Direct Bi3+–Bi3+ contacts mediated by lone pairs in the HP-BiNiO(PO4) polymorph

HP polytype of BiNiO(PO₄) (600 °C, 5 GPa) shows the same structural units as the AP one but in a denser form. Bi–Bi contacts intra/inter units are surprisingly identical due to lone pair electron interaction via sharp σ* bonding at the Fermi level.

Three different Ge environments in a new Sr5CuGe9O24 phase synthesized at high pressure and high temperature

In the framework of expanding the range of copper-based compounds in the pyroxene family, we have synthesized at high pressure and high temperature a powder containing a mixture of a new phase with stoichiometry Sr₅CuGe₉O₂₄ having two identified impurity phases. Electron crystallography showed that the new phase crystallizes in the monoclinic space group P2/c, with unit-cell parameters a = 11.8 Å, b = 8.1 Å, c = 10.3 Å and β = 101.3°. We applied the recently developed low-dose electron diffraction tomography method to solve the structure by direct methods. The obtained structure model contains all 9 independent cation positions and all 13 oxygen positions. A subsequent refinement against powder X-ray diffraction data ascertained the high quality of the structure solution, in particular, the unusual structural arrangement that there are three different environments for Ge in this phase.

The structure of nano-twinned rhombohedral YCuO2.66 solved by electron crystallography

In the search for frustrated spin interactions, a YCuO_2.66 phase has been synthesized by a treatment under oxygen pressure of YCuO_2.5. X-ray powder diffraction and electron diffraction studies have been conducted. Electron diffraction shows that the sample is twinned on a 10 nm scale. Precession electron diffraction data obtained from a twinned crystal was treated in order to obtain intensities corresponding to only one of the orientations of the twins. From this data a structure solution was obtained where, as in YCuO_2.5, the Cu atoms form triangular planes. The Cu atoms are linked in two dimensions by oxygen atoms in the present structure whereas in YCuO_2.5 they are only linked in one-dimensional chains.

Investigation of the Structure of the Modulated Doubly Ordered Perovskite NaLaCoWO6 and Its Reversible Phase Transition with a Colossal Temperature Hysteresis

Transmission electron microscopy, neutron diffraction, and synchrotron powder X-ray diffraction reveal a complex modulated structure on the doubly ordered perovskite NaLaCoWO₆. Electron diffraction patterns as well as high-resolution transmission electron microscopy images clearly show a periodicity of 12 a_p, where a_p is the cell parameter of the generic perovskite, along either the [100]_p or [010]_p direction. Annular bright-field scanning transmission electron microscopy of slightly tilted samples shows that there is no chemical origin for the superstructure but that it is caused by geometric rearrangements. An atomic model of the superstructure is proposed on the basis of octahedral tilt twinning. At low temperature, NaLaCoWO₆ undergoes a phase transition and the superstructure disappears. The compound takes on the more usual monoclinic P2₁ structure below the transition. Neutron powder diffraction reveals and electron diffraction confirms an unusually large temperature hysteresis, where the transition takes place at ∼180 K on cooling and at ∼320 K on heating. This hysteresis can be attributed to the necessity of rearranging the oxygen octahedra and the thus induced energy barrier for the transition.

Phase transitions and interface phenomena in the cryogenic temperature domain of a niobate nanostructured ceramic

Powder neutron diffraction and dielectric spectroscopy were used to investigate both crystallographic and dielectric permittivity properties of a Sr2KNb5O15 single phase ferroelectric oxide with nanosized grains ranging from 35 nm to 90 nm. Measurements were carried out in the temperature range from 10 K (cryogenic) to 550 K. All neutron diffraction data were indexed on the basis of a tetragonal double unit cell. From 10 K to room temperature the space group of the Sr2KNb5O15 ferroelectric phase was considered to be P4bm. The refinement of the paraelectric phase (at 550 K) was determined in the centrosymmetric space group P4/mbm. Dielectric spectroscopy measurements were performed in a thermal cycle. A set of four phase transitions non-related to symmetry changing was detected from Rietveld analysis of neutron powder diffraction data. During a thermal cycle, in the cryogenic temperature domain, strong thermal hysteresis is developed. Both phase transition and thermal hysteresis were correlated. These phenomena are associated with Nb-cation atomic displacements in the NbO6 octahedra along the c-axis direction and of the domain with different frequencies involving grains as well as an excess of interfaces ascribed to the grain boundary. The bulk/grain boundary interfaces in nanostructured ceramics are correlated with the thermal stability phenomenon.

A new Li-Mn-Ge-O phase solved by combining 3D electron diffraction methods

Pyroxene compounds are a common form of natural minerals and have been studied as such for a long time. More recently the research on quasi-one-dimensional magnetic and multiferroïc materials has renewed the interest in pyroxenes of the stoichiometry AMX2O6 (A = alkali metal, M = transition metal, X = Si or Ge), since the magnetic M3+ ions form chains. Chemical substitution on the A and M sites can change the magnetic coupling along these chains making this system a rich field for the exploration of new phases of interesting magnetic properties [1]. In this work we report the discovery of a new phase in the Li-Mn-Ge-O system. A HP-HT solid state reaction was performed on a mixture of nominal stoichiometry LiMnGe2O6 during 1 h at a temperature of 8500C and a pressure of 3 GPa in a belt press. Powder X-ray diffraction yielded a diffractogram that could not be indexed by known phases of this system. An electron diffraction study in a transmission electron microscope was conducted in order to identify any unknown phases. In the case of structures that promise interesting properties a more targeted synthesis can then be undertaken. For the purpose of this work, we studied one of several unknown phases in the powder in more detail. From standard selected area electron diffraction the unit cell was determined to be triclinic with cell parameters a = 2.51 nm, b = 1.30 nm, c = 1.30 nm, α = 96.00, β = 98.80and γ = 80.80. No comparable unit cell could be found in the databases neither in this system nor with different A, M or X ions. Intensities were recorded by in-zone axis precession electron diffraction and by electron diffraction tomography. Combining the data from both methods yielded the first model of the structure which we will present here.

First evidence of a phase transition in a high-pressure metal iodate

In the 1970s, a large number of metal iodates compounds were extensively investigated for their nonlinear optics (NLO) properties as well as for their ferroelectric, piezoelectric, and pyroelectric properties. Interest in these compounds resumed in the early 2000s. We have shown that metal iodates are particularly interesting for for quadratic NLO in mid IR, as they possess a large domain of transparency from the visible region to the beginning of the far IR region (12.5 μm), thus covering the three atmospheric transparency windows. The synthesis of metal iodates has so far been mainly investigated by solution chemistry, under hydrothermal conditions or by the flux method. The solid state synthesis of these compounds at high pressure has never been explored. To date, only the structural evolution of α-LiIO3 with pressure has been studied by X-ray powder diffraction [1]. It was shown that, at room temperature, α-LiIO3 is stable up to 75 GPa; only compression of the lattice parameters with pressure was observed. In this work, we present a new phase of silver iodate obtained at high pressure from α-AgIO3 and characterized by X-ray powder diffraction. The α-AgIO3 to β-AgIO3 transition was characterized by differential thermal analysis (DTA) at high pressure [2-3]. The thermal behaviors of α-AgIO3 and β-AgIO3 were studied by differential scanning calorimetry (DSC) at ambient pressure and in situ temperature-dependent X-ray powder diffraction. Structural studies of these two phases were carried out to understand the formation of β-AgIO3.

Structure, electric and magnetic properties of Pb(V1-xMx)O3, M=Ti, Fe compounds

It is well known that ferroelectricity and magnetic order are considered as hardly compatible in perovskite compounds. In this respect, PbVO3 is quite interesting: it is isostructural to ferroelectric PbTiO3 (P4mm) and contains V4+ spin ½ cations [1]. However, previous studies have failed to observe magnetic order in PbVO3, which was attributed either to a 2D magnetic behaviour or to magnetic frustration on a square lattice [2]. We present here the study of the substitution of V4+ by Fe3+ or Ti4+ cations, aiming at a better understanding of the relations between structural, magnetic and electric properties. PbVO3 single crystals and powders of substituted compounds were prepared at 6GPa , 9500C in belt and Conac type systems. A single crystal diffraction experiment confirmed the proposed structure for PbVO3, evidencing merohedral twinning related to ferroelectric domains also observed by SEM. For the Ti substitution, a complete Pb(V4+ 1-x Ti4+ x)O3 solid solution is observed for x = 0 to 1, while the Fe substitution stops at x=0.5 due to heterovalent cation replacement, the formula being Pb(V4+ 1-2x V5+ x Fe3+ x)O3. The cation oxidation states were checked by XANES (FAME-ESRF). The structures were studied by joint refinements of NPD (D1B-ILL) and XPD (Laboratory and ID31-ESRF) data, yielding the coordinations of V and M cations and the spontaneous polarization using a point charge model. A decrease of tetragonality, domain size along the c-axis and polarization is observed with increasing substitution. For the Ti series, the magnetic behaviour progressively changes from 2D to Curie-Weiss with increasing x. In the case of Fe, a broad peak in magnetic susceptibility is observed, at temperatures increasing from 12K to 30K for x going from 0.1 to 0.5. This was checked as due to a spin glass behaviour. No sign of magnetic order was observed by NPD. At the same time, a broad, frequency dependent anomaly of the dielectric constant is observed, reminiscent of a relaxor behaviour.

Identifying almost identical phases by 3D electron diffraction

Magnetically frustrated materials have been the subject of many studies over the last decades. In search for a 3-dimensional quantum spin liquid, where quantum-mechanical fluctuations prevent magnetic order, different phases of stoichiometry Ba3NiSb2O9 have recently [1] been synthesized some of them at high pressure. Two of these phases are hexagonal. The hexagonal phases (space groups P63/mmc and P63mc, respectively) have different structures but cell parameters that differ by less than 1%. Similar phases have been obtained with Cu [2] or Co [3]. These phases are well distinguished by powder X-ray diffraction when they appear in sufficient quantity in a newly synthesized powder. When these phases are present only in minor quantities, which is a common situation when synthesizing new materials, only transmission electron microscopy can give structural information on a very local scale. However, the accuracy of unit cell parameter determination by electron diffraction (usually 1% or worse) and the identical extinction conditions for the 2 space groups don't permit to distinguish between the two phases. Convergent beam electron diffraction could show the difference between the centrosymmetric and non-centrosymmetric space groups provided a suitably oriented particle can be found. In this work we propose a different method of distinguishing structures in such complicated cases by actually solving the structure. Sufficient in-zone axis precession electron diffraction and/or electron diffraction tomography data can be obtained from any crystal regardless of its orientation. In the subsequent structure solution we have tested both space groups. The quality (or absence thereof) of the structure solutions obtained clearly makes it possible to distinguish between the two hexagonal structures.

Structure, magnetic and magnetoelectric properties of Ca(Co,Mn)Ge2O6pyroxenes

Compounds belonging to the Pyroxene family are well known as rock-forming minerals, and have thus drawn substantial interest by mineralogists. In this family of general chemical formula AM(Si, Ge)2O6, A is usually an alkali metal monovalent cation or a divalent alkaline earth cation, and B may be a trivalent or divalent transition metal cation. Among pyroxene compounds, the monoclinic clinopyroxenes are characterized by isolated one-dimensional chains of MO6 octahedra linked by edge-sharing. Due to this specific arrangement, clinopyroxene compounds where M is a magnetic transition metal cation have attracted considerable attention in recent years. Investigations revealed that these compounds present a rich diversity of intriguing low-dimensional magnetic properties. The existence and possible interplay of low dimensionality and magnetic frustration results in multiferroic and/or magneto- electric (ME) properties. We have undertaken the study of the CaCo1-xMnxGe2O6 (0<x<1) solid solution to investigate the effect of the Co/Mn substitution on the magnetic and ME properties by means of neutron diffraction, magnetic and magneto-electric measurements. In CaCoGe2O6, strong FM interactions within the M chains dominate the AFM coupling between the chains. In contrary, the magnetic structure of CaMnGe2O6 is made of AFM chains coupled ferromagnetically. These two commensurate magnetic structures adopt two different magnetic point group that allows for linear (for Mn) and bilinear (for Co) magnetoelectric effect. For the Co/Mn solid solution, a competition exists between FM and AFM coupling within and between the chains. This results in the apparition of a spin glass state above the long range magnetic transition and for certain composition in a magnetic structure described by two propagation vectors. We will present detailed investigation of the relationship between structure, magnetic structure and ME properties for this rich series of ME compounds.

Jahn-Teller, polarity, and insulator-to-metal transition in BiMnO3 at high pressure

The interaction of coexisting structural instabilities in multiferroic materials gives rise to intriguing coupling phenomena and extraordinarily rich phase diagrams, both in bulk materials and strained thin films. Here we investigate the multiferroic BiMnO3 with its peculiar 6s2 electrons and four interacting mechanisms: electric polarity, octahedra tilts, magnetism, and cooperative Jahn-Teller distortion. We have probed structural transitions under high pressure by synchrotron x-ray diffraction and Raman spectroscopy up to 60 GPa. We show that BiMnO3 displays under pressure a rich sequence of five phases with a great variety of structures and properties, including a metallic phase above 53 GPa and, between 37 and 53 GPa, a strongly elongated monoclinic phase that allows ferroelectricity, which contradicts the traditional expectation that ferroelectricity vanishes under pressure. Between 7 and 37 GPa, the Pnma structure remains remarkably stable but shows a reduction of the Jahn-Teller distortion in a way that differs from the behavior observed in the archetypal orthorhombic Jahn-Teller distorted perovskite LaMnO3.

Magnetic phase diagram of the S = 1/2 triangular layered compound NaNiO(2): a single crystal study

Using magnetic torque measurements on a NaNiO(2) single crystal, we have established the magnetic phase diagram of this triangular compound. It presents five different phases depending on the temperature (4-300 K) and magnetic field (0-22 T) revealing several spin reorientations coupled to different magnetic anisotropies.

Pseudotumeur cardiaque révélant une maladie de Behçet

INTRODUCTION

Cardiac thrombosis is a rare complication of Behçet's disease (BD), which may present as a cardiac tumor. Its discovery precedes, in half of the cases, the diagnosis of BD. The high mortality may be associated to postsurgical complications and/or an associated involvement of pulmonary arteries.

CASE REPORT

We present the case of a 31 years old Caucasian French woman, with a history of venous thromboembolic disease, who had surgery after the discovery of a right ventricle tumor. That was an organised thrombus with endomyocardial fibrosis and a diagnosis of Behçet's disease was made after the surgery. The outcome was favourable under medical treatment associating corticosteroids, colchicine and antivitamin K (AVK), without relapse four years later.

CONCLUSION

The discovery of an intracardiac mass in a young patient must evoke the diagnosis of cardiac thrombus and Behçet's disease, even in the absence of predisposing ethnic or geographic factor.

[Aortitis after G-CSF injections]

INTRODUCTION

Aortitis consists in aortic wall inflammation from infectious or non infectious cause. It may lead to aortic aneurysm with a risk of rupture, which is life-threatening and may justify surgical procedures. The cause of the aortitis is sometimes obscure.

CASE REPORT

We report the case of a 55 years old woman who developed acute aortitis of the descending aorta after G-CSF (granulocyte-colony stimulating factor) injections for blood stem cells graft. No cause was found to the aortitis, the evolution was favorable after corticosteroid treatment, without aneurysm at six months.

CONCLUSION

The present case rises the question of G-CSF (Neupogen responsibility in aortic lesions. Neutrophilic mediated diseases (Sweet's syndrome, pyoderma gangrenosum) and leukocytoclastic vasculitis were reported after G-CSF therapy. Neutrophils induced by G-CSF injections present functional abnormalities which may play a role in the pathogenesis of these diseases.

[Glutathione peroxidase, an oxidative stress biomarker, in the menstrual cycle]

The oxygen, through his toxic effects, has determined the human organism to perfectionate multiple and efficient protection systems, especially the GSH-Px.

OBJECTIVES

To study the activity of GSHPx activity in the 0, 14 and 28 days of the menstrual cycle in a group of women with psychiatric disorders.

METHODS

The activity of GSH-Px was investigated in 24 women inpatients from the Psychiatric Department of Murgeni Hospital Vaslui. The GSH-Px level was determined in human serum using Fukuzawa method, modified in the Biochemistry Lab of the "Al. I. Cuza" University, Iaşi.

RESULTS

It has been no correlation between the type of psychiatric disorders and the level of GSHPx. This activity of GSHpx is in direct relationship with the concentration of sexual hormones, showing an hormone dependent enzymatic induction. A growth of the GSHPx activity from the day 0 to the 28th day of the menstrual cycle followed by a sudden decrease at menstruation time have been observed in all age groups. This fact demonstrated the existence of an enzymatic cycle.