ABSTRACT
Aging of the relaxors and PbMg1/3Nb2/3O3in particular was extensively studied in last two decades. Most of the results were related to the low temperature glass-like region. No systematic data around the freezing temperatures were reported. To cover this still missing information we have studied the evolution of the dielectric spectra in the broad frequency region from 10-1 Hz to 106 Hz both below and above the freezing temperatureTf≈240 K. Below freezing temperature the existence of the earlier reported waiting time-frequency scaling at frequencies below ≈50 Hz is confirmed. At higher frequencies this deviation from the scaling is observed that can be tentatively attributed to the complexity of the relaxing entities. AboveTfaging is observed only in the restricted frequency interval below the maximum of the dielectric loss spectrum. The observed effect can be attributed to the hardening and narrowing of the dielectric loss spectra and decreasing of the dielectric strength with time. The explanation is proposed based on the concept of the creation of the degenerate polar nanoregions covering several chemically ordered regions (COR) (multi PNRs-MPNRs). These MPNRs are large compare to the PNRs located at the single CORs and some of them may become frozen resulting in the described spectra changes.
ABSTRACT
A nanocomposite of porous glass and a NaNO(2) ferroelectric (channels of approximately 7 nm diameter) was studied using infrared reflectivity, THz transmission and Raman spectroscopy as a function of temperature in the range of 300-500 K, including the ferroelectric transition. From the infrared and THz response the effective dielectric function was calculated and compared with the dielectric functions calculated from the Bruggeman and Lichtenecker models of the effective medium, using the known data on the polar phonon modes of the NaNO(2) single crystals. The results show good qualitative agreement, indicating that the stiffening of the effective modes is due to local depolarization fields on the glass-ferroelectric interfaces. The nonpolar Raman modes show no substantial modification compared to those of the bulk NaNO(2). Some signatures of the ferroelectric transition were even seen. The results indicate that the intrinsic size effect (phonon confinement) is negligible in this nanocomposite.
