The recovery of European freshwater biodiversity has come to a halt.

Owing to a long history of anthropogenic pressures, freshwater ecosystems are among the most vulnerable to biodiversity loss1. Mitigation measures, including wastewater treatment and hydromorphological restoration, have aimed to improve environmental quality and foster the recovery of freshwater biodiversity2. Here, using 1,816 time series of freshwater invertebrate communities collected across 22 European countries between 1968 and 2020, we quantified temporal trends in taxonomic and functional diversity and their responses to environmental pressures and gradients. We observed overall increases in taxon richness (0.73% per year), functional richness (2.4% per year) and abundance (1.17% per year). However, these increases primarily occurred before the 2010s, and have since plateaued. Freshwater communities downstream of dams, urban areas and cropland were less likely to experience recovery. Communities at sites with faster rates of warming had fewer gains in taxon richness, functional richness and abundance. Although biodiversity gains in the 1990s and 2000s probably reflect the effectiveness of water-quality improvements and restoration projects, the decelerating trajectory in the 2010s suggests that the current measures offer diminishing returns. Given new and persistent pressures on freshwater ecosystems, including emerging pollutants, climate change and the spread of invasive species, we call for additional mitigation to revive the recovery of freshwater biodiversity.

Bioactive Glass Modified with Zirconium Incorporation for Dental Implant Applications: Fabrication, Structural, Electrical, and Biological Analysis.

Implantology is crucial for restoring aesthetics and masticatory function in oral rehabilitation. Despite its advantages, certain issues, such as bacterial infection, may still arise that hinder osseointegration and result in implant rejection. This work aims to address these challenges by developing a biomaterial for dental implant coating based on 45S5 Bioglass® modified by zirconium insertion. The structural characterization of the glasses, by XRD, showed that the introduction of zirconium in the Bioglass network at a concentration higher than 2 mol% promotes phase separation, with crystal phase formation. Impedance spectroscopy was used, in the frequency range of 102-106 Hz and the temperature range of 200-400 K, to investigate the electrical properties of these Bioglasses, due to their ability to store electrical charges and therefore enhance the osseointegration capacity. The electrical study showed that the presence of crystal phases, in the glass ceramic with 8 mol% of zirconium, led to a significant increase in conductivity. In terms of biological properties, the Bioglasses exhibited an antibacterial effect against Gram-positive and Gram-negative bacteria and did not show cytotoxicity for the Saos-2 cell line at extract concentrations up to 25 mg/mL. Furthermore, the results of the bioactivity test revealed that within 24 h, a CaP-rich layer began to form on the surface of all the samples. According to our results, the incorporation of 2 mol% of ZrO2 into the Bioglass significantly improves its potential as a coating material for dental implants, enhancing both its antibacterial and osteointegration properties.

Extensive Investigation on the Effect of Niobium Insertion on the Physical and Biological Properties of 45S5 Bioactive Glass for Dental Implant.

Dental implants have emerged as one of the most consistent and predictable treatments in the oral surgery field. However, the placement of the implant is sometimes associated with bacterial infection leading to its loss. In this work, we intend to solve this problem through the development of a biomaterial for implant coatings based on 45S5 Bioglass® modified with different amounts of niobium pentoxide (Nb2O5). The structural feature of the glasses, assessed by XRD and FTIR, did not change in spite of Nb2O5 incorporation. The Raman spectra reveal the Nb2O5 incorporation related to the appearance of NbO4 and NbO6 structural units. Since the electrical characteristics of these biomaterials influence their osseointegration ability, AC and DC electrical conductivity were studied by impedance spectroscopy, in the frequency range of 102-106 Hz and temperature range of 200-400 K. The cytotoxicity of glasses was evaluated using the osteosarcoma Saos-2 cells line. The in vitro bioactivity studies and the antibacterial tests against Gram-positive and Gram-negative bacteria revealed that the samples loaded with 2 mol% Nb2O5 had the highest bioactivity and greatest antibacterial effect. Overall, the results showed that the modified 45S5 bioactive glasses can be used as an antibacterial coating material for implants, with high bioactivity, being also non-cytotoxic to mammalian cells.

Litter Quality Is a Stronger Driver than Temperature of Early Microbial Decomposition in Oligotrophic Streams: a Microcosm Study.

Litter decomposition is an ecological process of key importance for forest headwater stream functioning, with repercussions for the global carbon cycle. The process is directly and indirectly mediated by microbial decomposers, mostly aquatic hyphomycetes, and influenced by environmental and biological factors such as water temperature and litter quality. These two factors are forecasted to change globally within the next few decades, in ways that may have contrasting effects on microbial-induced litter decomposition: while warming is expected to enhance microbial performance, the reduction in litter quality due to increased atmospheric carbon dioxide and community composition alteration may have the opposite outcome. We explored this issue through a microcosm experiment focused on early microbial-mediated litter decomposition under stream oligotrophic conditions, by simultaneously manipulating water temperature (10 °C and 15 °C) and litter quality (12 broadleaf plant species classified into 4 categories based on initial concentrations of nitrogen and tannins). We assessed potential changes in microbial-mediated litter decomposition and the performance of fungal decomposers (i.e., microbial respiration, biomass accrual, and sporulation rate) and species richness. We found stronger effects of litter quality, which enhanced the performance of microbial decomposers and decomposition rates, than temperature, which barely influenced any of the studied variables. Our results suggest that poorer litter quality associated with global change will have a major repercussion on stream ecosystem functioning.

Bioaccumulation and Dispersion of Uranium by Freshwater Organisms.

Uranium is the heaviest naturally occurring element on Earth. Uranium mining may result in ground and surface water contamination with potential bioaccumulation and dispersion by aquatic invertebrates with aerial stages. We investigated the effects of uranium contamination at community level in terms of abundance, richness, the composition of invertebrate communities, and functional traits. We also investigated uranium mobility across aquatic food webs and its transfer to land via the emergence of aquatic insects. We sampled water, sediment, biofilm, macrophytes, aquatic invertebrates, adult insects, and spiders in the riparian zone across sites with a gradient of uranium concentrations in stream water (from 2.1 to 4.7 µg L-1) and sediments (from 10.4 to 41.8 µg g-1). Macroinvertebrate assemblages differed between sites with a higher diversity and predominance of Nemouridae and Baetidae at the reference site and low diversity and predominance of Chironomidae in sites with the highest uranium concentration. Uranium concentrations in producers and consumers increased linearly with uranium concentration in stream water and sediment (p < 0.05). The highest accumulation was found in litter (83.76 ± 5.42 µg g-1) and macrophytes (47.58 ± 6.93 µg g-1) in the most contaminated site. Uranium was highest in scrapers (14.30 ± 0.98 µg g-1), followed by shredders (12.96 ± 0.81 µg g-1) and engulfer predators (7.01 ± 1.3 µg g-1). Uranium in adults of aquatic insects in the riparian zone in all sites ranged from 0.25 to 2.90 µg g-1, whereas in spiders it ranged from 0.96 to 1.73 µg g-1, with no differences between sites (p > 0.05). There was a negative relationship between δ15N and uranium, suggesting there is no biomagnification along food webs. We concluded that uranium is accumulated by producers and consumers but not biomagnified nor dispersed to land with the emergence of aquatic insects.

Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter.

Climate change and human pressures are changing the global distribution and the extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico-chemical changes (preconditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale. We experimentally simulated, under standard laboratory conditions, rewetting of leaves, riverbed sediments, and epilithic biofilms collected during the dry phase across 205 IRES from five major climate zones. We determined the amounts and qualitative characteristics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds. In addition, we evaluated the variance in leachate characteristics in relation to selected environmental variables and substrate characteristics. We found that sediments, due to their large quantities within riverbeds, contribute most to the overall flux of dissolved substances during rewetting events (56%-98%), and that flux rates distinctly differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contributed most to the areal fluxes. The largest amounts of leached substances were found in the continental climate zone, coinciding with the lowest potential bioavailability of the leached OM. The opposite pattern was found in the arid zone. Environmental variables expected to be modified under climate change (i.e. potential evapotranspiration, aridity, dry period duration, land use) were correlated with the amount of leached substances, with the strongest relationship found for sediments. These results show that the role of IRES should be accounted for in global biogeochemical cycles, especially because prevalence of IRES will increase due to increasing severity of drying events.

Nutrient enrichment in water more than in leaves affects aquatic microbial litter processing.

Nutrient enrichment of soils and water will intensify in the future and has the potential to alter fundamental ecosystem processes, such as litter decomposition. We tested the direct (via water nutrient enrichment) and indirect (via changes in leaf chemistry) effects of nutrient enrichment on microbial activity and decomposability of Quercus robur L. (oak) leaves in laboratory microcosms simulating streams. Senescent leaves of oak trees grown without and with fertilization were incubated under ambient and elevated water nutrient [nitrogen (N) and phosphorus (P)] concentrations for 60 days. Soil fertilization led to an increase in leaf (3.4×) and leaf litter (2.3×) N concentration. Increased water-dissolved nutrients concentrations stimulated microbial activity (N uptake, microbial respiration, fungal biomass buildup and conidia production by aquatic hyphomycetes) that translated into accelerated litter decomposition (2.1× for unfertilized and 1.6× for fertilized trees). Leaves from fertilized trees had higher microbial activity and decomposition rates than leaves from unfertilized trees only at low dissolved nutrient availability. When both litter and water nutrients concentration increased, microbial activity and leaf decomposition were stimulated, but the effects were additive and direct effects from increased dissolved nutrient availability were stronger than those mediated by increases in litter N concentration (indirect effects). Our results suggest that increases in water nutrient availability (within the range used in this study) may exert a stronger control on microbial activity and litter decomposition than litter nutrient enrichment.

Arsenic in stream waters is bioaccumulated but neither biomagnified through food webs nor biodispersed to land.

Human activities such as mining have contributed substantially to the increase of metals in aquatic environments worldwide. These metals are bioaccumulated by aquatic organisms and can be biomagnified along trophic webs. The dispersal of contaminants from water to land has been little investigated, even though most aquatic invertebrates in streams have aerial stages. We used field and laboratory approaches to investigate the effects of arsenic pollution on stream invertebrate assemblages, and its bioaccumulation, biomagnification and trophic transfer from aquatic to terrestrial environments by emergent insects. We conducted the study in an arsenic-impacted stream (40µgL-1 As at the most polluted site) and a reference stream (0.3µgL-1 As). Invertebrate abundance and richness were lowest at the most impacted site. Arsenic in biofilm and in invertebrates increased with the arsenic content in the water. The highest arsenic accumulators were bryophytes (1760µgg-1), followed by the biofilm (449µgg-1) and shredder invertebrates (313µgg-1); predators had the lowest arsenic concentration. Insects emerging from water and spiders along streambanks sampled from the reference and the impacted stream did not differ in their body arsenic concentrations. In the laboratory, the shredder Sericostoma vittatum had reduced feeding rates when exposed to water from the impacted stream in comparison with the reference stream (15.6 vs. 19.0mg leaves mg body mass-1 day-1; p<0.05), but they grew faster in the polluted water (0.16±0.04% day-1vs. 0.05±0.01% day-1, p<0.05). S. vittatum exposed to contaminated stream water accumulated arsenic from food, not through contact with water. We concluded that although arsenic is bioaccumulated, mainly by food ingestion, it is not biomagnified through food webs and is not transported from the aquatic to terrestrial environment when insects leave the stream water.

Chironomidae traits and life history strategies as indicators of anthropogenic disturbance.

In freshwater ecosystems, Chironomidae are currently considered indicators of poor water quality because the family is often abundant in degraded sites. However, it incorporates taxa with a large ecological and physiological diversity and different sensitivity to impairment. Yet, the usual identification of Chironomidae at coarse taxonomic levels (family or subfamily) masks genus and species sensitivities. In this study, we investigate the potential of taxonomic and functional (traits) composition of Chironomidae to detect anthropogenic disturbance. In this context, we tested some a priori hypotheses regarding the ability of Chironomidae taxonomic and trait compositions to discriminate Mediterranean streams affected by multiple stressors from least-disturbed streams. Both taxonomic and Eltonian trait composition discriminated sites according to their disturbance level. Disturbance resulted in the predicted increase of Chironomidae with higher number of stages with hibernation/diapause and of taxa with resistance forms and unpredicted increase of the proportion of taxa with longer life cycles and few generations per year. Life history strategies (LHS), corresponding to multivoltine Chironomidae that do not invest in hemoglobin and lack strong spring synchronization, were well adapted to all our Mediterranean sites with highly changeable environmental conditions. Medium-size animals favored in disturbed sites where the Mediterranean hydrological regime is altered, but the reduced number of larger-size/carnivore Chironomids suggests a limitation to secondary production. Results indicate that Chironomidae genus and respective traits could be a useful tool in the structural and functional assessment of Mediterranean streams. The ubiquitous nature of Chironomidae should be also especially relevant in the assessment of water bodies naturally poor in other groups such as the Ephemeroptera, Plecoptera, and Trichoptera, such as the lowland rivers with sandy substrates, lakes, or reservoirs.

Biotic and abiotic variables influencing plant litter breakdown in streams: a global study.

Plant litter breakdown is a key ecological process in terrestrial and freshwater ecosystems. Streams and rivers, in particular, contribute substantially to global carbon fluxes. However, there is little information available on the relative roles of different drivers of plant litter breakdown in fresh waters, particularly at large scales. We present a global-scale study of litter breakdown in streams to compare the roles of biotic, climatic and other environmental factors on breakdown rates. We conducted an experiment in 24 streams encompassing latitudes from 47.8° N to 42.8° S, using litter mixtures of local species differing in quality and phylogenetic diversity (PD), and alder (Alnus glutinosa) to control for variation in litter traits. Our models revealed that breakdown of alder was driven by climate, with some influence of pH, whereas variation in breakdown of litter mixtures was explained mainly by litter quality and PD. Effects of litter quality and PD and stream pH were more positive at higher temperatures, indicating that different mechanisms may operate at different latitudes. These results reflect global variability caused by multiple factors, but unexplained variance points to the need for expanded global-scale comparisons.

The Effect of Iron Oxide Insertion on the In Vitro Bioactivity, and Antibacterial Properties of the 45S5 Bioactive Glass.

The aging population and increasing incidence of trauma among younger age groups have heightened the increasing demand for reliable implant materials. Effective implant materials must demonstrate rapid osseointegration and strong antibacterial properties to ensure optimal patient outcomes and decrease the chance of implant rejection. This study aims to enhance the bone-implant interface by utilizing 45S5 bioglass modified with various concentrations of Fe3O4 as a coating material. The effect of the insertion of Fe3O4 into the bioglass structure was studied using Raman spectroscopy which shows that with the increase in Fe3O4 concentration, new vibration bands associated with Fe-related structural units appeared within the sample. The bioactivity of the prepared glasses was evaluated using immersion tests in simulated body fluid, revealing the formation of a calcium phosphate-rich layer within 24 h on the samples, indicating their potential for enhanced tissue integration. However, the sample modified with 8 mol% of Fe3O4 showed low reactivity, developing a calcium phosphate-rich layer within 96 h. All the bioglasses showed antibacterial activity against the Gram-positive and Gram-negative bacteria. The modified bioglass did not present significant antibacterial properties compared to the bioglass base.

Influence of the Addition of Zinc, Strontium, or Magnesium Oxides to the Bioglass 45S5 Network on Electrical Behavior.

45S5 Bioglass has been widely used in regenerative medicine due to its ability to dissolve when inserted into the body. Its typically amorphous structure allows for an ideal dissolution rate for the formation of the hydroxyapatite layer, which is important for the development of new bone. This bioactive capacity can also be controlled by adding other oxides (e.g., SrO, ZnO, and MgO) to the 45S5 Bioglass network or by storing electrical charge. Ions such as zinc, magnesium, and strontium allow for specific biological responses to be added, such as antibacterial action and the ability to increase the rate of osteoblast proliferation. The charge storage capacity allows for a higher rate of bioactivity to be achieved, allowing for faster attachment to the host bone, decreasing the patient's recovery time. Therefore, it is necessary to understand the variation in the structure of the bioglass with regard to the amount of non-bridging oxygens (NBOs), which is important for the bioactivity rate not to be compromised, and also its influence on the electrical behavior relevant to its potential as electrical charge storage. Thus, several bioactive glass compositions were synthesized based on the 45S5 Bioglass formulation with the addition of various concentrations (0.25, 0.5, 1, and 2, mol%) of zinc, strontium, or magnesium oxides. The influence of the insertion of these oxides on the network was evaluated by studying the amount of NBOs using Raman spectroscopy and their implication on the electrical behavior. Electrical characterization was performed in ac (alternating current) and dc (direct current) regimes.

Preparation and Characterization of Zinc Ferrite and Gadolinium Iron Garnet Composite for Biomagnetic Applications.

Cancer is a major worldwide public health problem. Although there have already been astonishing advances in cancer diagnosis and treatment, the scientific community continues to make huge efforts to develop new methods to treat cancer. The main objective of this work is to prepare, using a green sol-gel method with coconut water powder (CWP), a new nanocomposite with a mixture of Gd3Fe5O12 and ZnFe2O4, which has never been synthesized previously. Therefore, we carried out a structural (DTA-TG and X-ray diffraction), morphological (SEM), and magnetic (VSM and hyperthermia) characterization of the prepared samples. The prepared nanocomposite denoted a saturation magnetization of 11.56 emu/g at room temperature with a ferromagnetic behavior and with a specific absorption rate (SAR) value of 0.5 ± 0.2 (W/g). Regarding cytotoxicity, for concentrations < 10 mg/mL, it does not appear to be toxic. Although the obtained results were interesting, the high particle size was identified as a problem for the use of this nanocomposite.

Exploring the Impact of Copper Oxide Substitution on Structure, Morphology, Bioactivity, and Electrical Properties of 45S5 Bioglass®.

In recent decades, the requirements for implantable medical devices have increased, but the risks of implant rejection still exist. These issues are primarily associated with poor osseointegration, leading to biofilm formation on the implant surface. This study focuses on addressing these issues by developing a biomaterial for implant coatings. 45S5 bioglass® has been widely used in tissue engineering due to its ability to form a hydroxyapatite layer, ensuring a strong bond between the hard tissue and the bioglass. In this context, 45S5 bioglasses®, modified by the incorporation of different amounts of copper oxide, from 0 to 8 mol%, were synthesized by the melt-quenching technique. The incorporation of Cu ions did not show a significant change in the glass structure. Since the bioglass exhibited the capacity for being polarized, thereby promoting the osseointegration effectiveness, the electrical properties of the prepared samples were studied using the impedance spectroscopy method, in the frequency range of 102-106 Hz and temperature range of 200-400 K. The effects of CuO on charge transport mobility were investigated. Additionally, the bioactivity of the modified bioglasses was evaluated through immersion tests in simulated body fluid. The results revealed the initiation of a Ca-P-rich layer formation on the surface within 24 h, indicating the potential of the bioglasses to enhance the bone regeneration process.

Crystal Structural Characteristics and Electrical Properties of Novel Sol-Gel Synthesis of Ceramic Bi0.75Ba0.25(FeMn)0.5O3.

In this investigation, our primary objective is to explore the structural, morphological, and electrical characteristics of Bi0.75Ba0.25(FeMn)0.5O3 ceramic material synthesized by the sol-gel method. The prepared sample underwent synthesis through the conventional sol-gel technique. Examination through X-ray diffraction (XRD) unveiled a well-defined rhombohedral structure within the R3´C space group. Moreover, to evaluate the purity and nano-grain morphology, we utilized energy dispersive spectroscopy (EDX) and scanning electron microscopy (SEM). Electrical assessments were carried out over a frequency span of 100 Hz to 1 MHz and temperatures ranging from 200 to 340 K. Employing the correlated barrier hopping (CBH) model, we analyzed the AC conductivity of our specimen. The activation energy, determined from both DC conductivity and impedance spectra, demonstrated close correspondence, suggesting that both conductivity and r laxation processes are influenced by similar factors. Notably, the dielectric properties hold significant importance, potentially rendering our sample suitable for electronic applications. Furthermore, we calculated thermodynamic parameters, such as enthalpy (ΔH), entropy change (ΔS), and free energy of activation (ΔF), offering deeper insights into the material's behavior and conductivity mechanisms.

Study of biphasic calcium phosphate (BCP) ceramics of tilapia fish bones by age.

Biphasic calcium phosphate (BCP), consisting of bioceramics such as HAp + ß-TCP and Ca10(PO4)6(OH)2 + Ca3(PO4)2, is a popular choice for optimizing performance due to its superior biological reabsorption and osseointegration. In this study, BCP was produced by calcining the bones of tilapia fish (Oreochromis niloticus) reared in net cages and slaughtered at an age ranging from 15 to 420 days. The bones were cleaned and dried, calcined at 900 °C for 8 h, and then subjected to high-energy grinding for 3 h to produce BCP powders. After the calcination process, the crystalline phase's hydroxyapatite (HAp) and/or beta-tricalcium phosphate (ß-TCP) were present in the composition of the bioceramic. The age-dependent variation in phase composition was confirmed by complementary vibrational spectroscopy techniques, revealing characteristic peaks and bands of the bioceramic. This variation was marked by an increase in HAp phase and a decrease in ß-TCP phase. Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) from 25 to 1400 °C showed the characteristic mass losses of the material, with a greater loss observed for younger fish, indicating the complete removal of organic components at temperatures above 600 °C. Comparison of the results obtained by X-Ray Diffraction (XRD) and Rietveld refinement with Raman spectroscopy showed excellent agreement. These results showed that with temperature and environment control and adequate fish feeding, it is possible to achieve the desired amounts of each phase by choosing the ideal age of the fish. This bioceramic enables precise measurement of HAp and ß-TCP concentrations and Ca/P molar ratio, suitable for medical orthopedics and dentistry.

Dielectric Characterization of Solutions of Galactomannan Extracted from Adenanthera pavonina L.: Effects of Purification and Ethanol Concentration.

Galactomannans are polysaccharides obtained from legume seed extraction. They present a chemical structure consisting of D-mannose chains linked by glycosidic bonds and galactose branches. The main focus lies in their use as thickeners in the food industry, aimed at improving the dielectric properties of food during heating processes within the radiofrequency and microwave ranges. In this work, the prepared galactomannan samples were electrically analyzed through impedance spectroscopy, which is a powerful physical technique. From the experimental measurements, the dielectric permittivity and loss tangent of the galactomannan solutions were analyzed and the electrical modulus formalism was used to study the dielectric relaxations. Crude galactomannans exhibited higher values of permittivity, conductivity, and losses compared to purified galactomannans. Increasing ethanol concentration in galactomannan purification causes an increase in the permittivity and conductivity of galactomannan solutions. In a 1% solution, at 1 kHz, the permittivity increased from 378.56 to 538.09, while in the 2% solution, this increase was from 656.22 to 1103.24. Regarding the conductivity, at the same frequency, the increase was from 1.6 × 10-3 to 3.3 × 10-3 Ω-1m-1 and from 2.9 × 10-3 to 5.5 × 10-3 Ω-1m-1, respectively. The rise of the ethanol concentration in galactomannan purification led to a decrease in the relaxation time, from 448.56 to 159.15 µs and from 224.81 to 89.50 µs in the solution with 1 and 2%, respectively. The results suggest that galactomannan from Adenanthera pavonina L. has potential for use in the food industry.

Time series of freshwater macroinvertebrate abundances and site characteristics of European streams and rivers.

Freshwater macroinvertebrates are a diverse group and play key ecological roles, including accelerating nutrient cycling, filtering water, controlling primary producers, and providing food for predators. Their differences in tolerances and short generation times manifest in rapid community responses to change. Macroinvertebrate community composition is an indicator of water quality. In Europe, efforts to improve water quality following environmental legislation, primarily starting in the 1980s, may have driven a recovery of macroinvertebrate communities. Towards understanding temporal and spatial variation of these organisms, we compiled the TREAM dataset (Time seRies of European freshwAter Macroinvertebrates), consisting of macroinvertebrate community time series from 1,816 river and stream sites (mean length of 19.2 years and 14.9 sampling years) of 22 European countries sampled between 1968 and 2020. In total, the data include >93 million sampled individuals of 2,648 taxa from 959 genera and 212 families. These data can be used to test questions ranging from identifying drivers of the population dynamics of specific taxa to assessing the success of legislative and management restoration efforts.

Influence of the Preparation Method on the Structural, Morphological and Dielectric Properties of FeNbO4 Ceramics.

In this work, iron niobate (FeNbO4) was prepared via two processes based on the sol-gel method: colloidal gel and polymeric gel. The obtained powders were submitted to heat treatments at different temperatures based on the results obtained via differential thermal analysis. The structures of the prepared samples were characterized via X-ray diffraction and the morphology was characterized via scanning electron microscopy. The dielectric measurements were performed in the radiofrequency region using the impedance spectroscopy technique and in the microwave range using the resonant cavity method. The influence of the preparation method was noticeable in the structural, morphological and dielectric properties of the studied samples. The polymeric gel method promoted the formation of monoclinic and orthorhombic iron niobate at lower temperatures. The differences in the samples' morphology were also remarkable, both in the size and shape of the grains. The dielectric characterization revealed that the dielectric constant and the dielectric losses had the same order of magnitude and similar trends. A relaxation mechanism was identified in all the samples.

Barium Titanate/Gadolinium Ferrite: A New Material Composite to Store Energy.

This work investigates the dielectric properties of barium titanate/gadolinium ferrite ceramic composites, with different concentrations of each material. Our objective was to increase the storage ability of this material, finding a compromise between high permittivity and low dielectric losses. A two-step sintering procedure was used in the preparation of the composites to attain the desired results. Their morphological, structural and electrical properties were tested using scanning electron microscopy, X-Ray powder diffraction and impedance spectroscopy, respectively. Dielectric characterizations were performed on the frequency band of 100 Hz-1 MHz and for different temperatures (180-380 K). The best compromise between barium titanate and gadolinium ferrite in the composition was calculated in order to obtain a potential material for electrical energy storage. The sample with 25% gadolinium ferrite presented the best results. The dielectric constant reached values of the order of 2000, at 1 kHz and 340 K. It was also important not to have very high losses, and this was confirmed by the calculated loss tangent.