• Lalitha Sirdeshmukh

      Articles written in Bulletin of Materials Science

    • Dielectric properties of Bi4(GeO4)3 and Bi4(SiO4)3

      Lalitha Sirdeshmukh Y R Reddy

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      Dielectric constant, dielectric loss and conductivity of Bi4(GeO4)3 and Bi4(SiO4)3 single crystals have been measured as a function of frequency and in the temperature range from liquid nitrogen temperature to 400° C. The values of the static dielectric constant at room temperature are 16·4 and 13·7 for Bi4(GeO4)3 and Bi4(SiO4)3 respectively. The plots of log (σ) against reciprocal temperature at different frequencies of these crystals merge into a straight line beyond 250°C and the activation energies calculated in this region are found to be 0·95 eV and 1·2 eV for Bi4(GeO4)3 and Bi4(SiO4)3 respectively.

    • Dielectric and polarization studies on some organic materials

      B Jagannadh Lalitha Sirdeshmukh

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      Dielectric constant and dielectric loss (tanδ) of oxamide, thiooxamide, urea, thiourea and some methyl and ethyl derivatives of urea and thiourea have been measured. The deformation polarization for all the materials is calculated from the static dielectric constants. The electronic contribution to molecular polarization has been evaluated theoretically using atomic hybridization components. The atomic polarization is obtained as the difference between the deformation polarization and electronic contribution to the deformation polarization.

    • Dielectric properties of K2Zn2(SO4)3 and (NH4)2 Mg2(SO4)3

      Prameela Devi Lalitha Sirdeshmukh

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      Dielectric constant (ɛ), dielectric loss (tan δ) and conductivity (σ) for K2Zn2(SO4)3 and (NH4)2 Mg2(SO4)3 have been measured over the frequency range 100 Hz — 100 kHz and in temperature range 30°C — 400°C. The values of static dielectric constant at room temperature are 7.67 and 4.80 for K2Zn2(SO4)3 and (NH4)2 Mg2(SO4)3 respectively. The plots of log σ against reciprocal temperature at different frequencies of these samples merge into a straight line beyond 250°C and the activation energies calculated in this region are found to be 0.67 eV and 1.98 eV for K2Zn2(SO4)3 and (NH4)2 Mg2(SO4)3 respectively.

    • Characterization and dielectric properties of almandine-pyrope garnet

      K Krishna Kumar V Balaram Lalitha Sirdeshmukh

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      Some garnets collected from the Kothagudem area of Khammam district in Andhra Pradesh were characterized by chemical analysis. The results show the garnets to be of almandine (Fe+23 Al2Si3O12) pyrope (Mg3Al2Si3O12) group. Dielectric constant (ɛ) and dielectric loss (tanδ) were measured as a function of frequency and temperature in the frequency range of 100 Hz to 100 KHz and from room temperature to 400°C. The room temperature measurement was extended to 10 MHz, AC conductivity was calculated from the data on ε and tan δ. DC conductivity was also measured.

    • Dielectric properties and electrical conduction in yttrium iron garnet (YIG)

      Lalitha Sirdeshmukh K Krishna Kumar S Bal Laxman A Rama Krishna G Sathaiah

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      The dielectric properties (dielectric constant and loss) of a single crystal of yttrium iron garnet (Y3Fe5O12) were measured in the temperature range 77–725 K and in the frequency range 100 Hz-1 MHz. AC conductivity was derived from dielectric constant and loss. DC conductivity was measured in the temperature range 30–725 K. Thermoelectric power (TEP) was measured from 77–800 K. On the basis of the results, conduction in this garnet is interpreted as due to small polarons. The nature of conduction at different temperature ranges is discussed in the light of existing reports on defect formation.

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