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1

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Photoacoustic spectroscopic estimation of optical absorption and thermal diffusivity of amorphous Ge15AsxSe85−x (1996)

Ghosh, A. K. ; Chaudhuri, B. K.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 80 (1996), S. 5292-5296

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Photoacoustic spectroscopy (PAS) has been applied to measure the composition dependent optical energy gap (Eo), optical absorption coefficient (α), and thermal diffusivity (σs) of glassy Ge15AsxSe85−x (0≤x≤25) alloys. The energy gap is found to decrease with increase of As concentration and shows a threshold behavior around x∼15, which corresponds to the average coordination number 〈r〉∼2.45. This behavior is found to be consistent with the Phillips-Thorpe theory. The variation of the optical gap (Eo) with composition (x) is analyzed on the basis of the Kastner's model of bond energies. The observed exponential edge (Urbach edge) can be considered as an internal Franz-Keldysh effect arising due to the charged impurity generated, as well as "frozen-in'' optical phonon-generated, electric microfields. It could be described in the framework of Tauc and Dow-Redfield model which ascribes the Urbach rule to the ionization of the exciton as an extension of the stark shift. The concentration (x) dependent thermal diffusivity (σs) estimated from the PAS studies also showed a similar critical behavior at the same concentration x (≈15) which arises due to the threshold percolation of rigidity of the system. The measurements of glass transition temperatures (Tg) and the magnetic susceptibilities (χ) of the samples also support this critical behavior around x=15. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.363462

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2

Digitale Medien

Photoacoustic determination of the optical and thermal properties of isovalent S-substituted polymeric Ge–Se system (1996)

Ghosh, A. K. ; Chaudhuri, B. K.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 79 (1996), S. 723-728

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Isovalent sulfur (S) -substituted glassy Ge0.05SxSe0.95−x (0≤x≤0.15) alloys have been prepared by quick quenching from the melt. The concentration (x) dependences of optical absorption, band gap, and thermal diffusivity of these alloys have been investigated at room temperature (300 K) by the photoacoustic spectroscopic (PAS) method in the spectral range of 350–800 nm. The small variation of the optical gap E0 with composition is analyzed on the basis of Kastner's model [in the small Ge limit of M. Lannoo and M. Bensoussan, Phys. Rev. B 16, 3546 (1977)], considering the electronegativity difference between the substituting atoms (Se and S) and bond energy calculation. The observed exponential edge (Urbach edge) can be considered as an internal Franz–Keldysh effect arising from the charged impurity-generated as well as "frozen-in'' optical-phonon-generated fields. This can be described in the framework of the Tauc and Dow–Redfield model. The phonon-assisted indirect transition at the band-tail region is also obtained from the present studies. The concentration-dependent thermal diffusivity, estimated from the PAS studies, showed a minimum around x=0.05 similar to the behavior of the observed optical energy gap. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.360817

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3

Digitale Medien

Dielectric relaxation in the lead–iron oxide glass system (1997)

Mandal, S. ; Ghosh, A.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 106 (1997), S. 6310-6313

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The dielectric properties of the PbO–Fe2O3 glassy system are reported in the frequency range 102–106 Hz and in the temperature range 300–500 K. The experimental data have been analyzed in the light of the dipolar relaxation model. It is observed that this model is consistent with the frequency and temperature dependence of the complex dielectric constant. The network former PbO influences strongly the dielectric properties, yielding large values of static and high-frequency dielectric constants and a narrow distribution of relaxation times. © 1997 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.473619

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4

Digitale Medien

Transport properties of nonconventional lead cuprate glass (1995)

Hazra, S. ; Ghosh, A.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 103 (1995), S. 6270-6274

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The dc electrical transport properties of the nonconventional lead cuprate glasses of compositions (CuO)x(PbO)100−x for x=15–50 mol % are reported in the temperature range 150–500 K. The experimental results have been analyzed in the light of existing theoretical models. It has been observed that the high-temperature conductivity data are consistent with Mott's nearest-neighbor hopping model, while at low temperatures Mott's variable-range-hopping model fits the data very well. The polaron hopping models of Schnakenberg and Emin can predict the conductivity data in the entire temperature range of measurement. The percolation model of Triberis and Friedman is not consistent with the experimental results. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.470405

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5

Digitale Medien

Transport mechanism in nonconventional bismuth cuprate glass (1996)

Hazra, S. ; Mandal, S. ; Ghosh, A.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 104 (1996), S. 10041-10045

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: Temperature and compositional dependence of the electrical transport properties of the nonconventional binary bismuth cuprate glasses are reported for the first time. It has been observed that the phonon assisted small polaron hopping model in the nonadiabatic regime is consistent with the data only at high temperatures. The variable range hopping model can fit the low temperature data qualitatively. The polaron hopping models proposed by Schnakenberg [Phys. Status Solidi 28, 623 (1968)] and Emin [Phys. Rev. Lett. 32, 303 (1974)] can predict quantitatively the conductivity data in the entire temperature range of measurement for all glass compositions. The physical parameters obtained from the best fits of these models are found reasonable and consistent with the glass compositions. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.471748

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6

Digitale Medien

Transport properties of semiconducting ternary vanadate glasses (1995)

Ghosh, A.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 102 (1995), S. 1385-1389

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: Measurements are reported for the electrical dc conductivity of the semiconducting vanadium tellurite glasses containing P2O5, Sb2O3, or Bi2O3 in the temperature range 80–450 K. The experimental data have been analyzed in the light of existing theoretical models. It has been observed that the general behavior of the electrical conductivity is similar for all glass compositions. The high temperature conductivity data are consistent with Mott's models of phonon-assisted polaronic hopping in the nonadiabatic regime, while at low temperatures variable range hopping is valid. The small polaron hopping model of Schnakenberg is the best model to interpret the temperature dependence of the activation energy and the conductivity in the entire temperature range. The percolation model applied to the polaron hopping regime is also found to be consistent with the temperature dependence of the conductivity data at high and low temperatures. The various parameters obtained by fitting these models to the experimental data are found to depend on glass forming oxides other than the vanadium oxide. © 1995 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.468924

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7

Digitale Medien

Semiconducting properties of magnesium vanadate glasses (1999)

Sen, S. ; Ghosh, A.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 86 (1999), S. 2078-2082

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The electrical conductivity of semiconducting magnesium vanadate glasses has been reported for a wide composition range in the temperature range of 80–500 K. The experimental results have been analyzed in the framework of different hopping models. It has been observed that the multiphonon assisted hopping model of small polarons in the nonadiabatic regime, proposed by Emin, can interpret the temperature dependence of the conductivity data of these glasses over the entire temperature range of measurement. The parameters obtained from the fits of the experimental data to this model appear reasonable and are consistent with the glass composition. On the other hand, Mott's optical phonon assisted hopping model at high temperatures provides smaller values of the localization length. However, Mott's variable range hopping model is consistent with the low temperature data. Schnakenberg's model yields higher values of the hopping and the disorder energies than the activation energy obtained at the highest and the lowest temperature ranges. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.371012

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8

Digitale Medien

Electrical properties of iron-silica nanocomposites synthesized by electrodeposition (1999)

Banerjee, S. ; Ghosh, A. K. ; Chakravorty, D.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 86 (1999), S. 6835-6840

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Nanometer-sized iron particles with diameters in the range 5.5–11.1 nm were grown within a silica gel by an electrodeposition method. Electron diffraction measurements show that some of the iron particles were oxidized to Fe3O4. dc resistivity measurements over the temperature range 110–300 K show a T−1/4 variation indicating a variable range hopping transport. ac conductivity over the frequency range 100 Hz–2 MHz show an overlapping large polaron tunneling mechanism to be operative. The dielectric modulus spectra as a function of frequency were analyzed on the basis of a stretched exponential relaxation function. The values of the exponent β as extracted from this analysis were in the range 0.38–0.46. The activation energies corresponding to the maximum of the imaginary part of the dielectric modulus were in the range 0.13–0.20 eV. These are ascribed to an electron tunneling mechanism. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.371759

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9

Digitale Medien

Generalization of fluctuation induced conductivity in polycrystalline Y1−xCaxBa2Cu3Oy and Bi2Sr2Ca1Cu2O8+δ superconductors (1999)

Ghosh, A. K.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 86 (1999), S. 3247-3252

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We have investigated the fluctuation induced conductivity (FIC) of two high-Tc superconductors (HTSC) namely Bi2Sr2Ca1Cu2O8+δ and Y1−xCaxBa2Cu3Oy. The effective medium theory is used to formulate the Aslamazov–Larkin type equations for these polycrystalline superconductors. For the three dimensional case the temperature exponent remains unaltered since both the exponents for the ab plane and c direction FICs in the crystal are same. But the situation is more complex in the two dimensional case where the counterparts in the crystal have different temperature dependencies. The FIC is evaluated and compared with the theoretically obtained values from the model proposed. We have also evaluated the exponents, the coherence lengths, and the crossover temperature. The analysis based on the present model reveals that these two superconductors are similar concerning their nature of fluctuations. The extent of a particular fluctuation region of course differs from one HTSC to another. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.371197

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10

Digitale Medien

Electrical response of piezoelectric materials under mechanical excitation (1999)

Ghosh, A. K.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 86 (1999), S. 5753-5756

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The piezoelectric responses of different piezocrystals, rigidly backed, have been studied under constant and impulsive stress. Equations connecting electrical and mechanical interactions have been coupled to find the response. The rates of growth and decay of piezovoltage have been found to vary widely from material to material. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.371589

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