P. K. Mehta

Structure Correlated Enhancement in Dielectric and Electrical Properties of Strontium Based Niobates

Structural, dielectric and transport properties of single phase Sr(B′1/3Nb2/3)O3 where (B′ = Mg2+, Co2+, Cu2+) relaxor ferroelectric compounds synthesized by standard solid state reaction technique, are reported here. All the samples exhibit strong correlation between structure, dielectric and transport behavior. In this system significant Jahn-Teller distortion, induces enhancement in dielectric properties. Further, weak Jahn-Teller distortion due to unevenly occupied t2g levels in Co2+ produces intermediate rise in ϵ′ as well as inbuilt flexibility to conduction electron movement enhances dielectric loss (tanδ). On the other hand, strong Jahn-Teller effects in Cu2+ substituted compound, due to unevenly occupied eg levels, results in large enhancement in ϵ′ and frequency exponent ‘s’. This is accompanied by significant fall in dielectric loss due to localization of conduction electrons within oxygen octahedron.

Dielectric behavior of nanostructured Y0.95Ca0.05MnO3: Role of sintering temperature

Nanostructured Y0.95Ca0.05MnO3 (YCMO) samples have been synthesized using cost effective sol-gel method. The samples were sintered at various temperatures ranging between 700 – 1100°C (ST). XRD studies reveal the single phasic nature of the samples. Frequency dependent dielectric (e) and modulus (M) behaviors of YCMO samples imply the increase in e and activation energy (Ea) with ST which has been discussed in the light of oxygen vacancies and grain morphology.

Dielectric behaviour of PLD grown BiFeO3 multiferroic thin films

We report the dielectric behaviour of BiFeO3 thin films deposited on Nb doped STO substrate using Pulsed Laser Deposition technique. Frequency dependent real and imaginary dielectric permittivity in the temperature range 20°C to 350°C show good dielectric behaviour exhibited by 100 and 200 nm films.

Structure, microstructure and dielectric studies of PVA/Sr(Co1/3Nb2/3)O3 polymer composites

Polymer-Ceramic composite films of Polyvinyl alcohol (PVA) and Sr(Co1/3Nb2/3)O3 (SCN) as filler, were prepared by solution casting technique. The structure and microstructure of the samples has been characterized using X-ray diffraction, infrared spectroscopy (Fourier transformed infrared spectroscopy) and Scanning electron microscopy (SEM). Thermal properties of the samples are studied by means of Differential Scanning Calorimetry (DSC) revealed that the glass transition temperature increases for the composites [PVA + 10% SCN (Tg = 109°C)] compared to pure PVA (Tg = 97°C) samples. The dielectric characterization has been studied by means of impedance gain-phase analyzer. It is concluded that addition of 50% SCN lead to significant advantage on the dielectric properties of Polyvinyl alcohol polymers. Observed changes in the dielectric dispersion at high temperatures are essentially linked to the glass transition temperature (Tg) rather than due to lattice based dielectric dispersion.

Structure, I-V characteristics and optical studies of delafossite CuFeO2 and CuFe0.96Ti0.03V0.01O2 prepared under high vacuum

Most opted methods for the preparation of CuFeO2 involve chemical route or solid state synthesis in the presence of inert gases like Argon and Nitrogen for the purpose of maintaining Cu in 1+ state. Here CuFeO2 (CFO) and doped CuFe0.96Ti0.03V0.01O2 (CFTO) samples are prepared under newly developed simple synthesis process involving high vacuum sealed annealing. Delafossite phase is confirmed by means of XRD measurements and its Rietveld refinement. The room temperature I-V measurements performed with different top contacts on the pallets show that CFO samples having ‘Ag’ and ‘In’ contacts shows better semiconducting properties compared to ‘Cu’ and ‘Al’ contacts owing to Schottky effect. On the other hand CFTO show good semiconducting nature only with ‘Ag’ contacts. Bulk samples of CFO exhibiting better semiconducting nature compared to CFTO is mainly due to electron doping (substitution of Ti4+ at the Fe3+ site) induced enhancement in recombination in a system having predominantly holes as carries. Effect...

Replacement of Mg2+ at the B′-Site by Transition Elements in Ba(B′0.33Nb0.67)O3 Compound

Complex perovskite materials are considered as a boon in this revolutionary era of microelectronic and telecommunications. In this paper we have presented the effect of replacement of Mg2+ by divalent ions (Co2+, Cu2+) in Ba(Mg0.33Nb0.67)O3. We have studied the impact of replacement of Mg2+ by transition elements on structural, micro-structure, dielectric properties. It is observed that on replacing the Mg2+ by Co2+ and Cu2+ the structural symmetry shifts from hexagonal (BMN, BCoN) to tetragonal (BCuN). Further, the morphological study reveals agglomerated grain formation for BCoN and a spikes/elongated type of structure in BCuN samples. The frequency dependence of dielectric studies shows the polar behavior of BMN. On the other hand replacing Mg by cobalt or copper (having 3d7 and 3d9 configuration, respectively), leads to Jahn-Teller distortions introduced in the samples. The poly-dispersive natures of the samples were inferred through fitting the curves with Cole–Cole equation.

Structural and electrical studies of Ba(Fe0.25Gd0.25Nb0.5)O3

Structure and Impedance studies of Ba(Fe0.25Gd0.25Nb0.5)O3 (BFGN) are reported here. Two distinct Cubic phases co-existing in the BFGN compound related to two end compositions. The grain resistance (Rg), relaxation time (τ) and grain capacitance (Cg) suggests NTCR-PTCR transition around 378K and a possibility of phase transition around 558K. Gradual change in slope of the graph as a function of higher temperatures and the calculated activation energy suggests systematic changes in the mechanism of conduction with temperature.

Structure and Dielectric Study of Ca(Co1/3Nb2/3)O3 [CCoN]

The complex perovskite oxide Ca(Co1/3Nb2/3)O3 [CCoN] is synthesized by standard solid state reaction technique. Its structural and dielectric properties are reported here. The XRD pattern reveals that CCoN has monoclinic symmetry with space group P21/c. The dielectric study carried out from room temperature to 350 deg with frequency ranging from 50 hz–3.2 MHz found that dielectric constant is higher in CCoN compared to Ca3MgNb2O9 [CMN] along with low Transition temperature (Tm). The introduced weak John‐Taylor effect on replacement of Mg2+ by Co2+ has detrimental effect on its dielectric loses. This is mainly due to induced unwarranted mobility of electron in mixed bonds and Inter grain effect. If these charge mobility can be curbed while inducing structural distortions significantly useful dielectric properties can be achieved.

Structural and Impedance Studies of Ba(Mn0.5Nb0.5)O3

Structure and Impedance studies of single phase Ba(Mn0.5Nb0.5)O3 (BMN) are reported here. The equivalent circuit modeling of complex impedance data fits with parallel combination of a capacitor and resistor. The activation energy values are similar for impedance (conductance) and relaxation suggesting that, the mechanism involved is same. The substitution of Mn at the B‐site do not help in reducing dielectric loses due to oxygen vacancies and/or doping of holes.