Anisotropic dielectric function in polar nano-regions of relaxor ferroelectrics

The paper suggests to treat the infrared reflectivity spectra of single crystal perovskite relaxors as fine-grained ferroelectric ceramics: locally frozen polarization makes the dielectric function strongly anisotropic in the phonon frequency range and the random orientation of the polarization at nano-scopic scale requires to take into account the inhomogeneous depolarization field. Employing a simple effective medium approximation (Bruggeman symmetrical formula) to dielectric function describing the polar optic modes as damped harmonic oscillators turns out to be sufficient for reproducing all principal features of room temperature reflectivity of PMN. One of the reflectivity bands is identified as a geometrical resonance entirely related to the nanoscale polarization inhomogeneity. The approach provides a general guide for systematic determination of the polar mode frequencies split by the inhomogeneous polarization at nanometer scale.Comment: 5 pages, 2 figure

Low-temperature microwave and THz dielectric response in novel microwave ceramics

Low-temperature dielectric properties of BaZn1/3 Nb2/3O3-based ceramics, CeO2-based ceramics and Ruddlesden-Popper Srn+1Tin O3n+1 (n = 1-4) ceramics has been studied in microwave, THz and infrared frequency range down to 10 K. Extrinsic dielectric losses originating probably from diffusion of charged defects are observed in two families of compounds by a minimum in the temperature dependence of microwave quality Q. The rise of microwave permittivity and dielectric losses at low temperatures in Srn+1Tin O3n+1 (n = 2-4) ceramics was explained by softening of an optical polar mode in SrTiO3, which is in the Srn+1 TinO3n+1 (n = 3, 4) ceramics contained as a second phase. © 2005 Elsevier Ltd. All rights reserved

Relationship between microwave and lattice vibration properties in Ba(Zn1/3/Nb2/3)O3-based microwave dielectric ceramics

The dielectric properties of (1 - x)Ba(Zn1/3Nb 2/3)O3-xBa (Ga1/2Ta1/2)O3 (BZN-xBGT) microwave (MW) ceramics, with x between 0 and 0.2, and those of 0.9Ba(Zn0.6Co0.4)1/3Nb2/3O 3-0.1Ba(Ga0.5Ta0.5)O3 (BZCN-BGT) were studied at MW, terahertz (THz) and infrared (IR) frequencies at temperatures from 10 to 300 K. At room temperature, the temperature coefficient of resonance frequency (τf) near 3 GHz decreases from 28 ppm K-1 in undoped BZN to 2 ppm K-1 in BZN-0.2BGT and reduces to zero in BZCN-BGT. The addition of BGT to BZN depresses the dielectric Q value, but incorporation of Co improves the Q values, yielding Q ∼ 30 000 at 3 GHZ in BZCN-BGT. The relative permittivity (ε′) exhibits only limited variation with composition (ε′ values in the range 34.4-36.0). IR and THz spectra as well as the low-temperature MW dielectric measurements revealed a weak dielectric relaxation below phonon frequencies, possibly arising from charges caused by inhomogeneous distribution of the B-site ions with differing valences. The IR reflectivity spectrum of BZN-0.2BGT is significantly different (smeared) compared with other compositions, which may be caused by disorder on the B sites and by an amorphous phase at the grain boundaries

Polymer-Nanostructured Carbon Composites as Multifunctional Sensor Materials: Design, Processing, and Properties

Our recent achievements in design, processing and studies of physical properties of polymer-nanostructured carbon composites (PNCC) as prospective strain sensor and gas sensor materials are presented. Mechanical, electrical and gas sorption properties have been investigated. Electrically conductive atomic force microscopy (EC AFM), positron annihilation life-time spectroscopy (PALS) and broadband (100 Hz - 2.5 THz) dielectric spectroscopy have been used to investigate the causes of gigantic sensing effects in PNCC. As a result, multifunctional polymer-nanostructured carbon composites exhibiting simultaneously excellent strain sensor and gas sensor properties have been obtained and the existing models of sensing effects improved