Magnetic anisotropy, magnetization reversal and switching in Ni4Nb2O9single crystals.

Ni4Nb2O9is an insulating compensated ferrimagnet withTN= 77 K andTcomp= 33 K. We report here the study of the magnetic anisotropy using millimeter-size crystals grown in an image furnace. The magnetization measurements, vs temperature, performed withHaligned along the three main crystallographic axes, show similar Curie-Weiss temperatures (Θp≈ 190 K) and rather similar effective paramagnetic moments (from 3.5µBto 3.6µB). This suggests that the strongest magnetic interaction is the antiferromagnetic one, coupling the ferromagnetic distorted honeycomb layers and zigzag ribbons via face sharing NiO6octahedra. This strong antiferromagnetic coupling is supported by DFT calculations that do not evidence any inter site ferromagnetic interaction, leading to total compensation between magnetic moments of both Ni2+sites. Measurements vs magnetic field belowTNreveal an anisotropic behaviour, with square magnetization loops forHin theabplane, whereas linearM(H) curves without hysteresis are observed forH‖c. This anisotropy betweenabplane andcaxis occurs also in the magnetization reversal (MR), which is observed in theabplane only. Starting fromM(H) virgin curves collected just belowTcomp= 33 K withH‖aorH‖b, the memory-like effect was tested through magnetization switching induced byHorTalternating changes. BelowTcomp, smallerHis needed to switchMsymmetrically forHalongbthan alonga, and, forTswitching (2 K interval, constantH), a largerMchange is obtained alongathan alongb. The comparison with ferrimagnetic oxides which exhibit MR, like spinels or rare earth orthoferrites, shows that Ni4Nb2O9is unique since only one magnetic cation over two sites in octahedral coordination is at play, thus providing a unique platform to studyMswitching but also a challenge for theoretical interpretation.

Long-term results of dynamic graciloplasty for severe fecal incontinence.

BACKGROUND: Fecal incontinence is a common complaint. In the presence of extensive sphincter deterioration, after anorectal trauma, or failure of non-invasive surgical procedures, a sphincter reconstruction with dynamic graciloplasty can be proposed. The aim of our study was to evaluate the long-term results of dynamic graciloplasty. METHODS: A retrospective study was conducted on all the patients who underwent dynamic graciloplasty between 1997 and 2019 in one French tertiary referral center for severe fecal incontinence after previous unsuccessful treatments. Only patients with available long-term results (≥ 1 year) were included. RESULTS: Among 40 patients who underwent dynamic graciloplasty, 31 patients [77% women, median age = 57 years (range 17-74 years)] were included with a mean long-term follow-up of 11 ± 6 years. The mean duration of fecal incontinence was 8 ± 7.9 years and the mean Wexner score was 16 ± 3. Fecal incontinence was adult-acquired in 88% of patients. 74% of patients underwent previously unsuccessful surgical procedures. A diverting colostomy was present in 7 patients (23%). Postoperative overall, surgical and major morbidity occurred in 20 (64%), 17 (55%) and 7 (23%) patients, respectively. At the end of follow-up, 18 patients still used their stimulation device (58%), and 4 patients required a permanent colostomy (12.5%). Long-term efficacy of dynamic graciloplasty was reported by 17 patients (55%). CONCLUSION: The efficacy of dynamic graciloplasty is conserved in 55% of patients after a mean follow-up of 11 years. This procedure needs to be kept in the surgical armamentarium for persistent and severe fecal incontinence after previous surgical interventions or in the presence of large perineal defects, before the ultimate step of permanent stoma.

Value of early repeated abdominal CT in selective non-operative management for blunt bowel and mesenteric injury.

OBJECTIVES: To evaluate the performance of an early repeated computed tomography (rCT) in initially non-operated patients with blunt bowel and mesenteric injuries (BBMI). METHODS: This was a monocentric retrospective observational study from 2009 to 2017 of patients with a BBMI on initial CT (iCT). Patients initially non-operated on were scheduled for a rCT within 48 h. Initial CT and rCT diagnostic performance were compared based on a surgical injury prediction score previously described. For statistical analysis, we used the chi-square analyses for paired data (McNemar test). RESULTS: Eighty-four patients (1.9% of trauma) had suspected BBMI on iCT. Among these patients, 22 (26.2%) were initially operated on, 18 (21.4%) were later operated on, and 44 (52.4%) were not operated on. The therapeutic laparotomy rate was 85%. Thirty-four patients initially non-operated on had a rCT. The absolute value of the CT scan score increased for 15 patients (44.1%). The early rCT diagnostic performance, compared with iCT, showed an increase in sensitivity (from 63.6 to 91.7%), in negative predictive value (from 77.4 to 94.7%), and in AUC (from 0.77 to 0.94). CONCLUSION: In initially non-operated patients with BBMI lesions, the performance of an early rCT improved the sensitivity of lesion detection requiring surgical repair and the security of patient selection for non-operative treatment. KEY POINTS: • Selective non-operative treatment for hemodynamically stable patients with blunt bowel and/or mesenteric injuries on CT is developing but remains controversial. • An early repeated CT improved the sensitivity of lesion detection requiring surgical repair and the security of patient selection for conservative treatment.

Risk factors of exocrine and endocrine pancreatic insufficiency after pancreatic resection: A multi-center prospective study.

Management of functional consequences after pancreatic resection has become a new therapeutic challenge. The goal of our study is to evaluate the risk factors for exocrine (ExoPI) and endocrine (EndoPI) pancreatic insufficiency after pancreatic surgery and to establish a predictive model for their onset. PATIENTS AND METHODS: Between January 1, 2014 and June 19, 2015, 91 consecutive patients undergoing pancreatoduodenectomy (PD) or left pancreatectomy (LP) (72% and 28%, respectively) were followed prospectively. ExoPI was defined as fecal elastase content<200µg per gram of feces while EndoPI was defined as fasting glucose>126mg/dL or aggravation of preexisting diabetes. The volume of residual pancreas was measured according to the same principles as liver volumetry. RESULTS: The ExoPI and EndoPI rates at 6 months were 75.9% and 30.8%, respectively. The rate of ExoPI after PD was statistically significantly higher than after LP (98% vs. 21%; P<0.001), while the rate of EndoPI was lower after PD vs. LP, but this difference did not reach statistical significance (28% vs. 38.5%; P=0.412). There was no statistically significant difference in ExoPI found between pancreatico-gastrostomy (PG) and pancreatico-jejunostomy (PJ) (100% vs. 98%; P=1.000). Remnant pancreatic volume less than 39.5% was predictive of ExoPI. CONCLUSION: ExoPI occurs quasi-systematically after PD irrespective of the reconstruction scheme. The rate of EndoPI did not differ between PD and LP.

Localised Ag(+) vibrations at the origin of ultralow thermal conductivity in layered thermoelectric AgCrSe2.

In materials science, the substructure approach consists in imagining complex materials in which a particular property is associated with a distinct structural feature, so as to combine different chosen physical characteristics, which otherwise have little chance to coexist. Applied to thermoelectric materials, it has been used to achieve simultaneously phonon-glass and electron-crystal properties. Mostly studied for its superionic conductivity, AgCrSe2 is a naturally layered compound, which achieves very low thermal conductivity, ~0.4 W.K(-1).m(-1) at RT (room temperature), and is considered a promising thermoelectric. The Cr atoms of the [CrSe2]∞ layer bear a spin S = 3/2, which orders below TN = 55 K. Here we report low temperature inelastic neutron scattering experiments on AgCrSe2, alongside the magnetic field evolution of its thermal and electrical transport. We observe a very low frequency mode at 3 meV, ascribed to large anharmonic displacements of the Ag(+) ions in the [Ag]∞ layer, and 2D magnetic fluctuations up to 3 TN in the chromium layer. The low thermal conductivity of AgCrSe2 is attributed to acoustic phonon scattering by a regular lattice of Ag(+) oscillating in quasi-2D potential wells. These findings highlight a new way to achieve localised phonon modes in a perfectly crystalline solid.

A new active Li-Mn-O compound for high energy density Li-ion batteries.

The search for new materials that could improve the energy density of Li-ion batteries is one of today's most challenging issues. Many families of transition metal oxides as well as transition metal polyanionic frameworks have been proposed during the past twenty years. Among them, manganese oxides, such as the LiMn2O4 spinel or the overlithiated oxide Li[Li1/3Mn2/3]O2, have been intensively studied owing to the low toxicity of manganese-based materials and the high redox potential of the Mn(3+)/Mn(4+) couple. In this work, we report on a new electrochemically active compound with the 'Li4Mn2O5' composition, prepared by direct mechanochemical synthesis at room temperature. This rock-salt-type nanostructured material shows a discharge capacity of 355 mAh g(-1), which is the highest yet reported among the known lithium manganese oxide electrode materials. According to the magnetic measurements, this exceptional capacity results from the electrochemical activity of the Mn(3+)/Mn(4+) and O(2-)/O(-) redox couples, and, importantly, of the Mn(4+)/Mn(5+) couple also.

Searching for new thermoelectric materials: some examples among oxides, sulfides and selenides.

Different families of thermoelectric materials have been investigated since the discovery of thermoelectric effects in the mid-19th century, materials mostly belonging to the family of degenerate semi-conductors. In the last 20 years, new thermoelectric materials have been investigated following different theoretical proposals, showing that nanostructuration, electronic correlations and complex crystallographic structures (low dimensional structures, large number of atoms per lattice, presence of 'rattlers'…) could enhance the thermoelectric properties by enhancing the Seebeck coefficient and/or reducing the thermal conductivity. In this review, the different strategies used to optimize the thermoelectric properties of oxides and chalcogenides will be presented, starting with a review on thermoelectric oxides. The thermoelectric properties of sulfides and selenides will then be discussed, focusing on layered materials and low dimensional structures (TiS2 and pseudo-hollandites). Some sulfides with promising ZT values will also be presented (tetrahedrites and chalcopyrites).

On the effects of substitution, intercalation, non-stoichiometry and block layer concept in TiS2 based thermoelectrics.

TiS2 based layered sulfides have recently received increasing interest from the thermoelectric community. Due to its layered structure, the TiS2 compound with its enormous capacity for chemical substitution and intercalation offers different means to optimize the thermoelectric response through concomitant tuning of carrier concentration and decrease of the lattice thermal conductivity. In this review, we first discuss and summarize the crystal structures and physical/chemical properties of TiS2 based layered sulfides. Then, the approaches that successfully enhanced the thermoelectric performances in the TiS2 ceramic samples densified by Spark Plasma sintering are outlined, which include intercalation, non-stoichiometry, cationic substitution, and the block layer concept.

Oesophagogastric reconnection is possible.

INTRODUCTION: The first oesophagogastric dissociation was described by Bianchi in 1997 for the treatment of severe gastro-oesophageal reflux (GOR) in neurological patients to avoid serious respiratory complications. The dissociation leads to malabsorption and growth problems. We describe the first two cases of oesophagogastric reconnection long after lung growth. PATIENTS: Case no. 1 was a 12.7-year-old child with a history of type I oesophageal atresia. He required oesophagocoloplasty and gastric dissociation by the Bianchi procedure at the age of 3 months. He has oesophagogastric reconnection at 11 years old because he had a several macrocytic anaemia. Case no. 2 was also a 12-year-old boy, with an unlabelled multiple malformation syndrome with type I oesophageal atresia. He had an oesophagocoloplasty with gastric dissociation at the age of 3 months to protect his lungs. The reconnection was proposed at 10 years old because he developed multiple nutritional deficiencies and growth retardation. RESULTS: The two cases have no clinical symptom of reflux and their post-operative digestive contrasts are normal. Reconnection appears possible with or without preserving the Roux-en-Y loop. It improves absorption and corrects any vitamin deficiencies, allows the reconnected stomach to be monitored in terms of reflux and malignancy and enables enteral nutrition supplementation to be stopped. The possibility of reconnection after the Bianchi procedure therefore extends its indications, mostly in the case of oesophageal atresia complicated by severe GOR with pulmonary repercussions or tracheoesophageal cleft.

Oxygen storage capacity and structural flexibility of LuFe2O4+x (0≤x≤0.5).

Combining functionalities in devices with high performances is a great challenge that rests on the discovery and optimization of materials. In this framework, layered oxides are attractive for numerous purposes, from energy conversion and storage to magnetic and electric properties. We demonstrate here the oxygen storage ability of ferroelectric LuFe2O4+x within a large x range (from 0 to 0.5) and its cycling possibility. The combination of thermogravimetric analyses, X-ray diffraction and transmission electron microscopy evidences a complex oxygen intercalation/de-intercalation process with several intermediate metastable states. This topotactic mechanism is mainly governed by nanoscale structures involving a shift of the cationic layers. The ferrite is highly promising because absorption begins at a low temperature (~=200 °C), occurs in a low oxygen pressure and the uptake of oxygen is reversible without altering the quality of the crystals. The storage/release of oxygen coupled to the transport and magnetic properties of LnFe2O4 opens the door to new tunable multifunctional applications.

Sr7Co4(CO3)O(13-δ) (δ = 1.64), an original cobaltite derivative of the Ruddlesden-Popper series.

The oxycarbonate Sr7Co4(CO3)O11.36 exhibits a peculiar structure that has been characterized by combining transmission electron microscopy analyses and neutron diffraction. It consists of a regular intergrowth between the m = 2 and carbonated m = 3 members of the Sr(m+1)Co(m)O3(m+1) Ruddlesden-Popper (RP) series, Sr3Co2O5.87 and Sr4Co2(CO3)O5.49, respectively. A description of the structure is proposed to provide identification of the different building blocks. This material is semiconducting and presents a complex magnetic behavior, characteristic of what is observed for the RP(2) or RP(3) series, with a cobalt valency close to 2.7.

Pressure-induced structural transition in LuFe2O4: towards a new charge ordered state.

The electronic ferroelectric lutetium ferrite (LuFe(2)O(4)) was studied by x-ray diffraction as a function of pressure. Pressure is shown to induce an irreversible rhombohedral to orthorhombic transition leading to a supercell determined by the combination of electron and synchrotron x-ray diffraction. This new configuration is proposed to be charge ordered in agreement with the results of resistivity measurements.

Ising magnetism and ferroelectricity in Ca3CoMnO6.

The origin of both the Ising chain magnetism and ferroelectricity in Ca3CoMnO6 is studied by ab initio electronic structure calculations and x-ray absorption spectroscopy. We find that Ca3CoMnO6 has alternate trigonal prismatic Co2+ and octahedral Mn4+ sites in the spin chain. Both the Co2+ and Mn4+ are in the high-spin state. In addition, the Co2+ has a huge orbital moment of 1.7micro_{B} which is responsible for the significant Ising magnetism. The centrosymmetric crystal structure known so far is calculated to be unstable with respect to exchange striction in the experimentally observed upward arrow upward arrow downward arrow downward arrow antiferromagnetic structure for the Ising chain. The calculated inequivalence of the Co-Mn distances accounts for the ferroelectricity.

Metallicity and positive magnetoresistance induced by Pb substitution in a misfit cobaltate crystal.

We have synthesized single crystals of the misfit-layered cobalt oxide, [Bi(1.5)Pb(0.5)Sr(2)O(4-δ)][CoO(2)](1.86), with quadruple NaCl-type layers, using a flux method, and measured their transport properties. From structural refinements, it is found that the modulation in the BiO layer observed in [Bi(1.74)Sr(2)O(4-δ)](RS)[CoO(2)](1.82) is suppressed by Pb substitution. The in-plane resistivity, thermopower, and Hall coefficient are 4.3  mΩ cm, 101  µV K(-1), and 1 × 10(-2) cm(3) C(-1) at 300 K, respectively; these are consistent with those of the misfit-layered cobalt oxides. All of these values are smaller than those of [Bi(1.74)Sr(2)O(4)][CoO(2)](1.82), indicating that the carrier concentration is larger than that of the undoped crystal. Moreover, the low T upturn of resistivity observed for most of the cobalt misfit oxides is replaced by a metallic behavior, following a T(2) dependence, indicating strong correlations in the Pb-doped crystal. Also, the magnetoresistance, usually negative for misfit oxides, is replaced by a small positive magnetoresistance. Doping with Pb is thus an efficient way to suppress the low T localized behavior usually observed for misfits.

The crystal chemistry of ferric oxyhydroxyapatite.

Ferric hydroxyapatites (Fe-HAp) and oxyapatites (Fe-OAp) of nominal composition [Ca(10-x)Fe(x)(3+)][(PO(4))(6)][(OH)(2-x)O(x)] (0 < or = x < or = 0.5) were synthesized from a coprecipitated precursor calcined under flowing nitrogen. The solid solubility of iron was temperature-dependent, varying from x = 0.5 after firing at 600 degrees C to x approximately 0.2 at 1000 degrees C, beyond which Fe-OAp was progressively replaced by tricalcium phosphate (Fe-TCP). Crystal size (13-116 nm) was controlled by iron content and calcination temperature. Ferric iron replaces calcium by two altervalent mechanisms in which carbonate and oxygen are incorporated as counterions. At low iron loadings, carbonate predominantly displaces hydroxyl in the apatite channels (Ca(2+) + OH(-) --> Fe(3+) + CO(3)(2-)), while at higher loadings, "interstitial" oxygen is tenanted in the framework (2Ca(2+) + (vac) --> 2Fe(3+) + O(2+)). Although Fe(3+) is smaller than Ca(2+), the unit cell dilates as iron enters apatite, providing evidence of oxygen injection that converts PO(4) tetrahedra to PO(5) trigonal bipyramids, leading to the crystal chemical formula [Ca(10-x)Fe(x)][(PO(4))(6-x/2)(PO(5))(x/2)][(OH)(2-y)O(2y)] (x < or = 0.5). A discontinuity in unit cell expansion at x approximately 0.2 combined with a substantial reduction of the carbonate FTIR fingerprint shows that oxygen infusion, rather than tunnel hydroxyl displacement, is dominant beyond this loading. This behavior is in contrast to ferrous-fluorapatite where Ca(2+) --> Fe(2+) aliovalent replacement does not require oxygen penetration and the cell volume contracts with iron loading. All of the materials were paramagnetic, but at low iron concentrations, a transition arising from crystallographic modification or a change in spin ordering is observed at 90 K. The excipient behavior of Fe-OAp was superior to that of HAp and may be linked to the crystalline component or mediated by a ubiquitous nondiffracting amorphous phase. Fe-HAp and Fe-OAp are not intrinsically suitable magnetic agents for drug delivery but may be useful in reactive cements that promote osteoblast proliferation.

Transition-metal oxides with triangular lattices: generation of new magnetic and electronic properties.

The search for multifunctional materials as multiferroics to be applied in microelectronic or for new, chemically stable and nontoxic, thermoelectric materials to recover waste heat is showing a common interest in the oxides whose structures contain a triangular network of transition-metal cations. To illustrate this point, two ternary systems, Ba-Co-O and Ca-Co-O, have been chosen. It is shown that new phases with a complex triangular structure can be discovered, for instance, by introduction of Ga (3+) into the Ba-Co-O system to stabilize Ba 6Ga 2Co 11O 26 and Ba 2GaCo 8O 14, which both belong to a large family of compounds with formula [Ba(Co,Ga)O 3-delta] n [BaCo 8O 11]. In the latter, both sublattices contain triangular networks derived from the hexagonal perovskite and the spinel structure. Among the hexagonal perovskite, the Ca 3Co 2O 6 crystals give clear evidence where the coupling of charges and spins is at the origin of a magnetocapacitance effect. In particular, the ferrimagnetic to ferromagnetic transition, with a one-third plateau on the M( H) curve characteristic of triangular magnetism, is accompanied by a peak in the dielectric constant. A second class of cobaltites is the focus of much interest. Their 2D structure, containing CoO 2 planes isostructural to a CdI 2 slice that are stacked in an incommensurate way with rock salt type layers, is referred to misfit cobaltite. The 2D triangular network of edge-shared CoO 6 octahedra is believed to be responsible for large values of the Seebeck coefficient and low electrical resistivity. A clear relationship between the structuresincommensurability ratiosand the electronic properties is evidenced, showing that the charge carrier concentration can be tuned via the control of the ionic radius of the cations in the separating layers.

Electronic correlations in CoO2, the parent compound of triangular cobaltates.

A 59Co NMR study of CoO2, the x=0 end member of AxCoO2 (A=Na,Li,...) cobaltates, reveals a metallic ground state, though with clear signs of strong electron correlations: low-energy spin fluctuations develop at wave vectors q not equal to 0 and a crossover to a Fermi-liquid regime occurs below a characteristic temperature T* approximately 7 K. Despite some uncertainty over the exact cobalt oxidation state in this material, the results show that electronic correlations are revealed as x is reduced below 0.3. The data are consistent with NaxCoO2 being close to the Mott transition in the x-->0 limit.

Correlation of structural, magnetic and transport properties with the tolerance factor in a low-doped La(0.875)Sr(0.125-x)Ca(x)MnO(3), (0 ≤x≤0.125) system: cross-over from Mott to Shklovskii-Efros variable range hopping conduction.

Samples of the low-doped manganite La(0.875)Sr(0.125-x)Ca(x)MnO(3) (0≤x≤0.125) have been synthesized and the effect on the structural, magnetic and transport properties of decreasing the tolerance factor by replacing larger Sr(2+) ions with smaller Ca(2+) ions are reported. For samples with x≥0.0625, a concentration (x) dependent structural transition (rhombohedral ([Formula: see text]) to orthorhombic (Pnma)) has been detected at room temperature and the Curie temperature T(C) is found to decrease with increased Ca doping level. For samples with x≤0.0625, a narrow metallic region exists and the corresponding insulator to metal transition temperature T(MI) decreases with increasing Ca content, i.e. decreasing tolerance factor. In the paramagnetic region, x dependent crossover from Mott variable range hopping (Mott-VRH) to Shklovskii-Efros variable range hopping (SE-VRH) occurs as the Ca content increases. The thermoelectric power (TEP) of the samples increases substantially, varying inversely with the tolerance factor. These results are analysed from the consideration of increased bending of the Mn-O-Mn bond with the decrease of the average ionic radius of the A-site element [Formula: see text] and the tolerance factor t, which causes narrowing of the bandwidth, decrease of mobility of e(g) electrons and weakening of the double exchange (DE) interaction associated with the substitution of Ca.

Scaling behavior in thermoelectric misfit cobalt oxides.

We investigate both thermoelectric and thermodynamic properties of the misfit cobalt oxide [Bi1.7Co0.3Ca2O4]RS0.6CoO2. A large negative magnetothermopower is found to scale with both magnetic field and temperature, revealing a significant spin entropy contribution to thermoelectric properties giving rise to a constant S0 approximately 60 microV K-1. Specific heat measurements allow us to determine an enhanced electronic part with gamma approximately 50 mJ (mol K2)-1 attesting to strong correlations. Thereby, the comparison between cobaltites and other materials reveals a universal behavior of the thermopower slope as a function of gamma, testifying to a purely electronic origin. This potentially generic scaling behavior suggests here that the high room temperature value of the thermopower in misfit cobalt oxides results from the addition of a spin entropy contribution to an enlarged electronic one.

Re-entrant metallicity and magnetoresistance induced by Ce for Sr substitution in SrCoO(3-δ).

Cerium for strontium substitution allows an oxygen deficient perovskite Sr(1-x)Ce(x)CoO(3-δ) to be stabilized with a cerium solubility limited to x≤0.15 (Trofimenko et al 1997 Solid State Ion. 100 183). For these samples, the magnetic properties depend clearly upon the oxygen content: Sr(0.9)Ce(0.1)CoO(2.74) and Sr(0.9)Ce(0.1)CoO(2.83) are weak and strong ferromagnets (T(C) = 160 K), respectively, the maximum ac-magnetic susceptibility of the latter being larger by two orders of magnitude than that of the former. In contrast to other Sr(1-x)L(x)CoO(3-δ) series (L =  lanthanide, Y(3) or Th(4+)), the electrical resistivity (ρ) behaviour does not simply reflect the magnetic behaviour. For x = 0.10 the re-entrant ρ feature becomes more pronounced whereas the ferromagnetic fraction and cobalt oxidation state increase. This unexpected behaviour could be related to the Ce(3+)/Ce(4+) mixed valency, the 4f localized moment of the Ce(3+) cations interacting with the conduction electrons through a Kondo-like mechanism. It is also found that the increase of oxygen vacancies favours the appearance of magnetoresistance at low T, reaching -50% at 5 K in 7 T for the Sr(0.95)Ce(0.05)CoO(2.61) sample prepared in a sealed tube.