Magnetic-field-induced transition from metastable spin glass to possible antiferromagnetic-ferromagnetic phase separation in Cd0.5Cu0.5Cr2O4

Using ac susceptibility, dc magnetization and heat-capacity measurements, we have investigated the magnetic properties of Cd_0.5Cu_0.5Cr₂O₄. Cd_0.5Cu_0.5Cr₂O₄ has an extraordinary magnetic phase including a metastable spin-glass (SG) phase at zero field, a possible phase separation scenario of AFM/FM above ∼0.5 T field, and at intermediate fields, an apparent pseudo reentrant spin-glass (RSG) plateau is observed. These phenomena are closely correlated with the pinning effect of the Cu²⁺ sublattice on the frustrated lattice.     

Raman investigation of fibrous zeolites of the natrolite group at high pressures of an aqueous medium

The intermediate phases preceding overhydration are observed by Raman spectroscopy both in scolecite Ca[Al₂Si₃O₁₀] · 3H₂O and in thomsonite NaCa₂[Al₅Si₅O₂₀] · 6H₂O upon compression in an aqueous medium. The first intermediate phase of scolecite is attributed to a phase precursor revealed earlier using XRD at pressure of ～1 GPa. The widening of the Raman bands of O-H vibrations caused by the disordering of H₂O, which appears after additional water molecules are embedded in the zeolite channels, is typical of this intermediate phase. It is assumed on the basis of the Raman spectroscopy data that scolecite contains second overhydrated and second intermediate phases.     

Chemical,magnetic and charge ordering in the system hematite–ilmenite,Fe2O3–FeTiO3

Spin polarized electronic structure calculations of total energies for ordered supercells in the system Fe₂O₃–FeTiO₃ suggest that some layered ordered phases are more stable than an isocompositional mechanical mixture of hematite, Fe₂O₃, and ilmenite, FeTiO₃. This result contradicts established ideas about hematite–ilmenite phase relations because it suggests that there is at least one stable ordered phase with a bulk composition intermediate between hematite and ilmenite. It is not clear if this result is an artifact of the approximations made in generalized gradient spin density functional calculations, or if an intermediate phase, or phases, is in fact stable. The electronic structure of a 30-atom layered supercell was studied by a variety of techniques. The supercell structure is FTFFFT, where F is an Fe layer and T is a Ti layer perpendicular to the hexagonal c axis. The idea was to investigate possible charge ordering on Fe sites, that is a postulate of the ‘lamellar magnetism hypothesis’, but significant Fe²⁺–Fe³⁺ordering is not predicted.     

Structure of Artificial Grain Boundaries in Sapphire Bicrystals with Intermediate Layers

The structure of the artificial grain boundaries in Al₂O₃ bicrystals withY₃Al₅O₁₂ and Y-stabilizedZrO₂ (Y-ZrO₂) intermediate layers was studiedwith high resolution electron microscopy, electron diffraction and energydispersive X-ray analysis. TheY₃Al₅O₁₂ intermediate layer wasfound to be polycrystalline with three different orientation relationshipsbetween the ₂O₃ and theY₃Al₅O₁₂. The structure of theY₃Al₅O₁₂/₂O₃ interfaces is described.Also₂O₃ bicrystals with an Y-ZrO₂/₂O₃/Y-ZrO₂/₂O₃/Y-ZrO₂intermediate layer, prepared at two different temperatures, werestudied.Recry stallization of the intermediate layers occurred during thesolid phase intergrowth of the ₂O₃ bicrystalsparts and only an Y-ZrO₂ layer was found as intermediatelayer. The misorientation between the consecutive Y-ZrO₂grains was less than 1.5°. Misfit dislocations and atomic height stepsdecorate the Y-ZrO₂/₂O₃interface.     

Crystal structure of martensite and intermediate phases in Ni<Subscript>2</Subscript>MnGa studied by neutron diffraction

We have investigated crystal structures of martensite and intermediate phases in stoichiometric Ni₂MnGa. The neutron diffraction profile of the martensite phase measured at T = 4.2 K exhibits four satellites between [2 0 0]_P^* and [0 2 0]_P^* reflections (P stands for the parent phase) at incommensurate positions of [h 2-h 0]_P^* with h = 0.428, 0.863, 1.136 and 1.572. The profile of the intermediate phase measured at T = 210K exhibits two satellites between [2 0 0]_P^* and [0 2 0]_P^* reflections at incommensurate positions of [h 2-h 0]_P^* with h = 0.343 and 1.657. Although each satellite of the martensite phase moves toward its nearest fundamental reflection as temperature increases, that of the intermediate phase does not move significantly. On the contrary, the intensity of each satellite decreases significantly in the intermediate phase as temperature increases while not in the martensite phase. A synchrotron X-ray diffraction and a Rietveld analysis of the result reveal that, for both the phases, the displacement of atoms from the parent phase are represented by a sine wave whose propagation vector is parallel to [1 1 0]_P.     

Thermal and electrical properties of glass-ceramics based on lithium heptagermanate

Glass-ceramic samples based on lithium heptagermanate Li₂Ge₇O₁₅ have been prepared by rapid quenching and subsequent heat treatment. The calorimetric measurements have revealed that Li₂Ge₇O₁₅ crystallizes from the glass phase in two stages. An intermediate state is characterized by a significant increase in the electrical conductivity of the glass-ceramic materials.     

Mössbauer and magnetic studies of the phase state of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/La<Subscript>0.9</Subscript>Ca<Subscript>0.1</Subscript>MnO<Subscript>3</Subscript> composites

The formation of an intermediate phase in SrFe₁₂O₁₉/La_0.9Ca_0.1MnO₃ composites was demonstrated for the first time using only Mössbauer spectroscopy. The SrFe₁₂O₁₉/La_0.9Ca_0.1MnO₃ composite was prepared by the two-stage (sol–gel and hydrothermal) synthesis with varying initial conditions. The X-ray diffraction studies showed that the composite consisted of two phases: well-formed structures of manganite La_0.9Ca_0.1MnO₃ and hexagonal ferrite SrFe₁₂O₁₉. It was found that nanocrystalline La_0.9Ca_0.1MnO₃ particles with size d ? 150 nm formed in the composites at the surface of plate-like SrFe₁₂O₁₉ crystallites. The Mössbauer studies showed that the composite contained additional (intermediate) phase La_0.9Ca_0.1Mn(Fe)O₃ that formed at the interface between SrFe12O19 and La_0.9Ca_0.1MnO₃ phases. The intermediate phase concentration increased with the molar content of La_0.9Ca_0.1MnO₃; in this case, the fraction of the surface of SrFe₁₂O₁₉ crystallites coated with La_0.9Ca_0.1MnO₃ increased, which led to the increase in the total area of the interface surface and the intermediate phase concentration.     

Transport phenomena of aligned ybco polycrystals near vortex-glass transition temperature in weak magnetic field

Abstract

Transport phenomena of aligned polycrystalline Y₁Ba₂Cu₃O_7?δ samples in weak magnetic fields near the vortex-glass transition temperature T_g have been studied. In YBCO polycrystal a fully superconducting state develops via an “intermediate phase”. The non-ohmic dissipation in this “intermediate phase” is examined in terms of both the thermal activated flux-flow (TAFF) model and vortex-glass transition model. Our experimental results in low magnetic fields can better be explained by a vortex glass transition model rather than a TAFF model. We have reinterpreted the non-ohmic dissipative region below T_c , i.e., the so-called “intermediate phase” in terms of a vortex-glass phase.     

Study on reaction mechanism of YBa2Cu3O7-x film by TFA-MOD process

This paper systematically investigates the intermediate phases of YBa2Cu3O7-x (YBCO) film prepared by metalorganic deposition method using trifluoroacetates (TFA-MOD). According to x-ray diffraction and Raman analyses, the precursor film decomposed in a mixture of BaF2, Y2O3 and CuO after the pyrolysis process. Then these intermediate phases converted into tetragonal YBa2Cu3O6.5 at about 725°C. The influence of water vapour pressure on the YBa2Cu3O7-x film growth on LaAlO3 single-crystal substrates was also studied. The films prepared at low water vapour pressures (40-140 hPa) showed poor electrical performance due to the a-axis grain structure and impurity phases. However, the films prepared at 190 hPa exhibited the highest critical temperature of 90 K and the highest Jc of 3.8 MA/cm2, which was attributed to the formation of a purer YBCO phase and stronger biaxial texture.     

SYNTHESIS AT AMBIENT PRESSURE AND SUPERCONDUCTIVITY OF Hg-DOPED TI-BASED DOUBLE [(T1, Hg)-O]-LAYERED CDPHATES

The Hg-doped T1-based 2201 and 2212 phase layered cuprates have been successfully syn-thesized at ambient pressure and identified by X-ray powder diffraction and electron diffraction analysis. Compared with pure T1-based 2212 phase compound, there are indications that the corresponding Hg-doped T1-based compound (T1_1.8Hg_0.2)Ba₂CaCu₂O_z exhibits much higher T_c (> 132K).     

Crystallization of CaAl4O7 and CaAl12O19 powders

Calcium is always present in alumina systems as an unintentional (or intentional) dopant, and yet the fundamental effect of its incorporation into the aluminas is not well understood, and is further complicated by the presence of Si. The synthesis of powders of two calcium aluminate phases (CaAl₄O₇, which is also known as CaO · 2Al₂O₃ or CA₂, and CaAl₁₂O₁₉, which is also known as CaO · 6Al₂O₃ or CA₆) has been investigated using low-temperature chemical-processing techniques. The crystallization of these powders from the amorphous precursor has been examined using various characterization techniques. The precursors for the powders were prepared by mixing stoichiometric proportions of the nitrate salts into a 5 wt% aqueous solution of poly(vinyl alcohol). Conversion of the amorphous precursors to crystalline powders and the subsequent phase transitions were monitored using differential thermal analysis (DTA), thermogravimetric analysis (TGA) and powder X-ray diffractometry (XRD). While powders with CA₂ stoichiometry crystallized directly at 883°C, amorphous powders with CA₆ stoichiometry first crystallized into an intermediate structure without partitioning and then transformed into CA₆ at 1175°C. Fully and partially crystallized powders were analyzed using transmission electron microscopy and electron energy-loss spectroscopy (EELS). Measured near-edge structures (Al–L_2,3, Ca–L_2,3 and O–K) are presented for the CA₂, γ-Al₂O₃ and CA₆ phases. The intermediate phase, identified as γ-Al₂O₃, was found to accommodate a significant concentration of Ca.     

A Raman spectroscopic and TEM study on the structural evolution of Na2Ti3O7 during the transition to Na2Ti6O13

The synthesis of sodium hexatitanate from sodium trititanate was characterized by Raman spectroscopy, X‐ray diffraction (XRD) and high‐resolution transmission electron microscopy (HRTEM). The structural evolution from trititanate to hexatitanate was studied using Raman spectra, XRD and HRTEM techniques. It was found that the Raman bands at 279 cm⁻¹ corresponding to very long Ti O bonds and at 883 cm⁻¹ corresponding to the very short Ti O bonds decrease in intensity and finally disappear during the transition from sodium trititanate to sodium hexatitanate. The band at 922 cm⁻¹ corresponding to an intermediate‐length Ti O bond was observed to become stronger with the increase in temperature, indicating that there is no terminal oxygen atom in the crystal structure of Na₂Ti₆O₁₃ and that all the oxygen atoms become linearly coordinated by two titanium atoms. Furthermore, the TiO₆ octahedron in Na₂Ti₆O₁₃ are more regular because the very long (2.2 Å) or very short (1.7 Å) Ti O bonds disappear. It is revealed that the phase transition from trititanate to hexatitanate is a step‐by‐step slipping process of the TiO₆ octahedral slabs with the loss of sodium cations, and a new phase with formula Na_1.5H_0.5Ti₃O₇ has been discovered as an intermediate phase to interlink Na₂Ti₃O₇ and Na₂Ti₆O₁₃. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of strain-induced order-parameter coupling on the ferroelastic behaviour of lead phosohate-arsenate

The phase diagram of ferroelastic Pb₃(PO₄)₂-Pb₃(AsO₄)₂ has been reinvestigated and four new phase transitions have been found from birefringence measurements at low temperatures. The first-order phase transition between the phases b (C2/c) and c (P2₁/c) in Pb₃(AsO₄)₂ becomes continuous with increasing P-content.

In Pb₃(P_0.2As_0.8O₄)₂, a monoclinic intermediate phase b_c was identified from the measurements of the spontaneous strain, the morphic birefringence and the orientation of the optical indicatrix.

The experimental results are interpreted using the Landau theory of biquadratically coupled order parameters. Phase b is related to an order parameter of L-point symmetry in the paraelastic phase a (3). The phase c is due to a critical F-point in 3. The intermediate phase b_c is the consequence of the biquadratic coupling of order parameters with L-and F-point symmetry.

Model calculations for Pb₃(P_0.2As_0.8O₄)₂ relate the free energies of the phases b, b_c and c and the temperature dependence of the order parameters with the measured optical birefringence. They explain well the occurrence of an intermediate phase with monoclinic symmetry from the movement of the thermodynamic stability point in the vector space diagram of order parameters.     

Metamagnetic transitions of Lu2Cu2O5 studied by submillimeter-wave ESR measurement

Lu₂Cu₂O₅ is a related substance of Y₂Cu₂O₅ which is an unusual copper oxide with two successive metamagnetic transitions. We have performed the antiferromagnetic resonance (AFMR) measurements of Lu₂Cu₂O₅ in the millimeter and submillimeter wave region with the pulsed magnetic field up to 16 T at 1.8 K. Our measurements this time are very detailed frequency dependence measurements compared to the previous measurement and we found new AFMR modes which were not observed previously. From the analysis of the observed AFMR modes, we found that the magnetic phase aboveH _cl = 3.1 T in Lu₂Cu₂O₅ is different from that in Y₂Cu₂O₅.     

Elementary processes during collisions of ions with tryptophan molecules

The relative cross sections of elementary processes occurring in single collisions of tryptophan molecules in the gaseous phase with He²⁺ ions with energy 4 keV/u are measured using time-of-flight mass spectrometry for studying the mechanism of radiation damage of amino acid molecules. The fragmentation channels for intermediate singly and doubly charged tryptophan molecular ions formed during one-electron capture, two-electron capture, and electron capture with ionization are investigated. Significant difference is observed in the mass spectra of fragmentation of intermediate doubly charged ions formed during the capture with ionization and double capture, which is associated with different energies of excitation of {C₁₁H₁₂N₂O₂}²⁺* ions.     

Relative diffusion transform and quantum speedup of computations

It is shown that every function computable in time T(n) and space S(n) on a classical one-dimensional cellular automaton can be computed with certainty in time O(T ^1/2 S) and space $n\sqrt T $ on a quantum computer with relative diffusion transforms (RDTs) on parts of intermediate products of classical computation. However, in the general case, RDTs cannot be implemented by the conventional quantum computer even with oracles for intermediate results. Such a function can be computed only in time O(S4 ^S/2 T/T ₁) on the conventional quantum computer with oracles for the intermediate results of classical computations with time T ₁.     

Dielectric properties of Bi4Ti3O12–SrBi4Ti4O15 intergrowth ceramics synthesized by a modified oxalate route

In this study, Bi₄Ti₃O₁₂–SrBi₄Ti₄O₁₅ (BIT–SBTi) intergrowth ferroelectric ceramics was synthesized by a modified oxalate route. The phase formation behaviour, structure, morphology and electrical properties of the intergrowth ceramics were also investigated. The phase formation takes place through intermediate phases like SrBi₂O₄ and Bi₁₂TiO₂₀. The precursor mostly changes to Bi₄Ti₃O₁₂ at 600°C and to BIT–SBTi intergrowth at 800°C. Rietveld analysis of the X-ray diffraction pattern showed that the structure of the intergrowth compound was orthorhombic with lattice parameters a = 5.4408(3), b = 5.4505(1) and c = 74.0851(4) Å. The intergrowth ferroelectrics showed a phase transition at 610°C and a frequency-stable permittivity and dielectric loss behaviour. The intergrowth ferroelectrics also showed a larger 2P_r than their constituents BIT and SBTi.     

Lead zirconate titanate–barium titanate by mechanical activation of mixed oxides

For the first time, the perovskite phase in 0.9Pb (Zr_0.52Ti_0.48)O₃-0.1BaTiO₃(0.9PZT-0.1BT) is triggered to form in an oxide matrix consisting of PbO, ZrO₂, BaO, and TiO₂. Unlike in the solid-state reaction activated by calcination at an intermediate temperature, intermediate phases, such as PbTiO₃, were not observed with increasing degree of mechanical activation prior to the formation of perovskite 0.9Pb(Zr_0.52Ti_0.48)O₃-0.1BaTiO₃ phase. This suggests that the nucleation and subsequent growth of perovskite crystallites in the activated oxide composition are not a result of the interfacial reactions that normally occur in the temperature-driven solid-state reaction. The mechanical activation-derived powders can be sintered to a relative density of >97% theoretical at 1100 °C. Sintered 0.9Pb(Zr_0.52Ti_0.48)O₃-0.1BaTiO₃ derived from mechanical activation of constituent oxides exhibits a maximum dielectric constant of 775 and a minimum dielectric loss of <2% at room temperature when measured at 1.0 kHz. Received: 3 December 1998 / Accepted: 18 March 1999 / Published online: 24 June 1999     

γ-Fe2O3中的氢含量

利用热中子透射法测定γ-Fe₂O₃的氢含量。利用差热分析、磁分析以及穆斯堡尔效应研究γ-Fe₂O₃的相变,实验结果表明在γ-Fe₂O₃结构中确实含有一定量的氢,当γ-Fe₂O₃结构中的阳离子空位被H¹⁺,Co²⁺,Si⁴⁺,P⁵⁺等离子占据时,将 关键词：     

Sonochemical assisted synthesis of SrFe12O19 nanoparticles

We present the synthesis of M-type strontium hexaferrite by sonochemistry and annealing. The effects of the sonication time and thermal energy on the crystal structure and magnetic properties of the obtained powders are presented. Strontium hexagonal ferrite (SrFe₁₂O₁₉) was successfully prepared by the ultrasonic cavitation (sonochemistry) of a complexed polyol solution of metallic acetates and diethylene glycol. The obtained materials were subsequently annealed at temperatures from 300 to 900 °C. X-ray diffraction analysis shows that the sonochemical process yields an amorphous phase containing Fe³⁺, Fe²⁺ and Sr²⁺ ions. This amorphous phase transforms into an intermediate phase of maghemite (γ-Fe₂O₃) at 300 °C. At 500 °C, the intermediate species is converted to hematite (α-Fe₂O₃) by a topotactic transition. The final product of strontium hexaferrite (SrFe₁₂O₁₉) is generated at 800 °C. The obtained strontium hexaferrite shows a magnetization of 62.3 emu/g, which is consistent with pure hexaferrite obtained by other methods, and a coercivity of 6.25 kOe, which is higher than expected for this hexaferrite. The powder morphology is composed of aggregates of rounded particles with an average particle size of 60 nm.