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RISS 인기검색어
- 검색키워드
- 주제어 : Colossal permittivity (검색결과 3 건)
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Dielectric resonance effect with negative permittivity in a La1.5Sr0.5NiO4+δ ceramic
Tran Dang Thanh,Nguyen Van Dang,Le Van Hong,The-Long Phan,Seong-Cho Yu 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.10
A polycrystalline sample of La1.5Sr0.5NiO4+δ was prepared by using a solid-state reaction. Xraydiffraction proved the sample to be a single phase with a tetragonal structure (space group:I4/mmm). By using an iodometric titration method to determine the non-stoichiometric oxygenconcentration (δ) in La1.5Sr0.5NiO4+δ, we found δ = −0.017, which corresponds to a doping level ofnh = x + 2δ = 0.466. Also, a strong increase of the magnetization in theM(T) curve at temperaturesbelow the spin-ordering temperature (TSO 100 K) was observed. The M(H) curves show verysmall magnetic moments, which proves the weak ferromagnetic nature of La1.5Sr0.5NiO4+δ. Thedependences of the dielectric constant on the frequency and the temperature, "(!, T) = "0(!, T) +i"00(!, T), was investigated in the frequency range of 1 − 13 MHz. At temperatures around roomtemperature, the maximum of the real part ("0) was higher than 105. Particularly, an abnormaldependence of the permittivity on frequency was observed. Depending on temperature, a dielectricresonance was observed at about 500 kHz or 8 MHz. Interestingly, we observed the dielectricresonanceeffect with a negative permittivity. Such a feature is very similar to that observed inleft-handed materials. The fitting of the experimental data for the dielectric constant at frequenciesaround the resonance frequency to the equations associated with an equivalent RLC series circuitproves that La1.5Sr0.5NiO4+δ belongs to the class of multiferroic materials.
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Grain-Size Effect on the Dielectric Properties of La1.5Sr0.5NiO₄ Nano-Particle Materials
Tran Dang Thanh,Le Van Hong,Nguyen Xuan Phuc 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.6
We have manufactured ceramic samples of La1.5Sr0.5NiO₄and studied their dielectric proper-ties. The samples were prepared by using a reactive mechanical milling technique on D8000-Spex combined with an annealing at a temperature in the range of 700 ℃ - 1000 ℃. The crystalline structure and the sample's purity were checked by means of X-ray diffraction (XRD) on a SIEMENS D5000 spectrograph. The obtained XRD patterns conrmed that all the samples belonged to the F4K2Ni perovskite layer tetragonal structure with a space group of I4/mmm (139). The grain size of a ceramic sample was estimated based on the Field-emission scanning electron microscopy (FE- SEM) images and was calculated by using the Warren-Averbach method based on the Full Width at Half Maximum (FWHM) of the XRD lines. The results obtained by using the two methods were quite the same. The mean grain size (< D >) of the samples varied from 16.2 nm to 95 nm with the annealing temperature. Dielectric constant (ε) of all the samples was estimated from the capacitance measurement at different temperatures in the frequency range of 1 kHz - 13 MHz. The estimated ε of all the samples was about 105 over the whole frequency range up to 1 MHz. The temperature and the frequency dependences of ε(f T), the dielectric constant, were observed and are discussed for all the samples. We have manufactured ceramic samples of La1.5Sr0.5NiO₄and studied their dielectric proper-ties. The samples were prepared by using a reactive mechanical milling technique on D8000-Spex combined with an annealing at a temperature in the range of 700 ℃ - 1000 ℃. The crystalline structure and the sample's purity were checked by means of X-ray diffraction (XRD) on a SIEMENS D5000 spectrograph. The obtained XRD patterns conrmed that all the samples belonged to the F4K2Ni perovskite layer tetragonal structure with a space group of I4/mmm (139). The grain size of a ceramic sample was estimated based on the Field-emission scanning electron microscopy (FE- SEM) images and was calculated by using the Warren-Averbach method based on the Full Width at Half Maximum (FWHM) of the XRD lines. The results obtained by using the two methods were quite the same. The mean grain size (< D >) of the samples varied from 16.2 nm to 95 nm with the annealing temperature. Dielectric constant (ε) of all the samples was estimated from the capacitance measurement at different temperatures in the frequency range of 1 kHz - 13 MHz. The estimated ε of all the samples was about 105 over the whole frequency range up to 1 MHz. The temperature and the frequency dependences of ε(f T), the dielectric constant, were observed and are discussed for all the samples.
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The dielectric and electrical modulus properties of Ba(Al0.5Nb0.5)xTi1-xO3 ceramics
R.F. Niu,D.P. Wang,Z.H. Huang,W.T. Wang 한양대학교 청정에너지연구소 2024 Journal of Ceramic Processing Research Vol.25 No.2
In this work, a series of BaTiO3-based ceramic materials, Ba(Al0.5Nb0.5)xTi1-xO3 (x = 0, 0.04, 0.06, 0.08), was synthesized usinga standard solid-state reaction technique. In the temperature range of 100~380 K, the frequency-dependent dielectric andelectrical modulus properties were studied. A colossal dielectric permittivity (>1.5×104) and low dielectric loss (< 0.01) weredemonstrated at the optimal doping concentration x = 0.04. The observed dielectric behavior of Ba(Al0.5Nb0.5)xTi1-xO3 ceramicscan be attributed to the Universal Dielectric Response. The complex electrical modulus spectra indicate a significant decreasein capacitance and permittivity of the grains with increasing co-doping concentration. Our results provide insight into the roleof donor and acceptor co-doping on the properties of BaTiO3-based ceramics, which is important for their use in dielectric andenergy storage applications.
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