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1.
Dielectric constant ε, loss tan δ, a.c. conductivity Σ and dielectric breakdown strength of NaF-B2O3 glasses doped with certain transition metal ions (viz. Cu2+, VO2+, Ti4+ and Mn4+) are studied in the frequency range 102-107 Hz and in the temperature range 30–250°C. The values of ε, tan δ, Σa.c. are found to be the highest for Cu2+ doped glasses and the lowest for Mn4+ doped glasses. Activation energy for a.c. conduction and the value of dielectric breakdown strength are found to be the lowest
for Cu2+ doped glasses and the highest for Mn4+ doped glasses. With the help of infrared spectra, increase in the values of ε and tan δ of these glasses with frequency and
temperature are identified with space charge polarization. An attempt has been made to explain a.c. conduction phenomenon
on the basis of quantum mechanical tunneling model (QMT)/carrier barrier hopping model. 相似文献
2.
Results of dielectric and conduction properties of vacuum evaporated tellurium (Te) thin film capacitors (Al-Te-Al) have been
reported in the frequency range 1–100 kHz at various temperatures (303–423 K). Loss factor (tanδ) which shows a maximum with frequency increases with rise of temperature and tanδ
max shift towards high frequency region. The large values of capacitance and dielectric constant (ɛ′) in the low frequency region indicate the possibility of an interfacial polarization mechanism.I-V characteristics show ohmic, space charge limited (SCLC) and thermionic emission conduction mechanisms to operate at low,
intermediate and high voltages respectively. Various transport parameters have been calculated. It has been observed that
the Schottky type of conduction is predominant in the high field region and the Schottky barrier height has been determined.
The Hall coefficient, Hall mobility and carrier concentration are also discussed. 相似文献
3.
Elastic moduli (Y, η), Poisson’s ratio (σ), microhardness (H) and some thermodynamical parameters such as Debye temperature (θD), diffusion constant (D
i),latent heat of melting (ΔH
m) etc of PbO-Al2O3-B2O3 glasses doped with rare earth ions viz. Pr3+, Nd3+, Sm3+, Eu3+, Tb3+, Dy3+, Ho3+, Er3+ and Yb3+, are studied as functions of temperatures (in the temperature range 30–200°C) by ultrasonic techniques. All these parameters
are found to increase with increasing atomic numberZ of the rare earth ions and found to decrease with increasing temperature of measurement. From these results (together with
IR spectra of these glasses), an attempt is made to throw some light on the mechanical strength of these glasses. 相似文献
4.
Dielectric properties andI–V characteristics of solution-gas interface-formed PbS thin-film capacitors (Al/PbS/Al) of various thicknesses have been studied
in the frequency range 10-106 Hz at various temperatures (300–443 K). Current-voltage (I–V) characteristics show space-charge-limited conduction. Dielectric constant (ε) increases with increasing film thickness and temperature and decreases with increase of frequency. The loss factor (tanδ) peaks observed in tanδ vs frequency and tanδ vs temperature reveal relaxation effect from dipolar orientation. These maxima shift to higher-temperature region with increasing
frequency. The large increase in capacitance (C) and dielectric constant (ε) towards low-frequency (f) region indicates the possibility of an interfacial polarization mechanism in this region. 相似文献
5.
Liying Chen Shunhua Wu Shuang Wang Guoqing Wang 《Journal of Materials Science: Materials in Electronics》2008,19(4):327-331
The relationship between the microstructures and dielectric properties of BaTiO3-based X7R ceramics has been investigated at different calcination temperatures. The XRD and SEM results show that calcinations
of BaTiO3 raw powders increase the grain size and stabilize the tetragonality (c/a ratio) of the ceramics. The grain growth caused by
the calcination prevents the doped ions from diffusing into the interior of the grains, and then increases the volume fraction
of the tetragonal phased core. This process greatly increases the dielectric constant by improving the ferroelectricity. As
a result, the relaxation mechanism of the domain reorientation generates high loss tangent. The BaTiO3 ceramics with X7R specifications were prepared at the calcination temperature of 1200 °C and the sintering temperature of
1240 °C, whose dielectric properties were ɛ
r ≥ 4500, Δɛ
r/ɛ
r25 ≤ ± 10%(−55∼125 °C), tanδ ≤ 0.012(25 °C), respectively. 相似文献
6.
N. Ramamanohar Reddy M. Venkata Ramana K. Krishnaveni K. V. Siva Kumar V. R. K. Murthy 《Bulletin of Materials Science》2007,30(4):357-363
Ferroelectromagnetic composites with compositions, X Ni0·5Zn0·5Fe1·95O4−δ
+ (1 − X) Ba0·8Pb0·2TiO3, in which X varies as 0, 0·005, 0·010, 0·015, 0·020, 0·040, 0·060, 0·080 and 1 in mole %, were prepared by conventional ceramic double
sintering process. The presence of two phases was confirmed by X-ray diffraction. The temperature variation of dielectric
constant, ɛ′, dielectric loss, tan δ, d.c. conductivity, a.c. conductivity, elastic and anelastic behaviour of ferrite-ferroelectric composites were studied in
the temperature range 30–350°C. The a.c. conductivity measurements on these composites in the frequency range 100 Hz-1 MHz
at room temperature reveal that the conduction mechanism is due to small polaron hopping. The dielectric and elastic data
were discussed in the light of phase transitions. 相似文献
7.
Polycrystalline samples of Ba5RTi3Nb7O30 [R=Nd, Eu, Gd], were prepared using high-temperature solid-state reaction technique. Preliminary X-ray structural analysis
of the compounds shows the formation of single phase compounds (orthorhombic crystal system) at room temperature. Detailed
studies of dielectric properties (ɛ, tanδ,σ) as a function of frequency (400 Hz to 10 kHz) and temperature (30° to 380°C) show that these compounds exhibit diffuse ferroelectric
phase transition. 相似文献
8.
Glass samples of the system (15Li2O–30ZnO–10BaO–(45 − x)B2O3–xCuO where x = 0, 5, 10 and 15 mol%) were prepared by using the melt quenching technique. A number of studies, viz. density, differential
thermal analysis, FT-IR spectra, a.c. conductivity and dielectric properties (constant εφ, loss tan δ, a.c. conductivity,
σac, over a wide range of frequency and temperature) of these glasses were carried out as a function of copper ion concentration.
The analysis of the results indicate that the density increases while molar volume decreases with increasing of copper content
indicates structural changes of the glass matrix. The glass transition temperature, T
g, and crystallization temperature, T
c, increase with the variation of concentration of CuO referred to the growth in the network connectivity in this concentration
range, while glass-forming ability parameter (T
c − T
g) decreases with increasing CuO content, indicates an increasing concentration of copper ions that take part in the network-modifying
positions. The FT-IR spectra evidenced that the main structural units are BO3, BO4, and ZnO4. The structural changes observed by varying the CuO content in these glasses and evidenced by FTIR investigation suggest
that the CuO plays a network modifier role in these glasses while ZnO plays the role of network formers. The dielectric constant
decreased with increase in temperature and CuO content. The variation of a.c. conductivity with the concentration of CuO passes
through a maximum at 5 mol%. In the high temperature region, the a.c. conduction seems to be connected with the mixed conduction
viz., electronic conduction and ionic conduction. 相似文献
9.
Results of measurements on a thick-film capacitor based on a paste of mixed ferroelectric phases made out of crystallization
from a glassy phase are presented. This material can be used as a high dielectric constant paste for designing capacitors
in hybrid circuits. The tanδ is observed to decrease with rise in temperature. 相似文献
10.
R. H. Amnerkar C. S. Adgaonkar S. S. Yawale S. P. Yawale 《Bulletin of Materials Science》2002,25(5):431-434
A.c. conductivity, dielectric constant and loss, and variation with temperature (302–373 K) for four different compositions
of V2O5-B2O3 glasses were reported at 9.586 GHz microwave frequency. The quality factor (Q) and attenuation factor (α being the important parameters in the microwave range of applications were also studied. The change in the dielectric constant
and loss was observed with composition of V2O5. The maximum loss was found to be at 15V2O5 mol‰ The peak was observed in loss with temperature. 相似文献
11.
Hiroyuki Sasakura Yoshiya Akagi Shigeki Tsukui Motoaki Adachi 《Journal of Superconductivity and Novel Magnetism》2008,21(4):249-252
New Pb-based layered cuprates with the 1222 structure have been synthesized in the (Pb0.5B0.5)Sr2 (RE2−x−y
Ce
x
Sr
y
)Cu2O
z
(RE = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y) systems. The almost-single-phase samples in the systems can be obtained
for a nominal composition of x=0.7 and y=0.1. The crystal structure of the samples has a tetragonal symmetry, the lattice parameters of a and c are increasing with increasing the ionic radius of RE element. Despite treatment under high O2 pressure of 100 atm, the samples are semiconductors with the transport process characteristic of three-dimensional variable
range hopping conduction. 相似文献
12.
We measure the relative permittivity
r and dielectric loss tangent tan of substrate materials for high-T
c superconducting films at 18–300 K and at 5–10 GHz using the cavity-resonator method. The materials measured are single crystals of MgO, LaAlO3, YAlO3, LaSrGaO4, NdGaO3, sapphire, and ZrO2 ceramic. The
r values are 10–30 and become almost constant below about 50 K. The tan values decrease with decreasing temperature and are below 1×10–5 at 77 K except for those of NdGaO3 and ZrO2 ceramic. This suggests that the tan values of MgO, LaAlO3, YAlO3, LaSrGaO4, and sapphire do not limit the quality factors of microwave passive components fabricated using high-T
c superconducting films. It is also demonstrated that the tan of the substrate material is strongly affected by impurities. 相似文献
13.
The dielectric constant (K), loss (tanδ), and hence conductivity (σ) of SrTiO3 single crystals have been measured in the frequency region 102–107 Hz and in the temperature range 30°–350° C. Quenching, subjecting the crystals to high electric fields (a.c. or d.c.) and
X-ray orγ-ray irradiation, or a combination of these treatments, is found to bring about interesting changes in these properties. An
attempt is made to understand the results. 相似文献
14.
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
15.
Polycrystalline sample of Pb(Li1/4Eu1/4Mo1/2)O3 was prepared by usual ceramic route. X-ray diffraction, SEM and EDAX were used to check the formation, homogeneity and elements
present in the compound. The measurement of dielectric constant (ɛ), dielectric loss (tanδ), hysteresis loop parameters (e.g. spontaneous polarization) as function of frequency and temperature suggest that the compound
is a ferroelectric one and has a ferro-paraelectric phase transition at 112 ± 2°C. The measurement of dc resistivity both
as function of biasing electric field and temperature of the compound suggests that the compound has negative temperature
coefficient (NTC) of resistance above 100°C. 相似文献
16.
The dielectric constant (K), loss (tanδ) andac conductivity of a sepiolite sample have been measured as a function of frequency in the range 102-107 Hz and in the temperature region 30–400°C. Thedc conductivities of hot pressed pellets were measured in the temperature range 30–550°C.K and tanδ of these samples decrease with increasing frequency. Results of these measurements have been correlated with the structural
transformation accompanying dehydration, making use ofdta, ir and x-ray data. The moderately large value of activation energy (∼ 2·2 eV) in the intrinsic range suggests that the conduction
process is most probably associated with ions. 相似文献
17.
Shunhua Wu Shuang Wang Liying Chen Xiaoyong Wang 《Journal of Materials Science: Materials in Electronics》2008,19(6):505-508
The effects of Mn added during processing on the dielectric properties and microstructure of the BaTiO3-based ceramic materials system were discussed. Experiments show that a proper content of Mn can significantly increase dielectric
constant (ε) and reduce the dielectric loss (tanδ) in BaTiO3-based X7R ceramic materials. The results attribute to the reaction:
. When the system doped with 0.046mol% MnCO3 was sintered at 1240 °C for 4 h, the ε, tanδ and TCC were 5800, 1.6%, 0 ± 10% at 1 KHz respectively. 相似文献
18.
Chun Li Qian-feng Fang Xian-ping Wang Guo-guang Zhang 《Frontiers of Materials Science in China》2008,2(1):42-47
Based on the novel oxygen ion conductor La2Mo2O9, a series of Fe-doped samples of La2Mo2−x
Fe
x
O9−δ
(x = 0, 0.025, 0.05, 0.1) was prepared by conventional solid-state reaction method. The structure, phase transition, oxygen
ion diffusion and electrical conductivity were studied with X-ray diffraction (XRD), differential scanning calorimeter (DSC),
direct current (dc) resistivity, and dielectric relaxation (DR) measurements. One DR peak associated with the short-distance
diffusion of oxygen vacancies was observed in both temperature and frequency spectra. The activation energy for oxygen ion
diffusion in Fe-doped La2Mo2O9 samples was smaller than that in un-doped samples. Fe doping can increase the ionic conductivity of La2Mo2−x
Fe
x
O9−δ
samples as well as the ionic transference number in the temperature range from 680°C to 400°C in comparison with the un-doped
samples, although the electronic conductivity slightly increases. It is found that because of the small solubility of Fe2O3 in La2Mo2O9 (<5%), Fe doping cannot suppress the phase transition that occurred around 570°C, but 2.5% K doping at La site at the same
time (e.g. in sample La1.95K0.05Mo1.95Fe0.05O9−δ
) can completely suppress this phase transition and increase conductivity at lower temperatures. 相似文献
19.
In the present paper, a modified self-flux technique has been successfully employed for the growth of pure and praseodymium
substituted (partially) large single crystals of high temperature superconducting Y1−x
Pr
x
Ba2Cu3O7−δ
(x = 0·0,0·2,0·4). Typical sizes of the platy and bulky crystals of pure YBCO(123) material are ≈ 2 × 2 × 0·1 mm3 and 4 × 1 × 1 mm3, respectively. In case of Pr-substitution, the typical sizes of platy and bulky crystals of Y0·8Pr0·2Ba2Cu3O7−δ
and Y0·6Pr0·4Ba2Cu3O7−δ
materials are ≈ 2 × 3 × 0·1 mm3 and 5 × 1 × 1 mm3 and ≈ 1 × 1·5 × 0·1 mm3 and 7 × 0·2 × 0·1 mm3, respectively. The morphology and growth habit of the as-grown single crystals and the critical transition temperature (T
c) of the oxygenated crystals were found to depend on the Pr-content.
Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995 相似文献
20.
A well-known correlation of the maximum superconducting transition temperature (T
c,max) with ionic radius of rare earths and Y (R) in the series RBa2Cu3O7 – is converted to the intrinsic correlation of T
c,max with bond length between Ba and oxygen in CuO2 plane, being valid not only for RBa2Cu3O7 – but also for other cuprate superconductors containing BaO plane such as HgBa2CaCu2O6 + . It is pointed out that this correlation places a constraint on possible mechanisms inducing the high-T
c superconductivity. 相似文献