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1.
V. S. Sangawar P. S. Chikhalikar R. J. Dhokne A. U. Ubale S. D. Meshram 《Bulletin of Materials Science》2006,29(4):413-416
This paper describes the results of thermally stimulated discharge conductivity study of activated charcoal-polyvinyl chloride
(PVC) thin film thermoelectrets. TSDC has been carried out in the temperature range 308–400°K and at four different polarizing
fields. Results are discussed on the basis of mobility of activated charcoal and polyvinyl chloride chains. 相似文献
2.
The short-circuit thermally stimulated depolarization current (TSDC) through lead germanate single crystals has been measured
as a function of temperature (100–800 K) and time. The results indicate that poling of the crystals at elevated temperatures
(t ≥ 150°C) produces an electret state related to the spacecharge mechanism of polarization. Relatively mild poling conditions
(E = 0.75 kV/cm, t = 150°C) produce a well-defined, long-lived electret with an abnormally large electret charge (1400 μC/cm2). The electret discharge leads to heating of the crystal, in the form of a peak in the range 520–570 K, whose height exceeds
that of the pyroelectric peak near T
C by two to three orders of magnitude. From the TSDC data, we evaluated the stored electret charge, its density, and the activation
energy of traps for electret charges, and made preliminary conclusions as to the nature of the traps. We demonstrate that
neglect of the electret discharge current (which depends on a number of factors) when determining the pyroelectric coefficient
p
σ above 280 K leads to a significant scatter in data. 相似文献
3.
Girija Chitgopikar Mallikarjun Chickpatil Ravindra L. Raibagkar 《Journal of Materials Science: Materials in Electronics》2006,17(11):963-970
Monophasic oxides of the type Ba(Nb1-x
Sn
x
) O3 (0 ≤ x ≤ 1) have been synthesized by solid-state reaction method. All these compounds are found to have tetragonal structure except
x = 1. The cell parameters and their variation with composition x have been determined. The X-ray density is found to increase gradually with increase of dopant concentration. Tolerance factor
and volume of unit cell was found to be almost constant for all the compositions. Scanning electron microscopy showed the
presence of grains of approximately 1 μm in size. Dielectric measurements in the frequency range 100 Hz to 1 MHz and in the
temperature range from − 100°C to 500°C has been carried out to determine the dielectric parameters. A strong frequency dependence
of both dielectric constant (ɛ′) and dielectric loss (D) is observed in the frequency range 100 Hz to 100 kHz. At low frequency, the piling up of mobile charge carriers at the grain
boundary produces interfacial polarization giving rise to high dielectric constant. Dielectric loss showed a typical behaviour
in the temperature and frequency range studied. 相似文献
4.
Moti Ram 《Journal of Materials Science: Materials in Electronics》2011,22(8):1081-1084
The Li(Ni7/10Fe3/10)VO4 compound has been synthesized by solution-based chemical route. Its dielectric response is investigated using complex impedance
spectroscopy technique. Frequency dependence of dielectric constant (εr) at different temperatures shows low-frequency dispersion due to polarized structure of the material and mobile charge carriers.
Temperature dependence of εr at different frequencies exhibits the dielectric anomalies in εr at different temperatures. Dielectric relaxation process in the material is signified by the variation of tangent loss with
frequency at different temperatures. The variation of relaxation time with temperature obeys the Vogel–Fulcher law. 相似文献
5.
The manganese doped layered ceramic samples (Na1·9Li0·1)Ti3O7 : XMn(0·01 ≤ X ≤ 0·1) have been prepared using high temperature solid state reaction. The room temperature electron paramagnetic resonance
(EPR) investigations exhibit that at lower percentage of doping the substitution of manganese ions occur as Mn3+ at Ti4+ sites, whereas for higher percentage of doping Mn2+ ions occupy the two different interlayer sodium/lithium sites. In both cases, the charge compensation mechanism should operate
to maintain the overall charge neutrality of the lattice. The manganese doped derivatives of layered Na1·9Li0·1Ti3O7 (SLT) ceramics have been investigated through frequency dependence dielectric spectroscopy in this work. The results indicate
that the dielectric losses in these ceramics are the collective contribution of electric conduction, dipole orientation and
space charge polarization. Smeared peaks in temperature dependence of permittivity plots suggest diffuse nature of high temperature
ferroelectric phase transition. The light manganese doping in SLT enhances the dielectric constant. However, manganese doping
decreases dielectric loss due to inhibition of domain wall motion, enhances electron-hopping conduction, and impedes the interlayer
ionic conduction as well. Manganese doping also gives rise to contraction of interlayer space. 相似文献
6.
Dielectric properties such as dielectric constant (ε′) and dielectric loss tangent (tan□δ) of mixed Mn-Zn-Er ferrites having
the compositional formula Mn0.58Zn0.37Fe2.05−xErx04 (where itx = 0.2, 0.4, 0.6, 0.8 and 1.0) were measured at room temperature in the frequency range 1–13 MHz using a HP 4192A
impedance analyser. Plots of dielectric constant (ε′) vs frequency show a normal dielectric behaviour of spinel ferrites.
The frequency dependence of dielectric loss tangent (tan δ) was found to be abnormal, giving a peak at certain frequency for
all mixed Mn-Zn-Er ferrites. A qualitative explanation is given for the composition and frequency dependence of the dielectric
constant and dielectric loss tangent. Plots of dielectric constant vs temperature have shown a transition near the Curie temperature
for all the samples of Mn-Zn-Er ferrites. However, Mn0.58Zn0.37Er1.0Fe1.05O4 does not show a transition. On the basis of these results an explanation for the dielectric mechanism in Mn-Zn-Er ferrites
is suggested. 相似文献
7.
Dehua Xiong Hong Li Jinshu Cheng 《Journal of Materials Science: Materials in Electronics》2010,21(9):882-888
Temperature and frequency dependence on electrical properties (dielectric constant, dielectric loss and conductivity) of Li2O–Na2O–K2O–Al2O3–SiO2(R2O–Al2O3–SiO2) system glass–ceramics used as anodic bonding materials were discussed. The results showed that the main crystal phase of
glass–ceramics was lithium metasilicate (Li2SiO3). Compared with the parent glass, both the dielectric constant and dielectric loss of glass–ceramics decreased, the dielectric
constant and dielectric loss increased gradually with the increasing of the test temperature from room temperature to 400 °C,
Testing frequency (30–300 MHz) had very little influence on the dielectric properties of samples. The electrical conductivity
of glass–ceramics showed a trend of first decrease and then increase with the increasing of temperature. The glass–ceramics
which has a lower dielectric constant, dielectric loss and better stability under high frequency was obtained after an appropriate
heat treatment; it could be used as anodic bonding materials under very high frequency. 相似文献
8.
Mechanisms of charge generation and its persistence in one and both-side vacuum-aluminized ethyl cellulose (EC):polymethyl
methacrylate (PMMA) blend thermoelectrets, prepared under different fields (10, 25, 50 and 100 kV/cm) and temperatures (40,
60, 80 and 100°C), have been analysed using short- and open-circuit thermally stimulated depolarization current (TSDC) technique.
The TSDCs were recorded by reheating the samples at a linear heating rate of 4°C/min. The TSDC thermograms of polyblends containing
EC:PMMA in different weight ratio are, in general, characterized with two peaks in lower and higher temperature regions. However,
the polarity of the peaks was found to be just opposite in short- and open-circuit TSDC measurements. Moreover, results on
97:3, 93:7 and 90:10 EC:PMMA polyblends indicated that the current increases with concentration of PMMA. The results indicate
the existence of heterocharge due to dipole orientation and ionic charge drift together with the injection of charge carriers
from electrodes with their subsequent localization in surface and bulk traps. Further, the chances of charge trapping in polyblends,
at the interfaces are greater than in the individual polymers. 相似文献
9.
V. M. Manisha K. P. Murali S. N. Potty V. Priyadarsini R. Ratheesh 《Bulletin of Materials Science》2004,27(2):149-153
MXTi7O16 (M = Ba and Sr; X = Mg and Zn) ceramics have been synthesized by the conventional solid state ceramic route. The dielectric
properties such as dielectric constant (εr), loss tangent (tan δ) and temperature variation of dielectric constant (τεr) of the sintered ceramic compacts are studied using an impedance analyser up to 13 MHz region. The strontium compounds have
relatively high dielectric constant and low loss tangent compared to the barium analogue. The phase purity of these materials
has been examined using X-ray diffraction studies and microstructure using SEM method. 相似文献
10.
The electrical properties for 20Bi2O3–60B2O3 (20−x)–CaF2–xSm2O3 glasses (0 ≤ x ≤ 2) were measured in the temperature range 297 K up to 629 K and in the frequency range 0·1–100 kHz. The d.c. and a.c. conductivity
values and the dielectric loss (tan δ) values were found to increase with increasing Sm2O3 content, whereas the activation energy of conductivities and the dielectric constant decreased. These results were attributed
to the introduction of the rare earth ions; promote the formation of a high number of non-bridging oxygen atoms, which facilitate
the mobility of charge carriers. The frequency dependence of the a.c. conductivity follows the power law σ
ac(ω) = Aω
s
. The frequency exponent (s) values (0·64 < s < 0·8) decrease with increasing temperature. This suggested that the a.c. conduction mechanism follows the correlated barrier
hopping model (CBH). The dielectric constant (ε
′) and dielectric loss (tan δ values) were found to increase with increasing temperature and increasing Sm2O3 concentration in the glass. The a.c. conductivities as a function of frequency at different temperatures of a given glass
superimposed onto a master curve (Roling scaling model). Furthermore, we have performed to scale the data as a function of
composition. Two master curves were obtained, which suggested that there are differences in dominant charge carriers between
glasses having Sm2O3 concentration ≥1 and glass of Sm2O3 concentration <1. 相似文献
11.
Ashok Kumar R. S. Katiyar Ramesh Nath Premnath Carlos Rinaldi J. F. Scott 《Journal of Materials Science》2009,44(19):5113-5119
Layered nanostructures (LNs) of the commercial ferroelectric Pb(Zr0.53Ti0.47)O3 (PZT) and the natural ferroic relaxor Pb(Fe0.66W0.33)O3 (PFW) were fabricated with a periodicity of PZT/PFW/PZT (~5/1/5 nm, thickness ~250 nm) on MgO substrates by pulsed laser
deposition. The dielectric behavior of these LNs were investigated over a wide range of temperatures and frequencies, observing
Debye-type relaxation with marked deviation at elevated temperatures (>400 K). High dielectric constant and very low dielectric
loss were observed below 100 kHz and 400 K, whereas the dielectric constant decreases and loss increases with increase in
frequency, similar to relaxor ferroelectrics. Asymmetric ferroelectric hysteresis loops across UP and DOWN electric field
were observed with high remanent polarization (Pr) of about 33 μC/cm2. High imprint (~5–7 V across 250 nm thin films) were seen in ferroelectric hysteresis that may be due to charge accumulation
at the interface of layers or significant amount of strain (~3.21) across the layers. Room temperature ferromagnetic hysteresis
was observed with remanent magnetization 5.32 emu/cc and a coercive field of ~550 Oe. Temperature and field dependent leakage
current densities showed very low leakage ~10−7–10−5 A/cm2 over 500 kV/cm. We observed imprint in hysteresis that may be due to charge accumulation at the interface of layers or active
role of polar nano regions (PNRs) situated in the PFW regions. 相似文献
12.
This study reports the temperature and frequency dependence of dielectric constant (ε′) and dielectric loss (ε′′) in glassy
Se80−x
Te20Sn
x
(x = 0, 2, 4, 6) alloys. The measurements have been made in the frequency range (1–500 KHz) and in the temperature range 305–335 K.
The results indicate that the dielectric dispersion exists in the present glassy systems in the above frequency and temperature
range. The composition dependence of the dielectric constant, dielectric loss and activation energy thermally activated crystallization
is also discussed. 相似文献
13.
The (1−x) Ba0.40Sr0.60TiO3 (BST)−xZr0.80Sn0.20TiO4 (ZST) composite ceramics with x = 10, 20, 30, and 40 wt% were fabricated by conventional solid-state reaction method. With increasing of ZST content, the
dielectric constant of composite ceramics was decreased and dielectric loss increases. The effect of ZnO addition to 70 wt%
BST–30 wt% ZST composition on the microstructure and dielectric properties was investigated. The improvements in dielectric
constant, dielectric loss, and microwave dielectric properties of composite ceramics can be achieved by ZnO addition. The
sample with 98 wt% (70 wt% BST–30 wt% ZST)–2 wt%ZnO composition exhibits promising dielectric properties, with dielectric
constant, loss tangent and tunability at 4 kV/mm, of 125, 0.0016 and 12%, at 10 kHz and room temperature. At ~2 GHz, it possesses
a dielectric constant of 101 and a Q factor of 187, which makes it a good candidate for tunable microwave device applications. 相似文献
14.
Jie Su Xiaomei Lu Chao Zhang Junting Zhang Song Peng Xiaobo Wu Kangli Min Fengzhen Huang Jinsong Zhu 《Journal of Materials Science》2011,46(10):3488-3492
Ho3Fe5O12 ceramics were fabricated by the solid-state reaction method. The results revealed an increase of the grain size, dielectric
constant, and dielectric loss, while a decrease of the remnant magnetization and coercive field with increasing sintering
temperature. A dielectric relaxation behavior was observed, which might be associated with the charge carrier hopping between
Fe2+ and Fe3+. A cole–cole fitting to loss peaks revealed a dependence of the activation energy and the broaden factor on the relative density of the
samples. Furthermore, at appropriate frequencies, the 1250 °C-sintered samples showed high dielectric constant, low dispassion,
and good temperature stability around room temperature. 相似文献
15.
The fluorine micas (K-fluorine micas; KXMg3-XLiXSi4O10F2) having variable layer charges (x = 0.4–1.0) were synthesized. The lattice constant c decreased with a decrease in the layer charge while the lattice constants
a and b increased. As the layer charge decreased, K-fluorine micas were changed into Na-fluorine micas more rapidly by NaB(C6H5)4 treatment and were easier to cleave and change into the amorphous phase by grinding. The mica ceramics with lower layer charges
showed lower electrical resistance than those with higher layer charges in the low-temperature region but higher electrical
resistance in the high-temperature region. The results of the electrical resistance can be explained by the concentrations
of the lattice vacancy and K+ ion in the interlayer. The dielectric loss tangent was influenced by the layer charge while the dielectric constant was almost
unchanged. The chemical and physical properties of such micas are strongly dependent on the magnitude of the layer charge
because the layer charge determines the interlayer bonding strength and the stability of mica structure. 相似文献
16.
Shetty Aparna V. M. Jali Ganesh Sanjeev Jayanta Parui S. B. Krupanidhi 《Bulletin of Materials Science》2010,33(3):191-196
The present paper deals with the study of the effects of electron (8 MeV) irradiation on the dielectric and ferroelectric
properties of PbZrO3 thin films grown by sol-gel technique. The films were (0.62 μm thick) subjected to electron irradiation using Microtron accelerator
(delivered dose 80, 100, 120 kGy). The films were well crystallized prior to and after electron irradiation. However, local
amorphization was observed after irradiation. There is an appreciable change in the dielectric constant after irradiation
with different delivered doses. The dielectric loss showed significant frequency dispersion for both unirradiated and electron
irradiated films. T
c was found to shift towards higher temperature with increasing delivered dose. The effect of radiation induced increase of
ɛ′(T) is related to an internal bias field, which is caused by radiation induced charges trapped at grain boundaries. The double
butterfly loop is retained even after electron irradiation to the different delivered doses. The broader hysteresis loop seems
to be related to radiation induced charges causing an enhanced space charge polarization. Radiation-induced oxygen vacancies
do not change the general shape of the AFE hysteresis loop but they increase P
s of the hysteresis at the electric field forced AFE to FE phase transition. We attribute the changes in the dielectric properties
to the structural defects such as oxygen vacancies and radiation induced charges. The shift in T
C, increase in dielectric constant, broader hysteresis loop, and increase in P
r can be related to radiation induced charges causing space charge polarization. Double butterfly and hysteresis loops were
retained indicative of AFE nature of the films. 相似文献
17.
A. F. L. Almeida P. B. A. Fechine L. C. Kretly A. S. B. Sombra 《Journal of Materials Science》2006,41(14):4623-4631
The solid state procedure was used to produce bulk ceramics of BTO (BaTiO3), CCTO (CaCu3Ti4O12) and BTO0.5–CCTO0.5 that were studied in the medium-frequency (MF) range (100 Hz–1 MHz) and in the microwave range of frequencies. The presence of BTO is decreasing the dielectric constant (εr) of the BTO–CCTO composite. The CCTO and BTO samples present a strong tendency to the increase of the loss with frequency. The BTO substrates are presenting higher values of the εr in the range of 1–4 GHz (around 140). For pure CCTO the dielectric constant is around 37.6. Similar behaviour observed at the MF range, that the higher dielectric constant is also associated to the higher loss is also present in the microwave region. The study of a planar microstrip antenna, that uses the BTO
X
–CCTO(1−X) ceramic as a high εr substrate was done. Therefore, these measurements confirm the potential use of such materials for small high dielectric planar antennas (HDA). These materials are also very promising for capacitor applications and certainly for microelectronics, microwave devices (cell mobile phones for example), where the miniaturization of the devices is crucial. 相似文献
18.
P. K. Bajpai Kuldeep Ratre Mukul Pastor T. P. Sinha 《Bulletin of Materials Science》2003,26(5):461-464
Samples of Sr(1− 3x/2)YxSnO3 are prepared by usual solid state reaction route. X- ray diffraction studies confirm the formation of single cubic perovskite
single phase. The dielectric constant and dielectric loss at 1 kHz were measured in the temperature range from room temperature
up to -150†C. The dielectric constant decreases and losses increase with increased yttrium content in the samples. The percentage
porosity and unit cell parameters are also calculated for the samples. 相似文献
19.
Y. Zhang-Steenwinkel H. L. Castricum A. Bliek E. Esveld 《Journal of Materials Science》2007,42(14):5851-5859
Dielectric properties of La1−x
Ce
x
MnO3 perovskites are investigated in order to assess the heating behaviour in the wider context of the use of perovskite coatings
in microwave assisted soot filter regeneration. Dielectric permittivities in the radio and microwave region for these perovskites
were determined at room temperature. The dielectric constant and dielectric loss are related to ionic conduction at low frequencies,
while at microwave frequencies storage and loss mainly proceed through reorientation of molecular dipoles. The dielectric
constant rises for a higher degree of La substitution by Ce, which is explained by an increase of the number of cation/oxygen
vacancies. Concurrently the mean perovskite crystallite size decreases, which is possibly related to defect formation. The
dielectric constant declines for x ≥ 0.3, along with the formation of a separate, low dielectric permittivity CeO2 phase. The La–Ce–Mn perovskites are further shown to exhibit a high thermal stability during repeated heating/cooling cycles. 相似文献
20.
Results of dielectric and thermal studies on strontium tartrate pentahydrate crystals are described. The value of dielectric
constant is shown to be independent of temperature till 360 K at all the frequencies (110–700 kHz) of the applied a.c. field.
It increases abruptly achieving a peak value of 25.5 at 100 kHz; the peak value being strongly dependent on frequency. In
the temperature range, 87 < T < 117°C, the value of ɛ′ falls suggesting a transition at around 100°C or so. The dielectric constant, ɛ′, of the material is shown to be frequency dependent but temperature independent in the pre- or post-T
c range 87 < T < 117°C, suggesting that the contribution towards polarization may be due to ionic or space charge polarization which gets
eliminated at higher frequencies. The ferroelectric transition is supported by the results of thermoanalytical studies. It
is explained that crystallographic change due to polymorphic phase transition may be occurring in the material, besides the
change due to loss of water molecules, which leads to the dielectric anomaly at around 100°C. Coats-Redfern approximation
method is applied for obtaining non-isothermal kinetic parameters leading to calculation of activation energies corresponding
to three decomposition stages of material in the temperature ranging from 379–1113 K. 相似文献