High Temperature Dielectrics in the Ceramic System K₀.₅Bi₀.₅TiO₃-Ba(Zr₀.₂Ti₀.₈)O₃-Bi(Zn₂⁄₃Nb₁⁄₃)O₃

Ceramics in the system (1-x)[0.5 K₀.₅Bi₀.₅TiO₃-0.5Ba(Zr₀.₂Ti₀.₈)O₃]-xBi(Zn₂⁄₃Nb₁⁄₃)O₃ have been fabricated by a solid-state processing route for compositions x ≤ 0.3. The materials are relaxor dielectrics. The temperature of maximum relative permittivity, Tm, decreased from 150 °C for composition x = 0, to 70 °C for x = 0.2. The x = 0.2 sample displayed a wide temperature range of stable relative permittivity, εr, such that εr = 805 ± 15% from −20 °C to 600 °C (1 kHz). Dielectric loss tangent was ≤ 0.02 from 50 °C to 450 °C (1 kHz), but due to the tanδ dispersion peak, the value increased to 0.09 as temperatures fell from 50 °C to −20 °C. Values of dc resistivity were of the order of ~ 109 Ω m at 300 °C. These properties are promising in the context of developing new high temperature capacitor materials

Core–shell grain structures and ferroelectric properties of Na0.5K0.5NbO3–LiTaO3–BiScO3 piezoelectric ceramics

Legislation arising from health and environmental concerns has intensified research into finding suitable alternatives to lead-based piezoceramics. Recently, solid solutions based on sodium potassium niobate (K,Na)NbO3 (KNN) have become one of the globally-important lead-free counterparts, due to their favourable dielectric and piezoelectric properties. This data article provides information on the ferroelectric properties and core–shell grain structures for the system, (1−y)[(1−x)Na0.5K0.5NbO3 – xLiTaO3] – yBiScO3 (x=0–0.1, y=0.02, abbreviated as KNN–xLT–2BS). We show elemental analysis with aid of TEM spot-EDX to identify three-type grain-types in the KNN–LT–BS ternary system. Melting behaviour has been assessed using a tube furnace with build-in camera. Details for the ferroelectric properties and core–shell chemical segregation are illustrated

Temperature-stable dielectric properties from -20°C to 430°C in the system BaTiO3-Bi(Mg0.5Zr0.5)O3

Ceramics in the solid solution series (1-x)BaTiO3-Bi(Mg0.5Zr0.5)O3 are single-phase tetragonal for compositions x≤0.05, and cubic for x≥0.1. Plots of relative permittivity (er), versus temperature show double peaks for x=0.03 and x=0.05, changing to a single, frequency-dependent peak for compositions, x≥0.1. A progressive decline in ermax with increasing x leads to near temperature-stable dielectric properties over a wide temperature range. For x=0.3, er=570±15%, from -20°C to 430°C, and tanδ≤0.02 from 30°C to 420°C. For x=0.4, er=600±15% from 25°C to 420°C, and tanδ≤0.02 from 55°C to 280°C (at 1kHz). Values of dc resistivity were ~109Ωm at 250°C and ~106Ωm at 400°C. A piezoelectric strain of ~0.25% (at 40kV/cm) was recorded for composition x=0.03

Lead-free piezoelectric K0.5Bi0.5TiO3–Bi(Mg0.5Ti0.5)O3 ceramics with depolarisation temperatures up to ~220 C

The properties of K0.5Bi0.5TiO3-rich ceramic solid solutions in the system (1 - x)K0.5Bi0.5TiO3– xBi(Mg0.5Ti0.5)O3 are reported. The highest values of piezoelectric charge coefficient, d33, and field-induced strains are found in compositions located close to a compositional boundary between single-phase tetragonal and mixed tetragonal ? cubic perovskite phases. Maximum d33 values were *150 pC/N for x = 0.03, with positive strains of *0.25 %; the x = 0.04 composition had a d33 * 133 pC/N and strain of 0.35 % (bipolar electric field, 50 kV/ cm, 1 Hz). Depolarisation temperature Td is an important selection criterion for any lead-free piezoelectric for actuator or sensor applications. A Td of *220 C for x = 0.03 is *100 C higher than for the widely reported Na0.5Bi0.5TiO3–BaTiO3 system, yet d33 values and strains are similar, suggesting the new material is worthy of further attention as a lead-free piezoceramic for elevated temperature applications

Preparation and Evaluation of CaO-Based CO₂ Sorbents Deposited on Saffil Fiber Supports

Calcium-oxide-based sorbents were coated onto Saffil ceramic fibers by means of a wet impregnation method. The effect of synthesis parameters on the crystalline structure, morphology, and texture of the CaO layer was investigated by X-ray diffraction, scanning electron microscopy, and gas adsorption techniques. The analyses revealed that the optimized synthesis method produced a uniform coating composed of a network of CaO nanoflakes. The evaluation of the materials as CO₂ sorbents was performed under repeated carbonation–decarbonation cycles using thermogravimetric analysis (TGA). A nominal 25 wt % loading of CaO gave a CO₂ uptake capacity of 0.118 mg of CO₂/mg of sorbent (carbonation at 650 °C in 90% CO₂ and decarbonation at 850 °C in N₂). A 5 wt % loading exhibited improved durability with a ∼30% decay in carrying capacity after 30 TGA cycles but at the expense of the initial uptake capacity

Electrophysiological Evidence of Atypical Spatial Attention in Those with a High Level of Self-reported Autistic Traits

Selective attention is atypical in individuals with autism spectrum conditions. Evidence suggests this is also the case for those with high levels of autistic traits. Here we investigated the neural basis of spatial attention in those with high and low levels of self-reported autistic traits via analysis of ERP deflections associated with covert attention, target selection and distractor suppression (the N2pc, NT and PD). Larger N2pc and smaller PD amplitude was observed in those with high levels of autistic traits. These data provide neural evidence for differences in spatial attention, specifically, reduced distractor suppression in those with high levels of autistic traits, and may provide insight into the experience of perceptual overload often reported by individuals on the autism spectrum

Phase-transition induced giant negative electrocaloric effect in a lead-free relaxor ferroelectric thin film

The electrocaloric (EC) effect has been widely investigated during the past decade due to the potential applications in commercial solid state refrigeration devices. The positive EC effect in lead-based materials has been significantly enhanced from 12 K to 40 K since it is observed in 2006, but the negative EC effect still stays at a very low level of about −10 K, which limits further enhancement of cooling efficiency, especially when we attempt to combine both negative and positive EC effect in one cooling cycle. Due to the toxicity of lead, lead-free materials are always sought after to replace lead-containing materials. In this study, a giant negative EC effect (maximum ΔT ∼ −42.5 K) comparable to the best positive EC effects reported so far is demonstrated for 0.5(Ba0.8Ca0.2)TiO3–0.5Bi(Mg0.5Ti0.5)O3 lead-free relaxor ferroelectric thin films prepared by using a sol–gel method. An electric-field induced structural phase transition (nanoscale tetragonal and orthorhombic to rhombohedral) along the out-of-plane [111] direction plays a key role in developing the giant negative EC effect. This breakthrough will pave the way for practical applications of next-generation refrigeration devices with high cooling efficiency in one cycle by utilizing and combining both the giant negative and positive EC effects

Nanoscale compositional segregation and suppression of polar coupling in a relaxor ferroelectric

A number of relaxor ferroelectric ceramics have been demonstrated to possess a near stable value of relative permittivity over very wide temperature ranges. This cannot be explained by conventional theories of relaxors. One such system is based on the perovskite solid solution series: (1-x) (Ba₀.₈Ca₀.₂)TiO₃-xBi(Mg₀.₅Ti₀.₅)O₃, giving stable relative permittivity from 150 to 500 °C. We show by scanning transmission electron microscopy and electron energy loss spectroscopic elemental mapping that nanoscale compositional segregation occurs in the temperature stable relaxor composition (x = 0.55), with Ba/Ti clusters some 2–4 nm in extent, separated by Bi-rich regions of comparable size. This nanomosaic structure is consistent with phase separation into a ferroelectrically active BaTiO₃ – type phase (Ba/Ti rich) and a weakly polar Bi/(Mg) rich perovskite solid solution. The possibility that nanophase segregation is the cause of weak dipole coupling and suppression of the dielectric relaxation peak is considered

Spray-Dried Sodium Zirconate: A Rapid Absorption Powder for CO2 Capture with Enhanced Cyclic Stability

Improved powders for capturing CO2 at high temperatures are required for H2 production using sorption-enhanced steam reforming. Here, we examine the relationship between particle structure and carbonation rate for two types of Na2ZrO3 powders. Hollow spray-dried microgranules with a wall thickness of 100–300 nm corresponding to the dimensions of the primary acetate-derived particles gave about 75 wt % theoretical CO2 conversion after a process-relevant 5 min exposure to 15 vol % CO2. A conventional powder prepared by solid-state reaction carbonated more slowly, achieving only 50 % conversion owing to a greater proportion of the reaction requiring bulk diffusion through the densely agglomerated particles. The hollow granular structure of the spray-dried powder was retained postcarbonation but chemical segregation resulted in islands of an amorphous Na-rich phase (Na2CO3) within a crystalline ZrO2 particle matrix. Despite this phase separation, the reverse reaction to re-form Na2ZrO3 could be achieved by heating each powder to 900 °C in N2 (no dwell time). This resulted in a very stable multicycle performance in 40 cycle tests using thermogravimetric analysis for both powders. Kinetic analysis of thermogravimetric data showed the carbonation process fits an Avrami–Erofeyev 2 D nucleation and nuclei growth model, consistent with microstructural evidence of a surface-driven transformation. Thus, we demonstrate that spray drying is a viable processing route to enhance the carbon capture performance of Na2ZrO3 powder

Sensory Attenuation Assessed by Sensory Evoked Potentials in Functional Movement Disorders.

BACKGROUND: Functional (psychogenic) movement disorders (FMD) have features associated with voluntary movement (e.g. distractibility) but patients report movements to be out of their control. One explanation for this phenomenon is that sense of agency for movement is impaired. The phenomenon of reduction in the intensity of sensory experience when movement is self-generated and a reduction in sensory evoked potentials (SEPs) amplitude at the onset of self-paced movement (sensory attenuation) have been linked to sense of agency for movement. METHODS: We compared amplitude of SEPs from median nerve stimulation at rest and at the onset of a self-paced movement of the thumb in 17 patients with FMD and 17 healthy controls. RESULTS: Patients showed lack of attenuation of SEPs at the onset of movement compared to reduction in amplitude of SEPs in controls. FMD patients had significantly different ratios of movement onset to rest SEPs than did healthy controls at each electrode: 0.79 in healthy controls and 1.35 in patients at F3 (t = -4.22, p<0.001), 0.78 in healthy controls and 1.12 at patients C3 (t = -3.15, p = 0.004) and 0.77 in healthy controls and 1.05 at patients P3 (t = -2.88, p = 0.007). CONCLUSIONS: Patients with FMD have reduced sensory attenuation as measured by SEPs at onset of self-paced movement. This finding can be plausibly linked to impairment of sense of agency for movement in these patients