Changes In Dielectric Properties Research Articles

Microwave humidity sensor based on shorted split ring resonator with interdigital capacitance and α-Al2O3 nanoflakes/chitosan sensitive film for respiration monitoring

A microwave relative humidity (RH) sensor based on shorted split ring resonator with interdigital capacitance (SSRR-IDC) as a test platform and α-Al2O3 nanoflakes/chitosan (CS) composite as sensitive film is proposed for the detection of human respiration. The SSRR-IDC was designed by optimizing the finger spacing and width of the IDC. Electromagnetic simulation of the designed SSRR-IDC confirms a strong electric field distribution and high dielectric sensitivity in the IDC region. The porous α-Al2O3 nanoflakes/CS composite was coated onto the IDC region of the SSRR to obtain a microwave humidity sensor. Abundant hydrophilic groups and large specific surface area of the α-Al2O3 nanoflakes/CS contribute to the adsorption of water molecules. The proposed microwave humidity sensor shows excellent sensitivity in wide RH range, especially at high humidity condition. The working principle and the sensitivity enhancement mechanism of the proposed microwave sensor were explained by combining a circuit model analysis and the dielectric property and surface microstructure changes of the sensitive materials. Furthermore, the microwave sensor also demonstrates short response/recover time and outstanding repeatability, long-term stability, temperature stability, and selectivity. Additionally, the prepared microwave humidity sensor successfully records respiratory data from different volunteers. Changes in respiratory depth before and after drinking water of the volunteers can also be distinguished by this sensor.

Developing effective radio frequency drying processes for tiger nuts: Dynamic analysis of moisture state, dielectric properties and quality

Radio frequency (RF) heating technology is widely applied to dry agricultural products due to the advantages of fast and volumetric heating, but it lacks systematic and in-depth studies on combination drying methods. This study aimed to investigate the drying mechanism of tiger nuts with hot-air drying (HD), radio frequency drying (RFD), radio frequency assisted hot-air drying (RFHD), and radio frequency-vacuum drying (RFVD), in terms of analyzing dynamic changes of dehydration kinetics, moisture migration, and dielectric properties during the drying processes, as well as quality attributes of dried tiger nuts. The results indicated that the RF drying time (including RFD, RFHD and RFVD) was significantly reduced by 38.60–54.39%, compared with HD. Although RF drying had a positive effect on physical qualities, it caused clear changes to the microstructure. Among all drying methods, the free water content (A23) in the tiger nuts decreased as drying processed, while the immobilized water content (A22) increased first and then decreased. The A23 exhibited strong positive correlations with dielectric constant (ε′) and loss factor (ε″). Correspondingly, ε′ and ε″ gradually decreased due to a reduction in the A23 value. The results may comprehensively understand the RF drying mechanism of tiger nuts to provide high-quality products and optimize the drying process.

Evaluating the impact of artificial maturation on the petrophysical and geochemical properties of unconventional shale formations by integrating dielectric and NMR measurements

This paper addresses challenges in characterizing unconventional shale reservoirs. For the first time, the nuclear magnetic resonance (NMR) and dielectric responses are integrated to characterize intact, saturated, and kerogen-rich subsurface shale samples at various maturation stages. The NMR and dielectric were measured separately using independent pieces of equipment, and all NMR and dielectric measurements were carried out at surface conditions. A comprehensive assessment is provided to address the changes induced by maturation through combined geochemical and petrophysical analyses. Shale samples from the Upper Cretaceous sequence of Jordan were characterized using Rock-Eval analysis, before and after maturation treatments. The total organic carbon (TOC) was decreased from 17.4 to 13.8 and 11.3 wt% and the pyrolyzed sulfur content was decreased from 3.32 to 0.25 and 0.15 3.18%, after maturing the samples at 250 °C for 1 and 5 days, respectively. The study employed NMR to track changes in pore structure via T2 relaxation time and measured dielectric properties and conductivity dispersion across frequencies from 10 MHz to 1 GHz using a wideband open-ended coaxial probe. After the maturation treatments, the dielectric constant of saturated shale samples doubled, and the conductivity increased by over three times. These changes in dielectric properties can be attributed to increased fluid-rock interfacial polarization and the formation of new pore spaces during maturation. NMR findings also indicated the emergence of a new pore system within the organic matter and the development of new fractures, resulting in a 6 to 12% increase in total porosity. The results obtained indicate that maturation-induced microstructural changes have a more significant influence on the dielectric responses than alterations on total organic carbon.

Analysis of the Impact of Environmental Conditions on the Reliability in 5G PCB Assemblies

The designs of integrated systems are increasingly compact while the requirements of application, especially in the automotive sector, remain demanding. One main challenge is posed by the environmental conditions. In the present study, their impact on mmWave 5G PCB assemblies is evaluated with respect to both mechanical and highfrequency properties. To that end, material samples were stored at three temperatures for various durations in order to accelerate the ageing effects. Afterwards, the samples were tested by use of mechanical, dielectric and high-frequency test methods. Thermo-oxidative ageing processes were observed and lead to significant changes in mechanical and dielectric properties, with simultaneous changes of sample color. The combined approach of mechanical and high-frequency analysis allows for three innovative advantages: First, a correlation of the degradation in performance with other parameters, e.g. sample change of color, which is much easier to detect. Second, the definition of a Safe Area of Operation and a methodology to estimate the behaviour of a mmWave 5G PCB assembly over its lifetime. Finally, the study opens the pathway to a design for robustness of mmWave communication system in automotive applications.

Evaluation of the impact of wastewater irrigation on the soil's dielectric parameters

AbstractThis study investigates the impact of wastewater irrigation on soil dielectric parameters, focusing on the often‐overlooked aspect of dielectric properties in contaminated soil. Wastewater, a significant contributor to soil and groundwater degradation, has long‐term effects on soil physical, chemical, and dielectric characteristics. Experimental measurements conducted overtime at 2.45 and 5.8 GHz frequencies reveal a correlation between wastewater irrigation and changes in dielectric properties. Emphasizing time variation as a pivotal independent variable, the study sheds light on its substantial influence on soil dielectric behavior. Notably, the research introduces an alternative methodology for the comprehensive evaluation of wastewater‐induced pollution effects on soil properties. This approach is substantiated by meticulous physicochemical analyses conducted on both pollution sources and the affected soil. The study further presents a robust response surface method‐based model, showcasing impressive accuracy with dielectric properties (ε′ and ε″) and penetration depth with R2 values of 0.9845, 0.9831, and 0.9528, respectively. Beyond unveiling crucial insights into the intricate interplay of wastewater and soil dielectric behavior, this research contributes to the development of effective strategies for pollution monitoring and management in soil ecosystems.

TunGPR: Enhancing data-driven maintenance for tunnel linings through synthetic datasets, deep learning and BIM

Non-destructive Testing (NDT) techniques and data-driven technologies are increasingly applied in underground infrastructure maintenance, which can facilitate predictive monitoring for informed decision-making. Ground Penetrating Radar (GPR) is extensively utilised in rapid condition assessment of tunnel linings, particularly for detecting defects that lead to unforeseen changes of dielectric properties of materials. In this paper, a prototyped framework is proposed, namely TunGPR, for GPR-based tunnel lining assessment by incorporating Building Information Modelling (BIM), synthetic database and deep learning-enabled interpretation. The first module integrates laser-scanned point clouds and GPR Scan-to-BIM of tunnel lining with geological model. Subsequently, interoperability is achieved between the geo-integrated BIM and GPR simulation software. From the dielectric model retrieved from the BIM model, a database is established, considering a variety of condition combinations (i.e., voids, cavities, delamination, and water intrusion) leveraging domain randomisation and Finite-Difference Time-Domain (FDTD) modelling, as well as monitored field data. The dataset is then fed into the diagnostic module underpinned by a dual-rotational Convolutional Neural Network (CNN) that is customised to enhance accuracy and automation of hyperbola detection. Lastly, a preliminary risk assessment matrix is implemented into the BIM model for data management and action prioritisation. These efforts serve as an initial step to validate the feasibility and effectiveness of the GPR-enabled data-driven maintenance for tunnel linings in a BIM-centred framework.

Microwave dielectric characterization and loss mechanism of biowaste during pyrolysis

The effectiveness of microwave heating of biomass depends on the changes in dielectric properties. This study systematically investigated the microwave dielectric properties and loss mechanism of biowaste at different frequencies (915 and 2,450 MHz) and temperatures (25–800 °C) using the cavity perturbation method. The gas emissions and properties of the biochar produced during pyrolysis were characterised by SEM, XRD, and TG-FTIR. The findings revealed that the dielectric properties and penetration depth of the biomass and biochar changed significantly during microwave pyrolysis. The dielectric constant and dielectric loss coefficient first increased and then decreased during the drying stage, and they decreased continuously with the volatile’s generation in the pyrolysis stage, while the formation and high conductivity of biochar promoted a sharp increase in dielectric properties during the carbonisation stage. The loss tangent angle is 0.01–0.05 in the first two stages, while it increased to 0.10–0.25 in the carbonization stage, demonstrated that the biowaste is a low-loss material. However, the microwave absorption capacity was enhanced for pyrolyzed biochar. The loss mechanism revealed that dipole polarisation primarily contributes to the dielectric loss during the drying and pyrolysis stages, whereas interfacial polarisation plays an important role during the carbonisation stage. The data provided in this paper contribute to the evaluation of microwave penetration depth in biomass and the design of large-scale microwave-based heating systems. Furthermore, this study offers a theoretical basis for modelling and simulating the microwave heating of biomass and achieving efficient energy conversion.

Dy3+ and Sm3+ ratio variation effects on electrical properties of lithium fluoride bismuth borate glass system

Since less attention was paid to study of electric properties of glasses doped with RE ions, in present work conductivity (AC and DC) and dielectric properties of Dysprosium (Dy3+) and Samarium (Sm3+) ion co-doped 60B2O3•30LiF•10Bi2O3 glasses were examined. Conventional melt quench method was used to synthesize the amorphous glass samples. It was observed that dc conductivity obeyed the Arrhenius law and the ac conductivity followed Jonscher's Power Law. The Conductivity mechanism was investigated on the basis of the trend followed by frequency exponent “s” parameter and all the compositions satisfied the Overlapping large polaron tunnelling (OLPT) model. Dielectric properties: Dielectric Constant (ε′), Dielectric loss (ε'′) and tangent loss (tanδ) were also investigated and observed to decrease with frequency and finally attained a minimum constant value at higher frequencies. The high rate of change in dielectric properties at low frequencies was attributed to space charge polarization while at higher frequencies it was decreased due to inertia of ions. Cole-Cole plots encompasses depressed semicircular arcs which evidenced the presence of constant phase element and non-Debye relaxation behaviour.

The effects of chlorotrifluoroethylene (CTFE) units on the dielectric and energy storage properties of P(VDF‐CTFE)

AbstractPolyvinylidene fluoride‐based ferroelectric polymers are favoured in the field of advanced high‐energy‐storage dielectric capacitors due to their strong spontaneous polarisation and high dielectric constant (εr). It has been confirmed that the ferroelectric behaviour and energy storage performance can be regulated by copolymerising polyvinylidene fluoride with bulky monomers such as chlorotrifluoroethylene, and hexafluoropropylene. Past research based on these copolymers mostly focused on the preparation of composites, yet with limited discussion on the effect of copolymer composition. In this work, a series of P(VDF‐CTFE) films with different chlorotrifluoroethylene contents were fabricated through a solution‐casting method. The introduction of bulky chlorotrifluoroethylene units can tune the polymer crystal structure and crystallinity, alter the state of polymer chains and the response of dipoles to electric fields, and lead to dramatic changes in dielectric properties, breakdown strength (Eb), and energy storage density (Ue). As a result, the copolymer with a chlorotrifluoroethylene content of 15 wt% obtained the best overall performance, and the Ue reached 16.73 J/cm3 at 650 kV/mm. This work provides a basis for the optimisation of the properties of polyvinylidene fluoride‐based ferroelectric polymers and the development of high Ue dielectric.

Effect of 105 MeV gold ion irradiation on dielectric properties of PVC/PVDF@BaZrO3 nanohybrid thin film

The PVC/PVDF@BaZrO3 nanohybrid thin films were prepared by solution grown method. The dielectric constant of the films was higher due to BaZrO3 incorporation in the PVC/PVDF matrix. The PVDF and PVC/PVDF nanohybrid films were irradiated with 105 MeV Au2+ ion beam under vacuum condition at room temperature with two ion fluence. The irradiated thin film of PVC/PVDF@BaZrO3 exhibits relatively low dielectric constant with low loss at different temperature because of thermodynamic stability of β-phase. However, almost complete amorphization was observed in BaZrO3 filler in PVC/PVDF@BaZrO3 nanohybrid samples. After being irradiated with a 105 MeV Au2+ ion beam, the (ϵ′) dielectric constant, FTIR and SEM parameters were used to evaluate changes in dielectric and structural properties for all the samples. In FTIR spectra, new peaks appeared at 1705 cm−1, disappeared or minutely shifted due to high energy of ion beam. It is interesting to note that BaZrO3 phase becomes amorphized through 105 MeV Au2+ ion irradiation that causes an increased dielectric constant along with cross-linking effect of nanohybrid films.

Pathophysiology of acute graft-versus-host disease from the perspective of hemodynamics determined by dielectric analysis.

Numerous reports have demonstrated that the pathophysiology of graft-versus-host disease (GVHD) during hematopoietic stem cell transplantation (HSCT) is closely related to vascular endothelial disorders and coagulation abnormalities. We previously presented the discovery of a principle and the development of a novel instrument for measuring whole blood coagulation. This was achieved by assessing the variations in the dielectric properties of whole blood. To investigate how GVHD affects the changes of dielectric properties of whole blood in patients with HSCT. We examined the changes of dielectric properties of whole blood and erythrocyte proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis sequentially in patients with HSCT and compared it with clinical symptoms and inflammatory parameters of GVHD. During severe GVHD, the dielectric relaxation strength markedly increased and expression of band3 decreased. The dielectric relaxation strength normalized with the improvement of GVHD. In vitro analysis confirmed that the increase of relaxation strength was associated with severe erythrocyte aggregates, but not with decreased expression of band3. Severe erythrocyte aggregates observed in GVHD may cause coagulation abnor malities and circulatory failure, which, together with the irreversible erythrocyte dysfunction we recently reported, could lead to organ failure.

Assessment of the Impact of Surface Water Content for Temperate Forests in SAR Data at C-Band

This study addresses the escalating challenges posed by forest drought and wildfires, emphasizing the critical need to monitor forest conditions to mitigate associated risks. While traditional optical sensors have proven valuable for vegetation surface water (VSW) assessment, their limitations in regions with persistent cloud cover prompt an exploration of the alternatives. The study advocates the efficacy of Synthetic Aperture Radar (SAR) systems, known for their cloud-penetrating capabilities and sensitivity to changes in dielectric properties. Leveraging Sentinel-1 C-band dual polarization SAR data, the research investigates the impact of Vegetation Surface Water (VSW) on backscatter coefficients in a temperate coniferous forest through the application of generalized linear models. Despite the challenges posed by precipitation and canopy characteristics, the study unveils detectable modulation in backscatter, particularly in VH polarization, indicating the potential of SAR-based methods in forest monitoring. The occurrence of rain on the day of Sentinel-1 image acquisition, and therefore the presence of VSW, triggers an increase of 0.35 dB in VV backscatter, and an increase of 0.45 dB in VH backscatter. The findings underscore the importance of considering surface water content in radar backscatter analyses for accurate biomass estimations and change detection, suggesting avenues for future research and potential correction mechanisms.

ZrO2-doped Zn0.5Ti0.5TaO4 microwave dielectric ceramics with low dielectric loss and excellent temperature stability

Herein, the weight fraction of the tri-rutile and ixiolite structures in Zn0.5Ti0.5-xZr x TaO4 (ZTZTO x , 0 ≤ x ≤ 0.10) was successfully adjusted by the substitution of Ti4+ ions by Zr4+.Zn0.5Ti>0.48Zr0.02TaO4 ceramics exhibited excellent dielectric properties when sintered at 1290°C with τ f = -3.73 ppm/°C, εr = 33.22, and Q×f=79,266 GHz, respectively. As the amount of Zr4+- substitution increases, the tri-rutile structure content gradually decreases, and the tri-rutile structure is completely transformed into an ixiolite structure at 0.06 ≤x. This leads to the grain size showing a trend of decreasing and then increasing. Non-intrinsic factors suggest that ixiolite structures with lower εr and higher Q×f values are the main cause of the change in dielectric properties. Intrinsic factors suggest that an increase in the number of Raman characteristic waves leads to a gradual decrease in εr . The damping loss of the lattice vibrational behavior decreases, leading to a gradual increase in Q×f. In conclusion, Zn0.5Ti0.48Zr0.02TaO4 ceramics with aτf close to zero have good prospects for application in microwave communications.

Enhancement of Energy-Storage Properties and Temperature Stability in Complex Perovskite (1−x)NaNbO3−xBi(Li1/3Sn2/3)O3 Lead-Free Ceramics

In general, NaNbO3 (NN) ceramics are considered to be one of the most promising lead-free perovskites (AFE) materials with low cost, low density, and nontoxic advantages. However, the energy storage capability of this material is often greatly hindered by the hysteresis exhibited during the transition from the antiferroelectric to the ferroelectric phase. In this study, lead-free dielectric (1−x)NaNbO3−xBi(Li1/3Sn2/3)O3, x = 0.0 − 0.08, ceramics were synthesized by solid-state reaction method. The XRD data show a structural change from orthorhombic to pseudo-cubic at x = 0.06 composition. With increasing Bi(Li1/3Sn2/3)O3 content, changes in dielectric properties demonstrated that the AFE P phase was successively replaced by the relaxor AFE R phase, resulting in a thin P–E loop characteristic which leads to the improvement of the energy storage density and efficiency of the ceramic capacitors. The optimum recoverable energy storage density (W rec = 0.56 J/cm3) and efficiency (η = 74%) were obtained at x = 0.06 under an electric field of 120 kV/cm. The optimum composition also exhibited temperature stability in the range of 25 °C–100 °C. In addition, an increase in Bi(Li1/3Sn2/3)O3 content can lead to a decrease in leakage current density. This research shows that BLS modified NN ceramics are promising dielectric material candidates for energy storage applications.

Non-invasive diffused reflected/transmitted signature accompanied with hyperspectral imaging for breast cancer early diagnosis

IntroductionBreast cancer (BC) is a prevalent form of cancer worldwide and a leading cause of cancer-related deaths. There is an urgent need for the development of new methods to detect, diagnose, and monitor BC at an early stage. Light propagation and interaction with molecular species, could be utilized for diagnostic purposes. Incident light reflection and transmission are influenced by the changes of cell structure and dielectric properties. Any variations in these components could impact the reflected and transmitted signals, offering potential diagnostic applications. MethodsIn this study, non-invasive, polychromatic light source over the visible range (400–900 nm) was employed to illuminate controlled normal and BC tissue samples. The resulted diffused reflected and transmitted spectra were captured and analyzed using hyperspectral (HS) camera and designed cross-correlation algorithm. ResultsDiffused reflected signature demonstrated significant difference between normal and BC tissues over the band 500–700 nm. At 600 nm, normal tissue demonstrated diffused reflection intensity of 2304 relative to 764 for malignant tissues. Transmitted signature exhibited good discrimination capabilities over the band 600–900 nm. At 750 nm, normal tissue demonstrated transmission signal intensity of 34 relative to 21 for malignant tissues.Results were validated via generated HS 2D images, for diffused reflected and transmitted signals. Noise reduction, using moving average filter (K = 10), was adopted to enhance HS images. Contrast was improved through de-convolution with reference. Magnitude was calculated using fast Fourier transform for the concated diffused reflected and transmitted HS images. Additionally, phase shift analysis was performed to assess the differences in arrival time. ConclusionThe optimal wavelength to distinguish between normal and malignant breast tissues was 600 nm for the diffused reflected HS images; Furthermore, the transmitted HS images at 750 nm demonstrated high contrast and specificity. The developed HS imaging technique secured high levels of accuracy, specificity, and sensitivity for diffused reflected and transmitted images at 600 nm and 750 nm, respectively; K-means clustering algorithm offered precise outline and delineation of malignant areas at these wavelengths.

Improved Numerical Modeling of Terahertz Wave Propagation in Epoxy Coating with the Finite-Difference Time-Domain Method

Electromagnetic theoretical analysis was usually used to investigate the pulsed terahertz wave interaction with the medium. For epoxy coatings, the material dispersion of the coating was often simplified or ignored in the traditional propagation model. It is difficult to elaborate on the propagation mechanism and to differentiate the coating deterioration as serving time increases. An improved propagation model based on the finite-difference time domain was established to characterize the propagation in the epoxy protective coating under broad-band terahertz radiation. Either an intact or defective coating structure was investigated, and the simulated results were compared with the experimental test. The dissipation mechanism was considered in the proposed model. The results indicated that the terahertz reflections varied with the change in optical and dielectric properties caused by coating aging, which influences the intrinsic impedance of the medium. Moreover, it could well elucidate the propagation mechanism of pulsed terahertz waves in rusted, defective coating structures.

A Fused Learning and Enhancing Method for Accurate and Noninvasive Hydration Status Monitoring With UWB Microwave Based on Phantom

Hydration status is a critical indicator for human health, yet there are relatively few studies on monitoring the hydration status of the human body. Traditional methods for hydration monitoring have shortcomings such as being invasive, time-consuming to detect, and not being real time. Recently, microwave hydration monitoring has attracted research interest widely. This approach is noninvasive and based on the change of dielectric properties of human tissues with different hydration statuses. In this article, a fused learning and enhancing method is proposed to accurately monitor the hydration by using an ultrawideband (UWB) microwave. In the proposed method, an Elman neural network learning model and a joint enhancing method are designed. The joint enhancing algorithm is composed of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$</tex-math> </inline-formula> -medoids and least squares. To verify the performance of the proposed method, a muscle phantom is developed using bovine serum albumin. By changing the concentration, the phantom can mimic the muscle with different hydration statuses. In the evaluation experiment, the S-parameter and frequency data were measured with UWB microwave. Then, the data were employed for assessing the level of hydration with the proposed method. Experimental results showed that the relative error for estimating the concentration of the muscle phantom is less than 3.3%. These results demonstrated the feasibility of the proposed hydration monitoring method and proved that it is promising for monitoring human hydration status.

Micro-Structure and Dielectric Properties of Ti3C2Tx MXene after Annealing Treatment under Inert Gases

At present, the rapid development of electronic devices such as batteries, sensors, capacitors and so on is creating a huge demand for lightweight materials with a designed structure and function. Ti3C2Tx MXene, a lightweight two-dimensional (2D) nanomaterial with excellent electronic properties, has been favored in this field. In this work, Ti3C2Tx MXene was annealed under an inert gas (N2, Ar and CO2) atmosphere to design the crystal structure and interface of the nanosheets, and then the modified nanosheets with specific changes in dielectric properties were obtained. Among them, the key temperature points (100 °C, 300 °C, 500 °C and 800 °C) in the thermogravimetric (TG) test under an air atmosphere were used as the annealing temperature. When annealing under an air atmosphere, with the increase in temperature, the Ti layer gradually oxidized and evaporated, and the original two-dimensional structure was partly destroyed with some of the C atoms reacting with O2 to form CO2. In the inert gas atmosphere, however, the 2D structure is preserved, except that the surface end groups and layer spacing are changed. In addition, some N element doping was introduced into the nanosheets after N2 atmosphere treatment, which changed the original lattice structure. After the Ar atmosphere treatment, some Ti atoms on the surface were oxidized in situ to form TiO2 grains with different crystal forms, which increased the interfacial area. The C-TiO2 structure of the nanosheets was more complete after treatment with the CO2 atmosphere. All the nanosheets after heat treatment with an inert gas atmosphere retained the characteristic morphology of 2D materials, and different changes in the micro-structure caused changes in dielectric properties, thereby meeting the needs of 2D nanomaterials Ti3C2Tx MXene in different scenarios.

Achieving ultralow coercive electric field in (Ca1-1.5xGdx)3Ti2O7 ceramics via dual inhibitory effects on oxygen vacancies

(Ca1-1.5xGdx)3Ti2O7 ceramics with ultralow coercive field were obtained by the flowing oxygen sintering combined with donor doping, and their microstructure, dielectric properties ferroelectric properties, and negative piezoelectric properties were studied. The Gd3+ was introduced into A sites of Ca3Ti2O7 ceramics when x is less than 0.75%, but the Gd3+ occupied B sites of Ca3Ti2O7 ceramics when x is above 0.75%. The introduction of Gd3+ suppresses grain growth and leads to a transition from rod-like grain to irregularly shaped grain. The variation of oxygen vacancy induced by the doping of Gd3+ leads to the change of dielectric and ferroelectric properties of (Ca1-1.5xGdx)3Ti2O7 ceramics. The ultralow coercive field of (Ca1-1.5xGdx)3Ti2O7 (x = 0.25%) sample obtained at PUND and DHM modes reached 58.80 kV/cm and 45.76 kV/cm, respectively, and the higher room-temperature remnant polarization (1.797 μC/cm2/PUND and 2.055 μC/cm2/DHM) was achieved simultaneously. These results indicate that the inhibition of oxygen vacancies contributes to realizing the ultralow coercive field in (Ca1-1.5xGdx)3Ti2O7 ceramics. These findings demonstrate that introducing rare-earth ions as donor dopants into the A site of Ca3Ti2O7 ceramics combined with the flowing oxygen sintering is an essential strategy to achieve ultralow coercive field for Ca3Ti2O7-based materials.

Excellent temperature stability of strain in PZ-PT-BNT ternary ceramics

Lead-based Pb(Zr, Ti)O3 ceramics have been widely applied in piezoelectric actuators, and yet high temperature stability and large strain have been pursued for further application. In this work, a novel PbZrO3–PbTiO3-(Bi0.5Na0.5)TiO3 (PZ-PT-BNT) piezoelectric ceramic is designed and prepared by solid-state route. It is found that the introduction of BNT constituent enhances the relaxation behavior of PZ-PT ceramic, inhibits the abrupt change in dielectric properties near Curie temperature, and increases the proportion of tetragonal phase with high temperature stability. Meanwhile, the patterns of electric domains are intentionally modified by adjusting composition of PZ-PT-BNT. Short and broad electric domains in PZ-PT-0.03BNT ceramic are observed by piezoresponse force microscopy, which are insensitive to temperature and have faster response under electric field, contributing to strain characteristics. As a result, through integrating phase structure and electric domain configuration, a strain of 0.21% and excellent temperature stability where the variation of strain is less than 8% in the temperature range of 25–250 °C are achieved in PZ-PT-0.03BNT ceramic. The findings provide an effective strategy for improving the strain stability of PZ-PT-based piezoelectric ceramics, and demonstrate that PZ-PT-BNT ceramics have potential application prospects in high-temperature piezoelectric actuators.