Dielectric and polarization experiments in high loss dielectrics: a word of caution

The recent quest for improved functional materials like high permittivity dielectrics and/or multiferroics has triggered an intense wave of research. Many materials have been checked for their dielectric permittivity or their polarization state. In this report, we call for caution when samples are simultaneously displaying insulating behavior and defect-related conductivity. Many oxides containing mixed valent cations or oxygen vacancies fall in this category. In such cases, most of standard experiments may result in effective high dielectric permittivity which cannot be related to ferroelectric polarization. Here we list few examples of possible discrepancies between measured parameters and their expected microscopic origin

Controlling internal barrier in low loss BaTiO3 supercapacitors

Supercapacitor behavior has been reported in a number of oxides including reduced BaTiO3 ferroelectric ceramics. These so-called giant properties are however not easily controlled. We show here that the continuous coating of individual BaTiO3 grains by a silica shell in combination with spark plasma sintering is a way to process bulk composites having supercapacitor features with low dielectric losses and temperature stability. The silica shell acts both as an oxidation barrier during the processing and as a dielectric barrier in the final composite

Interface-driven magnetocapacitance in a broad range of materials

Triggered by the revival of multiferroic materials, a lot of effort is presently undergoing as to find a coupling between a capacitance and a magnetic field. We show in this report that interfaces are the right way of increasing such a coupling provided free charges are localized on these two-dimensional defects. Starting from commercial diodes at room temperature and going to grain boundaries in giant permittivity materials and to ferroelectric domain walls, a clear magnetocapacitance is reported which is all the time more than a few percent for a magnetic field of 90kOe. The only tuning parameter for such strong coupling to arise is the dielectric relaxation time which is reached on tuning the operating frequency and the temperature in many different materials

Polaron relaxation in ferroelectric thin films

We report a dielectric relaxation in ferroelectric thin films of the ABO3 family. We have compared films of different compositions with several growth modes: sputtering (with and without magnetron) and sol-gel. The relaxation was observed at cryogenic temperature (T<100K) for frequencies from 100Hz up to 10MHz. This relaxation activation energy is always lower than 200meV. It is very similar to the polaron relaxation that we reported in the parent bulk perovskites. Being independent of the materials size, morphology and texture, this relaxation can be a useful probe of defects in actual integrated capacitors with no need for specific shapin

Paediatric and adult bronchiectasis: Specific management with coexisting asthma, COPD, rheumatological disease and inflammatory bowel disease

Bronchiectasis, conventionally defined as irreversible dilatation of the bronchial tree, is generally suspected on a clinical basis and confirmed by means of chest high-resolution computed tomography. Clinical manifestations, including chronic productive cough and endobronchial suppuration with persistent chest infection and inflammation, may deeply affect quality of life, both in children/adolescents and adults. Despite many cases being idiopathic or post-infectious, a number of specific aetiologies have been traditionally associated with bronchiectasis, such as cystic fibrosis (CF), primary ciliary dyskinesia or immunodeficiencies. Nevertheless, bronchiectasis may also develop in patients with bronchial asthma; chronic obstructive pulmonary disease; and, less commonly, rheumatological disorders and inflammatory bowel diseases. Available literature on the development of bronchiectasis in these conditions and on its management is limited, particularly in children. However, bronchiectasis may complicate the clinical course of the underlying condition at any age, and appropriate management requires an integration of multiple skills in a team of complementary experts to provide the most appropriate care to affected children and adolescents. The present review aims at summarizing the current knowledge and available evidence on the management of bronchiectasis in the other conditions mentioned and focuses on the new therapeutic strategies that are emerging as promising tools for improving patients' quality of life

Non-cystic fibrosis bronchiectasis in children and adolescents: Neglected and emerging issues.

Pediatric non-cystic fibrosis (CF) bronchiectasis is characterized by endobronchial suppuration, airway neutrophilic inflammation and poor mucus clearance and is associated with persistent productive cough due to recurrent airway infections. Most recommendations are based on expert opinion or extrapolated from CF practice. The present narrative review aims to address some issues on the management of children or adolescents with non CF-bronchiectasis that still require attention, and analyze what available literature offers to reply to open questions. We focused on the potential offered by technological advances on lung disease assessment through novel chest imaging techniques and new or old pulmonary function tests. We also summarized the main novelties in the disease prevention and treatment. Finally, a novel diagnostic algorithm is proposed, that might help physicians in the daily clinical decision-making process. Future directions for research on pediatric non-CF bronchiectasis should include larger study populations and longer prospective clinical trials, as well as new clinical and laboratory endpoints to determine the underlying mechanisms of lung disease progression and support the role of new and existing treatments

High-frequency dielectric spectroscopy of batio3 core - silica shell nanocomposites: Problem of interdiffusion

Three types of BaTiO3 core - amorphous nano-shell composite ceramics were processed from the same core-shell powder by standard sintering, spark-plasma sintering and two-step sintering techniques and characterized by XRD, HRSEM and broad-band dielectric spectroscopy in the frequency range 10^3 - 10^13 Hz including the THz and IR range. The samples differed by porosity and by the amount of interdiffusion from the cores to shells, in correlation with their increasing porosity. The dielectric spectra were also calculated using suitable models based on effective medium approximation. The measurements revealed a strong dielectric dispersion below the THz range, which cannot be explained by the modeling, and whose strength was in correlation with the degree of interdiffusion. We assigned it to an effect of the interdiffusion layers, giving rise to a strong interfacial polarization. It appears that the high-frequency dielectric spectroscopy is an extremely sensitive tool for detection of any gradient layers and sample inhomogeneities even in dielectric materials with negligible conductivity

First evidence of a strong Magneto-capacitance coupling at room temperature in integrated piezoelectric resonators

In the vicinity of their resonance frequency, piezoelectric resonators are highly sensitive to small perturbations. The present report is focussed on the magnetic field as a perturbation source. First, magneto-dielectric modulation of more than 10% is achieved at room temperature on both ferroelectric single crystals and quartz discs. Since such piezoelectric resonators are now available as membranes directly integrated on Silicon wafer, we have checked the magneto-dielectric modulation in such resonators. We show here for the first time that a moderate magnetic field of 2.104 Oersteds is able to efficiently tune the impedance of these resonators in their resonance window.Comment: 11 Pages, 4 figure

Revised structural phase diagram of (Ba0.7Ca0.3TiO3)-(BaZr0.2Ti0.8O3)

The temperature-composition phase diagram of barium calcium titanate zirconate (x(Ba0.7Ca0.3TiO3)(1-x)(BaZr0.2Ti0.8O3); BCTZ) has been reinvestigated using high-resolution synchrotron x-ray powder diffraction. Contrary to previous reports of an unusual rhombohedral-tetragonal phase transition in this system, we have observed an intermediate orthorhombic phase, isostructural to that present in the parent phase, BaTiO3, and we identify the previously assigned T-R transition as a T-O transition. We also observe the O-R transition coalescing with the previously observed triple point, forming a phase convergence region. The implication of the orthorhombic phase in reconciling the exceptional piezoelectric properties with the surrounding phase diagram is discussed

Host genetics and gut microbiome: Perspectives for multiple sclerosis

As a complex disease, Multiple Sclerosis (MS)’s etiology is determined by both genetic and environmental factors. In the last decade, the gut microbiome has emerged as an important environmental factor, but its interaction with host genetics is still unknown. In this review, we focus on these dual aspects of MS pathogenesis: we describe the current knowledge on genetic factors related to MS, based on genome-wide association studies, and then illustrate the interactions between the immune system, gut microbiome and central nervous system in MS, summarizing the evidence available from Experimental Autoimmune Encephalomyelitis mouse models and studies in patients. Finally, as the understanding of influence of host genetics on the gut microbiome composition in MS is in its infancy, we explore this issue based on the evidence currently available from other autoimmune diseases that share with MS the interplay of genetic with environmental factors (Inflammatory Bowel Disease, Rheumatoid Arthritis and Systemic Lupus Erythematosus), and discuss avenues for future research