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1.
J.?S.?Almeida T.?S.?M.?Fernandes A.?J.?M.?Sales M.?A.?S.?Silva G.?F.?M.?P.?Júnior H.?O.?Rodrigues A.?S.?B.?Sombra
In this paper, the structural and dielectric properties of BNO (BiNbO4) was investigated as a function of the external RF frequency and temperature. The BNO Ceramics, prepared by the conventional
mixed oxide method and doped with 3, 5 and 10 wt. % Bi2O3–PbO were sintered at 1,025 °C for 3 h. The X-ray diffraction patterns of the samples sintered, shown the presence of the
triclinic phase (β-BNO). In the measurements obtained at room temperature (25 °C) was observed that the largest values of
dielectric permittivity (ε′
r
) at frequency 100 kHz, were for the samples: BNO5Bi (5 wt. % Bi2O3) and BNO5Pb (5 wt. % PbO) with values ε′
r
~ 59.54 and ε′
r
~ 78.44, respectively. The smaller values of loss tangent (tan δ) were for the samples: BNO5Bi and BNO3Pb (3 wt. % PbO) with
values tan δ ~ 5.71 × 10−4 and tan δ ~ 2.19 × 10−4, respectively at frequency 33.69 MHz. The analysis as a function of temperature of the dielectric properties of the samples,
obtained at frequency 100 kHz, showed that the larger value of the relative dielectric permittivity was about ε′
r
~ 76.4 at temperature 200 °C for BNO5Pb sample, and the value smaller observed of dielectric loss was for BNO3Bi sample at
temperature 80 °C, with about tan δ ~ 5.4 × 10−3. The Temperature Coefficient of Capacitance (TCC) values at 1 MHz frequency, present a change of the signal from BNO (−55.06 ppm/°C)
to the sample doped of Bi: BNO3Bi (+86.74 ppm/°C) and to the sample doped of Pb: BNO3Pb (+208.87 ppm/°C). One can conclude
that starting from the BNO one can increase the doping level of Bi or Pb and find a concentration where one have TCC = 0 ppm/°C,
which is important for temperature stable materials applications like high frequency capacitors. The activation energy (H)
obtained in the process is approximately 0.55 eV for BNO sample and increase with the doping level. These samples will be
studied seeking the development ceramic capacitors for applications in radio frequency devices. 相似文献
2.
Sharma H. Kumari Kiran Singh L. S. Choudhary R. N. P. 《Bulletin of Materials Science》2002,25(2):133-136
The polycrystalline samples of Ca4Bi2Ti4Nb6O30 (herein designated CBTN) were synthesized by the conventional ceramic method. Preliminary X-ray structural study of the compound
showed the formation of a single phase solid solution having orthorhombic structure in the paraelectric phase. Measurements
of the dielectric constant (ε) and dielectric loss (tan δ) as a function of temperature (−180–200°C) at 1 kHz and 10 kHz and
also as a function of frequency (102 Hz to 104 Hz) at five different temperatures [−180°C, −40°C, − 10°C 26°C (room temperature) and 75°C] have shown a dielectric anomaly
and a phase transition at − 13 ±1°C in CBTN. 相似文献
3.
Evaluation of a.c. conductivity behaviour of graphite filled polysulphide modified epoxy composites 总被引:1,自引:0,他引:1
Composites of epoxy resin having different amounts of graphite particles have been prepared by solution casting method. Temperature
dependence of dielectric constant, tan δ and a.c. conductivity was measured in the frequency range, 1–20 kHz, temperature
range, 40–180°C for 0.99, 1.96 and 2.91 wt% graphite filled and unfilled epoxy composites. It was observed that the dielectric
constant, tanδ and a.c. conductivity increase with increasing temperature. Near the transition temperature the materials show anomalous
behaviour for the observed properties. Peaks of dielectric constant, tan δ and a.c. conductivity were observed to shift towards
lower temperature with increasing frequency. Clear relaxation (tan δ) peaks around 169°C were observed in epoxy resin, which
shifted to lower temperature side on increasing the frequency. Addition of 2.91 wt% graphite shifted the tan δ peaks towards
higher temperature side by creating hindrances to the rotation of polymer dipoles. Addition of 2–91 wt% graphite leads to
an increased relaxation time τ of dipoles in polysulphide epoxy from 1.44 × 10−5− 3.92 × 10−5 (s) at 90°C by creating the hindrance to the rotation of dipoles. 相似文献
4.
Some garnets collected from the Kothagudem area of Khammam district in Andhra Pradesh were characterized by chemical analysis.
The results show the garnets to be of almandine (Fe+2
3 Al2Si3O12) pyrope (Mg3Al2Si3O12) group. Dielectric constant (ɛ) and dielectric loss (tanδ) were measured as a function of frequency and temperature in the
frequency range of 100 Hz to 100 KHz and from room temperature to 400°C. The room temperature measurement was extended to
10 MHz, AC conductivity was calculated from the data on ε and tan δ. DC conductivity was also measured. 相似文献
5.
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
6.
Dielectric properties of solution-gas interface-formed Fe(OH)3 thin-film capacitors (Al/Fe(OH)3/Al) of various thicknesses have been studied in the frequency range 10–106 Hz at various temperatures (300–443 K). Dielectric constant, ε, increases with increasing film thickness (d) and temperature (T) and decreases with increase of frequency (f). The loss factor (tan δ), showing pronounced minimum with frequency, increases with rise of temperature, and tan δmin shifts to a higher frequency. The large increase in dielectric constant towards low frequency region indicates the possibility
of an interfacial polarization mechanism in this region. 相似文献
7.
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
8.
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
9.
Feng Shi 《Inorganic Materials》2010,46(1):85-90
The effect of BaZrO3, MnCO3 additives on the dielectric properties, sintering temperature and microstructure of Ba(Zn1/3Nb2/3)O3 (BZN) and Ba(Zn1/3Nb2/3)O3-Sr(Zn1/3Nb2/3)O3 (BSZN) ceramics was studied in this paper. It indicates that both BaZrO3 and MnCO3 can lower the sintering temperature of the ceramics and accelerate the crystallization of BZN and BSZN. The dielectric constant
ɛ
r
increases after MnCO3 added, but decreases when BaZrO3 added alone. The existence of MnCO3 can modulate the temperature coefficient of capacitance τ
c
toward positive, while BaZrO3, can make c more negative. MnCO3 and BaZrO3 can restrain the appearance of the second phase; while BaZrO3, can prevent the appearance of the superstructure. In the BSZN system, when 1 mass % MnCO3 added, sintering temperature(t
s
) is lowered to 1240°C. In this study, the best sample that has the excellent properties is sample 5 with dielectric properties
of ɛ
r
= 43.6, τ
c
= −8 × 10−6 °C−1 and tan δ = 0.6 × 10−4 (1 MHz). The sintering temperature of BZN and BSZN system can be lowered to less than 1300°C. 相似文献
10.
A two-step sintering approach composed of spark-plasma-sintering (SPS) technique at 1000 °C for 1 min and under a uniaxial
pressure of 63 MPa followed by conventional sintering at 1400 °C for 3 h is proposed for synthesis of dense Ba(Ti0.87Sn0.13)O3 ceramics. Starting powders had grain size of about 90 nm and were obtained by co-precipitation. The SPS pellets consist of
submicron (300–500 nm) grains. X-ray diffraction analysis of as-prepared Ba(Ti0.87Sn0.13)O3 ceramic shows the occurrence of cubic and tetragonal phase coexistence for the pellets obtained after SPS processing and
the presence of only tetragonal phase in the samples after the second (conventional) sintering. Grain uniformity in the final
product is high, with average size of ~2 μm. The apparent densities of the sintered pellets at temperature of 1400 °C were
~92% of the theoretical value of Ba(Ti0.87Sn0.13)O3. The ceramics exhibit a high relative dielectric constant of 6,550 and a dielectric loss (tan δ) = 0.078 at Curie temperature
of 63 °C and 10 Hz. 相似文献
11.
B. M. Garin V. V. Parshin V. G. Ral’chenko V. I. Konov A. N. Kopnin A. B. Mazur M. P. Parkhomenko E. E. Chigrya 《Technical Physics Letters》1999,25(4):288-289
A theoretical and experimental investigation is made of the magnitude and nature of the dielectric losses in weakly absorbing
synthetic diamonds in the wavelength range 1.75–6.8 mm at temperatures T=20–500 °C. Some samples exhibited extremely low losses (tan δ <10−5) which makes plasma-chemically deposited diamond wafers suitable for fabricating windows for megawatt continuous gyrotrons.
It is shown that in principle, a further substantial reduction in losses can be achieved.
Pis’ma Zh. Tekh. Fiz. 25, 85–89 (April 12, 1999) 相似文献
12.
Dielectric measurements of pure Nylon 11 in comparison with metal (Zn) filled Nylon 11 have been carried out using an impendence
analyzer in the frequency range of 102–107 Hz and temperature range 20–120 °C. Two different concentrations (1% and 5% (w/w)) of metal (Zn) fillers were used. It was
observed that at low frequencies and particularly at high temperature dielectric permittivity (ε′) for 1% Zn filled sample
is more than that of pure Nylon 11 whereas ε′ for 5% Zn filler is less as compared to that for pure Nylon 11. But at very
high frequencies dielectric permittivity (ε′) for pure Nylon 11 is less than Zn filled samples. Also it is found that for
all frequencies and particularly at high temperature ε′′ as well as tan δ are maximum for pure Nylon 11 and decrease for filled Nylon 11 samples. The Cole–Cole arcs have also been plotted for these
samples. Using these plots the static and instantaneous values of dielectric permittivity and orientation polarization parameter
‘S’ have been calculated. 相似文献
13.
Solid solutions in the lead-based relaxor system Pb(Mg1/3Nb2/3)O3–PbTiO3 were modified by minor substitutions of Ba in the Pb-site of the perovskite lattice. The modified compositions were calcined
at 830 °C for 3 h to yield fine-grained, single-phase perovskite materials. A small amount of excess MgO(0.05 wt %), which
mostly served as a sintering aid, was added to the calcined batches and the resulting mixtures were sintered at temperatures
between 1150 and 1250 °C for periods ranging from 3 to 5 h. The substitutions of BaO for PbO in the perovskite solid solution
lattice caused a progressive lowering of the Curie point with increasing BaO content. On average, the Curie point decreased
by about 10 °C for each mole of BaO substituted for PbO. Among the various Ba-substituted solid solutions studied, the one
with a nominal composition Pb0.99Ba0.01[(Mg1/3Nb2/3)0.9Ti0.1]O3 which has a Curie point located near 28 °C, exhibited excellent dielectric properties. On sintering at 1250 °C for 3 h, this
composition yielded a density near 96% of the theoretical density. The peak dielectric constant of the composition at 1 KHz
was slightly higher than 22000, and the corresponding tan δ value was 1.5% with a specific resistivity of 2.5 × 1012 Ω cm-1.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
14.
Barium titanate (BaTiO3) thin films doped with Mn (0.1–1.0 at%) were prepared by r.f. magnetron sputtering technique. Oxygen/argon (O2/Ar) gas ratio is found to influence the sputtering rate of the films. The effects of Mn doping on the structural, microstructural
and electrical properties of BaTiO3 thin films are studied. Mn-doped thin films annealed at high temperatures (700 °C) exhibited cubic perovskite structure.
Mn doping is found to reduce the crystallization temperature and inhibit the grain growth in barium titanate thin films. The
dielectric constant increases with Mn content and the dielectric loss (tan δ) reveals a minimum value of 0.0054 for 0.5% Mn-doped
BaTiO3 films measured at 1 MHz. The leakage current density decreases with Mn doping and is 10−11 A/cm−2 at 6 kV/cm for 1% Mn-doped thin films. 相似文献
15.
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
16.
The effects of X-ray irradiation on the dielectric constant (K) and loss (tan ) in the frequency range 102 to 3 × 105 Hz, temperature range 30 to 105 ° C, and on optical absorption, have been studied. All these parameters are found to be decreased considerably with increasing doses of X-ray irradiation. The effects of irradiation on these parameters for KD2PO4 crystals are found to be greater than those of KH2PO4. 相似文献
17.
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
18.
N. L. Singh Anita Sharma V. Shrinet A. K. Rakshit D. K. Avasthi 《Bulletin of Materials Science》2004,27(3):263-267
The effect of high-energy (50 MeV) Li3+ ion beam irradiation on polypropylene (PP) film has been studied in the fluence range 2.4 × 1012−l.5 × 1014 ions/cm2. The a.c. electrical properties of PP films were measured in the frequency range from 0.05– 100 kHz, and at temperature range
between 30 and 140°C. This study indicates two peaks at 60°C and 120°C with comparatively high magnitudes. There is an exponential
increase in conductivity with log of frequency and the effect is significant at higher fluences. The loss factor (tan δ) vs
frequency plot suggests that PP film based capacitors may be useful below 10 kHz. The capacitance is constant over a wide
temperature range up to 130°C. FTIR spectra of the PP films before and after irradiation indicate that intensity of C-H stretching
vibration at 2900 cm−1 is modified. The presence of many new peaks with the increase of fluence suggests the formation of alkanes and alkynes which
might be responsible for the observed changes in the dielectric and electrical properties of PP films. 相似文献
19.
Dielectric constantɛ, loss tanδ and a.c. conductivityσ of LiF-B2O3: Ln3+ (where Ln=Ce, Pr, Nd and Tb) glasses are studied as functions of frequency (in the range 102–106 Hz) and temperature (range 30–200°C). The dielectric breakdown strength of these glasses was also determined at room temperature
in an air medium. The rate of increase ofɛ and tanδ with temperature decreases with decrease in the ionic radius of RE3+ ion whereas the dielectric breakdown strength, the activation energy for a.c. conduction in the high temperature region decreases
with increase in the ionic radius of RE3+ ion. An attempt has been made to explain the a.c. conduction in these glasses on the basis of quantum mechanical tunnelling
(QMT) model. 相似文献
20.
Haikui Zhu Hongqing Zhou Min Liu Pengfei Wei Guijun Xu Ge Ning 《Journal of Materials Science: Materials in Electronics》2009,20(11):1135-1139
CaO–B2O3–SiO2 (CBS) glass powders are prepared by traditional glass melting method, whose properties and microstructures are characterized
by Differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that the
pure CBS glass ceramics possess excellent dielectric properties (ε
r = 6.5, tan δ = 5 × 10−3 at 10 GHz), but a higher sintering temperature (>900 °C) and a narrow sintering temperature range (about 10 °C). The addition
of a low-melting-point CaO–B2O3–SiO2 glass (LG) could greatly decrease the sintering temperature of CBS glass to 820 °C and significantly enlarge the sintering
temperature range to 40 °C. The CBS glass ceramic with 30 wt% LG glass addition sintered at 840 °C exhibits better dielectric
properties: ε
r ≈ 6, tan δ < 2 × 10−3 at 10 GHz, and the major phases of the sample are CaSiO3, CaB2O4 and SiO2. 相似文献