engleski

Study on electrical properties of Bi2O3-Fe2O3-P2O5 glasses investigated by impedance spectroscopy

The electrical properties of bismuth iron phosphate glasses have been investigated by impedance spectroscopy. The electrical admittance measurements for phosphate glasses of different composition: 40Fe2O3-60P2O5 (F40), 3Bi2O3-38, 8Fe2O3-58, 2P2O5 (B3), 10Bi2O3-30Fe2O3-60P2O5 (B10), 20Bi2O3-20Fe2O3-60P2O5 (B20) have been performed in the frequency range from 0, 01 Hz to 4 MHz and over temperature range from 303 To 473 K. Structure of all samples was examined by Raman spectroscopy. Raman spectra indicate that all glasses consist of predominantly pyrophosphate units. With increasing Bi2O3 content up to 20 mol%, the bands related to the bismuth unit vibration grow in intensity. The electrical conductivity of bismuth iron phosphate glasses depends upon Fe2O3 content, Fe(II) ion concentration and distance between Fe ions. With increasing Fe(II) ion content from 17 to 34 % in Bi2O3-Fe2O3-P2O5 glasses containing up to 10 mol % Bi2O3, the dc conductivity increases. On the other hand, the decrease in dc conductivity for the glasses with 20 mol % Bi2O3 is attributed to the decrease in Fe2O3 content from 30 to 20 mol %, which indicates that the conductivity for these glasses depends on Fe2O3 content. The conductivity for these glasses is independent of the Bi2O3 content and arises mainly from polaron hopping between Fe(II) to Fe(III) ions. The electrical conductivity for these glasses is controlled by formation of small polaron and electron hopping from Fe(II) to Fe(III) ion. Relaxation times and theirs activations energies also depend on Fe2O3 content, Fe(II) ion concentration, polaron concentration and distance between Fe ions. Glasses with higher concentration of Fe(II) ions have smaller relaxation times and activation energies for relaxation. Activation energy for dc conductivity, Edc, and activation energy, EZ", are identical which indicates that they are related to the same relaxation process. These bismuth iron phosphate glasses exhibit electronic conduction mechanism.

Iron phosphate glasses; Raman spectroscopy; Impedance spectroscopy

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