Showing papers on "Tetragonal crystal system published in 2003"
TL;DR: The obtained hexagonal structured lanthanide orthophosphate LnPO(4) (Ln = La --> Tb) can convert to the monoclinic monazite structured products, and their morphologies remained the same after calcination at 900 degrees C in air.
Abstract: A simple hydrothermal method has been developed for the systematic synthesis of lanthanide orthophosphate crystals with different crystalline phases and morphologies. It has been shown that pure LnPO4 compounds change structure with decreasing Ln ionic radius: i.e., the orthophosphates from Ho to Lu as well as Y exist only in the tetragonal zircon (xenotime) structure, while the orthophosphates from La to Dy exist in the hexagonal structure under hydrothermal treatment. The obtained hexagonal structured lanthanide orthophosphate LnPO4 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy) products have a wirelike morphology. In contrast, tetragonal LnPO4 (Ln = Ho, Er, Tm, Yb, Lu, Y) samples prepared under the same experimental conditions consist of nanoparticles. The obtained hexagonal LnPO4 (Ln = La → Tb) can convert to the monoclinic monazite structured products, and their morphologies remained the same after calcination at 900 °C in air (Hexagonal DyPO4 is an exceptional case, it transformed to tetragonal DyPO...
444 citations
TL;DR: In this article, a non-hydrolytic sol−gel reaction between zirconium(IV) isopropoxide and ZrO2 chloride at 340 °C generated 4 nm sized Zirconia nanoparticles with an average size of 2.9 nm.
Abstract: A new and simple method has been developed to synthesize large quantities of highly monodisperse tetragonal zirconia nanocrystals. In this synthesis, a nonhydrolytic sol−gel reaction between zirconium(IV) isopropoxide and zirconium(IV) chloride at 340 °C generated 4 nm sized zirconia nanoparticles. A high-resolution transmission electron microscopic (HRTEM) image showed that the particles have a uniform particle size distribution and that they are highly crystalline. These monodisperse nanoparticles were synthesized without any size selection process. X-ray diffraction studies combined with Rietveld refinement revealed that the ZrO2 nanocrystals are the high-temperature tetragonal phase, and very close to a cubic phase. When zirconium(IV) bromide is used as a precursor instead of zirconium chloride, zirconia nanoparticles with an average size of 2.9 nm were obtained. The UV−visible absorption spectrum of 4 nm sized zirconia nanoparticles exhibited a strong absorption starting at around 270 nm. A fluoresce...
373 citations
TL;DR: In this article, a simple sol-gel method was used to synthesize nanometer-scale SnO 2 particles, which were characterized by X-ray diffraction, Fourier transform infrared (FTIR), UV-Vis absorption and photoluminescence spectroscopy.
366 citations
TL;DR: In this paper, the authors reported successful preparation of dense (Na 0.5 K 0.100) ceramics by ordinary sintering in air, and the dependence of phase structure on doping content of SrO and TiO 2 has been determined by the X-ray diffraction technique.
342 citations
TL;DR: In this paper, the spontaneous polarization of epitaxial BaTiO3/SrTiO 3 superlattices was studied as a function of composition using first-principles density-functional theory within the local density approximation.
Abstract: The spontaneous polarization of epitaxial BaTiO3/SrTiO3 superlattices is studied as a function of composition using first-principles density-functional theory within the local density approximation. With the in-plane lattice parameter fixed to that of bulk SrTiO3, the computed superlattice polarization is enhanced above that of bulk BaTiO3 for superlattices with BaTiO3 fraction larger than 40%. In contrast to their bulk paraelectric character, the SrTiO3 layers are found to be tetragonal and polar, possessing nearly the same polarization as the BaTiO3 layers. General electrostatic arguments elucidate the origin of the polarization in the SrTiO3 layers, with important implications for other nanostructured ferroelectrics.
279 citations
TL;DR: In this article, superlattice reflections at 12{hkl}p positions were observed in some electron diffraction patterns, which unambiguously demonstrates that the FeO6 octahedra are rotated in anti-phase about the pseudocubic [111] axis, consistent with the rhombohedral (R) space group R3c.
Abstract: X-ray diffraction and transmission electron microscopy have been performed on samples in the solid solution series (BiFeO3)x–(PbTiO3)1−x in which a morphotropic phase boundary occurs at x≈0.7. BiFeO3 exhibits superlattice reflections at 12{hkl}p positions in some electron diffraction patterns, the distribution of which unambiguously demonstrates that the FeO6 octahedra are rotated in anti-phase about the pseudocubic [111] axis, consistent with the rhombohedral (R) space group R3c. The amplitude of the rotations decreases in the R phase as PbTiO3 content increases and superlattice reflections are absent in electron diffraction patterns from the tetragonal (T) phase (x=0.6), indicating that it is untilted with space group P4mm. Electron diffraction patterns from samples where x=0.7 reveal superlattice reflections not associated with octahedral rotations and consistent with an intermediate phase with lower symmetry than T and R.
251 citations
TL;DR: In this article, the structural transitions associated with different cooling rates from the high temperature disordered state were investigated with X-ray diffraction of oriented single crystals of Fe-19 at% Ga.
218 citations
TL;DR: In this paper, a 2-step thermal decomposition method of barium titanyl oxalate (BaTiO(C2O4)24H2O) was used to obtain barium titanate (BTiO3) crystallites with various particle sizes from 17 to 100 nm.
Abstract: Barium titanate (BaTiO3) crystallites with various particle sizes from 17 to 100 nm were prepared by the 2-step thermal decomposition method of barium titanyl oxalate (BaTiO(C2O4)24H2O). The crystal structure of these BaTiO3 particles was assigned to cubic m-3m by a X-ray diffraction (XRD) measurement while it was assigned to tetragonal 4mm by a Raman scattering measurement. Investigation of impurity in these particles using both TG-DTA and FT-IR measurements revealed that no impurity was detected in the BaTiO3 lattice while hydroxyl and carbonate groups were detected only on the surface. The dielectric constants of these powders were measured using suspensions by a modified powder dielectric measurement method. As a result, the dielectric constant of BaTiO3 particles with a size of around 70 nm exhibited a maximum of over 15,000. This study revealed that BaTiO3 particles with a size around 70 nm were the most desirable for capacitor application.
198 citations
TL;DR: In this article, a theory of an adaptive ferroelectric phase has been developed to predict the microdomain-averaged crystal lattice parameters of this structurally inhomogeneous state.
Abstract: Ferroelectric and ferroelastic phases with very low domain wall energies have been shown to form miniaturized microdomain structures. A theory of an adaptive ferroelectric phase has been developed to predict the microdomain-averaged crystal lattice parameters of this structurally inhomogeneous state. The theory is an extension of conventional martensite theory, applied to ferroelectric systems with very low domain wall energies. The case of ferroelectric microdomains of tetragonal symmetry is considered. It is shown for such a case that a nanoscale coherent mixture of microdomains can be interpreted as an adaptive ferroelectric phase, whose microdomain-averaged crystal lattice is monoclinic. The crystal lattice parameters of this monoclinic phase are self-adjusting parameters, which minimize the transformation stress. Self-adjustment is achieved by application of the invariant plane strain to the parent cubic lattice, and the value of the self-adjusted parameters is a linear superposition of the lattice constants of the parent and product phases. Experimental investigations of Pb(Mg1/3Nb2/3)O3–PbTiO3 and Pb(Zn1/3Nb2/3)O3–PbTiO3 single crystals confirm many of the predictions of this theory.
198 citations
TL;DR: In this paper, the finite element method has been used to simulate the properties of panels with Kagome and tetragonal cores under compressive and shear loading, and the simulation has been performed for two different materials: a Cu-alloy with extensive strain hardening and an Al-aloy with minimal hardening.
195 citations
TL;DR: In this paper, the dielectric and structural properties of Bi(GaxFe1−x)O3−PbTiO3 (BGF-PT) crystalline solutions have been investigated.
Abstract: The dielectric and structural properties of Bi(GaxFe1−x)O3–PbTiO3 (BGF–PT) crystalline solutions have been investigated. Studies have focused on phase-pure perovskite materials. With increasing Ga content, we have found: (i) a coexistence of tetragonal and rhombohedral ferroelectric phases; (ii) a multicell perovskite structure for BGF–0.3PT; and (iii) a maximum tetragonal c/a ratio for the composition BGF–0.6PT with x=0.25. Also, Ga modification increases the electrical resistivity to ⩾1012 Ω cm, reduces the dielectric loss or tan δ over a wide temperature range, and increases the dielectric constant K. We have developed BGF–PT materials with values of K>400 and of tan δ<0.03.
TL;DR: In this paper, the phase diagram of BaZrO3-xCaZRO3 system was analyzed using a combination of X-ray and neutron powder diffraction, and transmission electron microscopy.
TL;DR: In this paper, the temperature dependence of the magnetic anisotropy of three different martensites known to exist in the Ni-Mn-Ga alloys was studied.
Abstract: We study the temperature dependence of the magnetic anisotropy of three different martensites known to exist in the Ni–Mn–Ga alloys. The anisotropy constants were determined from magnetization curves measured at different temperatures. The anisotropy of five-layered modulated tetragonal martensite is uniaxial with easy magnetization direction along short crystallographic axis. At room temperature K1(rt)=1.65×105 J m−3 and K2 is negligible. Seven-layered modulated orthorhombic martensite exhibits easy magnetization direction along the shortest crystallographic axis. K1(rt)=1.7×105 J m−3 and K2(rt)=0.9×105 J m−3 referring to hard and mid-hard magnetization axes. Nonmodulated tetragonal martensite possesses a uniaxial anisotropy with easy plane and hard magnetization direction along the long crystallographic axis with K1(rt)=−2.3×105 J m−3 and K2(rt)=0.55×105 J m−3. The temperature dependence of K1(T) of five-layered martensite follows magnetization power law with exponent n=3 suggesting a single ion origin ...
TL;DR: In this article, the microstructure in Y2O3-stabilized tetragonal zirconia polycrystal (Y-TZP) sintered at 1300°-1500°C was examined to clarify the role of Y3+ ions on grain growth and the formation of cubic phase.
Abstract: The microstructure in Y2O3-stabilized tetragonal zirconia polycrystal (Y-TZP) sintered at 1300°–1500°C was examined to clarify the role of Y3+ ions on grain growth and the formation of cubic phase. The grain size and the fraction of the cubic phase in Y-TZP increased as the sintering temperature increased. Both the fraction of the tetragonal phase and the Y2O3 concentration within the tetragonal phase decreased with increasing fraction of the cubic phase. Scanning transmission electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) measurements revealed that cubic phase regions in grain interiors in Y-TZP generated as the sintering temperature increased. High-resolution electron microscopy and nanoprobe EDS measurements revealed that no amorphous layer or second phase existed along the grain-boundary faces in Y-TZP and Y3+ ions segregated at their grain boundaries over a width of ∼10 nm. Taking into account these results, it was clarified that cubic phase regions in grain interiors started to form from grain boundaries and the triple junctions in which Y3+ ions segregated. The cubic-formation and grain-growth mechanisms in Y-TZP can be explained using the grain boundary segregation-induced phase transformation model and the solute drag effect of Y3+ ions segregating along the grain boundary, respectively.
TL;DR: In this paper, the X-ray diffraction (XRD) patterns and the Infrared, Raman and UV-visible spectra of CeO 2 ZrO 2 powders prepared by co-precipitation are presented.
TL;DR: In this article, it was observed that at temperatures above 150°C La2NiO4+δ transforms to the tetragonal I4/mmm structure and maintains this over the entire temperature range on both heating and cooling.
TL;DR: In this article, the authors performed x-ray diffraction and Raman spectroscopy measurements in the temperature range of 300-873 K on a single phase epitaxially oriented BaTiO3 thin film grown by pulsed laser deposition on a one crystal MgO substrate.
Abstract: We have performed x-ray diffraction and Raman spectroscopy measurements in the temperature range of 300–873 K on a single phase epitaxially oriented BaTiO3 thin film grown by pulsed laser deposition on a single crystal MgO substrate. The θ–2θ room temperature diffraction measurements and asymmetric rocking curves indicate that the film is very weakly tetragonal with the c-axis parallel to the plane of the film. X-ray diffraction measurements up to high temperature reveal only a change in slope in the perpendicular to the plane lattice parameter around 450 K (in bulk Tc=395 K) indicating that a diffuse-like of phase transition is taking place. Room temperature polarized Raman spectra show that the film is indeed tetragonal with C4v symmetry and with the a-axis perpendicular to the film plane. Monitoring of the overdamped soft mode and the 308 cm−1 mode confirms that the phase transition is taking place over a wide temperature range according to the x-ray results. The increase of the phase transition temper...
TL;DR: In this paper, the crystal chemistry of binary and ternary intermetallic compounds with tetragonal U 3 Si 2 or Zr 3 Al 2 type structure is reviewed.
Abstract: The crystal chemistry of binary and ternary intermetallic compounds with tetragonal U 3 Si 2 or Zr 3 Al 2 type structure is reviewed. Besides the preparation techniques and crystal chemistry, we especially focus on the structure-property relations and chemical bonding peculiarities.
TL;DR: In this article, the complete series of all nonradioactive lanthanide phosphates has been prepared in organic solution as ligand-capped nanoparticles, and very small nanoparticles are obtained for lanthanides for which the lattice energies of the bulk tetragonal xenotime phase and the bulk monoclinic monazite phase are similar.
Abstract: The complete series of all nonradioactive lanthanide phosphates has been prepared in organic solution as ligand-capped nanoparticles. In all cases, well-dispersed particles with mean sizes below 10 nm are obtained. Despite the similar chemical properties of the lanthanides, the growth, the crystal structure, and the mean size of the nanocrystals are found to be strongly affected by the lanthanide ion employed. Very small nanoparticles are obtained for lanthanides for which the lattice energies of the bulk tetragonal xenotime phase and the bulk monoclinic monazite phase are similar. These smaller nanoparticles do not show the expected phase transition from monoclinic to tetragonal and seem to have their own unique crystal structure. Possible explanations for these observations are discussed. Finally, we present the first results on the IR emission of Er3+-doped YbPO4 and (Lu, Yb)PO4 nanoparticles in solution.
TL;DR: In this article, the first order phase transition from tetragonal to cubic has been shown to correspond to the transition from normal and relaxor ferroelectric states in (Na 0.5Bi0.5)0.70Ba0.30TiO3 ceramic.
Abstract: A (Na0.5Bi0.5)0.70Ba0.30TiO3 ceramic has been studied by X-ray diffraction and by measurements of dielectric and ferroelectric properties between room temperature and 450 °C. A sharp increase in the electric permittivity and dielectric loss near 200 °C has been observed. This sharp increase in dielectric responses indicates a transformation between normal and relaxor ferroelectric states. It is found that polar regions can exist at higher temperatures. The X-ray diffraction study shows that the transformation corresponds to the first order phase transition from tetragonal to cubic. The use of the (Na0.5Bi0.5)0.70Ba0.30TiO3 ceramic for device application has also been indicated.
TL;DR: In this article, the authors synthesize dense KNbO3 ceramics by pressureless sintering under optimized heat-treatment conditions using a small amount of La2O3 and FeO3 additives.
Abstract: Dense KNbO3 ceramics have been successfully synthesized by pressure-less sintering under optimized heat-treatment conditions using a small amount of La2O3 and Fe2O3 additives KNbO3 forms (K1-xLax)(Nb1-xFex)O3 solid solutions and changes in the crystal system, depending on the additive content, from orthorhombic to tetragonal at x of 0020, and from tetragonal to cubic at x of 0200 or higher When only 0002 mol of La2O3 and Fe2O3 (x=0002) was added into KNbO3, the highest value (988%) of the theoretical density was obtained This specimen showed orthorhombic symmetry with a high Curie temperature of 420°C, and demonstrated a well-saturated ferroelectric hysteresis loop with large remanent polarization (Pr) of 18 µC/cm2, which is comparable to the value reported for pure KNbO3 ceramics fabricated by hot pressing Furthermore, the x=0002 specimen showed a planar electromechanical coupling ratio (kp) of 017 and piezoelectric d33 constant of 98 pC/N, regardless of the unsaturated poling state
TL;DR: Sr2CoWO6 perovskite has been prepared in polycrystalline form by solid-state reaction at 1150 °C, and the structure contains alternating CoO6 and WO6 octahedra, tilted in anti-phase by 7.24° in the basal ab plane along the [001] direction of the pseudocubic cell as discussed by the authors.
Abstract: Sr2CoWO6 perovskite has been prepared in polycrystalline form by solid-state reaction at 1150 °C. This material has been studied by high-resolution synchrotron X-ray and neutron powder diffraction (NPD), magnetic measurements, and differential scanning calorimetry (DSC). At room temperature, the crystal structure is tetragonal, space group I4/m, with a = 5.58277(1) A and c = 7.97740(1) A. The structure contains alternating CoO6 and WO6 octahedra, tilted in anti-phase by 7.24° in the basal ab plane along the [001] direction of the pseudocubic cell. This corresponds to the a0a0c- Glazer's notation as derived by Woodward for 1:1 ordering of double perovskites, consistent with space group I4/m. DSC and NPD measurements as a function of temperature indicate a structural transition from tetragonal to monoclinic (space group P21/n) at 260 K. At 2 K the cell parameters are a = 5.61267(8) A, b = 5.58753(8) A, c = 7.8994(1) A, and β = 90.041(3)°. The structure contains alternating CoO6 and WO6 octahedra, tilted in-...
TL;DR: In this paper, the effect of crystallite and grain size on the tetragonal → monoclinic phase transformation is examined more broadly across the yttria-zirconia system.
Abstract: In pure zirconia, ultrafine powders are often observed to take on the high-temperature tetragonal phase instead of the “equilibrium” monoclinic phase. The present experiments and analysis show that this observation is one manifestation of a much more general phenomenon in which phase transformation temperatures shift with crystallite/grain size. In the present study, the effect of crystallite (for powders) and grain (for solids) size on the tetragonal → monoclinic phase transformation is examined more broadly across the yttria–zirconia system. Using dilatometry and high-temperature differential scanning calorimetry on zirconia samples with varying crystallite/grain sizes and yttria content, we are able to show that the tetragonal → monoclinic phase transformation temperature varies linearly with inverse crystallite/grain size. This experimental behavior is consistent with thermodynamic predictions that incorporate a surface energy difference term in the calculation of free-energy equilibrium between two phases.
TL;DR: The structural evolution at 300 K of the series SrxBa1?xSnO3 and SrxCa 1?xsnO3 at 0.2 intervals has been determined by powder neutron diffraction.
Abstract: The structural evolution at 300 K of the series SrxBa1?xSnO3 and SrxCa1?xSnO3 at x = 0.2 intervals has been determined by powder neutron diffraction. All SrxCa1?xSnO3 samples (x = 0?1) have the Pbnm superstructure. In the series SrxBa1?xSnO3, the x = 1.0 and 0.8 samples have the Pbnm superstructure. The x = 0.6 sample has a second orthorhombic structure with space group Imma. There is a tetragonal I4/mcm phase at x = 0.4 and the undistorted cubic structure for x = 0.2 and BaSnO3. The octahedral tilt angles show a smooth variation with average A cation radius over the range of superstructures described by mean field theory close to the transition. The transitions are also analysed via the variation of spontaneous strains.
TL;DR: In this article, the phase transition from cubic to tetragonal phase arises for particles near 2 nm in diameter and first principles computer simulations of large zirconia clusters show that the critical size of the transition could occur for a diameter of 2.05 ± 0.15 nm, which is in good agreement with the experimental value.
Abstract: Pure (unstabilized) zirconia nanoparticles in the fluorite-type cubic phase are observed by transmission electron microscopy. Microscopic observations at a pressure of 5 × 10 -5 Pa suggest that the phase transition from the cubic to tetragonal phase arises for particles near 2 nm in diameter. First principles computer simulations of large zirconia clusters show that the critical size of the transition could occur for a diameter of 2.05 ± 0.15 nm, which is in good agreement with the experimental value.
TL;DR: In this article, the reconstructive tetragonal to monoclinic phase transition as a function of the size of zirconia nanoparticles is analyzed within the Landau theory and can be understood as a mechanism of size-dependent phase transition where the primary order parameter is altered by the nanoparticle size.
Abstract: Accurate neutron powder diffraction experiments at several temperatures allow one to monitor the reconstructive tetragonal to monoclinic phase transition as a function of the size of zirconia nanoparticles. The structure of the tetragonal phase observed in the nanocrystals is identical to that observed in micrometric zirconia above 1400 K. A uniaxial strain depending on grain size is observed. The phase transition occurs above a threshold crystal size. These results are analyzed within the Landau theory and can be understood as a mechanism of size-dependent phase transition where the primary order parameter is altered by the nanoparticle size.
TL;DR: In this paper, X-ray diffraction and FTIR-spectroscopy were used to characterise hexagonal, anhydrous tetragonal and orthorombic DyPO4 · H2O (Dy, Ho, Er, Tm, Yb, Lu and Y) powder.
Abstract: Powders of LnPO4 · H2O (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) prepared by crystallisation from boiling phosphoric acid (2 M H3PO4/1) solution were characterised by X-ray diffraction and FTIR-spectroscopy. Hexagonal LnPO4 · H2O (La → Tb), tetragonal (Ho → Lu and Y) and orthorombic DyPO4 · H2O crystalline modifications were identified. Ir-spectra of the hydrated hexagonal, anhydrous tetragonal LnPO4 · H2O (Dy, Ho, Er, Tm, Yb, Lu and Y) and anhydrous monoclinic (La → Tb) are consistent with those reported in the literature. However, the hydrated tetragonal LnPO4 · H2O (Ho, Er, Tm, Yb, Lu and Y) display a surplus band (625 cm−1) in the region of ν4, which was not reported in the literature. The band disappears after ignition at 950°C, while the tetragonal structure is still maintained, which may imply that it is attributed to hydrogen bonding of H2O molecules to the phosphate oxygen in hydrated salts. Some of the phosphates, after ignition at 950°C, display additional P2O7 4− band at 1265–1267 cm−1. That may be resulted from HPO4 2− for PO4 3− substitution in the phosphates crystallised in acidic (2 M H3PO4/1) solution.
TL;DR: In this paper, the effects of vanadium source, acid, addition of sodium hydroxide, chelating reagent, and even solvent on the crystalline size and shape were explored using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM).
Abstract: Yttrium orthovanadate (YVO4) crystals have been prepared hydrothermally in both strongly acidic and basic media. The effects of vanadium source, acid, addition of sodium hydroxide, chelating reagent, and even solvent on the crystalline size and shape were explored using X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Models for the generation of YVO4 crystals in both acidic and basic media are proposed from the experimental results. The influence of alkaline concentration on the sizes and shapes of YVO4 crystals has been investigated, and it has been found that the addition of sodium hydroxide can reduce the crystal sizes of YVO4. Well-defined YVO4 microcrystals with clear facets have been prepared, and dispersed YVO4 nanograins and nanoflakes with dimensions of 5–50 nm have been obtained. Both the size and shape of YVO4 crystals can be tailored by changing the reaction conditions even though YVO4 crystals generally show a tetragonal growth habit due to its tetragonal crystallographic symmetry.
Patent•
20 Jun 2003TL;DR: In this article, the first layer of a piezoelectric element is formed by an oriented control layer made of a cubic or tetragonal perovskite oxide (PZT).
Abstract: In a piezoelectric element 20, a first electrode layer 2 made of a an alloy of at least one metal selected from the group consisting of cobalt, nickel, iron, manganese and copper and a noble metal is formed on a silicon substrate 1, an oriented control layer 11 made of a cubic or tetragonal perovskite oxide is formed on the first electrode 2, and a piezoelectric layer 3 made of a rhombohedral or tetragonal perovskite oxide (e.g., PZT) is formed on the orientation control layer 11 so that the piezoelectric layer 3 is preferentially oriented along the (001) plane.
TL;DR: In this paper, a series of first-principles calculations were performed for ferromagnetic Ni2MnGa using density functional theory and PAW potentials, and it was shown that the modulation appears to be critically important for stability of the tetragonal structure with c/a < 1.
Abstract: A series of first-principles calculations were performed for ferromagnetic Ni2MnGa using density functional theory and PAW potentials. Theoretically, a tetragonal crystal structure homogeneous lattice-distortive strain is stabilized around c/a = 0.94 with respect to the L21 structure when, in addition, modulation shuffles with a period of five atomic planes are taken into account. This is in agreement with the observed structures in experimental works. The modulation appears to be critically important for stability of the tetragonal structure with c/a < 1. Here, we report a new feature which is related to the optimum amplitudes of the modulation in different atomic planes. Related to this are systematic changes in the minority spin density of states near the Fermi surface, like in the formalism of a pseudo-gap.