DIELECTRIC STUDIES IN Li2O AND CoO DOPED BOROPHOSPHATE GLASSES

2015 ◽  
Vol 8 (3) ◽  
pp. 2256-2266 ◽  
Author(s):  
Sankarappa Talari ◽  
J. S. Ashwajeet ◽  
R. Ramanna ◽  
K. Praveenkumar
Keyword(s):  
Activation Energy ◽  
Dielectric Properties ◽  
Small Polaron ◽  
Relaxation Mechanism ◽  
Frequency Exponent ◽  
Polaron Hopping ◽  
Borophosphate Glasses ◽  
Quantum Mechanical Theory ◽  
Quenching Method ◽  
Hopping Models

Borophosphate glasses in the compositions, (B2O3)0.2 . (P2O5)0.3 . (Li2O) 0.5-X . (CoO) X, wherex = 0.05, 0.1, 0.15, 0.25, 0.30, 0.35, 0.40 and 0.45 were prepared at 1400K by following melt quenching method. Their amorphous nature was confirmed by XRD studies and was investigated for dielectric properties in the frequency range from 100Hz to 1MHz and temperature range from 300K to 573K. The conductivity was derived from the dielectric spectrum. The frequency exponent, s, dc and ac components of the conductivity were determined. The temperature dependence of conductivity at different frequencies was analyzed using Mott’s small polaron hopping model, and the high temperature activation energy has been estimated and discussed. The variation of conductivity and activation energy with composition revealed a changeover of conduction mechanism from predominantly ionic to electronic regime for mole fractions of CoO between 0.3 and 0.35. This is a new result. Hunt’s model has been employed to analyze frequency dependence of conductivity. Relaxation features of the dielectric properties have been extracted from the analysis of electric moduli with frequency. Activation energy for relaxation mechanism has been determined. Frequency exponent was found to be temperature dependent. Quantum mechanical theory and correlated barrier hopping models were found to be inadequate to explain frequency exponent behavior with temperature.For the first time that borophosphate glasses doped with Li2O and CoO were studied for dielectric properties and ac conductivity as a function of temperature and frequency and the data has been analysed thoroughly. 

scholarly journals Nickel Manganite-Sodium Alginate Nano-Biocomposite for Temperature Sensing

Chemosensors ◽  
2021 ◽  
Vol 9 (9) ◽  
pp. 241
Author(s):  
Milena P. Dojcinovic ◽  
Zorka Z. Vasiljevic ◽  
Janez Kovac ◽  
Nenad B. Tadic ◽  
Maria Vesna Nikolic
Keyword(s):  
Activation Energy ◽  
Sodium Alginate ◽  
Room Temperature ◽  
Small Polaron ◽  
Spinel Phase ◽  
Sol Gel ◽  
Complex Impedance ◽  
Relaxation Frequency ◽  
Polaron Hopping ◽  
Ft Ir

Nanocrystalline nickel manganite (NiMn2O4) powder with a pure cubic spinel phase structure was synthesized via sol-gel combustion and characterized with XRD, FT-IR, XPS and SEM. The powder was mixed with sodium alginate gel to form a nano-biocomposite gel, dried at room temperature to form a thick film and characterized with FT-IR and SEM. DC resistance and AC impedance of sensor test structures obtained by drop casting the nano-biocomposite gel onto test interdigitated PdAg electrodes on an alumina substrate were measured in the temperature range of 20–50 °C at a constant relative humidity (RH) of 50% and at room temperature (25 °C) in the RH range of 40–90%. The material constant obtained from the measured decrease in resistance with temperature was determined to be 4523 K, while the temperature sensitivity at room temperature (25 °C) was −5.09%/K. Analysis of the complex impedance plots showed a dominant influence of grains. The decrease in complex impedance with increase in temperature confirmed the negative temperature coefficient effect. The grain resistance and grain relaxation frequency were determined using an equivalent circuit. The activation energy for conduction was determined as 0.45 eV from the temperature dependence of the grain resistance according to the small polaron hopping model, while the activation energy for relaxation was 0.43 eV determined from the Arrhenius dependence of the grain relaxation frequency on temperature.

Effect of iron chloride on the polaronic conduction in potassium phosphateglasses containing iron oxide

2000 ◽  
Vol 78 (12) ◽  
pp. 1091-1105 ◽  
Author(s):  
Y M Moustafa
Keyword(s):  
Activation Energy ◽  
Electrical Conductivity ◽  
Structural Changes ◽  
Small Polaron ◽  
Iron Chloride ◽  
Polaron Hopping ◽  
Exponential Factor ◽  
Order Of Magnitude ◽  
The Difference ◽  
Fe Ions

DC electrical conductivity measurements of Fe2O3–K2O–P2O5 glasses containing iron chloride have been carried out in the temperature range from room temperature to 360°C. The DC conductivity was analyzed in terms of small polaron hopping theory. The hopping regime between Fe ions was confirmed to be nonadiabatic. The increase in the conductivity was of the same order of magnitude as the change in the pre-exponential factor upon increasing the FeCl3 content. The decrease in the activation energy with increasing FeCl3 content was interpreted in terms of a decrease in the distance between the iron sites. The increase in electrical conductivity was ascribed to the difference in the activation energy. The variation in the conductivity parameters was interpreted in terms of the structural changes that take place upon increasing the FeCl3 content of the glasses. PACS No.72.20Ee

scholarly journals Dielectric and AC Conductivity Studies in PPy-Ag Nanocomposites

2015 ◽  
Vol 2015 ◽  
pp. 1-5 ◽  
Author(s):  
K. Praveenkumar ◽  
T. Sankarappa ◽  
J. S. Ashwajeet ◽  
R. Ramanna
Keyword(s):  
Activation Energy ◽  
Silver Nanoparticles ◽  
Dielectric Properties ◽  
Ac Conductivity ◽  
Conductivity Data ◽  
Chemical Route ◽  
Polaron Hopping ◽  
Dielectric Data ◽  
First Time ◽  
Hopping Model

Polypyrrole and silver nanoparticles have been synthesized at 277 K by chemical route. Nanoparticles of polypyrrole-silver (PPy-Ag) composites were prepared by mixing polypyrrole and silver nanoparticles in different weight percentages. Dielectric properties as a function of temperature in the range from 300 K to 550 K and frequency in the range from 50 Hz to 1 MHz have been measured. Dielectric constant decreased with increase in frequency and temperature. Dielectric loss decreased with increase in frequency and increased with increase in temperature. Using dielectric data AC conductivity has been determined. Conductivity was found to be in the order of 10−3 (Ω−1 m−1) and it increased with increase in temperature. Temperature variation of conductivity data has been analyzed in the light of Mott’s polaron hopping model. Activation energy for conduction has been determined. Activation energy was determined to be in the order of meV and it has increased with increase in frequency and Ag nanoparticles content. This is the first time that PPy-Ag nanocomposites have been investigated for dielectric properties and AC conductivity and data analyzed thoroughly.

Negative Thermal Sensitivity of La1-xSrxFeO3 Films Prepared by Screen-Printing Method

2017 ◽  
Vol 898 ◽  
pp. 1617-1624
Author(s):  
Xin De Zhu ◽  
Yu Zhou ◽  
Sheng Li Li
Keyword(s):  
Activation Energy ◽  
High Performance ◽  
Screen Printing ◽  
Small Polaron ◽  
Thermal Sensitivity ◽  
Negative Temperature ◽  
Electric Transport ◽  
Polaron Hopping ◽  
Screen Printing Method ◽  
Printing Method

The impacts of different Sr content on the phase structure, negative temperature coefficient (NTC) characteristic and conduction mechanism at high temperature of lanthanum strontium ferrite (La1-xSrxFeO3, x=0.1~0.6) (LSFO) films were systematically discussed. The LSFO films were prepared on the alumina substrate by the screen printing method. The results showed that the crystal structure transformed from orthorhombic (x=0.1~0.3) to rhombohedral (x=0.4~0.6). All the samples presented NTC performance. With increasing the Sr content, B values increased to the maximum 3885 K (x=0.4) and then decreased. Non-adiabatic small polaron hopping mechanism was dominant for their electric transport in the temperature range from 450 K to 873 K. The activation energy was calculated between 0.37 eV and 0.57 eV, and the sample La0.7Sr0.3FeO3 showed the minimum value of the activation energy. Therefore the La1-xSrxFeO3 (x=0.3, 0.4, 0.5) films have the potential to be developed into high-performance NTC resistors.

INFLUENCE OF La2O3 ADDITIONS ON CHEMICAL DURABILITY AND DIELECTRIC PROPERTIES OF BOROALUMINOSILICATE GLASSES

2012 ◽  
Vol 19 (06) ◽  
pp. 1250062 ◽  
Author(s):  
X. H. ZHANG ◽  
Y. L. YUE ◽  
H. T. WU
Keyword(s):  
Dielectric Properties ◽  
Chemical Durability ◽  
Tangent Loss ◽  
Frequency Range ◽  
Scanning Calorimetry ◽  
Glass Transition Temperatures ◽  
Weight Losses ◽  
Quenching Method ◽  
Scanning Electron

Boroaluminosilicate glasses containing La2O3 were prepared by the normal quenching method. The glass transition temperatures (Tg) were measured by differential scanning calorimetry (DSC). The structural role of RO was investigated by nuclear magnetic resonance (NMR). Chemical durability was evaluated by weight losses of glass samples after immersion in HC1 solution. High resolution scanning electron microscopy (HR-SEM) was used to examine the surface micrographs of corroded glass samples. The dielectric constant and tangent loss were measured in the frequency range 10–106 Hz. The results revealed that chemical durability and dielectric properties increased with increasing La2O3 content.

Small polaron hopping conduction mechanism in Fe doped LaMnO3

2011 ◽  
Vol 135 (5) ◽  
pp. 054501 ◽  
Author(s):  
Wasi Khan ◽  
Alim H. Naqvi ◽  
Maneesha Gupta ◽  
Shahid Husain ◽  
Ravi Kumar
Keyword(s):  
Conduction Mechanism ◽  
Small Polaron ◽  
Hopping Conduction ◽  
Polaron Hopping ◽  
Small Polaron Hopping

Synthesis and Electrical Transport Property of Sr and Cu-Doped LaFeO3-Based Cathode Material for IT-SOFC

2013 ◽  
Vol 710 ◽  
pp. 33-36
Author(s):  
Jie Zhao ◽  
Jiang Fu ◽  
Yong Fu ◽  
Yong Chang Ma
Keyword(s):  
Cathode Material ◽  
Electrical Transport ◽  
High Performance ◽  
Small Polaron ◽  
Negative Temperature ◽  
Rare Earth Oxide ◽  
Intermediate Temperature ◽  
Charge Balance ◽  
Mixed Conductivity ◽  
Polaron Hopping

In order to accelerate the commercialization of SOFCs technology, the key is the development of high performance cathode materials operated at intermediate temperature. Sr and Cu doped rare earth oxide La1-xSrxFe1-yCu.yO3-δ (x=0.1, 0.3 ; y=0.1, 0.2, denoted as LSFCu-11, LSFCu-31 and LSFCu-32 ) were synthesized by solid state reaction method (SSR). The formation process, phase structure and microstructure of the synthesized samples were characterized using TG/DSC, XRD and SEM. The thermal expansion coefficients (TEC) of the samples were analyzed by thermal dilatometry. The electrical conductivities of the samples were measured with DC four-terminal method from 25 to 950 °C. The results indicate that the samples exhibit a single phase with orthorhombic and hexagonal perovskite structure after sintered at 1200 °C for 4h. The electrical conductivity of the samples increases with temperature up to a maximum value, and then decreases gradually. The small polaron hopping is regarded as the conducting mechanism for synthesized samples at T 550 °C. The negative temperature dependence occurring at higher temperature is due to the creation of oxygen vacancies for charge balance. LSFCu-32 has higher mixed conductivity (> 100 S·cm-1) at intermediate temperature and can meet the demand of cathode material for IT-SOFC. In addition, the average TECs of LSFCu-11, LSFCu-31 and LSFCu-32 are 1.22 × 10-6 K-1 , 1.30 × 10-6 K-1 and 1.34 × 10-6 K-1 respectively.

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