Anomalous low frequency dispersion and dielectric relaxation in the layered intercalated compounds Cd_0.75PS₃A_0.5(H₂O) [A=K, Cs]

Abstract

The dielectric response in the layered Cd_0.75PS₃A_0.5(H₂O) [A=K, Cs] in which hydrated alkali cations reside in the interlamellar space, have been investigated as a function of frequency and temperature. In these materials the layers are electrically insulating, the alkali ions immobile and the electrical response due to the intercalated water molecules. The dielectric behavior shows two phenomena, an anomalous dispersion of the complex dielectric susceptibility at low frequencies and a dielectric relaxation at higher frequencies. At low frequencies the complex dielectric permittivity of both compounds show a power law dispersion with a transition to a smaller exponent above a crossover frequency, ω_c. It was found that although ω_c shifts to higher frequency with increasing temperature the magnitude of the complex permittivity at the crossover frequency showed no variation. The loss peak showed a similar shift to higher frequencies with temperature. The dielectric relaxation showed increasing departure from an ideal Debye response with temperature. The results have been rationalized by considering the intercalated water molecules as forming a H-bonded network structure. The dielectric behavior is described in the context of a percolation structure for this network. The anomalous low frequency dispersion arises due to imperfect transport on this structure and the dielectric loss due to the fact that the water molecules possess a permanent dipole moment.