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Synthesis and physical properties of Ca- and Ta-modified (K,Na)NbO3 lead-free piezoelectric ceramics
Indrani Coondoo Neeraj Panwar Radheshyam Rai Harvey Amorín Andrei L. Kholkin 《Phase Transitions》2013,86(11):1130-1140
Polycrystalline samples of lead-free Ca and Ta co-substituted potassium sodium niobate (K0.5Na0.5NbO3, KNN) ceramics have been prepared by solid state reaction technique. X-ray diffraction showed formation of a single-phase perovskite structure with orthorhombic symmetry. Substitution inhibits the grain growth, improves densification and decreases the ferro-paraelectric phase transition temperature. Temperature dependent dielectric permittivity studies demonstrate significant decrease in peak-permittivity values in the substituted samples. Bulk longitudinal piezoelectric coefficient is significantly enhanced, up to ~155 pC/N for (K0.48Na0.48Ca0.02)(Nb0.85Ta0.15O3) as compared to 95 pC/N for pristine KNN ceramic. Local piezoelectric properties have been observed by piezoresponse force microscopy (PFM) technique. Distinct piezocontrast was studied in both vertical and in-plane modes of PFM for all samples. The samples exhibit self-polarization effect in the unpoled state and effective local vertical piezoelectric coefficient was the largest in Ca and Ta co-substituted sample whereas the in-plane piezoelectric coefficient was maximum for Ca-substituted KNN sample. These studies are important for using substituted lead free KNN materials in various piezoelectric applications. 相似文献
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Kaphle GC Ganguly S Banerjee R Banerjee R Khanal R Adhikari CM Adhikari NP Mookerjee A 《J Phys Condens Matter》2012,24(29):295501
In this paper we shall study three binary alloy systems, one constituent of which is Mn. The other constituents are chosen from a particular column of the periodic table: Ni(3d), Pt (4d) and Pd (5d). As we go down the column, the d-bands become wider, discouraging spin-polarization. In a disordered alloy, the situation becomes more complicated, as the exchange interaction between two atoms is environment dependent. We shall compare and contrast their magnetic behaviour using robust electronic structure techniques. In all three alloy systems conjectures are made to explain experimental data. In this paper we shall examine whether there is any basis to these conjectures. 相似文献
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Radheshyam Rai 《Solid State Communications》2004,129(5):305-309
Polycrystalline samples of Pb0.9(La1−zBiz)0.1(Zr0.55Ti0.45)0.975O3 [referred as PLBZT] (z=0.0, 0.3, 0.5 and 0.7) have been synthesized by a high-temperature solid-state reaction technique. X-ray diffraction analysis suggests the formation of single-phase compounds with monoclinic structure. The dielectric studies of the compounds as a function of temperature (room temperature, RT to 350 °C) at frequency (1, 10 and 100 kHz) show that the compounds undergo a phase transition of diffuse type. Diffusivity (γ) study of phase transition of these compounds provided its value between 1 and 2, indicating the variation of degree of disordering in the system. Measurement of dc resistivity (ρ) as a function of temperature (RT to 350 °C) at a constant biasing field suggests the compounds have negative temperature coefficient of resistance. 相似文献
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Radheshyam Rai Kavita Verma Swapna S. Nair Andrei L. Kholkin 《Journal of Physics and Chemistry of Solids》2011,72(7):862-868
This report presents the synthesis of copper cadmium ferrite (Cu1−xCdxFe2O4, x=0.3, 0.4, 0.5, 0.6 and 0.7) by the citrate precursor method and its subsequent characterization by X-ray diffraction (XRD), differential scanning calorimetry, infrared spectroscopy and ferromagnetic resonance. XRD results confirm the single cubic spinel phase formation with the particle size of 40 nm, which decreased up to 20 nm with increase in Cd content, while the lattice parameter increased with increase in Cd content. A significant change in the magnetic properties was observed in the CuFe2O4 system with Cd doping. The line width and resonance field variation against change in temperature is noted and the data is fitted to the linearlized model (LM) and Smit and Beljers (SB) model to find out the parameters. The results recorded from the SB approach are in good agreement with those observed in the magnetic measurements carried out by vibrating sample magnetometer (VSM) techniques. 相似文献
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A series of substituted benzimidazoles, benzothiazoles, and benzoxazoles was synthesized by combining 1,2-phenylenediamine, 2-aminothiophenol, or 2-aminophenol with aryl, heteroaryl, aliphatic, α,β-unsaturated aldehydes in the presence of nano ceria (CeO2) as an efficient heterogeneous catalyst. 相似文献
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Radheshyam Rai Indrani Coondoo Rashmi Rani Igor Bdikin Seema Sharma Andrei L. Kholkin 《Current Applied Physics》2013,13(2):430-440
(1 ? x) K0.5Na0.5NbO3 ? xLiNbO3 (where x = 0.0, 5.0, 5.5, 6.0, and 6.5 wt.%) (KNLN) perovskite structured ferroelectric ceramics were prepared by the solid-state reaction method. X-ray diffraction patterns indicate that single phase was formed for pure KNN while a small amount of second phase (K6Li4Nb10O30, ~3%) was present in LN doped KNN ceramics. Phase analysis indicated the change in the crystal structure from orthorhombic to tetragonal with increase in LN content. The electrical behavior of the ceramics was studied by impedance spectroscopy technique in the high temperature range. Impedance analysis was performed using an equivalent circuit model. The impedance response in pure KNN and KNLN ceramics could be deconvoluted into two contributions, associated with the bulk (grains) and the grain boundaries. Activation energies for conductivity were found to be strongly frequency dependent. The activation energy obtained from dielectric relaxation data was attributed to oxygen vacancies. From PFM we found that the composition with 6.5 wt.% LN displays stronger piezocontrast as compared to pure KNN implying an evidence of a pronounced piezoelectric coefficient. 相似文献
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Polycrystalline samples of bismuth (Bi) doped lead lanthanum zirconate titanate (PLZT) with the general formula Pb0.9(La1−zBiz)0.1(Zr0.65Ti0.35)0.975O3, where [z=0.0, 0.3, 0.5, 0.7] near the morphotropic phase boundary (MPB) has been synthesized by a solid solution mixing technique. Some aspect of crystal structure of the compound at room temperature was studied using X-ray diffraction (XRD) technique. Detailed studies of dielectric constant (ε) and dielectric loss () obtained both as a function of frequency (100 Hz-100 kHz) at room temperature (RT) and temperature (RT-600 K) at 10 kHz suggest that compounds undergo ferroelectric-paraelectric phase transition of diffuse type. Both ac and dc conductivity have been studied over a wide range of temperature. The activation energy (Ea) of the samples was calculated from the plot of ac conductivity vs. inverse of absolute temperature. The temperature variation of resistivity shows that the compounds have negative temperature coefficient of resistance (NTCR). 相似文献
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