Effect of dispersed Al2O3 and SiO2 on the phase equilibria of NH4HSO4

Differential scanning calorimetry (DSC), impedance spectroscopy (IS) and X ray diffraction were used to study the composite solid electrolytes (1-x)NH4HSO4-xAl2O3 (x?0.5) and (1-x)NH4HSO4-xSiO2 (x=0.3. The DSC results shows that new morphological states are formed by the Al2O3 doping because new phase boundaries are observed below the melting point of AHS in the composites. The X-ray diffraction data also confirm that the composites with alumina be-comes more amorphous as x increases reaching completion for x >= 0.3. On the other hand, the dc-conductivity is only improved on adding either Al2O3 or SiO2 to AHS in the solid phases of the composites. The results are discussed in terms of the influence of the dispersed second phase on the overall electrical response and phase behaviour of the composites

Dielectric relaxation studies in Cs2SO4

Dielectric measurements of Cs2SO4 show a distinct relaxation at low frequencies at several isotherms (

Impedance spectroscopy studies of K2SO4 in the intermediate temperature regime

Impedance spectroscopy measurements of K2SO4 have been carried out from 5 Hz to 13 MHz over the temperature range 403-782 T. The plots of corrected imaginary part of permittivity, epsilon", and its real part epsilon\u27 vs. frequency clearly show a new dielectric relaxation around epsilon") = 1.4 X 10(4) Hz at 403 degrees C, which shifts to higher frequencies (similar to 1 MHz) as the temperatures increases. The fma (calculated from the peak position of epsilon") vs. reciprocal T shows an activated relaxation process over the temperature range 403-600 T with activation energy E-a = 1.02 eV, which is close to that derived from the dc-conductivity, E-a = 1.15 eV. We suggest that the observed dielectric relaxation could be produced by the K+ jump and SO4- reorientation that cause distortion and change the local lattice polarizability inducing dipoles like KSO4-

Dielectric relaxation studies in Cs2SO4

Dielectric measurements of Cs2SO4 show a distinct relaxation at low frequencies at several isotherms (

Impedance spectroscopy studies of KHSO4 above room temperature

The dielectric permittivity of polycrystalline KESO4 was measured from 5 Hz to 13 MHz over the temperature range 51-187 degrees C. The corrected imaginary part of permittivity, epsilon", and its real part epsilon' vs. frequency clearly show a new dielectric relaxation around f(max) = 1.5* 10(5) Hz at 51 degrees C which shifts to higher frequencies (similar to 1 MHz) as the temperatures increases. If the measurements are done when increasing the temperature, f(max) decreases sharply (more than two orders of magnitude) around 164 degrees C; however, above this transition temperature, it continues shifting to higher frequencies as the temperature increases. However, if the measurements are done when decreasing, the temperature, f(max) increases abruptly around 146 degrees C, thus showing a hysteretic behaviour. We suggest that the observed dielectric relaxation could be produced by proton jumps and SO4- reorientation, causing distortion and changing the local lattice polarizability to induce dipoles like HSO4-. (c) 2005 Elsevier B.V. All rights reserved

Impedance spectroscopy studies of K₂SO₄ in the intermediate temperature regime

Impedance spectroscopy measurements of K2SO4 have been carried out from 5 Hz to 13 MHz over the temperature range 403-782 T. The plots of corrected imaginary part of permittivity, epsilon", and its real part epsilon' vs. frequency clearly show a new dielectric relaxation around epsilon") = 1.4 X 10(4) Hz at 403 degrees C, which shifts to higher frequencies (similar to 1 MHz) as the temperatures increases. The fma (calculated from the peak position of epsilon") vs. reciprocal T shows an activated relaxation process over the temperature range 403-600 T with activation energy E-a = 1.02 eV, which is close to that derived from the dc-conductivity, E-a = 1.15 eV. We suggest that the observed dielectric relaxation could be produced by the K+ jump and SO4- reorientation that cause distortion and change the local lattice polarizability inducing dipoles like KSO4-

Efecto de la dispersión de alumina sobre el comportamiento de fases del (1-x)NH4H2PO4-xAl2O3

Modulated differential scanning calorimetry (MDSC), thermogravimetry (TG) and impedance spectroscopy (IS) were used to study the phase equilibria and electrical conductivity of the composite solid electrolytes (1-x)NH4H2PO4-xAl2O3 in the concentration range x=0.0-0.7. The composites were prepared by mechanical mixing of the components followed by heating at temperatures below the NH4H2PO4 (ADP) melting point at 210 oC. The MDSC curves show three endothermic peaks at 137, 157 and 200 oC, respectively, on the first heating run. The first peak at 137 oC is reported here for the first time. The third one decreas with the increase of the alumina concentration and disappears for x>0.5. The conductivity decreases with the alumina concentration except for x=0.5 where we observe a small maximum whose conductivity value is lower that of pure ADP.Se utilizaron las técnicas de calorimetría modulada de barrido diferencial (MDSC), termogravimetría y espectroscopía de impedancias para estudiar el equilibrio de fases y la conductividad eléctrica de la composita (1-x)NH4H2PO4-(x)Al2O3 en el rango de concentraciones x = 0.0 ¿ 0.7. Las compositas fueron preparadas por mezclado mecánico de sus componentes seguido por un calentamiento a una temperatura por debajo del punto de fusión del NH4H2PO4 en 210 oC. Las medidas de MDSC muestran una pequeña y nueva anomalía alrededor de 137 oC para x=0.5-0.7 la cual no ha sido reportada en la literatura. Una segunda anomalía alrededor de 157 oC y una tercera anomalía alrededor de 200 oC, la cual empieza a disminuir al aumentar la concentración de alúmina y desaparece para x >0.5. La conductividad decrece al aumentar la concentración de alumina excepto para x=0.5 donde se observa un pequeño máximo cuya conductividad no supera la del compuesto puro