Charge-Order Pattern of the Low-Temperature Phase of NaV2O5 Uniquely Determined by Resonant X-Ray Scattering from Monoclinic Single Domain

The present resonant x-ray scattering from each of monoclinically-split single domains of NaV2O5 has critically enhanced contrast between V4+ and V5+ ions strong enough to lead to unambiguous conclusion of the charge-order pattern of its low-temperature phase below Tc = 35 K. The zig-zag type charge-order patterns in the $ab$-plane previously confirmed have four kinds of configurations (A, A', B and B') and the stacking sequence along the c-axis is determined as the AAA'A' type by comparison with model calculations. By assigning the A and A' configurations to Ising spins, one can reasonably understand the previously discovered "devil's staircase"-type behavior with respect to the modulation of the layer-stacking sequences at high pressures and low temperatures, which very well resembles the global phase diagram theoretically predicted by the ANNNI model.Comment: 4 pages, 3 figure

Neutron Diffraction Study of Field Cooling Effects on Relaxor Ferroelectrics Pb[(Zn_{1/3} Nb_{2/3})_{0.92} Ti_{0.08}] O_{3}

High-temperature (T) and high-electric-field (E) effects on Pb[(Zn_{1/3} Nb_{2/3})_{0.92} Ti_{0.08}]O_3 (PZN-8%PT) were studied comprehensively by neutron diffraction in the ranges 300 <= T <= 550 K and 0 <= E <= 15 kV/cm. We have focused on how phase transitions depend on preceding thermal and electrical sequences. In the field cooling process (FC, E parallel [001] >= 0.5 kV/cm), a successive cubic (C) --> tetragonal (T) --> monoclinic (M_C) transition was observed. In the zero field cooling process (ZFC), however, we have found that the system does not transform to the rhombohedral (R) phase as widely believed, but to a new, unidentified phase, which we call X. X gives a Bragg peak profile similar to that expected for R, but the c-axis is always slightly shorter than the a-axis. As for field effects on the X phase, we found an irreversible X --> M_C transition via another monoclinic phase (M_A) as expected from a previous report [Noheda et al. Phys. Rev. Lett. 86, 3891 (2001)]. At a higher electric field, we confirmed a c-axis jump associated with the field-induced M_C --> T transition, which was observed by strain and x-ray diffraction measurements.Comment: 8 pages, 9 figures, revise

Relation between Fractal Inhomogeneity and In/Nb-Arrangement in Pb(In1/2Nb1/2)O3

Relaxor ferroelectrics show substantial responses to electric fields. The key difference from normal ferroelectrics is a temperature-dependent inhomogeneous structure and its dynamics. The lead-based complex perovskite Pb(In1/2Nb1/2)O3 is an intriguing system in which the inhomogeneous structure can be controlled by thermal treatment. Herein, we report investigations of the phase transitions in single crystals of Pb(In1/2Nb1/2)O3 via changing the degree of randomness in which In and Nb occupy the B site of the ABO3 perovskite structure. We studied the dynamic properties of the structure using inelastic light scattering and the static properties using diffuse X-ray scattering. These properties depend on the degree of randomness with which the B site is occupied. When the distribution of occupied In/Nb sites is regular, the antiferroelectric phase is stabilised by a change in the collective transverse-acoustic wave, which suppresses long-range ferroelectric order and the growth of the inhomogeneous structure. However, when the B site is occupied randomly, a fractal structure grows as the temperature decreases below T*~475 K, and nanosized ferroelectric domains are produced by the percolation of self-similar and static polar nanoregions

Observation of 90° domain walls in relaxor ferroelectrics PMN-28.6%PT by focusing upon the CTR scattering

Rod-shaped scattering has been observed in the tetragonal phase of Pb(Mg1/3Nb2/3)O3-28.7%PbTiO3 by use of the backscattering setting. We attribute it to crystal truncation rod (CTR) scattering associated with the boundary of 90$^\circ$ domains. The CTR scattering shows a characteristic temperature evolution, which enables us to discuss the properties of the domain walls, especially their temperature dependence on the domain wall widths. Though it is necessary to have a situation where the crystal coherence is suddenly truncated, like the 90 deg. domain wall, CTR scattering can be expected to be a powerful tool for examining the domain wall properties

Domain/heterophase fluctuations in the relaxor ferroelectrics studied by coherent x-ray diffraction

The CXD method have been shown to be applicable to the crystal characterization as well as the domain observation. The present CXD technique could evaluate the crystal coherence length up to 10 μm and the wide variety of samples were chosen in this study. We have shown how the ideal Bragg reflection deforms as the disorder and the defects increases and form the speckle patterns, the typical scattering patterns of CXD, by changing the samples. Finally we have successfully observed the μm/sub-μm domain arrangements in LuFe2O4/(1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (x = 0.09), where it is hard to be observed by the conventional diffraction techniques.Joint RCBJSF-IWRF Conferenc