Grain boundary effects in NTC-PTC composite thermistor materials

1999 ◽  
Vol 14 (1) ◽  
pp. 120-123 ◽  
Author(s):  
D. J. Wang ◽  
J. Qiu ◽  
Y. C. Guo ◽  
Z. L. Gui ◽  
L. T. Li
Keyword(s):  
Energy Level ◽  
Grain Boundary ◽  
Boundary Effect ◽  
Complex Impedance ◽  
Negative Temperature ◽  
Impedance Analysis ◽  
Composite Effect ◽  
Complex Impedance Analysis ◽  
Temperature Coefficient Of Resistivity ◽  
Grain Boundary Effect

Yttrium-doped (Sr0.45Pb0.55)TiO3 ceramics have been studied by complex impedance analysis. As a sort of NTC-PTC composite thermistor, it exhibited a significantly large negative temperature coefficient of resistivity below Tc in addition to the ordinary PTC characteristics above Tc. It is found that the NTC effect in NTC-PTC materials was not originated from the deep energy level of donor (bulk behavior), but from the electrical behavior of the grain boundary. Therefore, the NTC-PTC composite effect was assumed to be a grain boundary effect, and yttrium was a donor at shallow energy level. The NTC-PTC ceramics were grain boundary controlled materials.

scholarly journals Impedance spectroscopy studies on lead free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 ceramics

2012 ◽  
Vol 6 (4) ◽  
pp. 201-207 ◽  
Author(s):  
Ahcène Chaouchi ◽  
Sadia Kennour
Keyword(s):  
High Temperature ◽  
Impedance Spectroscopy ◽  
Grain Boundary ◽  
Boundary Effect ◽  
Complex Impedance ◽  
Negative Temperature ◽  
Polycrystalline Sample ◽  
Impedance Analysis ◽  
Wide Frequency Range ◽  
Nyquist Plot

The AC complex impedance spectroscopy technique has been used to obtain the electrical parameters of polycrystalline sample of (Ba0.85Ca0.15) (Ti0.9Zr0.1)O3 in a wide frequency range at different temperatures. This sample was prepared by a high temperature solid-state reaction technique and single phase formation was confirmed by X-ray diffraction technique. This study was carried out by the means of simultaneous analysis of impedance, modulus, and electrical conductivity. The Cole-Cole (Nyquist) plots suggest that the grains and grain boundaries are responsible in the conduction mechanism of the material at high temperature. The Cole- Cole (Nyquist) plot studies revealed the presence of grain and grain boundary effect at 485 ?C. On the other hand, it showed only the presence of grain boundary component of the resistivity at 535 ?C. Complex impedance analysis indicated the presence of non-Debye type dielectric relaxation. The bulk resistance of the material decreases with rise in temperature similar to a semiconductor, and the Cole-Cole (Nyquist) plot showed the negative temperature coefficient of resistance (NTCR) character of (Ba0.85Ca0.15 )(Ti0.9Zr0.1 )O3. The value of activation energy is found to be 0.7433 eV, which suggests that the conduction may be the result of defect and charge carriers present in the materials.

scholarly journals Grain boundary effects on piezoelectric properties of the core–shell-structured BaTiO3@TiO2 ceramics

2018 ◽  
Vol 08 (06) ◽  
pp. 1850044 ◽  
Author(s):  
Xixi Li ◽  
Zhonghua Yao ◽  
Juan Xie ◽  
Zongxin Li ◽  
Hua Hao ◽  
...  
Keyword(s):  
Electrical Properties ◽  
Grain Boundary ◽  
Boundary Effect ◽  
Ferroelectric Properties ◽  
Critical Role ◽  
Impedance Analysis ◽  
Ferroelectric Materials ◽  
Boundary Effects ◽  
Grain Boundary Effects ◽  
Grain Boundary Effect

Grain boundary effect on BaTiO3 has been widely investigated for several decades. However, all of them tailored the grain boundary by grain size of BaTiO3. In this case, a direct way was introduced to modify the grain boundary by coating technique to investigate the role of grain boundary in ferroelectric materials. Nonferroelectric phase TiO2 was employed to investigate grain boundary effects on the electrical properties of BaTiO3 piezoelectric ceramics. TiO2 coating can result in the reduction of piezoelectric and ferroelectric properties and the annealing process in oxygen can increase piezoelectric behavior of pure BaTiO3 due to valence state of Ti ions while that remains for Ti-modified composition possibly due to the increased grain boundary effect by impedance analysis. Compared with ferroelectric grain, grain boundary plays a critical role to impact the electrical properties of perovskite-type ferroelectric materials.

scholarly journals Dielectric, ferroelectrics properties and impedance spectroscopy analysis of the [(Na0.535K0.480)0.966Li0.058](Nb0.90Ta0.10)O3-based lead-free ceramics

2015 ◽  
Vol 05 (01) ◽  
pp. 1550007 ◽  
Author(s):  
M. Saidi ◽  
A. Chaouchi ◽  
S. D'Astorg ◽  
M. Rguiti ◽  
C. Courtois
Keyword(s):  
Complex Impedance ◽  
Negative Temperature ◽  
Impedance Analysis ◽  
Xrd Analysis ◽  
Ac Impedance ◽  
Nyquist Plot ◽  
X Ray Diffraction ◽  
Complex Impedance Analysis ◽  
Lead Free Ceramics ◽  
Different Temperatures

Polycrystalline of [( Na 0.535 K 0.480)0.966 Li 0.058] (Nb 0.90 Ta 0.10) O 3 samples were prepared using the high-temperature solid-state reaction technique. X-ray diffraction (XRD) analysis indicates the formation of a single-phase with orthorhombic structure. AC impedance plots were used as tool to analyze the electrical behavior of the sample as a function of frequency at different temperatures. The AC impedance studies revealed the presence of grain effect, from 425°C onwards. Complex impedance analysis indicated non-Debye type dielectric relaxation. The Nyquist plot showed the negative temperature coefficient of resistance (NTCR) characteristic of NKLNT. The AC conductivity results were used to correlate with the barrier hopping (CBH) model to evaluate the binding energy (Wm), the minimum hopping distance (R min ), the density of states at Fermi level (N(Ef)), and the activation energy of the compound.

FREQUENCY DEPENDENCE OF THE GRAIN-BOUNDARY CONDUCTIVITY IN (Y2O3, CaO)-STABILIZED ZrO2

2011 ◽  
Vol 25 (01) ◽  
pp. 131-142 ◽  
Author(s):  
TONGWEI LI ◽  
WEIWEI JU ◽  
JINCANG ZHANG
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Frequency Dependence ◽  
Power Law ◽  
Boundary Effect ◽  
Complex Impedance ◽  
Impedance Method ◽  
Boundary Conductivity ◽  
Grain Boundary Effect ◽  
Power Law Parameters

Five samples of mixed Y 2 O 3/ CaO doped ZrO 2 electrolytes, with the same nominal chemical composition of ( ZrO 2)0.90–( Y 2 O 3)0.04-( CaO )0.06, were sintered at 1600°C for 2, 4, 6, 8 and 10 h, respectively. The frequency dependence of the grain-boundary conductivity of each sample was measured using complex impedance method in the temperature range from 773 to 1073 K and experimental results were analyzed according to a power law, which was frequently referred to as the so-called universal dynamic response (UDR). Results indicated the apparent ac grain-boundary conductivity can be well-described by the power law and some useful information about the grain-boundary effect, such as the activation energy of the grain-boundary conduction and the dissociated energy of the charge carrier in the space charge layer, can be obtained by analyzing the temperature dependence of the power law parameters.

scholarly journals Impedance spectroscopy of nanocrystalline MgFe2O4 and MnFe2O4 ferrite ceramics: Effect of grain boundaries on the electrical properties

2016 ◽  
Vol 48 (1) ◽  
pp. 17-28 ◽  
Author(s):  
Dalibor Sekulic ◽  
Zorica Lazarevic ◽  
Cedomir Jovalekic ◽  
Aleksandra Milutinovic ◽  
Nebojsa Romcevic
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Complex Impedance ◽  
Equivalent Circuit Model ◽  
Average Crystallite Size ◽  
Impedance Analysis ◽  
Ceramic Materials ◽  
Xrd Analysis ◽  
Nanosized Powders ◽  
Complex Impedance Analysis

Two ferrite ceramic materials, MgFe2O4 and MnFe2O4, were successfully fabricated by a conventional sintering of nanosized powders (at 1373 K for 2 h) synthesized by soft mechanochemical route. The particle size and morphology of powders were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis was carried out for the determination of phase purity, crystal structure and average crystallite size of sintered ferrites. Both mechanosynthesized ferrite samples show mean crystallite sizes in the nm-range. Over the frequency range of 100 Hz to 1 MHz, impedance spectra of prepared ferrite ceramics are investigated at and above room temperature. Changes in the impedance plane plots with temperature have been discussed and correlated to the microstructure of materials. An equivalent circuit model is applied to explore the electrical parameters (resistance and capacitance) associated with grains and grain boundaries. Complex impedance analysis indicates the dominance of grain boundary effects which control the overall electrical behaviour of studied ferrites. The decrease in grain boundary resistance with temperature suggests a thermally activated conduction mechanism.

scholarly journals Electrical properties of Nb/Al-doped CuO-based ceramics for NTC thermistors

2020 ◽  
Vol 14 (1) ◽  
pp. 47-55
Author(s):  
Xianchi Wang ◽  
Zhicheng Li ◽  
Weiqin Yan ◽  
Pinji Wang ◽  
Hong Zhang
Keyword(s):  
Electrical Properties ◽  
Photoelectron Spectroscopy ◽  
Boundary Effect ◽  
Sol Gel ◽  
Complex Impedance ◽  
Negative Temperature ◽  
Impedance Analysis ◽  
B Value ◽  
Polaron Hopping ◽  
Ntc Thermistors

Nb/Al-modified CuO ceramics (yNb/0.02Al-CuO, 0 ? y ? 0.07, denoted as NACO) were synthesized using sol-gel method for applications in negative temperature coefficient (NTC) thermistors. The phase structure, microstructure and electrical properties of the ceramics were investigated. XRD investigation reveals that the NACO ceramics has the main phase with monoclinic crystalline structure. The analysis of X-ray photoelectron spectroscopy proved the existence of Cu2+/Cu+ and Nb5+/Nb4+ ions. Temperature dependence of the resistivity indicated that the NACO ceramics present typical NTC characteristic. The NTC materials? constant, B value, can be adjusted from 2430K to 3805K by changing the Nb-concentration in the Al-doped CuO ceramics. Among four applied calibration equations the Hoge-3 equation is the most effective one for the resistancetemperature calibration of the prepared NTC thermistors. The complex impedance analysis was performed and revealed that both grain effect and grain boundary effect similarly contribute to the electrical conductive behaviour and NTC feature of the NACO ceramics. The band conduction and polaron hopping conduction are proposed as the conduction mechanisms in the NACO thermistors.

scholarly journals Phase Transition, Dielectric Relaxation and Impedance Spectroscopy of Perovskite xBa0.95Sr0.05Tio3-(1‒X)BiFe0.9Sm0.1O3 Ceramics

2020 ◽  
Vol 27 (1) ◽  
pp. 23-42
Author(s):  
MJ Miah ◽  
SC Mazumder ◽  
AKM Akther Hossain
Keyword(s):  
Conduction Mechanism ◽  
Negative Temperature Coefficient ◽  
Boundary Effect ◽  
Structural Phase ◽  
Complex Impedance ◽  
Negative Temperature ◽  
Cubic Phase ◽  
Structural Phase Transitions ◽  
Impedance Data ◽  
Grain Boundary Effect

Polycrystalline xBa0.95Sr0.05TiO3-(1‒x)BiFe0.9Sm0.1O3[xBST-(1‒x)BFSO] ceramics were synthesized. The structural phase transitions were studied and it was found that structure of the compound transformed from rhombohedral to cubic phase. The compound exhibited a dielectric anomaly in the vicinity of Néel temperature of BiFeO3 except for x = 0.25. Enhanced dielectric properties were noticed and this might be attributed to the reduction of oxygen vacancies. Studies of electrical conductivity over a wide temperature range showed that the ceramics behaved like a semiconductor with the negative temperature coefficient of resistance. Contribution of grains in conduction mechanism of the materials dominated and the grain resistance was found to be decreased with the increase in temperature. A Non-Debye type relaxation was seen in the material. The impedance data were re-plotted using the modulus formulae to avoid the ambiguity arising out of the presence of grain/grain boundary effect. Activation energy was found to be 0.18 to 0.33 eV in modulus study which was very close to complex impedance observation and it was implied that the charge carrier had the same energy barrier during the relaxation. Bangladesh Journal of Physics, 27(1), 23-42, June 2020

Simulation of the Grain Boundary Effects in PTCR Ceramics

2008 ◽  
Vol 368-372 ◽  
pp. 1692-1694
Author(s):  
Chao Fang ◽  
Dong Xiang Zhou ◽  
Hu An Liu ◽  
Shu Ping Gong
Keyword(s):  
Differential Equation ◽  
Grain Boundary ◽  
Fermi Level ◽  
Boundary Effect ◽  
Positive Temperature Coefficient ◽  
Boundary Effects ◽  
Positive Temperature ◽  
Potential Well ◽  
Temperature Coefficient Of Resistivity ◽  
Grain Boundary Effect

The positive temperature coefficient of resistivity (PTCR) behavior of semiconductive BaTiO3 ceramics is often explained by the Heywang model. However, Heywang model couldn’t explain some experimental phenomena of jump range more than 106. This paper considered that the migration of donors, electrons and holes has important influence on grain boundary effect. A differential equation about Fermi level was established on the base of Heywang model. By solving the equation the jump range can be calculated quantitatively. It was found that a potential well exists on the edge of grain due to the donor ionization, and the experimental phenomena of PTC jump range more than 106 could be explained.

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