Electrical relaxation in proton conductor composites based on (NH4)H2PO4/TiO2 |
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Authors: | J Castillo E M Materón R Castillo R A Vargas P R Bueno J A Varela |
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Institution: | 1. Programa de Física, Universidad del Quindío, Armenia, Colombia 2. Departamento de Física, Universidad del Valle, A.A. 25360, Cali, Colombia 3. Departamento de Físico-Química, Instituto de Química, Universidade Estadual Paulista, P.O. Box 355, 14800-900, Araraquara, S?o Paulo, Brazil
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Abstract: | We report on electrical relaxation measurements of (1 − x)NH4H2PO4-xTiO2 (x = 0.1) composites by admittance spectroscopy, in the 40-Hz–5-MHz frequency range and at temperatures between 303 and 563 K.
Simultaneous thermal and electrical measurements on the composites identify a stable crystalline phase between 373 and 463 K.
The real part of the conductivity, σ’, shows a power-law frequency dependence below 523 K, which is well described by Jonscher’s expression , where σ
0 is the dc conductivity, ω
p
/2π = f
p
is a characteristic relaxation frequency, and n is a fractional exponent between 0 and 1. Both σ
0 and f
p
are thermally activated with nearly the same activation energy in the II region, indicating that the dispersive conductivity
originates from the migration of protons. However, activation energies decrease from 0.55 to 0.35 eV and n increases toward 1.0, as the concentration of TiO2 nanoparticles increases, thus, enhancing cooperative correlation among moving ions. The highest dc conductivity is obtained
for the composite x = 0.05 concentration, with values above room temperature about three orders of magnitude higher than that of crystalline
NH4H2PO4 (ADP), reaching values on the order of 0.1 (Ω cm) − 1 above 543 K. |
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Keywords: | Protonic composites Phase behavior Electrical relaxation |
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