Studies on dielectric behaviour of an oxygen ion conducting ceramic – CaMnO₃₋δ

191-195An oxygen deficient ceramic oxide having perovskite structure has been prepared by the conventional solid state reaction method. X–ray diffraction studies have confirmed the sample formation in single phase polycrystalline form. The scanning electron micrographs have confirmed polycrystalline texture of the material alongwith indications of porous microstructure. The temperature dependence of the dielectric properties (permittivity/loss tangent) in the sub-ambient and ambient temperature region suggests the possibility of a strong dipolar ordering. The appearance of maxima in both the permittivity and loss factor pattern at a very close temperature range (Ɛmax~1879 at 29oC, tan δmax~9.7 at 35oC at a common frequency of 10 kHz) supports the presence of dipolar interaction in CaMnO3-. It has been attributed to a strong interaction of the oxide ion-oxygen vacancy pair in the crystal lattice of an oxygen deficient perovskite (CaMnO₃₋) that in turn reduces the net mobility of oxygen ion at lower temperatures and imparts it a higher dielectric permittivity as well as high loss factor close to room temperature. A decrease in the permittivity and monotonous increase in loss factor with rise in temperature above the ambient value suggest a thermally activated weakening of the dipolar ordering in the system. In view of a very high value of loss factor at and above room temperature, it would be premature to conclude the existence of ferroelectric ordering in the material system just by the presence of a peak in both the permittivity and loss factor pattern

Studies on dielectric properties of a conducting polymer nanocomposite system

347-351Dielectric analysis of ion conducting solid polymer nanocomposite has been investigated as a function of temperature and frequency. Effect of clay concentration in changing the dielectric relaxation behaviour of polymer salt complex film is clearly visible, observed in terms of changes in polymer chain relaxation and dipolar contribution due to ion pairs. An enhancement in relative permittivity by 2 orders of magnitude has been recorded at room temperature in nanocomposite films controlled predominantly by clay concentration. Almost similar behaviour has been observed after crystalline to amorphous phase transition temperature at T ≥70°C for both polymer salt complex and nanocomposite films irrespective of clay concentration. A lowering of relaxation time, attributed to relaxing dipoles, with clay concentration suggests faster ion dynamics in nanocomposite films

Polyaniline–Carbon Nanofiber Composite by a Chemical Grafting Approach and Its Supercapacitor Application

Unlike conventional routes by van der Waals forces, a facile and novel approach using covalent bonding is established in the present work to synthesize polyaniline (PANI)-grafted carbon nanofiber (CNF) composites as promising supercapacitors. For this purpose, toluenediisocyanate was initially functionalized to carboxylated CNF via amidation followed by reaction with excess aniline to form a urea derivative and residual aniline, which was subsequently polymerized and grafted with a urea derivative. Amidation of CNF (TCNF) and, consequently, the grafting of PANI on TCNF were verified by IR, Raman, ¹H NMR, X-ray photoelectron, and UV–visible spectroscopic methods, X-ray diffraction, and thermogravimetric analysis. Morphological analysis revealed uniform distribution of PANI on the surface of TCNF, indicating strong interaction between them. Electrochemical tests of the composite containing 6 wt % TCNF demonstrated efficient capacitance of ∼557 F g^–1 with a capacity retention of 86% of its initial capacitance even after 2000 charge–discharge cycles at a current density of 0.3 A g^–1, suggesting its superiority compared to the materials formed by van der Waals forces. The remarkably enhanced electrochemical performance showed the importance of the phenyl-substituted amide linkage in the development of a π-conjugated structure, which facilitated charge transfer and, consequently, made it attractive for efficient supercapacitors

Low temperature ferroelectric behaviour of PVDF based composites

126-132A polymer nanocomposite based on poly (vinylidenefluoride) (PVDF) and unmodified montmorillonite clay has been studied for structural phase transformation, ferroelectric and piezoelectric properties. The effect of clay concentration in modifying PVDF crystalline phase structure has been substantial leading to α→β phase transformation in PVDF. This aspect has been confirmed through X-ray diffraction and infrared spectroscopy data. The effect of structural change has been clearly observed in inducing dipolar characteristics in PVDF matrix supported by changes in dielectric permittivity variation as a function of temperature and frequency. A close resemblance in the permittivity and loss tangent peak position as a function of temperature has been correlated with dipolar ordering in PVDF matrix induced by clay. However, this ordering depends on clay concentration. The clay induced dipolar ordering is also supported by piezoelectric coefficient measured for various compositions of clay

Dielectric anomaly and magnetic order in Ba(Mn₀․₅Nb₀․₅)O₃

187-190The polycrystalline barium manganese niobiate Ba(Mn₀․₅Nb₀․₅)O₃ has been prepared by a solid state reaction technique. The formation of single phase compound is confirmed by an X-ray diffraction analysis. The surface morphology examined through scanning electron microscope (SEM) confirmed polycrystalline texture of the material. Detailed studies of dielectric properties are carried out at different temperatures (23-350°C) and in a wide frequency range of 10²-10⁶ Hz . A dielectric anomaly with transition temperature at 283°C is observed. The real and imaginary part of permittivity (Ɛ' and Ɛ") were found to be strongly frequency and temperature dependent. The variation of ac conductivity with inverse of absolute temperature is found to obey Arrhenius law. The activation energy in lower temperature range was found to be 0.19 eV and its value in higher temperature range was 0.87 eV. Magnetization as a function of temperature from 2 K to 300 K is measured in different fields in both zero-field cooled (ZFC) and field-cooled (FC) mode. An antiferromagnetic transition is observed at 7 K. Non-linear M-H and a finite opening in the hysteresis loop at 2 K substantiate the presence of ferromagnetic component in the antiferromagnetic matrix

<span style="font-size:14.0pt;line-height: 115%;font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman"; color:black;mso-ansi-language:EN-IN;mso-fareast-language:EN-IN;mso-bidi-language: HI" lang="EN-IN">Polyethylene oxide based sodium ion conducting composite polymer electrolytes dispersed with <span style="font-size:14.0pt; line-height:115%;font-family:"Times New Roman";mso-fareast-font-family:Fd1177103-Identity-H; color:black;mso-ansi-language:EN-IN;mso-fareast-language:EN-IN;mso-bidi-language: HI" lang="EN-IN">N<span style="font-size:14.0pt;line-height:115%; font-family:"Times New Roman";mso-fareast-font-family:"Times New Roman"; color:black;mso-ansi-language:EN-IN;mso-fareast-language:EN-IN;mso-bidi-language: HI" lang="EN-IN">a₂SiO₃</span></span></span>

302-305<span style="font-size:14.0pt;line-height: 115%;font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" color:black;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">A composite polymer electrolyte based on polyethylene oxide (PEO): NaI system dispersed with sodium metasilicate (Na2SiO3) has been reported. The structural, thermal and electrical behaviour of the materials have been characterised using optical microscopy, X-ray diffraction, differential scanning calorimetry and impedance spectroscopy. A maximum electrical conductivity of  ~10-6 S.cm-1 at 45°C and 1.2 × 10-3 S.cm -1 at 100°C has been achieved with the dispersion of the adduct, <span style="font-size:14.0pt; line-height:115%;font-family:" times="" new="" roman";mso-fareast-font-family:fd1177103-identity-h;="" color:black;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">N<span style="font-size:14.0pt;line-height:115%; font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" color:black;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">a2SiO3.<span style="font-size:14.0pt; line-height:115%;font-family:" times="" new="" roman";mso-fareast-font-family:fd1177110-identity-h;="" color:black;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN"> The <span style="font-size:14.0pt;line-height:115%; font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" color:black;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">temperature dependence of the conductivity follows an Arrhenius type plots before and after the melting <span style="font-size:14.0pt; line-height:115%;font-family:" times="" new="" roman";mso-fareast-font-family:fd1177110-identity-h;="" color:black;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">temperature (Tm) of PEO in the composite materials.</span