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1.
Effects of additives on the piezoelectric properties of Pb(Mg1/3Nb2/3)O3-PbTiO3-PbZrO3 ceramics in a perovskite-type structure are described. The tetragonality of Pb(Mg1/3Nb2/3)0.375-Ti0.375Zr0.25O3 ceramics increased with the addition of NiO, Cr2O3, or Fe2O3 but decreased with the addition of MnO2 or CoO. The dielectric and piezoelectric properties of the base composition were improved markedly through selection of additives in proper amounts. Addition of NiO yielded a high dielectric constant and planar coupling coefficient for compositions at the morphotropic transition boundary. High mechanical Q -factors and low electrical dissipation factors were obtained by addition of MnO2. Addition of both NiO and MnO2 produced a mechanical Q -factor of 2051 and a planar coupling coefficient of 0.553. The resonant frequency of Pb(Mg1/2Nb2/3)0.4375Ti0.4375 zr0.125O3 containing MnO2 had very low temperature and time dependence. The microstructure indicated that ceramics with a high mechanical Q -factor had a fine, uniform grain structure. Addition of Cr2O3 retarded grain growth and addition of MnO2, NiO, CoO, or Fe2O3 promoted grain growth in the ternary system.  相似文献   

2.
Lead-free piezoelectric (K0.5Na0.5)NbO3– x wt% Bi2O3 ceramics have been synthesized by an ordinary sintering technique. The addition of Bi2O3 increases the melting point of the system and improves the sintering temperature of (K0.5Na0.5)NbO3 ceramics. All samples show a pure perovskite phase with a typical orthorhombic symmetry when the Bi2O3 content <0.7 wt%. The phase transition temperature of orthorhombic–tetragonal ( T O − T ) and tetragonal–cubic ( T C) slightly decreased when a small amount of Bi2O3 was added. The remnant polarization P r increased and the coercive field E c decreased with increasing addition of Bi2O3. The piezoelectric properties of (K0.5Na0.5)NbO3 ceramics increased when a small amount of Bi2O3 was added. The optimum piezoelectric properties are d 33=140 pC/N, k p=0.46, Q m=167, and T C=410°C for (K0.5Na0.5)NbO3–0.5 wt% Bi2O3 ceramics.  相似文献   

3.
Sintering and microstructural evolution were studied in Fe3O4 as a model system for spinel ferrites. Fe3O4 powder, purified by the salt-crystallization method, was sintered to ∼99.5% density in a CO-CO2 atmosphere. The p O2 Of the sintering atmosphere drastically affects the microstructure (grain size) of sintered Fe3O4 without significantly affecting density. The measured grain-boundary mobilities, M , of Fe3O4 fit the equation M=M 0( T ) p O2−1/2 with M 0( T ) = 2.5×105 exp[-(609kJ·mol-1/ RT ](m/s)(N/m2)−l. The grain-boundary migration process appeared to be pore-drag controlled, with lattice diffusion of oxygen as the most likely rate-limiting step.  相似文献   

4.
Sb2O5 were selected to substitute (Nb0.8Ta0.2)2O5 and the effects of Sb substitution on the dielectric properties of Ag(Nb0.8Ta0.2)O3 ceramics were studied. The perovskite Ag(Nb0.8Ta0.2)1− x Sb x O3 ceramics showed no obvious change with x value being no more than 0.08, and the pseudoperovskite unit cell parameters a = c , b and monoclinic angle β decrease with Sb concentration increasing. The dielectric properties of Ag(Nb0.8Ta0.2)1− x Sb x O3 ceramics were found to be affected greatly by the substitution of Sb for Nb/Ta. The ɛ value of Ag(Nb0.8Ta0.2)1− x Sb x O3 ceramics sintered at their densified temperature increased from 480 to 825 with x from 0 to 0.08, the tan δ value decreased sharply from 0.0065 to 0.0023 (at 1 MHz) with x increasing from 0 to 0.04, and then kept a stable lower tan δ value ∼0.0024 with x to 0.08. The temperature coefficient of capacitance values continuously decreased from a positive value of 1450 ppm/°C for x =0 to a negative value of −38.52 ppm/°C for x =0.08.  相似文献   

5.
Extensive solid solution was observed in the system Pb(Sc1/2/,Nb1/2,)1-x,Tix,O3. In the range 0 ≤ x ≤ 0.425 a rhombohedral ferroelectric phase was stable at 25° C. In the range 0.45 ≤ x ≤ 1.00 a tetragonal ferroelectric phase was stable at this temperature. The phase diagram of the system below 500° C strongly resembles that of PbZrO3−PbTiO3. The compound Pb(Sc1/2Nb1/2)O3 exhibited rhombohedral perovskite cell symmetry below the ferroelectric ↔ paraelectric transition temperature, and the angle a was acute. The radial coupling coefficient was 0.46 for the composition Sc1/2Nb1/2)0.575Ti0.4250O3. At 25°C this composition consisted primarily of the rhombohedral phase with a small amount of the tetragonal phase present. The ferroelectric ↔ paraelectric transition occurred over a temperature range in the rhombohedral phase field. The spontaneous polarization was finite at temperatures considerably above the temperature of the permittivity maximum for a given rhombohedral solid solution.  相似文献   

6.
The phase diagram of the system BaO-Fe203 was determined by X-ray diffraction, melting-point measurement, and microscopic methods. Since the reduction of Fe3+ to Fe2+ was observed by chemical analysis in the samples heated at high temperature, especially in molten samples, the samples were heated at 1 atmosphere pressure of oxygen in the temperature region in which the liquid was in equilibrium; 1 atmosphere pressure of oxygen was su5cient to restrain the reduction of Fe3+. In the temperature region of solid-solid equilibrium, the dissociation was not observed even when the samples were heated in air. BaO - 6Fe2O3 formed a solid solution with BaO.Fe203. The BaO:Fe203 ratio of the solid solution was BaO.4.5Fe203 at 1350°C. and BaO. 5.0Fe20a at 800°C. The precipitation micro-structures of each primary solid solution were observed.  相似文献   

7.
The mechanism of formation of the perovskite phase and the dielectric properties of Pb(Zn,Mg)1/3Nb2/3O3 (PZMN) ceramics were examined using two different types of columbite precursors, (Mg,Zn)Nb2O6 (MZN) and MgNb2O6+ ZnNb2O6 (MN + ZN). The formation of perovskite phase in the PbO + MN + ZN system is characterized by an initial rapid formation of Mg-rich perovskite phase, followed by a sluggish formation of Zn-rich perovskite phase. On the other hand, due to the formation of pyrochlore phase of mixed divalent cations Pb2– x (Zn,Mg)yNb2−yO7− x −3y/2, the pyrochlore/perovskite transformation in the PbO + MZN system proceeded uniformly with a spatial homogeneity. Further analysis suggested that the formation of perovskite phase is a diffusion-controlled process. The degree of diffuseness of the rhombohedral/cubic phase transition (DPT) is higher in the PbO + MN + ZN system than in the PbO + MZN specimen for T > T max (temperature of the dielectric permittivity maximum), indicating a broadened compositional distribution of the B-site cations in the PbO + MN + ZN system.  相似文献   

8.
Fe3O4–BaTiO3 composite particles were successfully prepared by ultrasonic spray pyrolysis. A mixture of iron(III) nitrate, barium acetate and titanium tetrachloride aqueous solution were atomized into the mist, and the mist was dried and pyrolyzed in N2 (90%) and H2 (10%) atmosphere. Fe3O4–BaTiO3 composite particle was obtained between 900° and 950°C while the coexistence of FeO was detected at 1000°C. Transmission electron microscope observation revealed that the composite particle is consisted of nanocrystalline having primary particle size of 35 nm. Lattice parameter of the Fe3O4–BaTiO3 nanocomposite particle was 0.8404 nm that is larger than that of pure Fe3O4. Coercivity of the nanocomposite particle (390 Oe) was much larger than that of pure Fe3O4 (140 Oe). These results suggest that slight diffusion of Ba into Fe3O4 occurred.  相似文献   

9.
Subsolidus phase equilibria in the system Fe2O3–Al2O3–TiO2 were investigated between 1000° and 1300°C. Quenched samples were examined using powder X-ray diffraction and electron probe microanalytical methods. The main features of the phase relations were: (a) the presence of an M3O5 solid solution series between end members Fe2TiO5 and Al2TiO5, (b) a miscibility gap along the Fe2O3–Al2O3 binary, (c) an α-M2O3( ss ) ternary solid-solution region based on mutual solubility between Fe2O3, Al2O3, and TiO2, and (d) an extensive three-phase region characterized by the assemblage M3O5+α-M2O3( ss ) + Cor( ss ). A comparison of results with previously established phase relations for the Fe2O3–Al2O3–TiO2 system shows considerable discrepancy.  相似文献   

10.
Two cubic pyrochlore phases exist in the system ZnO–Bi2O3–Sb2O5. Neither has the supposed "ideal" stoichiometry, Zn2Bi3Sb3O14. One, P 1, is a solid solution phase, Zn2+ x Bi2.96−( x − y )Sb3.04− y O14.04+δ where 0< x <0.13(1), 0< y <0.017(2) and a =10.4285(9)−10.451(1) Å. The other, P 2, is a line phase, Zn2Bi3.08Sb2.92O13.92 with a =10.462(2) Å. Subsolidus phase relations at 950°C involving phases P 1 and P 2 in the ZnO–Bi2O3–Sb2O5 phase diagram have been determined.  相似文献   

11.
Phase equilibrium data, obtained by using the quenching technique, are presented for the system iron oxide-A12O3 in air and at 1 atm. O2 pressure in the temperature interval 1085° to 1725°C. Stability ranges of the various phases are delineated, and approximate compositions of crystalline and liquid phases are determined. Special attention is focused on the phase Fe2O3·A12O3(ss) and its stability relationships.  相似文献   

12.
Dielectric and piezoelectric properties of 0.02Pb(Y2/3W1/3)O3 0.98Pb(Zr0.52Ti0.48)O3 ceramics doped with additives (Nb2O5, La2O3, MnO2, and Fe2O3) were investigated. The grain sizes of these ceramics decreased with increasing amounts of additives. For additions of MnO2 and Fe2O3, dielectric losses decreased, while for Nb2O5 and La2O3, these values increased. The maximum values of the mechanical quality factor Qm were found to be 956 and 975 for additions of 0.9 wt% Fe2O3 and 0.7 wt% MnO2, respectively, but donor dopants (Nb2O5 and La2O3) did not change the values of Qm . On the other hand, the piezoelectric constant d33 and the electromechanical coupling factor kp decreased with additions of MnO2 and Fe2O3, but improved with additions of Nb2O5 and La2O3.  相似文献   

13.
A Ce-TZP/platelike La(Co(Fe0.9Al0.1)11)O19 composite was synthesized in situ while sintering from a mixture of Ce-TZP, La(Fe0.9Al0.1)O3, Fe2O3, Al2O3, and CoO powders. Platelike La(Co(Fe0.9Al0.1)11)O19 crystals were grown in a dense Ce-TZP matrix after sintering at temperatures of 1200°–1350°C. The temperature range for sintering Ce-TZP/La(Fe,Al)12O19 composites was expanded widely by substituting Co2+ ions for Fe2+ ions in its structure. The highest value of the bending strength of the Ce-TZP/La(Co(Fe0.9Al0.1)11)O19 composites was 880 MPa, which was higher than that of the Ce-TZP/La(Fe,Al)12O19 composite (780 MPa) and Ce-TZP (513 MPa). The saturation magnetization of the Ce-TZP/La(Co(Fe0.9Al0.1)11)O19 composite was a constant value of 7.7 emu/g after the composite was sintered at 1200°–1350°C.  相似文献   

14.
Liquidus equilibrium relations for the air isobaric section of the system Y2O3–Fe2O3–FeO–Al2O3 are presented. A Complete solid-solution series is found between yttrium iron garnet and yttrium aluminum garnet as well as extensive solid solutions in the spinel, hematite, orthoferrite, and corundum phases. Minimum melting temperatures are raised progressively with the addition of alumina from 1469°C in the system Y–Fe–O to a quaternary isobaric peritectic at 1547°C and composition Y 0.22 Fe 1.08 Al 0.70 O 2.83* Liquidus temperatures increase rapidly with alumina substitutions beyond this point. The thermal stability of the garnet phase is increased with alumina substitution to the extent that above composition Y 0.75 Fe 0.65 Al 0.60 O 3 garnet melts directly to oxide liquid without the intrusion of the orthoferrite phase. Garnet solid solutions between Y 0.75 Fe 1.25 O 3 and Y 0.75 Fe 0.32- Al 0.93 O 3 can be crystallized from oxide liquids at minimum temperatures ranging from 1469° to 1547°C, respectively. During equilibrium crystallization of the garnet phase, large changes in composition occur through reaction with the liquid. Unless care is taken to minimize temperature fluctuations and unless growth proceeds very slowly, the crystals may show extensive compositional variation from core to exterior.  相似文献   

15.
The formation mechanism of the synthesis of MoO3-doped YSr2Cu3O y powders using the citrate process was investigated. It was shown that the precursor phase (Sr1- x Y x )14Cu24O41 played a crucial role in forming the superconducting phase. It was found that the precursor phase (Sr1- x Y x )14Cu24O41 interacted with water and decomposed when it was heavily milled and heated.  相似文献   

16.
When sintered 95Al2O3-5Fe2O3 (wt%) specimens constituting corundum grains and iron aluminate spinel precipitates were annealed under high oxygen partial pressure (Po2) where only a corundum phase is stable, fast dissolution of particulate spinel precipitates occurred, together with the migration of corundum grain boundaries. Behind the migrating boundaries, a corundum solid solution enriched with Fe2O3 formed. Discontinuous dissolution (DD) of particulate spinel precipitates thus occurred by Po2 increase. In contrast, when 95Al2O3-5Fe2O3 specimens constituting only corundum grains were annealed under low Po2 where both corundum and spinel phases are stable, grain boundaries migrated without spinel precipitation, leaving behind a corundum phase depleted of Fe2O3, similar to chemically induced grain-boundary migration (CIGM) observed during solute depletion. The volatilization of Fe2O3 appeared to cause the boundary migration without precipitation. The observed CIGM and DD would suggest various possibilities of microstructure control in other oxide systems through oxygen partial pressure change.  相似文献   

17.
The Ba-doped superconducting (Bi,Pb)2Sr2- x Ba x Ca2Cu3O y and (Bi,Pb)2Sr2Ca2- x Ba x Cu3O y (0 ≦ x ≦ 1.0) were prepared by using a melt-quenching method, and the effect of Ba additions on the glass-forming ability and the crystalline phase was examined. The glass-forming ability was not improved by substitution of Ba for Sr or Ca, and particularly BaPbO3 as well as CaO was observed in the melt-quenched sample of (Bi,Pb)2SrBaCa2Cu3O y . BaPbO3 crystals were precipitated in all glass-ceramics with Ba substituted for Sr or Ca. The partial substitution of Ba substituted for Sr was effective for the formation of the high- T c phase, and (Bi,Pb)2Sr1.4Ba0.6Ca2Cu3O y glass-ceramics obtained by annealing at 830°C for 100 h exhibited superconductivity with a T c of 103 K, although BaPbO3 and the low- T c phase were still largely present.  相似文献   

18.
The crystals of Ca2(Al x Fe1− x )2O5 with 0 ≤ x ≤ 0.4 were examined using powder XRD at temperatures between 25° and 1000°C. The Pcmn to Ibm 2 phase transition was readily detected by the disappearance of the 131 and 151 reflections ( h + k + l odd). Thus, the phase relationship has been determined as combined functions of the temperature and x -value. At 25°C, the space group changed from Pcmn (0 ≤ x ≤ 0.23) to Ibm 2 (0.24 ≤ x ≤ 0.40) across x = 0.235. With increased x -value, the cell dimensions of both phases steadily decreased, showing the nearly complete continuity at that phase boundary. For the crystal with x = 0 (Ca2Fe2O5), the cell dimensions steadily increased during heating to 685°C, at which temperature the phase transition occurred. There was a slight discontinuous decrease in cell dimensions just after the transition. Subsequent heating to 1000°C of the Ibm 2 phase led to a steady thermal expansion along the b -axis and c -axis, while a slight contraction occurred along the a -axis up to 800°C.  相似文献   

19.
Phase equilibria of the quasi-quinary system Bi3O3-PbO-SrO-CaO-CuO were studied between 650° and 900°C in air with emphasis on the high-temperature superconducting phase (Bi,Pb)2+ x Sr2Ca2Cu3O10+ d (2223). The 2223 phase lies in equilibrium with a number of nonsuperconducting phases and also with the superconducting phase (Bi,Pb)2Sr2CaCu2O8+ d (2212). The single-phase region was found to be very limited. The Pb solubility of the 2223 phase is strongly temperature dependent. The phase relations are very sensitive to variations of the cation concentration and temperature. This effect significantly influences the preparation of 2223 ceramics.  相似文献   

20.
Preferential X-ray line broadenings in γ-Fe2o3 samples prepared from γ-FeOOH, α-FeOOH, N2H5Fe(N2H3-COO)3-H2O, FeOOCH3, and colloidal Fe3O4 are compared. Isotropic size and small crystallites are the origin of the uniform and enhanced X-ray line broadening in samples derived from hydrazinate and colloidal Fe3O4. Nonuniform line broadening in ex-α-FeOOH and ex-γ-FeOOH is due to an elongated crystallite shape and the presence of stacking faults, respectively. The thermal behavior of samples with low crystallite size and uniform line broadening is characterized by an exothermal recrystallization process simultaneous to the phase transformation γ-Fe203→α-Fe2O3.  相似文献   

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