AC transport properties of nanocrystalline SnO2 semiconductor

Nanocrystalline SnO2 materials were prepared by the chemical co-precipitation route by adding ammonia solution to 0.1 M solution of SnCl4·5H2O. The resulting precipitate after thorough washing with distilled water and calcination at 600 °C for 10 h was investigated by XRD for phase identification and crystallite size determination. The materials have been found to be polycrystalline SnO2, possessing tetragonal rutile crystal structure and nanocrystalline in grain size of approximately 30 nm. The TEM micrograph shows agglomerated particles (cluster of primary crystallites) with an average size of 37.4 nm. A corresponding selected area electron diffraction pattern reveals the different Debye rings of SnO2, as analyzed in XRD. The complex dielectric constant ɛ* has been found to vary with frequency which is attributed to the multi-relaxation time constants of the energy states responsible for conduction mechanism. At any particular frequency, ɛ* has been found to increase with temperature. The frequency dependence of loss tangent tan δ has been explained with the help of the equivalent circuit model. The observed frequency dependence of ac conductivity has been found to obey the power law: σac ∝ ωS, where variation of S with temperature indicates multi-hopping conduction mechanism in nanocrystalline SnO2 samples. The complex impedance plots of Z′ versus Z″ at different temperatures have been found to be single semicircular arcs with a non-zero intersection with the real axis in the high frequency region and have their centres lying below the real axis at a particular angle of depression, indicating multirelaxation processes in the material.