• G Prasad

      Articles written in Bulletin of Materials Science

    • Studies on electrical properties of SrBi4Ti4−3xFe4xO15

      N Venkat Ramulu G Prasad S V Suryanarayana T Bhima Sankaram

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      The system SrBi4Ti4−3xFe4xO15 belonging to bismuth layer structured ferroelectric (BLSF) materials withx = 0, 0.1 and 0.2 has been prepared through solid-state double sintering method. Increase of iron content in SrBi4Ti4O15 resulted in densification of the samples. The normal puckering observed in the sample has been found to decrease and the lattice distortion increased. Dielectric measurements indicate the ferroelectric transition temperature of the samples to be 530°C, 560°C and 606°C. The increase of transition temperature with increasing iron content is correlated with lattice distortion. Conductivity measurements show two slopes and the activation energies have been found to increase with the iron content. Impedance spectroscopy measurements confirm insulating behaviour at lower temperatures. With increase in temperature the samples become conducting and show relaxational effects. The Cole-Cole plots at higher temperatures are found to be semicircles. The relaxation times decrease with the increase of iron content.

    • Synthesis, impedance and dielectric properties of LaBi5Fe2Ti3O18

      N V Prasad G Prasad T Bhimasankaram S V Suryanarayana G S Kumar

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      The compound, LaBi5Fe2Ti3O18, is a five-layered material belonging to the family of bismuth layered structure ferroelectromagnetics. D.c. and a.c. conductivity measurements were performed on the samples. Dielectric measurements were also performed on these samples. Combined impedance and modulus plots were used as tools to analyse the sample behaviour as a function of frequency. Cole–Cole plots showed non-Debye relaxation.

    • Effect of lanthanum doping on electrical and electromechanical properties of Ba1–𝑥La𝑥TiO3

      M Aparna T Bhimasankaram S V Suryanarayana G Prasad G S Kumar

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      The effect of lanthanum doping is studied on ferroelectric properties of Ba1–𝑥La𝑥TiO3 with 𝑥 = 0.0005, 0.001, 0.003 prepared through solid state sintering route. Dielectric and impedance spectroscopic studies have been carried out. The tetragonal distortion of the unit cell decreased and ferroelectric transition temperature, 𝑇c increased with the increase of lanthanum content.

      Combined impedance and admittance spectroscopy was used to analyse impedance data. The electromechanical parameters were calculated from the resonant and anti-resonant frequencies from vector admittance plots. The electromechanical coefficients for Ba1–𝑥La𝑥TiO3 with 𝑥 = 0.003 were found to be much larger than that of pure barium titanate.

    • Electrical conduction in (Na0.125Bi0.125Ba0.65Ca0.1)(Nd0.065Ti0.87Nb0.065)O3 ceramic

      Syed Mahboob G Prasad G S Kumar

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      Polycrystalline ceramic samples of sodium bismuth titanate with simultaneous doping at A and B sites have been studied for the influence of these dopants on the electrical conduction mechanism. A.C. conductivity measurements were done on the prepared sample in a wide range of frequency and temperature. These studies revealed that the conduction in the sample arises due to hopping of bound charges. Four-term power law is used to characterize the frequency dependence of a.c. conductivity. From the temperature dependence of the exponents, the a.c. conduction in the samples is explained.

    • Impedance and a.c. conductivity studies on Ba(Nd0.2Ti0.6Nb0.2)O3 ceramic prepared through conventional and microwave sintering route

      Syed Mahboob G Prasad G S Kumar

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      Electrical conduction studies on Ba(Nd0.2Ti0.6Nb0.2)O3 ceramic samples prepared through conventional and microwave sintering route are presented in this paper. D.C. and a.c. conductivities of these samples as a function of temperature from 300–900 K have been studied. Two types of conduction processes are evident from the frequency dependant conductivity plots, i.e. low-frequency conduction due to short-range hopping and high-frequency conduction due to the localized relaxation (reorientational) hopping mechanism. Grain and grain boundary contributions to the conductivity in these samples are obtained from impedance/admittance measurements via equivalent circuit modelling.

    • Preparation, characterization and conductivity studies of Li3–2𝑥Al2–𝑥Sb𝑥(PO4)3

      N Anantharamulu G Prasad M Vithal

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      New NASICON type materials of composition, Li3–2𝑥Al2–𝑥Sb𝑥(PO4)3 (𝑥 = 0.6 to 1.4), have been prepared and characterized by powder XRD and IR. D.C. conductivities were measured in the temperature range 300–573 K by a two-probe method. Impedance studies were carried out in the frequency region 102–106 Hz as a function of temperature (300–573 K). An Arrhenius behaviour is observed for all compositions by d.c. conductivity and the Cole–Cole plots obtained from impedance data do not show any spikes on the lower frequency side indicating negligible electrode effects. A maximum conductivity of 4.5 × 10-6 S cm-1 at 573 K was obtained for 𝑥 = 0.8 of the Li3–2𝑥Al2–𝑥Sb𝑥(PO4)3 system.

    • Characterization of piezoelectric polymer composites for MEMS devices

      C V Madhusudhana Rao G Prasad

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      Composite piezoelectric ceramics are important materials for transducer applications in medical diagnostic devices and MEMS devices. In micrometer scale the material properties of piezopolymers or piezoceramics do not coincide with that of bulk materials. The present work is aimed at simulating the material properties of piezoceramics and piezo-polymer composite thin films in the micrometer scale and then to determine the piezo-composite material properties. Piezoceramics have very high electromechanical coupling coefficient (𝑘). But they have very high acoustic impedance and they are very brittle especially when thin films are fabricated. Piezopolymer like PVDF has low acoustic impedance and can be fabricated into thin films but it has very low 𝑘 value and high dielectric losses. The combination of piezoceramics and piezopolymers form the piezocomposites, which have suitable material properties for transducer applications. The composites can have different connectivities. For 2–2 composite, we can select two layers or a stack of PZT and PVDF layers. It is intended to determine the material properties both analytically and by simulation using computer simulation ANSYS software which implements finite element method (FEM). Although the simulation process presents approximate results, it can be verified from the large available experimental data from the literature with the simulated data.

    • Effect of HIPing on conductivity and impedance measurements of DyBi5Fe2Ti3O18 ceramics

      N V Prasad G Prasad Mahendra Kumar S V Suryanarayana T Bhimasankaram G S Kumar

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      X-ray diffraction, a.c. impedance and conductivity (a.c. and d.c.) have been used to characterize DyBi5Fe2Ti3O18. Samples were prepared by solid state double sintering method. A few samples were also subjected to hot isostatic pressing (HIP) at 800°C for 2 h at 100 MPa pressure. The data on XRD, impedance and conductivity of two sets of samples are compared to understand study of effect of HIPing on the properties of DyBi5Fe2Ti3O18

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