Suman Rani

Study of optical band gap and FTIR spectroscopy of Li2O.Bi2O3.P2O5 glasses.

Glasses having composition (25+x)Li(2)O.(65-x)P(2)O(5).10Bi(2)O(3) (0< or =x< or =25 mol%) were prepared by normal melt quenching technique. The optical absorption spectra of the polished samples were recorded in spectral range from 200 to 3300 nm at room temperature. The optical absorption edge (lambda(cutoff)), optical band gap (E(g)) and Urbach energy (DeltaE) were determined from the absorption spectra. Variation in these optical parameters has been associated with the structural changes occurring in these glasses with increase in Li(2)O:P(2)O(5) ratio. Variation in density (D), molar volume (V(M)) and glass transition temperature (T(g)) has also been correlated with structural changes in the glass samples. The FTIR spectra have been recorded in the spectral range from 400 to 1400 cm(-1). The FTIR spectra show the rapid depolymerization of phosphate chains with increase in Li(2)O content and P-O-Bi bonds are formed.

Structural and dielectric properties of Ca0.95 Nd0.05Cu3Ti3.95Zr0.05O12 ceramic

ABSTRACT The unique dielectric properties of CaCu3Ti4O12 (CCTO) are a promising feature for capacitor applications. Polycrystalline Ca0.95Nd0.05Cu3Ti3.95Zr0.05O12 ceramic was synthesized via conventional solid state method. XRD and Rietveld studies confirmed that crystal structure is cubic with space group Im3. Microstructural study by scanning electron microscopy (SEM) suggests that the compound has some abnormal grains embedded with small grains depict inhomogeneous microstructure. The dielectric properties were analyzed in frequency range from 100 Hz to 5 MHz at different temperatures. A giant dielectric constant (∼19,426) with minimal loss tangent (∼0.067 at 1 KHz) at room temperature is achieved in studied composition.

Study of Structure and Li+ Ions Dynamics in Presence of Fe2O3 in Bi2O3∙B2O3 Glasses

Glasses having composition xLi2O∙(30-x)Fe2O3∙20Bi2O3∙50B2O3 (0 ≤ x ≤ 30, in mol%) have been prepared using normal melt-quench technique. The variation in density and molar volume with composition has been investigated in terms of the structural modification that takes place in the glass matrix on decreasing Fe2O3. Infrared spectra of these glasses were recorded over continuous spectral range (400-4000 cm-1) in an attempt to study their structure systematically. IR spectra show that with increase in Li2O/Fe2O3 ratio there is formation of more structural units (e.g. [FeO4/2]-Li+) in the glass network. Bi3+ cations are present as [BiO6] octahedral units and acts as modifier in this glass system. Further, the effect of transition metal ions (iron) on the dynamics of lithium bismuth borate glasses has been studied in the frequency range of 20 Hz - 1 MHz and in the temperature range 240 – 350 °C using impedance spectroscopy. Possible conduction mechanisms are discussed. Various AC and DC electrical and dielectric parameters have been calculated and analyzed. The results show that the contribution of electronic conduction towards conductivity decreases with decreasing iron concentration, which is understood to be due to hopping of electrons from Fe2+→Fe3+. The frequency dependent conductivity has been studied using both conductivity and modulus formalism. The absence of maximum observed in dielectric permittivity in the temperature and frequency range studied, indicate the non-ferroelectric behavior of the glasses.

Structural investigation and giant dielectric response of CaCu 3 Ti 4 O 12 ceramic by Nd/Zr co-doping for energy storage applications

High performance dielectric materials are highly required for practical application for energy storage technologies. In this work, high-k pristine and modified calcium copper titanate having nominal formula Ca0.95Nd0.05Cu3Ti4−xZrxO12 (xu2009=u20090.01, 0.03 & 0.10) were synthesized and characterized for structural and dielectric properties. Single phase formation of the synthesized compositions was confirmed by X-ray diffraction patterns and further analysed using Rietveld refinement technique. Phase purity of the synthesized ceramics was further confirmed by Energy-dispersive X-ray Spectroscopy (EDX) analysis. SEM images demonstrated that grain size of the modified CCTO ceramics was controlled by Zr4+ ions due to solute drag effect. Impedance spectroscopy was employed to understand the grain, grain boundaries and electrode contribution to the dielectric response. Nyquist plots were fitted with a 2R-CPE model which confirms the non-ideality of the system. Substitution of specific concentration of Nd and Zr improved the dielectric properties of high dielectric permittivity (ε′ ~u200916,902) and minimal tanδ (≤u20090.10) over a wide frequency range. The giant ε′ of the investigated system was attributed to internal barrier layer capacitance (IBLC) effect and reduced tanδ accredited to enhanced grain boundaries resistance due to substitution of Zr4+ ions at Ti4+ site.

Effect of microwave-assisted sintering on dielectric properties of CaCu3Ti4O12 ceramic

In this present work, CaCu3Ti4O12 (CCTO) was synthesized by conventional solid-state reaction technique. The synthesis process was carried out in two phases; by conventional process (calcination and sintering at 1080°C for 10 hours) and phase II involves the micro assisted pre sintering of conventionally calcined CCTO for very short soaking time of 30u2005min at 1080°C in a microwave furnace followed by sintering at 1080°C for 10 hours in conventional furnace. X-ray diffraction (XRD) patterns confirmed the formation of single phase ceramic. Dielectric properties were studied over the frequency range from 50Hz -5MHz at temperatures (273K-343K). It was observed that pre- microwave sintering enhance the dielectric constant values from 10900 to 11893 and respectively reduces the dielectric loss values from 0.49 to 0.34 at room temperature(1u2005KHz). CCTO ceramics which are found desirable for many technological applications. The effect is more pronounced at low frequencies of applied electric field.

Effect of lithium on thermal and structural properties of zinc vanadate tellurite glass

Glasses having composition 60TeO2-15V2O5-(25-x) ZnO-xLi2O where x= 0, 5, 10u2005mol% were prepared by standard melt quench technique. The glass transition temperature is measured by DSC technique using TA instrument and found to decrease with increase in Li2O signifies that glass formation tendency, thermal stability and compactness of glass structure decreases. The deconvolution of FTIR spectra evidenced the existence of TeO4, TeO3 and TeO6 structural units in glass network and vanadium exists as VO4 and VO5 structural units.

Effect of temperature on structure, dielectric and ferroelectric properties of modified BaZrTiO3 ceramic

BaZr0.045(Mn0.03Ti0.97)0.955O3(BZMT) ceramic was prepared via mixed-oxide solid state reaction method. XRD technique confirmed formation of single phase crystalline material. Rietveld refinement of XRD data revealed that the material has tetragonal phase with space group P4mm. The scanning electron microscope (SEM) investigation shows that grains are dense and irregular. The dielectric properties were study as a function of frequency and temperature. The relaxation mechanism was found thermally activated with activation energy 1.21eV and follows Arrhenius law. Modified ceramic showed ferroelectric properties with a high remnant polarization, saturation polarization and coercive field and Pr/Ps ratio.