Impedance of Sn24P19.3BrxI8-x semiconducting clathratesстатья
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Дата последнего поиска статьи во внешних источниках: 18 июля 2013 г.
Аннотация:The temperature and frequency dependences of the real and imaginary parts of the complex impedance of ceramic samples of the clathrates of variable composition Sn24P19.3BrxI8-x are investigated in the frequency range from 20 to 10(6) Hz at temperatures from 4.2 to 200 K. The conductivity of the samples is measured in the dc regime at temperatures from 4.2 to 300 K; it is characterized by the presence of an activation part, with energy increasing monotonically from 18 to 77 meV as the bromine concentration increases. The impedance spectra are investigated by a graphoanalytical method. As an approximating equivalent circuit, an RC circuit with a frequency-dependent capacitance is considered. It is shown that the capacitive contribution to the admittance falls off sharply with decreasing temperature below 75 K and with increasing frequency above 150 kHz. The observed dielectric anomalies are attributed to a substantial contribution to the complex impedance from the grain boundaries.