• G S Kumar

      Articles written in Bulletin of Materials Science

    • Studies on electrical conduction in Bi4SrTi4O15

      A R James G S Kumar T Bhimasankaram S V Suryanarayana

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      The ferroelectric Bi4SrTi4O15 has been synthesized and a study of the electrical (AC) conductivity was made on both poled and unpoled samples in the frequency range from 100 Hz to 1 MHz and from room temperature to 550°C. In the case of unpoled samples the activation energy was found to be 0·54 eV and subsequent to poling it was lowered to 0·39 eV indicating an increased conductivity after poling. Further the conductivity increased with increasing frequency and temperature. DC conductivity measurements were also carried out. Dielectric measurements indicate a peak in the dielectric constant at 530°C.

    • Dielectric measurements in vanadium doped barium titanate

      A Hanumaiah T Bhimasankaram S V Suryanarayana G S Kumar

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      Ceramic samples of Li0·1Ba0·95(VxTi1−x)O3, wherex=0 to 0·2 were prepared by solid state reaction method. The samples were characterized by XRD. The dielectric measurements have been carried out on the sintered disks as a function of the frequency (100 Hz-1 MHz) and temperature (300–420 K). The variation of dielectric constant with temperature indicates a diffuse phase transition in all the samples studied.

    • Dielectric properties of cobalt doped cadmium oxalate crystals

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

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      CoxCd1−xC2O44H2O crystals grown by gel technique are characterized for dielectric properties by optical absorption measurements. Loss curve shows a relaxation peak at 500 KHz corresponding to a relaxation time of 0·3 µs. Cole-Cole diagrams give exponent of universal power law to be equal to 0·22. Optical absorption shows peaks due to Co+2 ion and water of hydration. An attempt is made to understand the results.

    • An experimental setup for dynamic measurement of magnetoelectric effect

      M Mahesh Kumar A Srinivas S V Suryanarayana G S Kumar T Bhimasankaram

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      An experimental setup is developed for the measurement of dynamic magnetoelectric effect (ME) in polycrystalline materials, using a time varying DC magnetic field on which an AC magnetic field is superimposed. The experimental data on ME on Bi5FeTi3O15 and a solid solution of (90%)BiFeO3-(10%)BaTiO3 are obtained using this setup. The linear and higher order ME coefficients can be evaluated from the output voltage. The temperature variation of ME data gives additional information corroborating with the data on magnetization.

    • Pyroelectricity in calcium substituted sodium bismuth titanate layer structured ferroelectric ceramics

      P S Rama Sastry G S Kumar T Bhimasankaram G Prasad

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      Pyroelectric properties of bismuth layer structured calcium substituted sodium bismuth titanate (Na0·5Bi0·5)1−xCaxBi4Ti4O15 withx=0 (NBT) andx=0·1 (0·1 NCBT) were studied by measuring the current under short circuit condition. Spontaneous polarization and figures of merit were evaluated from the measured values of pyroelectric coefficients, dielectric constant and loss tangent. The pyroelectric properties were studied in poled and short circuit condition from 30°C to 700°C. The results obtained were discussed in the light of dielectric and conductivity properties of the samples.

    • Electrical properties of SiO2-doped sodium metavanadate sintered discs

      B V Bahuguna Saradhi G Prasad G S Kumar T Bhimasankaram

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      Impedance of sintered discs of 0·1, 0·25, 0·4 mol% of sodium metavanadate was measured in the frequency range 10 kHz-1 MHz and in the temperature region from room temperature (=30°C) to 450°C. AC conductivity was calculated from the data. DC conductivity was measured in the temperature range 150–450°C. Debye type of relaxation effects were observed in the dielectric loss. The activation energy of the dipoles involved in relaxation was estimated. The activation energy for AC conduction in the temperature above 380°C was calculated. These values are larger than the activation energy of pure sodium metavanadate sample. The relaxation phenomenon observed is explained.

    • Enhanced dielectric and piezoelectric properties in microwave sintered (Ba$_{0.997}$Nd$_{0.003}$)TiO$_3$ ceramic when compared to conventional sintered ceramics

      S MAHBOOB RIZWANA G PRASAD G S KUMAR

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      Dielectric, conductivity and piezoelectric properties have been studied on (Ba$_{0.997}$Nd$_{0.003}$)TiO$_3$ ceramic samples prepared through microwave sintered (MWS) and conventional sintered (CS) routes and the results are presented in this paper. The room temperature dielectric constant at 10 kHz for CS and MWS samples are 1245 and 5250 respectively. Roomtemperature dielectric constant in MWS sample was almost four times higher than that of the CS sample. The value of $K_t$ is found to be 0.998 and 0.997; whereas the value of $d_{33}$ is 7.72 nm V$^{−1}$ (573 K) and 444.66 nm V$^{−1}$ (573 K) for CS and MWS samples, respectively. In the present study almost 57 times enhancement in piezoelectric charge constant ($d_{33}$) isobserved for the MWS Ba$_{0.997}$Nd$_{0.003}$TiO$_3$ ceramic when compared to the CS ceramic.

    • Simulation of dielectric and resonance and anti-resonance data using modified Lorentz equation ($T$ and $\omega$ simultaneously) of relaxor ferroelectric and piezoelectric ceramics

      S MAHBOOB RIZWANA G PRASAD G S KUMAR

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      Dielectric data of new [Ba(Nd$_x$ Ti$1−2xNbx )O$_3$]$_{0.30}$[Na$_{0.5}$Bi$_{0.5}$TiO$_3$]$_{0.70} ($x = 0.075$) relaxor ceramic was modelled using a new modified Lorentz equation ($T$ and $\omega$ simultaneously) as proposed by us. The activation energy forthermally activated orientation of dipoles and relaxation times were estimated. Dielectric resonance and anti-resonance data as a function of temperature and angular frequency of other piezoelectric compound [Ba(Nd$_{0.1}$Ti$_{0.8}$Nb$_{0.1}$)O$_3$]$_{0.35}$ [(Na$_{0.5}$Bi$_{0.5}$)TiO$_{3}$]$_{0.65}$ was also modelled using the modified Lorentz equation as proposed by us. It is shown that using thisequation, it is possible to obtain the polarizability, piezoelectric charge constant, piezoelectric voltage constant and activationenergy for resonance and anti-resonance.

    • Dielectric studies on Sm-modified two-layered BLSF ceramics

      MD ABDUL BASHEER G PRASAD G S KUMAR N V PRASAD

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      Sm$_x$Bi$_{3−x}$TiNbO$_9$ (SBTN) with $x = 0$, 0.2, 0.4, 0.6, 0.8 and 1.0, a novel type of ceramic was prepared by a conventional solid-state reaction method. X-ray diffraction patterns confirm the formation of a single-phase, and lattice parameters were calculated based on the parent compound Bi$_3$TiNbO$_9$ (BTN). Well-defined grains were seen in the scanningelectron microscopy pictures. A kink observed near 400$^{\circ}$C for all the samples in the dielectric plot as well as in the stretched exponential parameter ($\beta$) vs. temperature plot reveals the dielectric relaxation of the samples. The tolerance factor ($t$) was found to increase with increase in the size of the A-site (Bi-site) modified ion (Sm). Impedance and modulus spectroscopicstudies were conducted to understand the plausible reason for the dielectric relaxation. The relaxation was found to be well-fit with Arrhenius equation. SBTN samples showed lower dielectric loss compared to BTN. The remnant polarization, obtained from experimental, was found to be less than that of theoretically calculated polarization, using Shimakawa’s formula. The proposed defect mechanism was interpreted using FTIR and Raman spectroscopic studies.

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