ANOMALOUS LOW-FREQUENCY DISPERSION AND DIELECTRIC-RELAXATION IN THE LAYERED INTERCALATED COMPOUNDS CD(0.75)PS(3)A(0.5)(H2O) [A = K, CS]

The dielectric response in the layered Cd(0.75)PS(3)A(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. I n these materials the layers art electrically insulating, the alkali i ons 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 la w dispersion with a transition to a smaller exponent above a crossover frequency, omega(c),. It was found that although omega(c), shifts to higher frequency with increasing temperature the magnitude of the comp lex permittivity at the crossover frequency showed no variation. The l oss 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 bean rationalized by considering the intercalated water molecules as forming a H-bonded ne twork structure. The dielectric behavior is described in the context o f a percolation structure for this network. The anomalous low frequenc y dispersion arises due to imperfect transport on this structure and t he dielectric loss due to the fact that the water molecules possess a permanent dipole moment. (C) 1998 American Institute of? Physics. [S00 21-9606(98)51703-5].