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T. A. Shaplygina - One of the best experts on this subject based on the ideXlab platform.

  • neutron scattering study of pbmg _ mathsf 1 3 ta _ mathsf 2 3 o _ mathsf 3 and bamg _ mathsf 1 3 ta _ mathsf 2 3 o _ mathsf 3 Complex Perovskites
    European Physical Journal B, 2004
    Co-Authors: S N Gvasaliya, S G Lushnikov, B Roessli, Denis Sheptyakov, T. A. Shaplygina
    Abstract:

    Neutron scattering investigations were carried out in PbMg1/3Ta2/3O3 and BaMg1/3Ta2/3O3 Complex Perovskites. The crystal structure of neither compound shows any phase transition in the temperature range 1.5-730 K. Whereas the temperature dependence of the lattice parameter of BaMg1/3Ta2/3O3 follows the classical expectations, the lattice parameter of relaxor ferroelectric PbMg1/3Ta2/3O3 exhibits anomalies. One of these anomalies is observed in the same temperature range as the peak in the dielectric susceptibility. Below $T\sim180$ K PbMg1/3Ta2/3O3 exhibits very small thermal expansion, similar to invar alloys. We find that in PbMg1/3Ta2/3O3, 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.

  • neutron scattering study of pbmg _ 1 3 ta _ 2 3 o _3 and bamg _ 1 3 ta _ 2 3 o _3 Complex Perovskites
    arXiv: Materials Science, 2004
    Co-Authors: Severian Gvasaliya, S G Lushnikov, B Roessli, Denis Sheptyakov, T. A. Shaplygina
    Abstract:

    Neutron scattering investigations were carried out in PbMg$_{1/3}$Ta$_{2/3}$O$_3$ and BaMg$_{1/3}$Ta$_{2/3}$O$_3$ 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 BaMg$_{1/3}$Ta$_{2/3}$O$_3$ follows the classical expectations, the lattice parameter of relaxor ferroelectric PbMg$_{1/3}$Ta$_{2/3}$O$_3$ exhibits anomalies. One of these anomalies is observed in the same temperature range as the peak in the dielectric susceptibility. We find that in PbMg$_{1/3}$Ta$_{2/3}$O$_3$, 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.

  • neutron scattering study of pbmg1 3ta2 3o3and bamg1 3ta2 3o3 Complex Perovskites
    European Physical Journal B, 2004
    Co-Authors: S N Gvasaliya, S G Lushnikov, B Roessli, Denis Sheptyakov, T. A. Shaplygina
    Abstract:

    Neutron scattering investigations were carried out in PbMg 1/3 Ta 2/3 O 3 and BaMg 1/3 Ta 2/3 O 3 Complex Perovskites. The crystal structure of neither compound shows any phase transition in the temperature range 1.5-730 K. Whereas the temperature dependence of the lattice parameter-of BaMg 1/3 Ta 2/3 O 3 follows the classical expectations, the lattice parameter of relaxor ferroelectric PbMg 1/3 Ta 2/3 O 3 exhibits anomalies. One of these anomalies is observed in the same temperature range as the peak in the dielectric susceptibility. Below T ∼ 180 K PbMg 1/3 Ta 2/3 O 3 exhibits very small thermal expansion, similar to invar alloys. We find that in PbMg 1/3 Ta 2/3 O 3 , 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.

  • Density of vibration states and ferroelectric properties of Complex Perovskites
    Journal of Applied Physics, 2003
    Co-Authors: Severian Gvasaliya, S G Lushnikov, I L Sashin, T. A. Shaplygina
    Abstract:

    We studied the effect of temperature on density of vibrational states of model Complex Perovskites PbMg1/3Nb2/3O3 (PMN), PbMg1/3Ta2/3O3 (PMT), and BaMg1/3Ta2/3O3 (BMT) by inelastic neutron scattering. It has been found that PMN and PMT relaxor ferroelectrics exhibit an anomalous temperature evolution of the density of vibrational states G(E), while G(E) in the BMT compound does not demonstrate any temperature evolution. It is shown that there is a correlation between the temperature behaviors of the dielectric response and vibrational spectra of all the Complex Perovskites studied. Possible reasons for variation in G(E) in these materials are discussed.

R L Moreira - One of the best experts on this subject based on the ideXlab platform.

  • crystal structures and phonon modes of ba ca1 2w1 2 o3 ba ca1 2mo1 2 o3 and ba sr1 2w1 2 o3 Complex Perovskites investigated by raman scattering
    Journal of Raman Spectroscopy, 2010
    Co-Authors: Anderson Dias, Kisla P F Siqueira, R L Moreira
    Abstract:

    This work investigates the crystal structures and phonon modes of Ba(Ca1/2W1/2)O3, Ba(Ca1/2Mo1/2)O3 and Ba(Sr1/2W1/2)O3 Perovskites by Raman spectroscopy. The samples were produced by conventional solid-state processing at 1200 °C. X-ray diffraction showed that single-phase homogeneous materials were produced, which are cubic or pseudo-cubic in symmetry. The existing controversies in the literature for these Complex Perovskites were investigated by comparing experimental Raman data with group-theory analysis. Ceramics with Ca and W or Mo were found to be cubic, space group Fm3m. For these materials, four Raman-active bands were observed and the fitting parameters showed that the Ba(Ca1/2Mo1/2)O3 ceramic presents bands at lower wavenumbers if compared with the Ba(Ca1/2W1/2)O3 sample. For the Ba(Sr1/2W1/2)O3 material, two hypotheses were investigated for monoclinic or triclinic structures. The experimental results showed 12 Raman-active modes for this ceramic, which is in perfect agreement with the theoretical predictions for a monoclinic (I2/m) structure. Copyright © 2009 John Wiley & Sons, Ltd.

  • vibrational spectroscopy and electron phonon interactions in microwave hydrothermal synthesized ba mn1 3nb2 3 o3 Complex Perovskites
    Journal of Physical Chemistry B, 2009
    Co-Authors: Anderson Dias, F M Matinaga, R L Moreira
    Abstract:

    Ba(Mn 1/3 Nb 2/3 )O 3 ceramics were synthesized by the microwave-hydrothermal process. Crystalline, single-phase, needle-like materials were obtained with high anisotropy and aspect ratio. Large crystals could be prepared from a direct combination of nanosized crystals under microwaves through an oriented attachment mechanism. Infrared and Raman spectroscopies showed perfect agreement with group-theoretical approaches for a trigonal, P3ml structure. Franck-Condon modes were identified in Raman scattering experiments conducted in different wavelengths, laser powers, and temperatures. The results showed that the Mn ions exhibit a particular role in the lattice dynamics in Complex Perovskites.

Matthew J Rosseinsky - One of the best experts on this subject based on the ideXlab platform.

J A Alonso - One of the best experts on this subject based on the ideXlab platform.

  • enhanced magnetoresistance in cacu3 mn4 xrex o12 x 0 0 1 0 2 Complex Perovskites prepared at moderate pressures
    Journal of Alloys and Compounds, 2017
    Co-Authors: Ben R Hassine, J Sanchezbenitez, J A Alonso, W Cherif, F J Mompean, M T Fernandezdiaz
    Abstract:

    Abstract New Complex Perovskites of the series CaCu 3 (Mn 4−x Re x )O 12 have been prepared from citrate precursors under moderate pressure conditions of 2 GPa and 1000 °C, in the presence of KClO 4 as oxidizing agent to stabilize Mn 3+ /Mn 4+ mixed valence. The polycrystalline samples have been characterized by x-ray diffraction, neutron powder diffraction (NPD), magnetic, and magnetotransport measurements. The crystal structures are cubic, space group Im-3. The unit-cell parameters increase from a = 7.2379(2) A for the parent (x = 0) compound to a = 7.2420(4) A for CaCu 3 (Mn 3.9 Re 0.1 )O 12 . Both oxides adopt a superstructure of the Perovskites ABO 3 with long-range 1:3 ordering for Ca 2+ and Cu 2+ ions at the A sublattice. For the compound doped with Re (x = 0.1), the result of a NPD study shows that Re 6+ ions are randomly located at the octahedral positions, being the (Mn,Re)O 6 octahedra strongly tilted, with superexchange (Mn,Re)-O-(Mn,Re) angles of 142.03°. Neutron diffraction data clearly show that some Mn 3+ ions are located together with Cu 2+ at the square-planar 6 b positions. The magnetic structure determined from low-temperature NPD data unveils a ferromagnetic coupling between (Mn,Re) 8 c spins at octahedral positions and weak antiferromagnetism with (Cu 2+ ,Mn 3+ ) 6 b spins. Interestingly, an enhancement of the magnetoresistance effect is observed for the Re-doped compound, well beyond that found for the parent perovskite.

  • enhancement of magnetoresistance and ferromagnetic coupling in the Complex Perovskites cacu3 mn4 xalx o12 x 0 0 2 0 4 and 0 6 a neutron diffraction study
    Journal of Applied Physics, 2015
    Co-Authors: Ben R Hassine, J Sanchezbenitez, M T Fernandezdiaz, W Cherif, F J Mompean, F Elhalouani, J A Alonso
    Abstract:

    New compounds of the series CaCu3(Mn4−xAlx)O12 have been prepared under high pressure conditions (2 GPa), in the presence of KClO4 as oxidizing agent to stabilize Mn3+,4+ mixed valence. The polycrystalline samples have been characterized by x-ray diffraction, neutron powder diffraction (NPD), magnetic, and magnetotransport measurements. All the samples are cubic, space group Im-3. These oxides adopt a superstructure of ABO3 perovskite given by the long-range 1:3 ordering of Ca2+ and Cu2+ ions at the A sublattice. The NPD study for x = 0.4 shows that Al3+ ions are statistically distributed at the octahedral positions, being the (Mn,Al)O6 octahedra strongly tilted, with superexchange (Mn,Al)-O-(Mn,Al) angles of 142.1°. Also, neutron data clearly show that some Mn3+ ions (0.65(2) per formula) are located together with Cu2+ at the square-planar 6b positions. Regarding the magnetic properties, all the compounds present a spontaneous increase of the magnetization below TC, typical of ferro-or ferrimagnetic materials, with TC decreasing upon Al introduction. The magnetic structure determined from low-temperature NPD data unveils a ferromagnetic coupling between (Cu2+, Mn3+)6b spins and Mn8c spins at octahedral positions; this is in contrast with the ferrimagnetic structure observed for RCu3Mn4O12 and CaCu3Mn4O12, where an AFM coupling is observed between both magnetic sublattices. Interestingly, an enhancement of the magnetoresistance effect is observed for x = 0.2, well beyond that found for the parent compound. This effect, in materials subtly doped with non-magnetic elements at the Mn positions, may be of interest for applications.

  • high pressure synthesis and characterization of bicu3 mn4 xfex o12 x 0 1 0 2 0 Complex Perovskites
    ChemInform, 2013
    Co-Authors: Paula Kayser, M J Martinezlope, J Sanchezbenitez, J A Alonso, M T Fernandez
    Abstract:

    The series of title compounds is prepared from citrate precursors at 3.5 GPa and 1000 °C (1 h) in the presence of KClO4.

  • high pressure synthesis and characterization of bicu3 mn4 xfex o12 x 0 1 0 2 0 Complex Perovskites
    Journal of Solid State Chemistry, 2013
    Co-Authors: Paula Kayser, M J Martinezlope, J Sanchezbenitez, J A Alonso, M T Fernandez
    Abstract:

    Abstract We have studied the series of nominal composition BiCu3(Mn4−xFex)O12 (x=0, 1.0, 2.0) where Mn is replaced by Fe cations in the ferrimagnetic perovskite BiCu3Mn4O12. These compounds have been prepared from citrate precursors under moderate pressure conditions (3.5 GPa) and 1000 °C in the presence of KClO4 as oxidizing agent. All the samples have been studied by x-ray and neutron powder diffraction (NPD) at room temperature and 4 K. The crystal structure has been defined in a cubic Im 3 ¯ (No. 204) space group with a 2a0×2a0×2a0 unit-cell. The doubling of the unit-cell occurs due to the ordering of Bi3+ and Cu2+ cations over A sites of the AA′3B4O12 structure. The A-site accommodates 12-fold coordinated Bi3+ ions and, at the A′-site, Jahn–Teller Cu2+ ions form pseudo-square planar units aligned perpendicular to each other. Mn4+/Fe3+ cations randomly occupy the centre of slightly distorted octahedra. These materials have also been characterized by magnetic and magnetotransport measurements. We found that all the samples are ferrimagnetic and show a progressive decrease of TC as the Fe content increases, since Fe ions disturb the ferromagnetic interactions within the B magnetic sublattice. In fact, the Curie temperature diminishes from TC=360 K (x=0) to TC=219 K (x=2). The magnetic structures, studied by low-temperature NPD data, correspond to an antiferromagnetic arrangement of spins at 8c and 6b sites; the ordered moments are in excellent agreement with those obtained from the saturation magnetization at 4 K. A significant magnetoresistant effect is determined for the x=1.0 oxide, with low-field values as high as 5% at 300 K and 1 T.

  • correlation between the crystal structure and the curie temperature in rcu3 mn3fe o12 r rare earth Complex Perovskites
    Dalton Transactions, 2012
    Co-Authors: Paula Kayser, Maria Retuerto, M J Martinezlope, J Sanchezbenitez, M T Fernandezdiaz, J A Alonso
    Abstract:

    New members of the family of Complex-perovskite oxides with the formula RCu3(Mn3Fe)O12 (R = Ce, Pr, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) have been synthesized and characterized. Polycrystalline samples have been prepared from citrate precursors treated under moderate pressure conditions (2–3.5 GPa) and 1000 °C in the presence of KClO4 as an oxidizing agent. All the samples have been studied by neutron powder diffraction (NPD) at 300 K and 2 K. These oxides crystallize in the cubic space group Im (no. 204). Mn4+/Mn3+ and Fe3+ occupy at random the octahedral B positions of the perovskite structure. These materials have also been characterized by magnetic and magnetotransport measurements. The observed enhancement of TC along the RCu3(Mn3Fe)O12 series is understood as an effect of the chemical pressure on the (Mn,Fe)–O bonds as R3+ size decreases. The semiconducting behaviour observed in all of the samples is related with the introduction of Fe at B position. Despite the drastic change of the transport properties, significant negative magnetoresistance values are observed in the Fe-containing compounds both at 10 K and 300 K.

S G Lushnikov - One of the best experts on this subject based on the ideXlab platform.

  • neutron scattering study of pbmg _ mathsf 1 3 ta _ mathsf 2 3 o _ mathsf 3 and bamg _ mathsf 1 3 ta _ mathsf 2 3 o _ mathsf 3 Complex Perovskites
    European Physical Journal B, 2004
    Co-Authors: S N Gvasaliya, S G Lushnikov, B Roessli, Denis Sheptyakov, T. A. Shaplygina
    Abstract:

    Neutron scattering investigations were carried out in PbMg1/3Ta2/3O3 and BaMg1/3Ta2/3O3 Complex Perovskites. The crystal structure of neither compound shows any phase transition in the temperature range 1.5-730 K. Whereas the temperature dependence of the lattice parameter of BaMg1/3Ta2/3O3 follows the classical expectations, the lattice parameter of relaxor ferroelectric PbMg1/3Ta2/3O3 exhibits anomalies. One of these anomalies is observed in the same temperature range as the peak in the dielectric susceptibility. Below $T\sim180$ K PbMg1/3Ta2/3O3 exhibits very small thermal expansion, similar to invar alloys. We find that in PbMg1/3Ta2/3O3, 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.

  • neutron scattering study of pbmg _ 1 3 ta _ 2 3 o _3 and bamg _ 1 3 ta _ 2 3 o _3 Complex Perovskites
    arXiv: Materials Science, 2004
    Co-Authors: Severian Gvasaliya, S G Lushnikov, B Roessli, Denis Sheptyakov, T. A. Shaplygina
    Abstract:

    Neutron scattering investigations were carried out in PbMg$_{1/3}$Ta$_{2/3}$O$_3$ and BaMg$_{1/3}$Ta$_{2/3}$O$_3$ 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 BaMg$_{1/3}$Ta$_{2/3}$O$_3$ follows the classical expectations, the lattice parameter of relaxor ferroelectric PbMg$_{1/3}$Ta$_{2/3}$O$_3$ exhibits anomalies. One of these anomalies is observed in the same temperature range as the peak in the dielectric susceptibility. We find that in PbMg$_{1/3}$Ta$_{2/3}$O$_3$, 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 behaviour of the specific heat of ab b o3 Complex Perovskites at low temperatures
    Ferroelectrics, 2004
    Co-Authors: S N Gvasaliya, S G Lushnikov, Yosuke Moriya, Hitoshi Kawaji, Tooru Atake, M B Smirnov, V Kazimirov
    Abstract:

    Specific heat of PbMg1/3Nb2/3O3, PbMg1/3Ta2/3O3, and BaMg1/3Ta2/3O3 Complex Perovskites has been measured from 2 K up to 295 K. At low temperatures a drastic difference of the behaviour of the specific heat of BaMg1/3 Ta2/3O3 with respect to other two compounds was found. Different approaches to describe the specific heat at the low temperatures of the PbMg1/3Nb2/3O3 relaxor ferroelectric are discussed.

  • neutron scattering study of pbmg1 3ta2 3o3and bamg1 3ta2 3o3 Complex Perovskites
    European Physical Journal B, 2004
    Co-Authors: S N Gvasaliya, S G Lushnikov, B Roessli, Denis Sheptyakov, T. A. Shaplygina
    Abstract:

    Neutron scattering investigations were carried out in PbMg 1/3 Ta 2/3 O 3 and BaMg 1/3 Ta 2/3 O 3 Complex Perovskites. The crystal structure of neither compound shows any phase transition in the temperature range 1.5-730 K. Whereas the temperature dependence of the lattice parameter-of BaMg 1/3 Ta 2/3 O 3 follows the classical expectations, the lattice parameter of relaxor ferroelectric PbMg 1/3 Ta 2/3 O 3 exhibits anomalies. One of these anomalies is observed in the same temperature range as the peak in the dielectric susceptibility. Below T ∼ 180 K PbMg 1/3 Ta 2/3 O 3 exhibits very small thermal expansion, similar to invar alloys. We find that in PbMg 1/3 Ta 2/3 O 3 , 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.

  • brillouin light scattering in Complex Perovskites
    Ferroelectrics, 2004
    Co-Authors: S G Lushnikov, Seiji Kojima
    Abstract:

    Results of Brillouin light scattering studies of the behavior of acoustic phonons in PMN, PMT and BMT crystals in a wide temperature range are presented. It is shown that the behavior of a transverse acoustic phonon in PMN crystals is not adequately described by the mode-coupling model.