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1.
This paper reports about the double phase transition (at 315 and 366 °C) in the polycrystalline sample of K 2Pb 2Sm 2W 2Ti 4Nb 4O 30 prepared by a high-temperature solid-state reaction technique. The calcination temperature was decided based on thermogravimetry analysis. Room temperature X-ray structural analysis confirms the formation of a single phase compound. The surface morphology recorded by scanning electron microscope exhibits a uniform grain distribution with high density. Detailed studies on the nature of variation (1) of dielectric parameters with temperature, and (2) polarization with temperature confirmed the existence of ferroelectricity in the material at room temperature. The temperature dependence of dc conductivity shows a typical Arrhenius behavior. The frequency dependence of ac conductivity suggests that the material obeys Jonscher’s universal power law. The variation of current with temperature shows that the material has high pyroelectric co-efficient and figure of merit, thus making it useful for pyroelectric sensors. 相似文献
2.
The polycrystalline sample of ZnFe 2O 4 was prepared by a high-temperature solid-state reaction technique. Preliminary X-ray diffraction studies of the compound showed the formation of a single-phase compound at room temperature. Studies of dielectric properties (ε r, tan δ) of the above compound as a function of frequency in a wide temperature range show dielectric anomalies signifying existence of possible ferroelectric to paraelectric phase transition in the material. The confirmation of this assumption was made with observation of ferroelectric hysteresis loop at room temperature. Magnetic measurement exhibits anti-ferromagnetic nature of the sample. Studies of the zero-field cooled and the field-cooled magnetization in dc field provided the blocking temperature T B. The temperature dependence of electrical parameters (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation between the microstructure (i.e., bulk, grain boundary, etc.) and electrical parameters of the material. Detailed studies of impedance parameters have provided an insight into the electrical properties and understanding of types of relaxation process in the material. The temperature variation of dc resistivity/conductivity exhibits negative temperature coefficient of resistance behaviour of the material. The frequency dependence of ac conductivity suggests that the material obeys Jonscher’s universal power law. 相似文献
3.
The polycrystalline sample of K 2Pb 2Dy 2W 2Ti 4Nb 4O 30 was synthesized by high—temperature solid—state reaction method (calcinations temperature ~1,050?°C and sintering temperature ~1,075?°C). The phase formation of the desired compound was confirmed by preliminary X-ray structural analysis. The scanning electron micrograph shows uniform plate and rod like grain distribution throughout the surface of the sample without much pores. Detailed studies of the nature of (1) variation of dielectric parameters with temperature (27–480?°C) and frequency (1?kHz–5?MHz) and (2) polarization (at three different temperatures) confirmed the existence of ferroelectricity in the material, with phase transition occurring at 316?°C. The temperature dependence of electrical parameters (impedance, modulus, conductivity, etc.) of the material exhibits a strong correlation between its micro-structure (i.e., bulk, grain boundary, etc.) and electrical properties. The nature of temperature dependent dc conductivity follows the Arrhenius equation, and reveals the negative temperature coefficient of resistance (NTCR) behaviour of the material. The material obeys Jonscher’s universal power law which is evident from the graphs of frequency dependence of ac conductivity. 相似文献
4.
A lead free polycrystalline material Ba(Bi 0.5Nb 0.5)O 3 was prepared using a high-temperature mixed oxide technique using high purity ingredients. The formation of the material in monoclinic crystal structure was confirmed by an X-ray structural analysis at room temperature. The nature and texture of microstructure by scanning electron microscopy show that the compound has well defined grains uniformly distributed throughout the surface of the sample. Detailed studies of dielectric and impedance properties of the material, carried out in the frequency range of (1 kHz–1 MHz) at different temperatures (30 °C to 475 °C), have shown many interesting properties. Dielectric study showed an existence of diffuse phase transition around 317 °C. The temperature dependence of impedance parameters (impedance, modulus etc.) of the material exhibits a strong correlation of its micro-structure (i.e., bulk, grain boundary, etc.) with the electrical parameters. An existence of negative temperature coefficient of resistance (NTCR) type behavior in the material similar to that of semiconductors was also observed. The complex electric modulus analysis indicates the existence of hopping conduction mechanism in the system with non-exponential type of conductivity relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius behavior of the material. The ac conductivity spectra show a typical signature of an ionic conducting system, and are found to obey Jonscher’s universal power law. The temperature dependent pre-exponential factor ( A) shows peak and frequency exponent ( n) possesses a minimum at transition temperature. 相似文献
5.
The polycrystalline sample of CaBa 4SmTi 3Nb 7O 30, a member of tungsten bronze family, was prepared by solid-state reaction method. X-ray diffraction analysis shows the formation
of single-phase compound with an orthorhombic structure at room temperature. Scanning electron micrograph of the material
shows uniform distribution of grains. Detailed studies of dielectric properties of the compound as a function of temperature
at different frequencies suggest that the compound has a dielectric anomaly of ferroelectric to paraelectric type at 198°C,
and exhibits non-relaxor kind of diffuse phase transition. The ferroelectric nature of the compound has been confirmed by
recording polarization-electric field hysteresis loop. Piezoelectric and pyroelectric studies of the compound have been discussed
in this paper. Electrical properties of the material have been analyzed using complex impedance technique. The Nyquist plots
manifest the contribution of grain boundaries (at higher temperature), in addition to granular contribution (at all temperatures)
to the overall impedance. The temperature dependence of dc conductivity suggests that the compound has negative temperature
coefficient of resistance (NTCR) behaviour. The frequency dependence of ac conductivity is found to obey Jonscher’s universal
power law. The observed properties have been compared with calcium free Ba 5SmTi 3Nb 7O 30 compound. 相似文献
6.
Li 2Pb 2La 2W 2Ti 4Nb 4O 30 complex ferroelectric oxide was prepared by using a high-temperature solid-state reaction method (calcination temperature, ~1100 °C and sintering temperature, ~1150 °C). Room temperature preliminary structural analysis shows formation of a single-phase compound. The nature of microstructure (i.e. grain distribution, presence of voids, grain size, etc) recorded using scanning electron microscope (SEM) clearly suggests the formation of high quality and density of pellet samples. Studies of temperature dependence of dielectric constant, tangent loss and polarization show the existence of ferroelectric phase transition in the material at high temperature (307 °C). Detailed studies of temperature dependence of electrical parameters (i.e. impedance (400?475 °C), modulus, conductivity, etc) of the material clearly suggest a strong correlation between its microstructure (i.e. bulk, grain boundary, etc) and electrical properties. The nature of temperature variation of d.c. conductivity showed an Arrhenius behaviour of the material. A signature of ionic conductivity in the material was observed in its a.c. conductivity spectrum. The nature of frequency dependence of a.c. conductivity of the material can be explained by Jonscher’s universal power law. Electrical transport properties of the material show existence of non-exponential type of conductivity relaxation. 相似文献
7.
The polycrystalline sample of Nd 3/2Bi 3/2Fe 5O 12 was prepared by a high- temperature solid-state reaction technique. Preliminary X-ray structural analysis exhibits the formation
of a single-phase tetragonal structure at room temperature. Microstructural analysis by scanning electron microscopy shows
that the sintered sample has well defined grains. These grains are distributed uniformly throughout the surface of the sample.
Detailed studies of dielectric response at various frequencies and temperatures exhibit a dielectric anomaly at 400 °C. The
electrical properties (impedance, modulus and conductivity) of the material were studied using a complex impedance spectroscopy
technique. These studies reveal a significant contribution of grain and grain boundary effects in the material. The frequency
dependent plots of modulus and the impedance loss show that the conductivity relaxation is of non-Debye type. Studies of electrical
conductivity with temperature demonstrate that the compound exhibits Arrhenius-type of electrical conductivity. Study of ac
conductivity with frequency suggests that the material obeys Jonscher’s universal power law. 相似文献
8.
Polycrystalline (Bi 1?x, K x) (Fe 1?x, Ta x) O 3 (x = 0.0, 0.1, 0.2, 0.3) materials were synthesized by a mixed-oxide method. The formation of single-phase compound in hexagonal crystal system was confirmed by X-ray diffraction analysis. Through scanning electron microscope the surface texture of the prepared material was recorded. It exhibits a uniform grain distribution with few small voids suggesting the formation of high-density (except BiFeO 3) pellet samples. For different concentration (x) of KTaO 3 the impedance and dielectric properties of the materials were investigated as a function of temperature and frequency. The grain and grain boundary contributions in the resistive and capacitive components of the samples were estimated using complex impedance spectroscopy technique. A strong correlation between these electrical parameters and microstructures (bulk, grain boundary, nature of charge carriers, etc.) of the material was established. The value of activation energy due to both grain and grain boundary is nearly same, but increases with an increase in composition (x). The nature of variation of direct-current conductivity confirms the Arrhenius-behavior of the materials. Study of frequency dependence of alternating-current conductivity suggests that the material obeys Jonscher’s universal power law, and the presence of ionic conductivity is observed. I–V characteristics curve confirms the NTCR-type behavior. 相似文献
9.
Bi 5Ti 3FeO 15 (BTF) is a multiferroic material of Aurivillius structural family with (perovskite) layered structure. This material has special interest and position in the family because it is a combination of multiferroic BiFeO 3 and ferroelectric Bi 4Ti 3O 12, and can be used as new magneto-electric material for devices. The compound (Bi 5Ti 3FeO 15) was synthesized by a standard and widely used a high-temperature solid-state reaction method using high purity oxides. Preliminary structural analysis of the compound from the room temperature X-rays diffraction data confirmed the formation and good quality of the material. The nature of the microstructure (i.e., distribution, size and shape of grains, etc.) of sample recorded at room temperature using scanning electron microscopy exhibits formation of high-density sample. Studies of capacitive (permittivity and tangent loss) and resistive (impedance, electrical modulus and electrical conductivity) properties of the material as a function of frequency (1–1,000 kHz) at different temperatures (30–500 °C) using a complex impedance spectroscopy technique have provided many interesting and vital information on contribution of grains, grain boundary and interface in the material. 相似文献
10.
The polycrystalline sample of bismuth based-complex multiferroic of a composition Bi 0.5Pb 0.5Fe 0.5Ce 0.5O 3 was prepared by a high-temperature solid-state reaction technique (calcinations temperature = 900 °C, sintering temperature = 960 °C, time = 4 h). Preliminary structural analysis using XRD data exhibits the formation of a single-phase compound. Studies of surface morphology of the ceramic sample of the compound, recorded at room temperature using a scanning electron microscope, show uniform distribution of grains of different size with few voids. Detailed studies of dielectric properties (ε r, tan δ) supported the existence of multiferroic properties in the above complex system. The analysis of impedance parameters, recorded in a wide frequency (1 kHz–1 MHz) and temperature (room temperature to 450 °C) range of the material provide better understanding of (a) role of grains and grain boundaries in resistive and capacitative characteristics, (c) structure-properties relationship and (b) type of relaxation process occurred in the material. Study of temperature dependence of dc conductivity of the compound shows the existence of negative temperature coefficient of resistance in it. The nature of variation of ac conductivity with temperature of the material follows the Josher’s universal power law. Study of magneto-electric characteristics of the sample at room temperature has provided many useful and new data on magneto-electric coupling coefficient of different orders. 相似文献
11.
The polycrystalline materials [Li 2Pb 2R 2W 2Ti 4Nb 4O 30 (R = Y, Eu)] of tungsten bronze structural family have been synthesized using a high-temperature solid-state reaction (mixed-oxide) technique. Study of electrical properties (impedance, modulus, conductivity, etc.,) of the materials exhibits a strong correlation between their bulk, grain boundary and electrical parameters. The value and nature of temperature dependence of ac conductivity clearly exhibits that the materials have thermally activated transport properties of Arrhenius-type. 相似文献
12.
Complex polycrystalline materials [Li 2Pb 2R 2W 2Ti 4Nb 4O 30 (R = Dy, Sm)] of the tungsten bronze structural family have been synthesized using a high-temperature solid-state reaction (mixed-oxide) technique. The formation of the single phase compounds was checked using preliminary X-ray structural data/pattern. The nature and distribution of grains in the samples in the scanning electron micrographs confirm the good quality of the samples used for electrical characterization. Detailed studies of dielectric constant, tangent loss and electrical polarization as a function of temperature at different frequency confirmed the existence of ferroelectric properties in the materials at room temperature. Study of electrical properties (impedance, modulus, conductivity, etc.,) of the materials exhibits a strong correlation between their micro-structures (i.e., bulk, grain boundary, etc.) and electrical parameters. The frequency dependence of ac conductivity suggests that the materials obey Jonscher’s universal power law. Pyroelectric study shows that the materials have good pyroelectric coefficient and figure of merit. 相似文献
13.
The polycrystalline sample of Na 1/2Nd 1/2TiO 3 was prepared by a high-temperature solid-state reaction technique. The formation of the compound was confirmed by both XRD
and EDX studies. Preliminary structural analysis ofNa 1/2Nd 1/2TiO 3 using X-ray diffraction data exhibits a tetragonal phase of the material at room temperature. The dielectric permittivity
and the loss tangent of the pellet sample were obtained in a wide frequency range (1 kHz to 1 MHz) at different temperatures
(30 °C to 425 °C). The dielectric anomaly at 114 °C, appearance of hysteresis loop and piezoelectric properties at room temperature
confirmed the ferroelectric properties of the compound. Measurements of frequency and temperature dependence of impedance
over a wide frequency range (100Hz–1MHz) were carried out by complex impedance spectroscopy as a non-destructive tool and
indicate that the electrical properties of the material are strongly temperature dependent. Evidence of temperature dependence
of electrical relaxation phenomenon as well as the negative temperature coefficient (NTC)-type of resistance behavior of the
sample has also been observed. The dc conductivity graph follows the Arrhenius law. Studies of dielectric modulus suggest
the non-Debye type of relaxation in the materials, which is supported by the impedance data. 相似文献
14.
The polycrystalline sample of KBa 2V 5O 15 ceramics was prepared by a mixed oxide method at low temperature (i.e., at 560 °C). The formation of the compound was confirmed using an X-ray diffraction technique at room temperature. Scanning electron micrograph of the material showed uniform grain distribution on the surface of the sample. Detailed studies of dielectric properties of the compound as a function of temperature at different frequencies suggest that the compound has a dielectric anomaly of ferroelectric to paraelectric type at 323 °C, and exhibits diffuse phase transition. Electrical properties of the material were analyzed using a complex impedance technique. The Nyquists plot showed the presence of both grain (>10 3 Hz) and the grain boundary (<10 3 Hz) effects in the material. Studies of electrical conductivity over a wide temperature range suggest that the compound exhibits the negative temperature coefficient of resistance behavior. The ac conductivity spectrum was found to obey Jonscher's universal power law. 相似文献
15.
A series of LaNb 3O 9 samples was prepared at 1325-1360 °C by the solid state reaction. The structures, temperature dependence of thermally stimulated currents and impedances were investigated. The samples show single phase of LaNb 3O 9 by XRD analysis. The SEM analysis exhibits that the grain size increases and the porosity factor decreases with increasing sintering temperature. The stimulated current decreases with increasing sintering temperature and a large current of ∼ 110 µA without applied voltage was observed in the LaNb 3O 9 sample sintered at 1325 °C. The polarization-electric field and temperature dependence of impedance results suggest that the temperature dependence of current does not originate from pyroelectric effect, but from the release of thermally stimulated current. 相似文献
16.
This paper highlights the dielectric and pyroelectric properties of two new complex tungsten bonze ceramics (K 2Pb 2Eu 2W 2Ti 4Nb 4O 30 and K 2Pb 2Nd 2W 2Ti 4Nb 4O 30) which were prepared by a high temperature mixed oxide method. Room temperature X-ray structural analysis confirms the formation of single phase compounds. The SEM micrographs show uniform distribution of densely packed rod like grains. Variation of dielectric parameters with temperature (27–500 °C) and frequency (1–5 MHz) shows the phase transition at 315 and 299 °C for the above mentioned respective samples. The temperature dependence of hysteresis loops confirms the existence of ferroelectricity in the materials below transition temperature. The current variation with voltage at different temperatures shows the semiconducting behaviour of the materials. The nature of temperature dependent dc conductivity follows the Arrhenius equation, and reveals the negative temperature coefficient of resistance behaviour of the materials. The current (for a fixed voltage) variation with temperature shows that the materials have high pyroelectric co-efficient and figure of merit, thus making them useful for pyroelectric sensors. 相似文献
17.
Complex impedance analysis of polycrystalline Pb 2Bi 3LaTi 5O 18, prepared by a high-temperature solid-state reaction technique has been carried out. XRD analysis indicated the formation
of a single-phase orthorhombic structure. Impedance plots were used as a tool to analyse the behaviour of the sample as a
function of frequency and temperature. The bulk resistance has been observed to decrease with rise in temperature showing
a typical negative temperature coefficient of resistance (NTCR) type behaviour like that of semiconductors. The ac impedance
studies revealed the presence of grain boundary effect at 450°C and showed polydispersive non Debye-type dielectric relaxation.
The frequency dependent ac conductivity at different temperatures indicated that the conduction process is thermally activated
process. The activation energy for bulk (0.67 eV) and grain boundary (0.73 eV) was estimated from the temperature variation
of respective conductivities. 相似文献
18.
Nowadays, several research groups are extensively trying to develop by synthesizing and characterizing single/co-doped single-phase bismuth ferrite (BFO) in order to get a highly efficient eco-friendly multifunctional devices. In this process, this report is an attempt to provide the detailed studies of structural, dielectric, impedance and ferroelectric properties of Bi(Fe0.85Dy0.15)O3 ceramic fabricated via the solid-state reaction method. Analysis of X-ray diffraction (XRD) data confirms a single phase of orthorhombic symmetry. The average crystallite (particle) size is found to be in the order of?~?41 nm. The field emission scanning electron microscopy (FE-SEM) spectrum shows a homogeneous grain distribution of the sample. The elemental composition examined by means of energy dispersive X-ray spectroscopy (EDXS) shows the existence of constituent elements of the sample. The electrical measurements and analysis, carried out using a computer-controlled phase sensitive multimeter (PSM) in a frequency range of 1 kHz–1 MHz at different sets of temperature (25–325 °C), provide many interesting features to explain further conduction mechanism. The dielectric analysis exhibits high value of dielectric constant (?r) and small value of dielectric loss (tanδ). Due to the effect of electronic and space charge polarization, the ?r value falls with an increasing frequency. The frequency–temperature dependence of impedance and electrical modulus analysis reveals the presence of semiconductor nature and non-Debye type of relaxation process in the sample. The analysis of ac-conductivity (σac) with respect to frequency and temperature obeys the universal Jonscher’s power law. The electric polarization study shows an enhancement in ferroelectric property of the material. Hence, based on the significant enhancement in electrical and ferroelectric properties of the Bi(Fe0.85Dy0.15)O3 material, the material may be considered for some applications. 相似文献
19.
Polycrystalline sample of LiCa 2Nb 5O 15 was prepared by a high-temperature solid-state reaction technique. Structural and microstructural characterizations were
performed by X-ray diffraction (XRD) and scanning electron microscope (SEM). X-ray studies reveal that the material has orthorhombic
structure at room temperature. Electrical properties of the material have been studied using a complex impedance spectroscopy
(CIS) technique in a wide temperature (31–500 °C) and frequency (10 2–10 6 Hz) ranges. The complex impedance plots reveal the main contribution of bulk effects in it. The bulk resistance, evaluated
from complex impedance spectrum, has been observed to decrease with rise in temperature showing a typical negative temperature
coefficient of resistance (NTCR) behavior. Variation of dc conductivity (bulk) with temperature demonstrates that the compound
exhibits Arrhenius type of electrical conductivity. 相似文献
20.
Bi 2Fe 2W 3O 15 was prepared in the polycrystalline form using a standard solid-state reaction technique in order to study its dielectric and electrical properties. The formation of a single-phase compound was confirmed by preliminary X-ray structural studies of the material. Studies of electrical properties (impedance, modulus and conductivity) of the compound over a wide range of temperature and frequency provide many interesting results. The impedance and modulus parameters were calculated using complex plane formalism, and suitable equivalent circuits have been proposed for different temperature and frequency regions. The nature of variation of ac conductivity with frequency at different temperatures obeys the Jonscher’s universal power law. The temperature-dependence of dc conductivity pattern follows the Arrhenius behavior. 相似文献
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