Pulsed Density Research Articles

Enhanced energy storage performance of lead-free Sr0.7Bi0.2TiO3 ceramics via tape casting

Abstract The development of pulsed power technology demands high energy storage density dielectric materials. In this study, Sr0.7Bi0.2TiO3 relaxor ferroelectric (rFE) ceramic thick films were prepared using a tape-casting process. The ceramics exhibit a dense structure and typical rFE hysteresis curves, achieving an energy storage density of 4.77 J cm−3 and efficiency of 94.4%, attributed to the high polarization intensity, low remnant polarization, and low hysteresis loss of rFE. Additionally, the material demonstrates good temperature stability. Moreover, the Sr0.7Bi0.2TiO3 ceramic thick films show advantages in charge-discharge performance, capable of discharging within hundreds of nanoseconds and achieving a power density of 137 MW cm−3. Overall, the Sr0.7Bi0.2TiO3 ceramic thick film exhibits a comprehensive performance advantage in terms of energy storage density, efficiency, and power density. Additionally, the material was fabricated using the tape-casting process, which is compatible with subsequent multilayer ceramic capacitor production, indicating potential for further performance enhancement.

Mykonos: A pulsed power driver for science and innovation

Sandia National Laboratories has been operating the Mykonos linear transformer driver (LTD) in a five-cavity configuration since 2014. The machine operates at 1MA output current, 500kV output voltage, with a 10–90% current rise time of 85ns, which enables small scale physics and engineering pulsed power experiments. Mykonos provides hands-on pulsed power experimental training for students and staff alongside senior Sandia scientists in an environment that is more accessible than the Z Facility. Over the years, we have fielded and accumulated a wide variety of optical, x-ray and electrical diagnostics and we are preparing to open this facility to outside users. Here, we are presenting the pulsed power and diagnostic capability of Mykonos as well as some recent experiments that have been performed on the facility. The goal of this publication is to attract researchers across the pulsed power and high energy density (HED) community to collaborate with Sandia on exciting, innovative science and to train the next generation of researchers for the National Nuclear Security Agency (NNSA) and the nation. As such, we have established a Mykonos Academic Access Program (MAAP) as part of ZNetUS to enable academic utilization of the Mykonos Pulsed Power Facility.

High energy storage performance in BTO-based ferroelectric films

Dielectric capacitors play an increasingly important role in modern electronic power systems due to their ultrahigh charging and discharging speeds and power density. Much research has focused on enhancing dielectric breakdown strength to achieve better energy storage performance; however, this increases the potential for heat generation and unexpected insulation failures, thereby affecting the stability and lifespan of devices. This study introduces a small amount of Na+ dopants at the A-site of BaTiO3, inducing lattice distortions and enhancing local polarization to increase energy storage density rather than through enhancing breakdown strength. The introduction of Na+ enhances the ferroelectric properties, with polar nano-regions (PNRs) gradually evolving into long-range ordered large domains. In the Ba0.985Na0.015TiO3 films, the coexistence and coupling of abundant PNRs with a few long-range ordered ferroelectric domains result in high saturation polarization and low residual polarization. At a moderate electric field of 2.3 MV cm−1, an ultrahigh energy density of 44.3 J cm−3 and a high energy storage efficiency of 78.6 % were obtained. Additionally, the film exhibits excellent frequency stability (100 Hz-20 kHz), temperature stability (30–180 °C), fatigue resistance (107 cycles), and high pulsed discharge energy density, along with great thermal stability. This work provides new insights into achieving exceptional energy storage performance in single-phase films.

Optimization of Pulsed Laser Energy Density for the Preparation of MoS2 Film and Its Device by Pulsed Laser Deposition.

This article aims to explore the most optimal pulsed laser energy density when using the pulsed laser deposition (PLD) process to prepare the MoS2 films. We gradually increased the pulsed laser energy density from 70 mJ·cm-2 to 110 mJ·cm-2 and finally determined that 100 mJ·cm-2 was the best-pulsed laser energy density for MoS2 films by PLD. The surface morphology and crystallization of the MoS2 films prepared under this condition are the best. The films consist of a high-crystallized 2H-MoS2 phase with strong (002) preferential orientation, and their direct optical band gap (Eg) is 1.614 eV. At the same time, the Si/MoS2 heterojunction prepared under the optimal pulsed laser energy density shows an opening voltage of 0.61 V and a rectification ratio of 457.0.

Synthesis of nanocrystalline nickel via pulsed current electrodeposition in additive-free deposition bath and comparison of nanoscale characterization

An experimental investigation on synthesis of nanocrystalline nickels by pulsed current electrodeposition has been carried out in an additive-free Watts bath employing nickel-sulphate solution with similar nickel ion concentrations. Aluminum was used as a substrate. It demonstrated the advantage of easier removal process of electrodeposited nanocrystalline nickel from its substrate. Whereas the use of high-purity nickel anode was intended to replace nickel ions, which decreased during electrodeposition. Different peak current densities of 450, 750 and 1000 mA/cm2 were applied. A pulsed current was set at a similar pulse pattern of on-time and off-time of 1 ms and 9 ms respectively. The shorter on-time demonstrated the ability to limit ion deposition, which was related to the formation of finer grains. The off-time arrangement was targeted to ensure that the ion mobility had completely stopped. Higher current density demonstrated a dominant impact on deposits, generating a higher nucleation rate that is related to depositing nanocrystalline nickel. A peak current density of 1000 mA/cm2 produced grain sizes in the nanoscale regime. Without any additional additive, nanocrystalline nickel was successfully yielded. Investigation of grain size obtained from the 1000 mA/cm2 has been conducted by extracting full width at half maximum peak intensity (FWHM) revealed from X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) exhibited consistent results of 22 nm and 25.4±3.4 nm, respectively. It is also evidence of the significant role of pulsed current density. In inclusion, nanocrystalline nickel can be synthesized in an electrodeposition bath without any addition of additives

On density measurement using various radiation sources: Cs-137, X-ray and pulsed neutron

The use of controllable sources for density measurement is gaining more attention as a safer alternative to chemical sources, since chemical sources pose risks to both humans and the environment. Nuclear density tools using electronically controlled sources, such as X-ray tubes and pulsed neutron generators, are being researched as a replacement for radiological gamma sources such as Cs-137. This study, based on the real gamma density tool structure, optimizes the design of the X-ray and pulsed neutron-gamma density tools, providing a reference for the optimization of source-less density tools. Firstly, the study gives a comparison of density measurement using three sources through a combination of theory and simulation results. And the performance of the tools is evaluated using indicators such as detection efficiency, formation density sensitivity, and depth of investigation. Finally, based on the characteristics of different sources, the aforementioned indicators are balanced to obtain the optimal value of the source-to-detector distance, thus the structure of the X-ray density tool and pulsed neutron-gamma density tool are optimized.

Mitigating Heavy Ion Irradiation‐Induced Degradation in p‐type SnO Thin‐Film Transistors at Room Temperature

The study investigates the mitigation of radiation damage on p‐type SnO thin‐film transistors (TFTs) with a fast, room‐temperature annealing process. Atomic layer deposition is utilized to fabricate bottom‐gate TFTs of high‐quality p‐type SnO layers. After 2.8 MeV Au4+ irradiation at a fluence level of 5.2 × 1012 ions cm−2, the output drain current and on/off current ratio (Ion/Ioff) decrease by more than one order of magnitude, field‐effect mobility (μFE) reduces more than four times, and subthreshold swing (SS) increases more than four times along with a negative shift in threshold voltage. The observed degradation is attributed to increased surface roughness and defect density, as confirmed by scanning electron microscopy (SEM), high‐resolution micro‐Raman, and transmission electron microscopy (TEM) with geometric phase analysis (GPA). A technique is demonstrated to recover the device performance at room temperature and in less than a minute, using the electron wind force (EWF) obtained from low‐duty‐cycle high‐density pulsed current. At a pulsed current density of 4.0 × 105 A cm−2, approximately four times increase in Ion/Ioff is observed, 41% increase in μFE, and 20% decrease in the SS of the irradiated TFTs, suggesting effectiveness of the new annealing technique.

Simultaneously achieving high energy storage and charge-discharge performance by Nd-doped Sr0.7Bi0.2TiO3 lead-free relaxor ferroelectric ceramics

Dielectric capacitors have been extensively studied in electronic and power systems based on their high power density and ultra-fast discharge rates. In this study, the dielectric, energy storage and charge-discharge properties of Sr0.7Bi0.2TiO3-based lead-free relaxor ferroelectric ceramic were investigated. The dielectric breakdown strength was significantly improved by introducing the rare earth element Nd, which was attributed to the rise in resistivity and large band gap. The results show that Sr0.7Bi0.15Nd0.05TiO3 obtain a high recoverable energy storage density of 2.34 J/cm3 with high efficiency of 92%. In addition, pulsed charge-discharge tests demonstrated that Sr0.7Bi0.15Nd0.05TiO3 possesses a high power density of 73.5 MW/cm3, a short discharge period of 0.1 μs, and a pulsed discharge energy density of 2.0 J/cm3. Meanwhile, the energy storage performance of Sr0.7Bi0.15Nd0.05TiO3 exhibits excellent stability of temperature, frequency and cycling. This work provides a systematic study and a new strategy for enhancing the performance of SBT ceramics.

The TRAPUM L-band survey for pulsars in Fermi-LAT gamma-ray sources

ABSTRACT More than 100 millisecond pulsars (MSPs) have been discovered in radio observations of gamma-ray sources detected by the Fermi Large Area Telescope (LAT), but hundreds of pulsar-like sources remain unidentified. Here, we present the first results from the targeted survey of Fermi-LAT sources being performed by the Transients and Pulsars with MeerKAT (TRAPUM) Large Survey Project. We observed 79 sources identified as possible gamma-ray pulsar candidates by a Random Forest classification of unassociated sources from the 4FGL catalogue. Each source was observed for 10 min on two separate epochs using MeerKAT’s L-band receiver (856–1712 MHz), with typical pulsed flux density sensitivities of $\sim 100\, \mu$Jy. Nine new MSPs were discovered, eight of which are in binary systems, including two eclipsing redbacks and one system, PSR J1526−2744, that appears to have a white dwarf companion in an unusually compact 5 h orbit. We obtained phase-connected timing solutions for two of these MSPs, enabling the detection of gamma-ray pulsations in the Fermi-LAT data. A follow-up search for continuous gravitational waves from PSR J1526−2744 in Advanced LIGO data using the resulting Fermi-LAT timing ephemeris yielded no detection, but sets an upper limit on the neutron star ellipticity of 2.45 × 10−8. We also detected X-ray emission from the redback PSR J1803−6707 in data from the first eROSITA all-sky survey, likely due to emission from an intrabinary shock.

Photoacoustic testing of shear viscoelastic properties of soft tissues using annular beam illumination.

This Letter reports a new, to the best of our knowledge, photoacoustic excitation method for evaluating the shear viscoelastic properties of soft tissues. By illuminating the target surface with an annular pulsed laser beam, circularly converging surface acoustic waves (SAWs) are generated, focused, and detected at the center of the annular beam. The shear elasticity and shear viscosity of the target are extracted from the dispersive phase velocity of the SAWs based on the Kelvin-Voigt model and nonlinear regression fitting. Agar phantoms with different concentrations, and animal liver and fat tissue samples have successfully been characterized. Different from previous methods, the self-focusing of the converging SAWs allows sufficient SNR to be obtained even with low pulsed laser energy density, which makes this approach well compatible with soft tissues under both ex vivo and in vivo testing conditions.

High-performance quantum cascade lasers at λ ∼ 9 µm grown by MOCVD.

We demonstrate a high power InP-based quantum cascade laser (QCL) (λ ∼ 9 µm) with high characteristic temperature grown by metalorganic chemical vapor deposition (MOCVD) in this article. A 4-mm-long cavity length, 10.5-µm-wide ridge QCL with high-reflection (HR) coating demonstrates a maximum pulsed peak power of 1.55 W and continuous-wave (CW) output power of 1.02W at 293 K. The pulsed threshold current density of the device is as low as 1.52 kA/cm2. The active region adopted a dual-upper-state (DAU) and multiple-lower-state (MS) design and it shows a wide electroluminescence (EL) spectrum with 466 cm-1 wide full-width at half maximum (FWHM). In addition, the device performance is insensitive to the temperature change since the threshold-current characteristic temperature coefficient, T0, is as high as 228 K, and slope-efficiency characteristic temperature coefficient, T1, is as high as 680 K, over the heatsink-temperature range of 293 K to 353 K.

Improving the pulsed neutron-gamma density method with machine learning regression algorithms

Formation bulk density is one of the critical parameters for formation evaluation. As a safe and environmentally friendly method, the pulsed neutron-gamma density (NGD) measurement is emerging as an alternative to the traditional chemical source-based gamma-gamma density (GGD) measurement. However, in the NGD measurement, the initial energy spectrum, source intensity, and spatial distribution of the secondary inelastic gamma-ray source vary with formation components. Moreover, the energy of inelastic gamma rays is at the MeV level, leading to a non-negligible pair production effect. All these factors affect the accuracy of the bulk-density measurement. In addition, the impact of borehole configuration on NGD is evident, and correction for borehole effects is essential. To improve density accuracy: first, we forgo exploring an explicit theoretical formula for density calculation and instead treat the NGD mathematically as a regression problem and introduce the machine learning regressor, a powerful and popular tool for solving regression problems, into the NGD for the first time; second, we select features less affected by changes in formation chemical composition as input features. Our results show that the final three tuned machine learning regressors selected from the 39 candidate regressors outperform the optimized polynomial model (an optimization of conventional density calculation models) in both accuracy and generalization ability. They complete density prediction and borehole correction in one step, avoiding complex exploration of borehole effects as in the optimized polynomial model and dramatically simplifying the borehole correction process. Moreover, the GaussianProcessRegressor can complete borehole correction without the standoff information and perform well, which is impossible for the optimized polynomial model, broadening application scenarios.

Studying the bioeffects of complexly organized electromagnetic impacts of low intensity

Introduction. One of the modern tasks of hygienic assessment of the human environment is the accumulation of data on the bioeffects of electromagnetic fields (EMF), formed by the simultaneous action of several microwave sources. There is virtually no literature on the corresponding comparative analysis of the results of identical in conditions and energy effects on animals and humans. The purpose of this work is to compare bioeffects and analyze possible mechanisms of their formation, as a result of the action of electromagnetic fields (EMF) of one, two and three carrier frequencies, within 0.9-1.4 GHz with equivalent energy and modulation characteristics. Materials and methods. The work was performed in experiments on 11 rabbits (2.5-3 kg) of the Chinchilla breed and clinical- physiological studies involving 14 volunteers - men, aged 40-50 years. Irradiation was subjected mainly to the head of the object. The series differed in the number of carrier frequencies, their specific value and modulation within different EEG ranges, while maintaining an energy flux density (EPR) in the total pulse - 300 μW/cm2. We analyzed a set of indicators related to the functional assessment of central nervous, cardiovascular, respiration and muscular vbody systems. Results. The results on the dependence of the EMF effect of complex organization on the carrier frequency, their number and modulation nature are presented. It was established that each of the observed reactions was within the physiological norm, but along with the gain in the number of carrier frequencies and the specific modulation value, their qualitative and quantitative characteristics increased. Analysis of their phenomenology (of the alpha EEG range only at one carrier; + delta with a reflection of the reaction in other indicators - at two; an increase in the percentage of reactions in a complex of indicators, especially EMG - at three) indicated a different degree of synchronization of the bioelectric activity of the brain and the neurophysiological mechanism of their formation. The information obtained, of course, is limited to specific EMF parameters. It complements the relevant information available by highlighting the need for more research on a case-by-case basis. Limitations. The study of the phenomenology and mechanism of bioeffects of several low-intensity EMFs at the same time is a complex task that requires the involvement of a larger number of electromagnetic sources and a variety of indicators of the body’s response than this work was limited to and which, undoubtedly, is promising in the development of this area of research. Conclusion. In this study, there were no reactions that would go beyond the physiological norm. However, further strengthening of synchronization processes in the central nervous system, according to the analysis of the literature, can lead to such changes. This circumstance dictates the need to take it into account in the formation of the appropriate sanitary and hygienic assessment.

Bulk Density Response and Experimental Study of Pulsed Neutron-Gamma Density Logging

The pulsed neutron-gamma density logging technique is used to measure the bulk density of formations based on the detection of gamma rays from the inelastic scattering of neutrons in the formations. However, the induced gamma ray source is regarded as a function of neutron transport and cannot be considered a “point” source. Due to the high energy level of gamma rays, the attenuation of inelastic gamma rays is affected by Compton scattering and pair production. Therefore, bulk density can be measured using inelastic gamma rays while considering the effects of neutron transport and pair production. In this article, a novel density measurement method that uses a completely different response model is proposed to improve the accuracy of density measurement. The process of neutron-gamma density measurement is divided into the neutron transport group and the gamma ray transport group in accordance with the neutron-gamma coupled field theory. A novel density estimation algorithm is derived from the diffusion equation and the gamma ray attenuation law. The accuracy and specification of density measurement are investigated through the Monte Carlo simulation and the calibration of test pits. Theoretical and experimental analyses show that the neutron transport and gamma ray transport are not entirely independent of each other in the pulsed neutron-gamma density measurement. The newly developed model can effectively enable the inelastic gamma rays to conform to the gamma ray attenuation law and keep the measurement accuracy at ±0.025 g/cm3. Moreover, neutron-gamma density is insensitive to the porosity and lithology of the formation. The proposed novel algorithm successfully establishes the calculation model for the relationship between inelastic gamma rays and bulk density, providing a new perspective for density measurement in pulsed neutron-gamma density logging.

Improving a high-power laser-based relativistic electron source: the role of laser pulse contrast and gas jet density profile

A relativistic electron source based on high power laser interaction with gas jet targets has been developed at the Institute of Plasma Physics and Lasers of the Hellenic Mediterranean University. Initial measurements were conducted using the ‘Zeus’ 45 TW laser with peak intensities in the range of 1018–1019 W cm−2 interacting with a He pulsed gas jet having a 0.8 mm diameter nozzle. A significant improvement of the electron signal was measured after using an absorber to improve the laser pulse contrast from 10−10 to 10−11. A high stability quasi-mono-energetic electron beam of about 50 MeV was achieved and measured using a magnetic spectrometer for pulsed gas jet backing pressure of 12 bar. Supplementary studies using a 3 mm diameter nozzle for backing pressures in the range of 35–40 bar showed electron beam production with energies spread in the range from 50 to 150 MeV. The pulsed jet density profile was determined using interferometric techniques. Particle-in-cell simulations, at the above experimentally determined conditions, support our experimental findings.

Численное моделирование динамики температурных полей в монокристаллическом кремнии при импульсно-периодической высокоинтенсивной ионной имплантации и энергетическом воздействии пучка на поверхность

Methods to modify surface and near-surface layers of materials and coatings by ion beams are used in many fields of science and technology. The method of high-intensity implantation by high-power density ion beams with submillisecond duration involves significant pulsed heating of the irradiated target’s near-surface layer, followed by its rapid cooling due to heat transfer into the material due to thermal conductivity and the implementation of repetitively-pulsed radiation-enhanced diffusion of atoms to depths exceeding the projective ion range. Using the numerical simulation, this work studies the dynamics of changes in temperature fields into silicon wafer under single-pulse and repetitively-pulsed exposure to submillisecond titanium ion beam with a pulsed power density in the range up to 109 W/m2. The conditions are determined under which the temperature in the ion-doped layer will correspond to the conditions of radiation-stimulated diffusion of the implanted element, and the temperature in the matrix material will not deteriorate its microstructure and properties.

Investigation on improved micro-formability and forming mechanism under high strain rate of H62 brass in pulsed current-assisted laser impact micro-forming

An innovative processing technology called pulsed current assisted-laser impact micro-forming was proposed to further improve the forming quality of microparts under a high strain rate. The experimental results showed that compared with the traditional annealing heat treatment, the pulsed current treatment significantly improved the formability of H62 brass under laser impact, and the enhancement amplitude increased with increasing pulsed current density. After the pulsed current treatment, the forming depth of the micro-parts under laser impact significantly improved, the necking phenomenon at the transition corner and the bottom of the microgroove was significantly alleviated, and the surface roughness of the micro-parts was effectively reduced. The microstructure of samples was also analyzed by transmission electron microscopy, electron backscattering diffraction, and other advanced characterization techniques. It was found that pulsed current pretreatment can further improve the micro-formability of materials under high strain rate by enhancing the inertial effect of materials, refining grains, and reducing the surface texture density evolution rate.

Flow characteristics and microstructural evolution in pulsed current assisted micro-scaled compression of stainless steel sheet

Electrically assisted (EA) microforming has pervasive benefits for the fabrication of high-performance microproducts. In this research, the coupled effect between the microstructural size effect and pulsed current on the flow characteristics of 304 stainless steel sheets along thickness direction was explored by using EA micro-compression tests. The results revealed that the strain hardening rate and the deformation stress of 304 stainless steel decreases during the EA deformation, especially when the current density exceeds 57.16 A/mm2. Besides, the effect of grain size on the micro-scaled compression is gradually weakened with the augment of current density and plastic strain. The electron backscatter diffraction (EBSD) results showed in the perspective of microstructure that the decrease of flow stress and strain hardening rate with the rise of pulsed current density is related to the reduction of dislocation density and texture strength due to the dynamic recrystallization during EA deformation. The pulsed current suppresses the grain refinement of fine-grained material and promotes that of coarse-grained material, and the recrystallization rate of EA deformation increases with the decrease of initial grain size. In addition, the recrystallization texture induced by the pulsed current can promote grain deflection and weakens the effect of twins in coarse-grained material. That can explain the reason for the weakening of the grain size effect. The findings in the research have important guiding significance for understanding the coupled mechanism of electroplastic and grain size effect on the flow characteristics of difficult-to-deform material, and further promoting the application of EA micro-rolling of high-strength materials.

Electrochemical Polishing of Extruded and Laser Powder-Bed-Fused Inconel 718

ABSTRACT Electro-chemical polishing (ECP) was utilized to produce sub-micron surface finish on Inconel 718 parts manufactured by Laser Powder-Bed-Fusion (L-PBF) and extrusion methods. The L-PBF parts had very rough surfaces due to semi-welded powder particles, surface defects, and difference layer steps that were generally not found on surfaces of extruded and machined components. This study compared the results of electro-polishing of these differently manufactured parts under the same conditions. Titanium electrode was used with an acid-based electrolyte to polish both the specimens at different combinations of pulsed current density, duty cycle, and polishing time. Digital 3D optical profiler was used to assess the surface finish, while optical and scanning electron microscopy was utilized to observe the microstructure of polished specimens. At optimal condition, the ECP successfully reduced the surface of L-PBF part from 17 µm to 0.25 µm; further polishing did not improve the surface finish due to different removal rates of micro-leveled pores, cracks, nonconductive phases, and carbide particles in 3D-printed Inconel 718. The microstructure of extruded materials was uniform and free of processing defects, therefore can be polished consistently to 0.20 µm. Over-polishing of extruded material could improve its surface finish, but not for the L-PBF material due to defects and the surrounding micro-strain.

Novel lead-free (1-x)Sr0.7Bi0.2TiO3-xLa(Mg0.5Zr0.5)O3 energy storage ceramics with high charge-discharge and excellent temperature-stable dielectric properties

In this study, novel lead-free (1-x)Sr0·7Bi0·2TiO3-xLa(Mg0·5Zr0.5)O3 ((1-x)SBT-xLMZ) ceramics were designed and fabricated by the conventional solid-state reaction method. The dielectric performance, energy storage characteristics and charge-discharge behavior of the ceramics were systematically investigated. Specifically, the temperature stability of dielectric constant is improved by doping SBT with LMZ. On a separate note, BDS is also enhanced ascribed to the reduction of the grain size. Consequently, the 0.87SBT-0.13LMZ exhibits high critical electric field of 340 kV/cm with ultrahigh efficiency (η) of 98.2% and recoverable energy storage density (Wrec) of 1.22 J/cm3. Moreover, pulsed charge-discharge test elucidates that 0.87SBT-0.13LMZ possesses great thermal stability (30 °C–150 °C) along with a fast discharge period of 0.125 μs, high power density (PD) of 72.38 MW/cm3 as well as a high pulsed discharge energy density (1.2 J/cm3) at 380 kV/cm. Based on these outstanding characteristics, the 0.87SBT-0.13LMZ is considered as a potential candidate for pulse systems.