99 research outputs found
Peculiar Bi-ion dynamics in Na1/2Bi1/2TiO3 from terahertz and microwave dielectric spectroscopy
Dynamics of the main dielectric anomaly in Na1/2Bi1/2TiO3 (NBT) was studied
by time-domain THz and microwave spectroscopy, using also previously published
data and their new overall fits. Above the dielectric maximum temperature Tm ~
600 K, the response consists of coupled sub-THz oscillator and a relaxation
mode, assigned to strongly anharmonic Bi-ion vibrations and hopping, whose
slowing down explains the paraelectric-like permittivity increase to Tm. Below
Tm, the main relaxation continues slowing down and additional relaxation,
assigned to quasi-Debye losses, appears in the 10^11 Hz range. The oscillator
hardens on cooling and takes over the whole oscillator strength. The
permittivity decrease below Tm is caused by the reduced strength of the
relaxations due to dominance of the rhombohedral phase within the coexistence
region with the tetragonal phase. The anharmonic dynamics of Bi is supported by
previous structural studies. NBT represents a hybrid between standard and
relaxor ferroelectric behaviour
High-frequency dielectric spectroscopy of batio3 core - silica shell nanocomposites: Problem of interdiffusion
Three types of BaTiO3 core - amorphous nano-shell composite ceramics were
processed from the same core-shell powder by standard sintering, spark-plasma
sintering and two-step sintering techniques and characterized by XRD, HRSEM and
broad-band dielectric spectroscopy in the frequency range 10^3 - 10^13 Hz
including the THz and IR range. The samples differed by porosity and by the
amount of interdiffusion from the cores to shells, in correlation with their
increasing porosity. The dielectric spectra were also calculated using suitable
models based on effective medium approximation. The measurements revealed a
strong dielectric dispersion below the THz range, which cannot be explained by
the modeling, and whose strength was in correlation with the degree of
interdiffusion. We assigned it to an effect of the interdiffusion layers,
giving rise to a strong interfacial polarization. It appears that the
high-frequency dielectric spectroscopy is an extremely sensitive tool for
detection of any gradient layers and sample inhomogeneities even in dielectric
materials with negligible conductivity
Recommended from our members
Design and Performance of Microlith Implemented Projectiles During the Middle and the Late Epipaleolithic of the Levant: Experimental and Archaeological Evidence
The study comprises an experimentally based investigation of interaction between temporal change in the morphology of microlithic tools and transformations in projectile technology during the Late Pleistocene in the Levant. Archery experiments with differently designed arrows fitted with various types of microliths representing subsequent Epipaleolithic cultures of the Levant allowed analyzing performance abilities of the arrows, identifying projectile damage types characteristic of particular hafting modes, detecting factors influencing the frequency of projectile damage and estimating the frequency of projectile damage expected to be found in archaeological samples. The data obtained through the experiments applied in the analysis of the archaeological microliths from Geometric Kebaran and Natufian sites in Israel indicate different approaches to the design of projectiles fitted with microliths characteristic for these cultures. The shift in design, associated with such important economic and social transformations as transition to sedentary settlements and a broad-spectrum economy, may reflect a demand for light, flexible and efficient projectile weapons requiring low time and labor investment for preparation and retooling. The use of such efficient weapons in conditions of growing population density and restricted areas available for Natufian hunter–gatherers can be considered as one of the factors that could have affected the subsequent transition to food production that took place in the early Holocene.Anthropolog
Infrared and THz studies of polar phonons and improper magnetodielectric effect in multiferroic BFO3 ceramics
BFO3 ceramics were investigated by means of infrared reflectivity and time
domain THz transmission spectroscopy at temperatures 20 - 950 K, and the
magnetodielectric effect was studied at 10 - 300 K, with the magnetic field up
to 9 T. Below 175 K, the sum of polar phonon contributions into the
permittivity corresponds to the value of measured permittivity below 1 MHz. At
higher temperatures, a giant low-frequency permittivity was observed, obviously
due to the enhanced conductivity and possible Maxwell-Wagner contribution.
Above 200 K the observed magnetodielectric effect is caused essentially through
the combination of magnetoresistance and the Maxwell-Wagner effect, as recently
predicted by Catalan (Appl. Phys. Lett. 88, 102902 (2006)). Since the
magnetodielectric effect does not occur due to a coupling of polarization and
magnetization as expected in magnetoferroelectrics, we call it improper
magnetodielectric effect. Below 175 K the magnetodielectric effect is by
several orders of magnitude lower due to the decreased conductivity. Several
phonons exhibit gradual softening with increasing temperature, which explains
the previously observed high-frequency permittivity increase on heating. The
observed non-complete phonon softening seems to be the consequence of the
first-order nature of the ferroelectric transition.Comment: subm. to PRB. revised version according to referees' report
Magnetodielectric effect and optic soft mode behaviour in quantum paraelectric EuTiO3 ceramics
Infrared reflectivity and time-domain terahertz transmission spectra of
EuTiO3 ceramics revealed a polar optic phonon at 6 - 300K, whose softening is
fully responsible for the recently observed quantum paraelectric behaviour.
Even if our EuTiO3 ceramics show lower permittivity than the single crystal due
to a reduced density and/or small amount of secondary pyrochlore Eu2Ti2O7
phase, we confirmed the magnetic field dependence of the permittivity, also
slightly smaller than in single crystal. Attempt to reveal the soft phonon
dependence at 1.8K on the magnetic field up to 13T remained below the accuracy
of our infrared reflectivity experiment
- …