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1.
Ceramic solid solution of nanocrystalline barium zirconium titanate in the form of Ba(Zr 0.52Ti 0.48)O 3 substituted by samarium (Sm 3+) was prepared using the conventional solid state reaction method. The phase assemblage analyzed by the X-ray diffraction technique was fitted for cubic-crystal-symmetry. The change in the grain size depicted the influence of Sm 3+ ions on the microstructure. The electrical behavior was studied in the temperature range from 323 to 773 K. The sintered samples exhibited a negative temperature coefficient of resistance (NTCR) and superior semiconducting behavior above 513 K. Addition of Sm 3+ increased the room temperature resistivity of Ba(Zr 0.52Ti 0.48)O 3 solid solution. The results obtained from the thermoelectric power measurement confirm electrons as the majority charge carriers. 相似文献
2.
We report on the studies of lattice dynamics and crystal structure of natural perovskite with the general formula CaTiO 3:0.01Fe by dielectric spectroscopy and X-ray diffraction in a wide temperature range. In contrast to the “chemically pure” synthetic perovskite, the lattice dynamics of the Fe-containing natural sample exhibits a structural instability in the vicinity of 240 K. Our studies of the behavior of magnetic moment of CaTiO 3:0.01Fe demonstrate that in the temperature region from 4.3 to 300 K this material is paramagnetic. No changes in the crystal symmetry have been observed in the structural studies, which can be explained by the small degree of lattice distortions, as has been observed previously for isotopically substituted SrTiO 3 18 . Conductivity measurements and analysis of the dielectric response dispersion of CaTiO 3:0.01Fe have shown that the dispersion is due to the Maxwell–Wagner mechanism and can be attributed to oxygen vacancies present in the mineral. 相似文献
3.
Micro-ferrotitanium powders have been prepared by molten salt electrolysis via directly electrochemical reduction of solid ilmenite in eutectic CaCl2-NaCl melt at 973 K. In the direct electrochemical reduction process, the reduction of FeTiO3 first gives rise to the formation of Fe and CaTiO3, which as intermediates will be further deoxidized at the interface of iron metals, solid CaTiO3 matrix, and electrolyte to directly form ferrotitanium alloy powders in porous structure. Furthering the electrolytic time can promote the dense structure of ilmenite pellet turn to be more porous, indicating pores inside the pellet are sufficient for the diffusion of oxygen ions. Based on the reduction behavior of partially reduced powders in metallic cavity electrode during the cathodic potentiostatic electrolysis, it shows that the slow deoxidization rate is mainly caused by the more and more difficult reduction of CaTiO3 than that of FeTiO3. 相似文献
4.
Microcosmic investigations of weak red-emitting materials are crucial for their further development and application. In this work, we have focused on the band structures and electronic properties of Pr mono- and (Zn, Pr) co-doped CaTiO 3 using density functional theory. Zn substitution for Ca or Ti tends to form clusters energetically with Pr substituting for Ca in CaTiO 3. In Pr mono-doped CaTiO 3, the O 2p→Ti 3d transition in CaTiO 3 host corresponds to the centered 330 nm excitation spectra. The gap states above the valence band of ∼1.30 eV and ∼2.06 eV are hybridized by Pr 4f, O 2p and Ti 3d orbitals. They are mainly due to Pr 4f orbitals in CaTiO 3:Pr. The former gap level is related to red emission at 614 nm due to 1D 2→ 3H 4 transition of Pr 3+ activator. The latter is related to the excitation spectra centered at 380 nm due to the low-lying Pr-to-mental intervalence charge transfer transitions (Pr 3+-O 2−-Ti 4+?Pr 4+-O 2−-Ti 3+). The band structures of (Zn, Pr) co-doped CaTiO 3 keep the similar gap levels to those in Pr mono-doped CaTiO 3. The incorporation of Zn brings out the two stronger localized gap states, which are hybridized by Pr 4f, O 2p and Ti 3d orbitals, in comparison with those in Pr mono-doped CaTiO 3. Therefore, when Zn impurities are added into Pr doped CaTiO 3, the present calculations visualize the two enhanced levels and the distorted structures around Pr. 相似文献
5.
利用扩展x射线吸收精细结构和x射线衍射研究了机械合金化制备的体心立方(bcc)的亚稳态Fe 80Cu 20合金固溶体的结构随退火温度的变化特点.结果表明,在300—873 K温度范围内,随着退火温度的升高,bcc结构物相的晶格常数近于线性降低,这主要是由于Cu原子从bcc结构Fe 80Cu 20合金固溶体中逐渐偏析出来,生成面心立方(fcc)结构的Cu物相所致.经603K退火后,Cu原子的平均键长R Cu—Cu增加了0.003 nm左右,大约有50%的Cu原子从bcc结构的Fe 80Cu 20合金固溶体中偏析出来.在773 K退火后,bcc结构Fe 80Cu 20合金固溶体近于完全相分离,生成了bcc结构的α-Fe与fcc结构的Cu物相.
关键词:
扩展x射线吸收精细结构
x射线衍射
80Cu 20合金')" href="#">Fe 80Cu 20合金
机械合金化 相似文献
6.
SrTiO 3 and CaTiO 3 conventional bulk materials are incipient ferroelectrics. In this note, we report for the first time that ferroelectricity could occur in SrTiO 3 nanocrystalline disks even at room temperature. The peak in the temperature dependence of permittivity for a CaTiO 3 nanocrystalline disk at a low temperature is also observed. The observed ferroelectricity (or permittivity peak) in SrTiO 3 (or CaTiO 3) nanocrystalline disks could be attributed to the strain effect. 相似文献
7.
采用基于第一性原理密度泛函理论的平面波赝势方法,对0.5NdAlO 3-0.5CaTiO 3晶体进行结构优化,并对其能带结构,态密度和光学性质进行了理论计算.结构优化后晶格参数与实验数据相符合,误差小于1%;能带计算结果表明0.5NdAlO 3-0.5CaTiO 3为间接带隙,带隙值为0.52eV;费米面附近的能带由Nd-4f,O-2p,Nd-4p,Al-3p,Ti-4d层的电子态密度确定.同时也计算了该结构的介电函数,反射率和复折射率等光学性质. 相似文献
8.
Formation energies of native defects and Pr impurities in orthorhombic CaTiO 3 are explored using the first-principles calculations. The Ca vacancy ( VCa), Ti vacancy ( VTi) and Ca antisite (Ca Ti) are found to be energetically preferable. The Ti antisite (Ti Ca) and O vacancy ( VO) are not energetically favorable in the wide range of Fermi level. In Pr-doped CaTiO 3, Pr substituting for Ca (Pr Ca) is likely to form under condition A in which CaTiO 3 is in equilibrium with CaO and O 2. Under condition B (TiO 2, CaTiO 3 and O 2 are in equilibrium), Pr Ti defect is energetically preferable depending on the Fermi levels. Several native defects and the two sites of Pr impurities in CaTiO 3 are coincided with several different defects in Pr-doped CaTiO 3 reported in the literature. Based on the present calculations, we can elucidate that the Ca deficiency design of the traditional formula Ca 1−xVCa(x/2)Pr xTiO 3 is not the best for efficient red photoluminescence, which is realized via the experimental measurements. 相似文献
9.
Structural phase transitions in Cu 2–x Te crystals have been investigated by high-temperature X-ray diffraction. At room temperature Cu 2Te and Cu 1.90Te specimens are two-phased, i.e. they consist of an orthohombic phase with a = 7.319, b = 22.236, c = 36.458 Å and a hexagonal phase with a = 4.150, c = 7.188 Å. The changes in both compounds take place generally in the hexagonal phase with increasing temperature. At 821, 873 K they transform to a FCC phase. Monocrystals of the other compounds at room temperature crystallize in the hexagonal system and at 673, 773, 723 K, respectively, they transform to a FCC phase. It is determined that as the cation deficiency increases the crystal quality becomes better. 相似文献
10.
This work reports the gas/solid equilibration kinetics for the O 2/CaTiO 3 system. The electrical conductivity measurement was applied for monitoring the kinetics in the ranges of temperature 973-1323 K and oxygen partial pressure 10 Pa-72 kPa. It was found that the gas/solid equilibration kinetics for the polycrystalline CaTiO 3 specimen in the above experimental conditions is determined by bulk diffusion rather than by grain boundary conditions. The obtained data of the electrical conductivity vs. time were used for the determination of the chemical diffusion coefficient as a function of temperature at low and high p(O 2), respectively:
11.
A series of Nb5+ codoped red long afterglow phosphors CaTi1 xNbxO3:Pr03.+002 (0 ≤ x ≤ 0.05) is prepared by a solid state reaction method. Their photoluminescence, phosphorescence and thermoluminescence are investigated. The results indicate that codoping Nb5+ can improve the photoluminescence and phosphorescence property of CaTiO3:Pr3+ significantly. When 3-mol% Nb5+ is codoped, the emission intensity of CaTiO3:Pr3+ is enhanced twice, while the afterglow time is extended from 10 min to about 40 min. Thermoluminescence results reveal that the trapping level of CaTiO3:Pr3+ is reduced from 0.82 eV to 0.62 eV by codoping Nb5+. The effect of Nb5+ doping on enhancing the photoluminescence intensity and afterglow time of CaTiO3:Pr3+ is discussed. 相似文献
12.
Enhancement of the 1D 2-3H 4 red emission in CaTiO 3:Pr 3+ with addition of nanosized SiO 2 fabricated by a solid state reaction method is reported. The dynamical processes for the improvement of red emission were systematically investigated using photoluminescence (PL) and PL excitation spectra, and diffused reflectance spectra as well as time decay patterns of PL and persistent afterglow. Higher efficiency of energy transfer from CaTiO 3 host to the activator Pr 3+ due to the improvement of crystallinity by SiO 2 addition was discussed in comparison with that of the SiO 2 free sample. The enhancement of persistent afterglow after the cessation of excitation in SiO 2 added CaTiO 3:Pr 3+ was also analyzed by theoretically fitted results. 相似文献
13.
High-energy ball milling of monoclinic ZrO 2–30 mol% anatase TiO 2 mixture at different durations results in the formation of m-ZrO 2–a-TiO 2 solid solution from which the nucleation of nanocrystalline cubic (c) ZrO 2 polymorphic phase sets in. Post-annealing of 12 h ball-milled sample at different elevated temperatures for 1 h results in almost complete formation of c-ZrO 2 phase. Microstructure of the unmilled, all the ball milled and annealed samples has been characterized by Rietveld's X-ray powder structure refinement method. Particle size, rms lattice strain, change in lattice parameters and phase content of individual phases have been estimated from Rietveld analysis, and are utilized to interpret the results. In course of milling, (1 1 1) of cubic lattice became parallel to () plane of monoclinic lattice due to the orientation effect and cubic phase may have been formed on the (0 0 1) of the m-ZrO 2–a-TiO 2 solid solution lattice. A comparative study of microstructure and phase transformation kinetics of ZrO 2–10, 20 and 30 mol% a-TiO 2 ball-milled and post-annealed samples reveals that rate of phase transformation m→c-ZrO 2 increases with increasing a-TiO 2 concentration and 30 mol% of nanocrystalline c-ZrO 2 phase can be obtained within 4 h of milling time in the presence of 30 mol% of a-TiO 2. The post-annealing treatment at 773, 873 and 973 K for 1 h duration each reveals that rate of c-ZrO 2 formation with increasing temperature is retarded with increasing a-TiO 2 concentration but the amount of c-ZrO 2 becomes almost equal (95 mol%) at 973 K. It suggests that almost fully stabilized nanocrystalline c-ZrO 2 can be formed by adding a tetravalent solute to m-ZrO 2. 相似文献
14.
An investigation into the phase stabilities of CaTiO 3 under high pressure was conducted using first-principles calculations based on density functional theory. We have identified three candidate structures of CaTiO 3, Pbnm, Pm3 m and Cmcm, respectively. Our results demonstrate that a phase transition from orthorhombic ( Pbnm) to cubic ( Pm3 m) is impossible for CaTiO 3 under high pressure at ambient temperature, and further predict that Pbnm-CaTiO 3 will transform to post-perovskite phase ( Cmcm) at enough temperature and pressure. 相似文献
15.
Aluminium-based rapidly quenched alloys of nominal composition of Al 90Fe 7Nb 3 and Al 94Fe 2V 4 were studied by Mössbauer spectroscopy. Samples annealed up to 573K showed amorphous structure represented by quadrupole-split doublets. From the corrected spectra areas, the values of f-factor and Debye temperature were calculated for both samples in the as-cast state. In the case of AlFeNb sample, f-factor was estimated to be f = 0.26 and for AlFeV, f = 0.31. High-temperature annealing at 773K and 873K induced a formation of nano-and microcrystalline structures. Mössbauer spectra of both compositions (with vanadium as well as with niobium) annealed at 773K showed superposition of crystalline phases with dominant contribution of Al 3Fe alloy. During annealing at 873K, phases with large grains and a small amount of the FeAl metastable phase were developed. 相似文献
16.
CaTiO 3 is a well-known incipient ferroelectric material that does not undergo a ferroelectric phase transition in spite of the intriguing dielectric constant behavior. Especially, unlike a prototypical incipient ferroelectric SrTiO 3, the paraelectric state of CaTiO 3 cannot be easily destroyed by small perturbations, including cation doping and epitaxial strain. We present that a nearly strain-free epitaxial CaTiO 3 film grown at a low oxygen partial pressure exhibits polarization–voltage hysteresis loops and the distinct difference of piezoresponse force microscopy phase signals, implying that a ferroelectric phase is induced. Such results are shown even at room temperature. We suggest that the observed ferroelectric behavior in CaTiO 3 film comes from the defect dipoles composed of vacancies inside the film. Using electron-probe microanalysis and optical absorption spectra measurements, we found that CaTiO 3 film has considerable Ca and O vacancies, forming the localized defect state in electronic structure. This work highlights the importance of vacancies and their clusters, such as defect dipoles, in understanding the electronic properties of perovskite oxide thin films, including ferroelectricity. 相似文献
17.
The Zinc Selenide (ZnSe) thin films have been deposited on SnO 2/glass substrates by a simple and inexpensive chemical bath deposition (CBD). The structural, optical and electrical properties of ZnSe films have been characterized by X-ray diffraction (XRD), Energy Dispersive X-ray Analysis (EDAX), optical absorption spectroscopy, and four point probe techniques, respectively. The films have been subjected to different annealing temperature in Argon (Ar) atmosphere. An increase in annealing temperature does not cause a complete phase transformation whereas it affects the crystallite size, dislocation density and strain. The optical band gap ( Eg) of the as-deposited film is estimated to be 3.08 eV and decreases with increasing annealing temperature down to 2.43 eV at 773 K. The as-deposited and annealed films show typical semiconducting behaviour, d ρ/d T > 0. Interestingly, the films annealed at 373 K, 473 K, and 573 K show two distinct temperature dependent regions of electrical resistivity; exponential region at high temperature, linear region at low temperature. The temperature at which the transition takes place from exponential to linear region strongly depends on the annealing temperature. 相似文献
18.
This paper reports surface electrical properties of thin film of indium sesquioxide, In 2O 3, during oxidation and reduction at elevated temperatures (298 K and 873 K). The studies involved monitoring of surface potential
during oxidation and reduction experiments using work function measurements. The obtained experimental data are considered
in terms of the effect of temperature on reactivity between oxygen and In 2O 3, involving chemisorption and oxygen incorporation. The reactivity in the range 298 – 773 K is limited to chemisorption resulting
in the formation of surface dipoles exhibiting positive surface charge. Oxidation at 873 K results in slow oxygen incorporation. 相似文献
19.
The Eu-doped CaTiO 3 particles with a good crystallinity were prepared via sol-gel method. The phosphors showed a strong red emission corresponding to 5D 0→ 7F 2 (618 nm) of Eu 3+ under the near-ultraviolet excitation (400 nm). X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), photoluminescent (PL) analysis and Brunauer-Emmett-Teller (BET) specific surface area measurement were utilized to characterize the CaTiO 3:Eu 3+ particles. The concentration quenching and thermal quenching of the samples were discussed as well. The optimal concentration and the calcination temperature were 16 mol% of Eu 3+ and 1400 °C for these phosphors, and the possible reason was discussed as well. CaTiO 3:Eu 3+ is a promising red phosphor under near-ultraviolet excitation for various applications. 相似文献
20.
The present work describes the electrical conductivity of undoped CaTiO 3 in terms of the electrical conductivity components corresponding to electrons, electron holes and ionic charge carriers in
the temperature range 973 K — 1323 K and under controlled oxygen partial pressure (10 Pa — 72 kPa). These data are considered
in terms of the transference numbers of the respective charge carriers. It appears that the ionic conductivity component assumes
maximum at the n-p transition when the ionic transfer number reaches 50% of the total conductivity value at 1323 K. The present
study also includes the determination of the activation energy of the conductivity component related to ions (162.1 kJ/mol),
electrons (134.2 kJ/mol) and electron holes (86.2 kJ/mol). The data obtained in this work indicate that undoped CaTiO 3 exhibits a substantial level of ionic conduction that cannot be ignored in a quantitative analysis of electrical conductivity
data. 相似文献
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