160 research outputs found
Effects of ac-field amplitude on the dielectric susceptibility of relaxors
The thermally activated flips of the local spontaneous polarization in
relaxors were simulated to investigate the effects of the applied-ac-field
amplitude on the dielectric susceptibility. It was observed that the
susceptibility increases with increasing the amplitude at low temperatures. At
high temperatures, the susceptibility experiences a plateau and then drops. The
maximum in the temperature dependence of susceptibility shifts to lower
temperatures when the amplitude increases. A similarity was found between the
effects of the amplitude and frequency on the susceptibility.Comment: 8 pages, 7 figures, Phys. Rev. B (in July 1st
Barkhausen Noise in a Relaxor Ferroelectric
Barkhausen noise, including both periodic and aperiodic components, is found
in and near the relaxor regime of a familiar relaxor ferroelectric,
PbMgNbO, driven by a periodic electric field. The
temperature dependences of both the amplitude and spectral form show that the
size of the coherent dipole moment changes shrink as the relaxor regime is
entered, contrary to expectations based on some simple models.Comment: 4 pages RevTeX4, 5 figures; submitted to Phys Rev Let
Neutron and X-ray diffraction study of cubic [111] field cooled Pb(Mg1/3Nb2/3)O3
Neutron and x-ray diffraction techniques have been used to study the
competing long and short-range polar order in the relaxor ferroelectric
Pb(MgNb)O (PMN) under a [111] applied electric field.
Despite reports of a structural transition from a cubic phase to a rhombohedral
phase for fields E 1.7 kV/cm, we find that the bulk unit cell remains cubic
(within a sensitivity of 90- =0.03)for fields up to
8 kV/cm. Furthermore, we observe a structural transition confined to the near
surface volume or `skin' of the crystal where the cubic cell is transformed to
a rhombohedral unit cell at T=210 K for E 4 kV/cm, for which
90-=0.08 0.03 below 50 K. While the bulk unit
cell remains cubic, a suppression of the diffuse scattering and concomitant
enhancement of the Bragg peak intensity is observed below T=210 K,
indicating a more ordered structure with increasing electric field yet an
absence of a long-range ferroelectric ground state in the bulk. The electric
field strength has little effect on the diffuse scattering above T,
however below T the diffuse scattering is reduced in intensity and adopts
an asymmetric lineshape in reciprocal space. The absence of hysteresis in our
neutron measurements (on the bulk) and the presence of two distinct temperature
scales suggests that the ground state of PMN is not a frozen glassy phase as
suggested by some theories but is better understood in terms of random fields
introduced through the presence of structural disorder. Based on these results,
we also suggest that PMN represents an extreme example of the two-length scale
problem, and that the presence of a distinct skin maybe necessary for a relaxor
ground state.Comment: 12 pages, 9 figure
Polarization rotation via a monoclinic phase in the piezoelectric 92%PbZn1/3Nb2/3O3-8%PbTiO3
The origin of ultrahigh piezoelectricity in the relaxor ferroelectric
PbZn1/3Nb2/3O3-PbTiO3 was studied with an electric field applied along the
[001] direction. The zero-field rhombohedral R phase starts to follow the
direct polarization path to tetragonal symmetry via an intermediate monoclinic
M phase, but then jumps irreversibly to an alternate path involving a different
type of monoclinic distortion. Details of the structure and domain
configuration of this novel phase are described. This result suggests that
there is a nearby R-M phase boundary as found in the Pb(Ti,Zr)O3 system.Comment: REVTeX file. 4 pages. New version after referees' comment
Ion Mobility Shift of Isotopologues in a High Kinetic Energy Ion Mobility Spectrometer (HiKE-IMS) at Elevated Effective Temperatures
Ion mobility spectrometers (IMS) separate ions mainly by ion–neutral collision cross section and to a lesser extent by ion mass and effective temperature. When investigating isotopologues, the difference in collision cross section can be assumed negligible. Since the mobility shift of isotopologues is thus mainly caused by their difference in mass and effective temperature, the investigation of isotopologues can provide important insights into the theory of ion mobility. However, in classical IMS operated at ambient pressure, cluster formation with neutral molecules occurs, which significantly influences the mobility shift of isotopologues and thus makes a sound investigation of the effect of ion mass and effective temperature on the ion mobility difficult. In this work, the relative ion mobility of several organic compounds and their 13C-labeled isotopologues is studied in a High Kinetic Energy Ion Mobility Spectrometer (HiKE-IMS) at high reduced electric fields up to 120 Td, which allows the investigation of nonclustered ion species and thus enables a sound investigation of the mobility shift of isotopologues. The results show that the measured relative ion mobilities of isotopologues having the same effective temperature and, thus, their ion mass dominating the relative ion mobility agree well with theoretical relative ion mobilities predicted by the theory of ion mobility
Prediction of collective characteristics for ion ensembles in quadrupole ion traps without trajectory simulations
Transport and cooling of singly-charged noble gas ion beams
The transport and cooling of noble gas singly-charged ion beams by means of a
Radio Frequency Quadrupole Cooler Buncher (RFQCB) have been studied at the
LIMBE low energy beam line of the GANIL facility. Ions as light as
have been cooled and stored before their extraction in bunches using as
buffer gas. Bunches characteristics have been studied as a function of the
parameters of the device. Sizeable transmissions of up to 10 have been
obtained. A detailed study of the lifetime of ions inside the buncher has been
performed giving an estimate of the charge exchange cross-section. Results of a
microscopic Monte-Carlo transport code show reasonable agreement with
experimental data.Comment: 13 figure
Development of Ferroelectric Order in Relaxor (1-x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3
The microstructure and phase transition in relaxor ferroelectric
Pb(Mg1/3Nb2/3)O3 (PMN) and its solid solution with PbTiO3 (PT), PMN-xPT, remain
to be one of the most puzzling issues of solid state science. In the present
work we have investigated the evolution of the phase symmetry in PMN-xPT
ceramics as a function of temperature (20 K < T < 500 K) and composition (0 <=
x <= 0.15) by means of high-resolution synchrotron x-ray diffraction.
Structural analysis based on the experimental data reveals that the
substitution of Ti^4+ for the complex B-site (Mg1/3Nb2/3)^4+ ions results in
the development of a clean rhombohedral phase at a PT-concentration as low as
5%. The results provide some new insight into the development of the
ferroelectric order in PMN-PT, which has been discussed in light of the
kinetics of polar nanoregions and the physical models of the relaxor
ferroelectrics to illustrate the structural evolution from a relaxor to a
ferroelectric state.Comment: Revised version with updated references; 9 pages, 4 figures embedde
Evidence for and phases in the morphotropic phase boundary region of : A Rietveld study
We present here the results of the room temperature dielectric constant
measurements and Rietveld analysis of the powder x-ray diffraction data on
(PMN-PT) in the composition range
to show that the morphotropic phase boundary (MPB)
region contains two monoclinic phases with space groups Cm (or type) and
Pm (or type) stable in the composition ranges and
, respectively. The structure of PMN-PT in the
composition ranges 0.26, and is found to be
rhombohedral (R3m) and tetragonal (P4mm), respectively. These results are
compared with the predictions of Vanderbilt & Cohen's theory.Comment: 20 pages, 11 pdf figure
A Monte Carlo simulation of ion transport at finite temperatures
We have developed a Monte Carlo simulation for ion transport in hot
background gases, which is an alternative way of solving the corresponding
Boltzmann equation that determines the distribution function of ions. We
consider the limit of low ion densities when the distribution function of the
background gas remains unchanged due to collision with ions. A special
attention has been paid to properly treat the thermal motion of the host gas
particles and their influence on ions, which is very important at low electric
fields, when the mean ion energy is comparable to the thermal energy of the
host gas. We found the conditional probability distribution of gas velocities
that correspond to an ion of specific velocity which collides with a gas
particle. Also, we have derived exact analytical formulas for piecewise
calculation of the collision frequency integrals. We address the cases when the
background gas is monocomponent and when it is a mixture of different gases.
The developed techniques described here are required for Monte Carlo
simulations of ion transport and for hybrid models of non-equilibrium plasmas.
The range of energies where it is necessary to apply the technique has been
defined. The results we obtained are in excellent agreement with the existing
ones obtained by complementary methods. Having verified our algorithm, we were
able to produce calculations for Ar ions in Ar and propose them as a new
benchmark for thermal effects. The developed method is widely applicable for
solving the Boltzmann equation that appears in many different contexts in
physics.Comment: 14 page
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