Study of Na substitution in La0.67Ba0.33MnO3 perovskites

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Critical Behavior of La0.67Ba0.33Mn0.95Fe0.05O3 Manganite

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Synthesis, structural, magnetic and electrical properties of nominal La0.67Ba0.33-xNaxMnO3 (0 ≤ x ≤ 0.33) manganites

Complete nominal solid solutions La0.67Ba0.33-xNaxMnO3 (0 ≤ x ≤ 0.33) have been elaborated by ceramic route at 1200°C. ICPAES chemical analysis and XRD Rietveld structure refinement revealed that the nominal Na content is not achieved by our ceramic method. The chemical formula should be rather written as LaαBaβNaλMnO3-δ with a significantly lower Na content (λ), than the nominal one (x), and with a slight deficit (δ) in oxygen content, leading to the appearance of two minor secondary phases identified as Mn3O4 and Na0.55Mn2O4·1.5H2O. Magnetization and electrical resistance vs. temperature show paramagnetic/semiconductor – ferromagnetic/metallic transitions with only a slight decrease in magnetic and electrical transition temperatures when Na content increases. Such amount of this decrease is not expected according to the nominal Na content giving a significant difference between nominal and experimental Mn4+/Mn3+ ratios

Size mismatch, grain boundary and bandwidth effects on structural, magnetic and electrical properties of Pr0.67Ba0.33MnO3 and Pr0.67Sr0.33MnO3 perovskites

International audienceWe have studied the effect of size mismatch on the structural, magnetic and electrical properties of Pr0.67Ba0.33MnO3 (PBMO) and Pr0.67Sr0.33MnO3 (PSMO) perovskites with considerable difference in their variance sigma(2) values. Samples were prepared by ceramic route at 1200 degrees C. Morphological study, microstructure and chemical composition were examined by scanning electron microscopy, EDX analyses and Rietveld structure refinement. Both compounds exhibit single orthorhombic Pnma crystalline phase and with strongly connected and larger grains for PSMO than for PBMO that gives a beginning of single crystal growth in PSMO case. PBMO with higher variance exhibits distinct intrinsic (due to grains) and extrinsic (due to grain boundaries) transitions in the resistivity behaviour, and with higher transition temperatures than those usually reported in the literature. Extrinsic effects, however, are not observed in the lower sigma(2) PSMO sample. Both compounds exhibit Curie temperature (T-c) values significantly higher than those reported in the literature, and with higher T-c for PSMO due to its larger bandwidth W. The experimental paramagnetic effective moment for PSMO is very close to the theoretical one, whereas there is a significant difference between these moments for PBMO sample, probably due to the considerable size mismatch effect between Pr and Ba, and to the ferromagnetic correlations in the paramagnetic state. Ferromagnetic-metallic regime in the two compounds seems to emanate from the electron-(phonon, magnon) scattering processes with a larger effect for PBMO than that for PSMO, due to the prominent role of the grain boundary in PBMO. Above paramagnetic-insulating transition temperature the data were well fitted by both variable range hopping (VRH) and small polaron hopping (SPH) models giving higher density state, and lower activation energy and Mott temperature T-0 for PSMO than those for PBMO, essentially due to their considerable difference in their variance values. (C) 2010 Elsevier B.V. All rights reserved

Impedance Spectroscopy Properties of Pr0.67A0.33MnO3 (A = Ba or Sr) Perovskites

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Percolation Model of the Temperature Dependence of Resistivity in Pr(0.67)A(0.33)MnO(3) (A = Ba or Sr) Manganites

International audienceThe analyses of resistivity experimental results of Pr0.67Ba0.33MnO3 (PBMO) and Pr0.67Sr0.33MnO3 (PSMO) manganites are presented. The electrical resistivity curves are fitted with the phenomenological percolation model, which is based on the phase segregation of ferromagnetic-metallic (FMM) clusters and paramagnetic-insulating (PMI) regions. The estimated results are in good agreement with experimental data. We found that the transition to the metallic state occurs if the volume fraction of the ferromagnetic phase reaches a percolation threshold, suggesting that the percolation of ferromagnetic (FM) domains is responsible for the observed metal-insulator (M-I) transition. According to the percolation model, we found that the energy gap of the quasi-particles in the phase separated FM and PM states is significantly smaller for PBMO than that for PSMO confirming that PSMO is more conductive than PBMO. We also found that the volume fraction of the ferromagnetic phase has the same physical meaning as the reduced magnetization

Sociodemographic characteristics of children born to HIV-infected mothers in Western French Guiana

Background: French Guiana is the French department most affected by HIV. The situation in Western French Guiana is complicated by the transborder context and isolation of many patients. This study aims to describe the epidemiological characteristics of children born to mothers living with HIV followed in Western French Guiana. Methods: This was a retrospective and descriptive study. All children born to HIV-infected mothers between 2014 and 2018 were included. Data were collected using a survey sheet to generate an Excel database. Results: We recorded 177 newborns exposed to maternal HIV, four of whom (2.26 %) were infected. The majority of women (87 %) were of foreign origin, and only 7 % had conventional health insurance coverage. The infection was discovered during pregnancy in 20 % of women. Overall 21.71 % of newborns were preterm and 22.5 % hypotrophic. All neonates had received antiretroviral prophylaxis for four weeks, either as monotherapy (AZT) (67.43 %) or triple therapy (AZT/3TC/NVP) (25.71 %). Twenty-two neonates had at least one neonatal illness: transient respiratory distress (9 cases), asphyxia (3 cases), hyaline membrane disease (8 cases), and there were two cases with birth defects: clubfoot (1 case) and heart disease (1 case). The follow-up rate at 24 months was 65 % and 35 % of cases were lost to follow-up. The most common biological anomalies were anemia (69.14 %), hyperlacticaemia (23 %), and neutropenia (9.14 %). Conclusion: The prevalence of mother-to child transmission of HIV was high; a quarter of maternal infections were discovered during pregnancy. The mother’s socio-economic situation was often precarious and follow-up interruptions common

Early Prediction of Blood Loss and Postpartum Hemorrhage after Vaginal Delivery by Ultrasound Measurement of Intrauterine Content.

The ability of ultrasound to predict postpartum hemorrhage remains poorly described. The aim of this study was to evaluate whether ultrasound measurement of intrauterine content can predict blood loss and postpartum hemorrhage after vaginal delivery. We used a preliminary prospective monocentric study of 201 women who delivered vaginally after 34 wk of gestation. Measurements were performed 30-45 min after normal vaginal delivery according to strict ultrasonographic criteria. Analysis of the relationship between ultrasound measurements and hemoglobin loss showed a strong linear correlation (R² = 0.59 and R² = 0.4 for isthmic and fundal measurements). The maximal value between the fundal and isthmic measurements seems to provide the best accuracy to predict loss of hemoglobin higher than 3 g/dL (area under the curve [AUC] of the receiver operating characteristic curve, 0.9; 95% confidence interval [CI], [0.76-0.97]) and post-partum hemorrhage (AUC, 0.99; 95%CI, [0.984-0.99]). In case of intrauterine content >2 cm (135/201), the risks of loss of hemoglobin higher than 3 g/dL (5/135 vs. 0/66) and post-partum hemorrhage (11/135 vs. 0/66) were increased, all the more if the intrauterine content was >4 cm (4/16 and 11/16, respectively). Considering the maximal measurement, the most optimal cut-off value for clinical practice could be 2.4 cm (sensibility 100%, specificity 57%) and 4.1 cm (sensibility 100%, specificity 97%) for loss of hemoglobin higher than 3 g/dL and post-partum hemorrhage, respectively