66 research outputs found
Neutron scattering study of PbMgTaO and BaMgTaO complex perovskites
Neutron scattering investigations were carried out in
PbMgTaO and BaMgTaO complex
perovskites. The crystal structure of both compounds does not show any phase
transition in the temperature range 1.5 -- 730 K. Whereas the temperature
dependence of the lattice parameter of BaMgTaO follows the
classical expectations, the lattice parameter of relaxor ferroelectric
PbMgTaO exhibits anomalies. One of these anomalies is
observed in the same temperature range as the peak in the dielectric
susceptibility. We find that in PbMgTaO, lead ions are
displaced from the ideal positions in the perovskite structure at all
temperatures. Consequently short-range order is present. This induces strong
diffuse scattering with an anisotropic shape in wavevector space. The
temperature dependences of the diffuse neutron scattering intensity and of the
amplitude of the lead displacements are similar
Anomalous pressure dependence of the atomic displacements in the relaxor ferroelectric PbMgTaO
The crystal structure of the PbMgTaO (PMT) relaxor
ferroelectric was studied under hydrostatic pressure up to GPa by
means of powder neutron diffraction. We find a drastic pressure-induced
decrease of the lead displacement from the inversion centre which correlates
with an increase by 50 % of the anisotropy of the oxygen temperature
factor. The vibrations of the Mg/Ta are, in contrast, rather pressure
insensitive. We attribute these changes being responsible for the previously
reported pressure-induced suppression of the anomalous dielectric permittivity
and diffuse scattering in relaxor ferroelectrics
Evolution of the neutron quasi-elastic scattering through the ferroelectric phase transition in 93%PbZnNbO - 7% PbTiO
We show that the neutron diffuse scattering in relaxor ferroelectric
(1-x)PbZnNbO - x PbTiO (x=0.07) consists of two
components. The first component is strictly elastic but extended in q-space and
grows below 600 K. The second component, that was not reported before for the
(1-x)PbZnNbO - x PbTiO (x=0.07) relaxor
ferroelectrics, is quasi-elastic with a line-width that has a similar
temperature dependence as the width of the central peak observed by Brillouin
spectroscopy. The temperature dependence of the susceptibility of the
quasi-elastic scattering has a maximum at the ferroelectric transition
Double-k phase of the Dzyaloshinskii-Moriya helimagnet Ba2CuGe2O7
Neutron diffraction is used to re-investigate the magnetic phase diagram of
the noncentrosymmetric tetragonal antiferromagnet Ba2CuGe2O7. A novel
incommensurate double-k magnetic phase is detected near the
commensurate-incommensurate phase transition. This phase is stable only for
magnetic field closely aligned with the 4-fold symmetry axis. The results
emphasize the inadequacy of existing theoretical models for this unique
material, and points to additional terms in the Hamiltonian or lattice effects.Comment: 4 pages, 5 figure
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