. The ergodic relaxor behavior of all ceramics was observed and revealed a trend of increase as a function of composition. It accelerated the improvement of the temperature stability of the dielectric constant. All samples showed a single grain conduction mechanism and the activation energy decreased with the addition of composition. It is related to the generation of oxygen vacancies induced by the defect dipoles. BNTBT-6YN ceramic revealed excellent dielectric temperature stability within the temperature range from 87 to 479 °C and the loss tangent less than 0.05 between 25 °C and 474 °C. Besides, a high recoverable energy density of?~?0.91 J/cm3 with the corresponding efficiency of?~?78.5% at applied 115 kV/cm field was achieved for BNTBT-5YN ceramic. Hence, BNTBT-5YN and BNTBT-6YN ceramics will become one of the outstanding dielectric ceramics for the electronic components. 相似文献
15.
Nanocrystalline monophasic Ce 0.5Zr 0.5O 2 solid solution (1:1 molar ratio) has been synthesized by microwave-induced combustion method in a modified domestic microwave
oven (2.45 GHz, 700 W) in approximately 40 min from cerium nitrate and zirconium nitrate precursors using urea as ignition
fuel. For the purpose of better comparison, a Ce
x
Zr 1 − x
O 2 solid solution (1:1 molar ratio) was also synthesized by a conventional co-precipitation method from nitrate precursors and
subjected to different calcination temperatures. The synthesized powders of both methods were characterized by means of X-ray
powder diffraction, thermogravimetry/differential thermal analysis, scanning electron microscopy, and BET surface area techniques.
Oxygen storage capacity (OSC) measurements were performed to understand the usefulness of these materials for various applications.
The characterization results reveal that the sample obtained by microwave-induced combustion-synthesis route exhibits homogeneous
monophasic Ce 0.5Zr 0.5O 2 solid solution whereas the co-precipitated sample displays compositional heterogeneity. The OSC measurements reveal that
the materials synthesized by both methods exhibit comparable oxygen vacancy content (δ). 相似文献
16.
We have investigated the effect of Fe substitution on the structural and superconducting properties of La 2.5Y 0.5CaBa 3(Cu 1–x
Fe
x
) 7O
z
system by Rietveld refinement of the neutron diffraction patterns of three samples with x = 0.02 (labelled B 1), x = 0.06 (B 2), and x = 0.10 (B 3) along with X-ray diffraction, resistivity, AC susceptibility, and oxygen-content measurements. Samples B 1, B 2, and B 3 are superconducting with T
c
R=0 values of 73, 62, and 41 K, respectively. Neutron diffraction studies confirm (i) the formation of a single phase tetragonal structure (space group P4/mmm) for all three samples, (ii) Ca and Y ions substitution at the La site concomitantly displaces La onto Ba sites, and (iii) increasing x from 0.02 to 0.10 increases oxygen content (the amount of oxygen per unit cell), as well as Cu(1)— O(4) and Cu(1)— O(1) bond lengths whereas Cu(2)— O(4) bond length decreases with corresponding decrease in T
c to 41 K due to increasing occupancy of Fe ions at Cu(2) site. The change in bond lengths with oxygen content are essentially the same as those of Fe content ( x). Present studies establish a correlation between the bond lengths (Cu(1)— O(1), Cu(1)— O(4), and Cu(2)— O(4)) and the measured T
c values of three samples. 相似文献
17.
LaBa 2Cu 3–y
Fe
y
O
x
ceramic samples with y = 0.00–1.50 are synthesized by the solid-state reaction technique. Rietveld analysis for X-ray diffraction is performed on these iron-doped samples. A BaCuO 2 impurity phase and a ceramic cuprate phase coexist in each sample. An orthorhombic-to-tetragonal (OT) phase transition occurs in the doping range of 0.03 y0.06, and a tetragonal-to-orthorhombic (TO) one occurs in the doping level of 0.10 y0.25. There is a jump in the structural parameters due to the iron doping. The occupancy of oxygen at the O(4) site, which is in the La plane at z = 1/2, increases with increase in iron content. These results may relate to the iron preferential occupancy for the Cu(1) site at the lower doping level, and for Cu(2) sites at the higher doping level. 相似文献
18.
Nanocrystalline Cu 0.5Co 0.5Fe 2O 4 powders were prepared via a metal-cellulose precursor synthetic route. Cellulose was used as a fuel and a dispersing agent. The resulting precursors were calcined in the temperature range of 450–600 °C. The phase development of the samples was determined by using Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (XRD). The field-dependent magnetizations of the nanopowders were measured by vibrating sample magnetometer (VSM). All XRD patterns are of a spinel ferrite with cubic symmetry. Microstructure of the ferrites showed irregular shapes and uniform particles with agglomeration. From XRD data, the crystallite sizes are in range of 16–42 nm. Saturation magnetization and coercivity increased with increasing calcining temperature due to enhancement of crystallinity and reduction of oxygen vacancies. 相似文献
19.
Relaxor ferroelectric thin films of 0.7Pb(Mg 1/3Nb 2/3)O 3-0.3PbTiO 3 (PMN-PT) deposited on platinized silicon substrates with and without template layers were studied. Perovskite phase (80% by volume) was obtained through proper selection of the processing conditions on bare Pt/Ti/SiO 2/Si substrates. The films were initially grown at 300 °C using pulsed-laser ablation and subsequently annealed in a rapid thermal annealing furnace in the temperature range of 750-850 °C to induce crystallization. Comparison of microstructure of the films annealed at different temperatures showed change in perovskite phase formation and grain size etc. Results from compositional analysis of the films revealed that the films initially possessed high content of lead percentage, which subsequently decreased after annealing at temperature 750-850 °C. Films with highest perovskite content were found to form at 820-840 °C on Pt substrates where the Pb content was near stoichiometric. Further improvement in the formation of perovskite PMN-PT phase was obtained by using buffer layers of La 0.5Sr 0.5CoO 3 (LSCO) on the Pt substrate. This resulted 100% perovskite phase formation in the films deposited at 650 °C. Dielectric studies on the PMN-PT films with LSCO template layers showed high values of relative dielectric constant (3800) with a loss factor (tan δ) of 0.035 at a frequency of 1 kHz at room temperature. 相似文献
20.
In this work an attempt is made to study [Pb(Zr 0.53Ti 0.47O 3)O 3] 1-X-[Pb(Y 0.5Nb 0.5)O 3] X system with x = 0.0125, 0.025, 0.05, 0.075 and 0.1. It was shown that there is limited solid solubility (2.5 mol%) of Pb(Y 0.5Nb 0.5)O 3 (PYN) in PZT (53/47). The substitution of PYN gave rise to the reduction of the volume of PZT’s unit cell. For the samples
doped above this level of PYN, an extra phase comprising of Y 3+, Zr 4+ and Ti 4+ cations were detected based on EDS-SEM and XRD analysis and also a structural shift towards a rhombohedral phase was noticed
for the main PZT phase. Further, the addition of PYN up to 2.5 mol% was seen to increase the room temperature relative permittivity
and d 33 parameter. However, these parameters declined for the samples substituted with more than 2.5 mol% PYN due to the formation
of non ferroelectric extra phase. 相似文献
|