Wydział Chemii

Beata Świątek-Tran

Hubert A. Kołodziej

Andrzej Vogt

V. H. Tran

2015

RSC Advances

5

9539-9545

10.1039/c4ra13950j

Naukowa

Angielski

Artykuł

We have investigated the dielectric permittivity (’, ”) of Co(CO3)(H2O)2(C3H4N2)2 and two samples of [Co(C3H3N2)2]n at low frequencies (0.1 – 1000 kHz) and in the temperature range 80 - 400 K. For the studied materials, a diffuse peak in the real part ’(T) of the dielectric permittivity is observed at Tmax  315 K. A detailed analysis of the data of [Co(C3H3N2)2]n revealed that the temperature dependence of ’(T) deviates from Curie-Weiss law below (Tmax + 15 K), showing a (T-Tmax)-2 dependence. A clear dielectric dispersion occurs above Tf  287 K and it is characterized by a distribution of relaxation times according to the Kohlrausch-Williams-Watts formula. The temperature and frequency dependence of the loss tangent (tan)max can be described by the Vogel-Fulcher law, indicating thermal slowing down of non-Debye dynamics. We attribute the observed dielectric properties to a relaxor ferroelectric behaviour, which is caused by the development of a freezing state below Tf. We have analysed the electrical conductivity using the Jonscher formula () = dc + As. The obtained results may be explained with the model, where the dc-conductivity is governed by thermally activated electrons and ac-conductivity due to the tunnelling of the overlapping large polarons. A large value of the dielectric permittivity ’ is found for samples absorbing the moisture from the air and the phenomenon has been associated to a cooperation between the H+ and HCO3- ions and the others in the relaxation process. Due to a moisture absorption property of [Co(C3H3N2)2]n, we suggest that this material is a potential candidate for a low cost room-temperature humidity sensor.

http://dx.doi.org/10.1039/c4ra13950j

https://www.rsc.org/