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Rare earth element substituted bismuth ferrites (BiFeO3) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi
x
La1−x
FeO3 (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of
these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz
to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz).
All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature
shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds
to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity
as well as ε′ are found to be maximum for the sample x=0.2 at room temperature. 相似文献
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CoFe2O4-BaTiO3 composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases
in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in
the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac
conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric
conversion factor has been studied as a function of magnetic field. 相似文献
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Nijegorodov NI Downey WS Danailov MB 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2000,56(4):783-795
Absorption, fluorescence and laser properties of ten selected aromatic compounds from the oligophenylene family are studied experimentally at room temperature (293 K). The first eight compounds are arranged in such way that odd numbered compounds reveal 1Lb --> 1A fluorescence, while even numbered compounds show 1La --> 1A fluorescence. All compounds are family related in pi-structure and are of the same degree of planarity and rigidity. The quantum yield of fluorescence, gamma, and the decay times, tau(f), of non-deaerated and deaerated cyclohexane solutions are measured. The oscillator strength, f(e), the fluorescence rate constant, Kf, natural lifetimes, tau(o)T, and intersystem crossing rate constant, K(ST), are calculated. The lowest 1Lb and 1La singlet and 3La, triplet (77 K) levels are determined. Investigations showed that transition from a polyphenyl molecule which shows 1La --> 1A fluorescence to a family related in the pi-structure molecule which reveals the 1Lb --> 1A fluorescence is accompanied by certain changes in all the fluorescence parameters. This indicates that gamma decreases, tau(f) increases, Kf and the FWRE of the fluorescence spectrum decrease. Moreover, K(ST) also decreases, sometimes very significantly. The decrease in the K(ST) value is explained by the fact that matrix elements of the spin-orbit coupling of the S alpha and Ti states are much lower in value than analogous elements of the spin-orbit coupling of Sp and Ti states. It is shown that all p-polyphenyles exhibit excellent laser action, while m-polyphenyles do not produce laser oscillation under any conditions. The values of K(ST) and other fluorescence parameters measured can be used for various practical purposes and theoretical considerations. 相似文献
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C. J. Bocchetta D. Bulfone P. Craievich M. B. Danailov G. D’Auria G. DeNinno 《Synchrotron Radiation News》2013,26(6):30-35
The importance of industrial use of national and international infrastructure projects such as Diamond Light Source is well understood, with the facilities ever mindful of the impact agenda of their funding agencies and governments. Diamond opened its doors for academic users in January 2007, with industrial users following a year later. Since that time, more than 40 companies have used Diamond's beamlines and support laboratories through the proprietary access mode, i.e. paying for their usage. In addition, many more have collaborated with university partners and used facilities through the peer review route. 相似文献
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A. A. Kananovich S. V. Voitikov A. A. Demidovich M. B. Danailov V. A. Orlovich 《Applied physics. B, Lasers and optics》2012,106(1):9-17
The paper presents experimental investigation and modeling of an end-pumped quasi-continuous-wave YVO4/Nd:YVO4 mini self-Raman laser. The dependence of the Stokes output power on the pump power in the range from 3 to 17.5 W has been
measured. As much as 1.76 W of an average Stokes power, corresponding to a total optical-to-optical conversion efficiency
of about 10%, has been obtained. The transverse profiles of the laser (at the fundamental wavelength) and the Stokes beam
intensity have been recorded at the output mirror and in the vicinity of the boundary between the pure and Nd-doped parts
of the Raman crystal. These distributions have been approximated by the sum of Gaussian and super-Gaussian distributions with
corresponding weights. We propose a model of such lasers that takes into account the features of intracavity self-frequency
Raman conversion in lasers with highly inhomogeneous non-Gaussian spatial distributions of the pump, laser, and Stokes beam
intensity in the cavity. The results of modeling are in good agreement with the experimental data. 相似文献
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Allaria E Curbis F Coreno M Danailov M Diviacco B Spezzani C Trovó M De Ninno G Deninno G 《Physical review letters》2008,100(17):174801
We present an experimental characterization of the process of coherent harmonic generation in single-pass free electron lasers. The harmonic radiation is obtained by seeding the electron beam stored in the Elettra storage ring with a Ti:sapphire laser. Different methods for generating harmonics are compared between them, and a detailed characterization of the emitted light is performed for different polarizations. Our results also contribute to the debate about the possible presence of a coherent on-axis signal in helical undulators. In this respect, we provide an experimental confirmation of recent theoretical studies that predict no coherent on-axis signal. 相似文献
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