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Dielectric and conductivity measurements were carried out on the potassium niobate ceramics both as a function of temperature (50 to 550 °C) and frequency (102 to 106 Hz). A low-frequency dielectric relaxation in the temperature range of 100 to 200 °C is observed and analyzed with the Cole–Cole function. The activation energy of dielectric relaxation is estimated to be 0.84 eV. Frequency dependent conductivity data are analyzed with an augmented Jonscher relation. Potassium niobate exhibits universal conductivity behavior. Activation energies obtained for the dc conductivity and the hopping frequency are 1.01 and 0.94 eV, respectively. A possible mechanism for both the low-frequency dielectric relaxation and the frequency dependent conductivity is proposed based on activation energies and off stoichiometry of KNbO3, which is resulted due to potassium oxide evaporation during preparation processes.

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We report here the first observation of the low frequency Raman scattering from acoustic phonons in semiconducting zinc oxide (ZnO) nanoparticles without embedding in any solid matrix. ZnO nanoparticles (size 5-10 nm) with nearly spherical shape have been synthesized using a chemical route. A shift in the phonon peaks toward higher frequencies along with broadening was observed with a decrease in particle size. The size dependence of the acoustic phonons in ZnO nanoparticles is explained using Lamb's theory that predicts the vibrational frequencies of a homogeneous elastic body of spherical shape. Our results show that the observed low frequency Raman scattering originates from the spherical (l = 0) and quadrupolar vibrations (l = 2) of the spheroidal mode due to the confinement of acoustic vibrations in ZnO nanoparticles.

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