Dielectric Tunability Research Articles

Critical Insight into Pretransitional Behavior and Dielectric Tunability of Relaxor Ceramics.

This model discussion focuses on links between the unique properties of relaxor ceramics and the basics of Critical Phenomena Physics and Glass Transition Physics. It indicates the significance of uniaxiality for the appearance of mean-field type features near the paraelectric-to-ferroelectric phase transition. Pretransitional fluctuations, that are increasing up to the size of a grain and leading to inter-grain, random, local electric fields are responsible for relaxor ceramics characteristics. Their impact yields the pseudospinodal behavior associated with "weakly discontinuous" local phase transitions. The emerging model redefines the meaning of the Burns temperature and polar nanoregions (PNRs). It offers a coherent explanation of "dielectric constant" changes with the "diffused maximum" near the paraelectric-to-ferroelectric transition, the sensitivity to moderate electric fields (tunability), and the "glassy" dynamics. These considerations are challenged by the experimental results of complex dielectric permittivity studies in a Ba0.65Sr0.35TiO3 relaxor ceramic, covering ca. 250 K, from the paraelectric to the "deep" ferroelectric phase. The distortion-sensitive and derivative-based analysis in the paraelectric phase and the surrounding paraelectric-to-ferroelectric transition reveal a preference for the exponential scaling pattern for ε(T) changes. This may suggest that Griffith-phase behavior is associated with mean-field criticality disturbed by random local impacts. The preference for the universalistic "critical & activated" evolution of the primary relaxation time is shown for dynamics. The discussion is supplemented by a coupled energy loss analysis. The electric field-related tunability studies lead to scaling relationships describing their temperature changes.

Enhancement of Dielectric Response and Optical Bandgap Tuning with Improving Surface Morphology of Recyclable Polyvinyl Alcohol–CeO2 Polymer Nanocomposites

Motivated from the extraordinary properties of CeO2 nanomaterial, this article is directed toward the synthesis of recyclable polyvinyl alcohol–CeO2 polymer nanocomposite with variable wt% of CeO2 and investigating their improvements in structural, electrical, optical, and surface properties. The crystalline size and micro‐strain are measured using X‐ray diffraction (XRD) data. Ultraviolet–visible–near‐infrared spectrophotometer is used to study the optical characteristics. Absorbance with redshift is found to enhance; while optical bandgap is reduced from 2.51 to 2.36 eV on increasing wt% of CeO2 nanofiller. The mechanism of reduction in bandgap is supported by the XRD analysis. Refractive index is found to vary from 2.54 to 2.59 and the range of Urbach energy varies from 1.19 to 0.42 eV on increasing the amount of nanofillers. Surface morphology, dielectric constant, and electrical conductivity are also found to improve with increasing wt% of nanofiller. The dielectric constant is improved from 60 to 120 at 1.5 Hz. The rise in conductivity with increasing wt% of CeO2 and rising frequency is due to the enhancement of mobility of the charge carriers and ionic hopping mechanism in conduction process. Characterization outcomes suggest that the prepared composites can be claimed as useful in fabricating the flexible optoelectronic devices.

Improved Dielectric Tunability in Stretched P(VDF-DB)

Improved Dielectric Tunability in Stretched P(VDF-DB)

PES-g-BST/PEEK composites modified by surface grafting with high dielectric tunability

Ceramic/polymer composites have been widely utilized due to their outstanding dielectric and mechanical properties. The interfacial bonding between ceramic and organic phases has a significant effect on the properties of composites. Therefore, enhancing the interfacial bond strength has become a hot issue. In this work, a chemically modified PES-g-BST/PEEK composite was prepared via cold-pressing sintering. The chemical bond was constructed to connect one end of PES (polyether sulfone) with BST (barium strontium titanate) and the other end with PEEK (polyether ether ketone) by using 4,4′-Diaminodiphenylsulfone (DDS), which enhanced the interface combination between ceramic fillers and organic phase. The influence of the surface grafting method and the amount of DDS on the microstructure and dielectric characteristics of the PES-g-BST/PEEK composite was investigated, and the amount of DDS was optimized. The permittivity, dielectric tunable efficiency, and dielectric tunability of the composites were improved. A chemically modified PES-g-BST/PEEK composite with improved dielectric properties and high dielectric tunability was obtained. The dielectric tunability amounts to 38.16% under a 7 kV/mm bias, accompanied by a low dielectric constant of 14.5 and a dielectric loss of 0.076 (1 kHz). This work provides a way of enhancing the interface bonding of ceramic/polymer composites to improve dielectric tunability.

High Entropy Nonlinear Dielectrics with Superior Thermally Stable Performance.

A high configurational entropy, achieved through a proper design of compositions, can minimize the Gibbs free energy and stabilize the quasi-equilibrium phases in a solid-solution form. This leads to the development of high-entropy materials with unique structural characteristics and excellent performance, which otherwise couldnot be achieved through conventional pathways. This work develops a high-entropy nonlinear dielectric system, based on the expansion of lead magnesium niobate-lead titanate. A dense and uniform distribution of nano-polar regions isobserved in the samples owing to the addition of Ba, Hf, and Zr ions, which lead to enhanced performance of nonlinear dielectrics. The fact that no structural phase transformation isdetected up to 250°C, and no noticeable change or a steep drop in structural and electrical characteristics isobserved at high temperatures suggests a robust thermal stability of the dielectric systems developed. With these advantages, these materials hold vast potential for applications such as dielectric energy storage, dielectric tunability, and electrocaloric effect. Thus, this work offers a new high-entropy configuration with elemental modulation, with enhanced dielectric material features.

Interface Structure, Dielectric Behavior and Temperature Stability of Ba(Mg1/3Ta2/3)O3/PbZr0.52Ti0.48O3 Thin Films.

Multilayer films can achieve advanced properties and a wide range of applications. The heterogeneous interface plays an important role in the performances of multilayer films. In this paper, the effects of the interface of Ba(Mg1/3Ta2/3)O3/PbZr0.52Ti0.48O3 (BMT/PZT) thin films on dielectric behavior and temperature stability are investigated. The heterogeneous interface structures are characterized by Auger electron spectroscopy (AES). The PZT-BMT interface is different from the BMT-PZT interface in thickness. For the PZT-BMT interface, the PZT thin films are diffused to the whole BMT layers, and the interface thickness is about 90 nm, while the BMT-PZT interface's thickness is only about 8.6 nm. The presence of heterogeneous interfaces can improve the performances of BMT/PZT thin films and expand their applications. The dielectric constant of BBPP thin films is significantly lower than BPBP thin films, while the dielectric loss is exactly the opposite. The more interfaces there are, the greater the dielectric constant. The relationship between the electric-field-dependent dielectric constant curve and the P-E curve is established. The equivalent interface barrier of the diode is used to show that the dielectric peaks under the positive and negative voltage are different. Similarly, heterogeneous interfaces show a certain improvement in dielectric tunability and temperature stability.

Achieving excellent ferroelectric and dielectric performance of HfO2/ZrO2/HfO2 thin films under low operating voltage

Although the HfO2-based ferroelectric thin films are compatible with the complementary metal-oxide-semiconductor (CMOS) technology and exhibit excellent scalability, they still suffer from low dielectric tunability, metastable ferroelectric orthorhombic phase and poor endurance. Here, we fabricated the HfO2/ZrO2/HfO2 sandwich structured thin films via atomic layer deposition process as well as the influence of voltage cycling, Hf/Zr ratios and annealing temperature on ferroelectricity and dielectric tunability of them was investigated systematically. At pristine states, the antiferroelectric-like behavior of polarization-voltage hysteresis loops become more and more obvious with the decrement of ZrO2 content in the middle layers. After waking-up, the large remnant polarization (2Pr, ∼43 μC/cm2) and high dielectric tunability (∼51 %) can be achieved under low operating voltage of 2.5 V. Noting that the 2Pr is still higher than 40 μC/cm2 and the dielectric tunability remains about 50 % after 109 cycles. In addition, the HfO2/ZrO2/HfO2 thin films also exhibited high energy storage properties with the total energy storage density of ∼62 J/cm3 and the recoverable energy storage density of ∼32 J/cm3. These results indicated that the strategy of sandwich structure design is beneficial to promoting the development of electronic devices towards miniaturization, integrated, and multifunction along with high performance and reliability.

Biobased Electronics: Tunable Dielectric and Piezoelectric Cellulose Nanocrystal-Protein Films.

Cellulose has been a go-to material for its dielectric properties from the onset of capacitor development. The demand for an energy storage solution continues to grow, but the supply remains limited and relies too often on fossil and mined materials. This work proposes a fully sustainable and green method with which to produce dielectric thin films made of renewable and degradable materials. Cellulose nanocrystals (CNC) made an excellent matrix for the dispersion of proteins and the fabrication of robust transparent thin films with enhanced dielectric permittivity. A range of proteins sources, additives and concentrations allowed for us to control the dielectric permittivity from εr = 4 to 50. The proteins screened came from animal and plant sources. The films were formed from drying a water suspension of the CNC and proteins through evaporation-induced self-assembly. This yielded nano-layered structures with very high specific surface areas, ideal for energy storage devices. The resulting films were characterized with respect to the electrical, mechanical, piezoelectric, and optical properties to be compared. Electrically conductive (σ = 1.53 × 103 S/m) CNC films were prepared with carbon nanotubes (CNT). The fabricated films were used to make flexible, sustainable, and degradable capacitors by layering protein-based films between CNC-CNT composite films.

Hybrid Quantum Systems for Higher Temperature Quantum Information Processing

The ability to operate superconducting quantum computers at higher temperatures would greatly expand their utility and range of applications. This could be achieved by increasing resonance frequencies and/or utilizing collective modes that are less noisy and more robust against decoherence. We discuss several nonlinear resonator concepts in which the roles of linear and nonlinear elements are reversed vs. the transmon. The simplest version is a nonlinear <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonator with a linear superconducting inductor and a nonlinear capacitor employing a nonlinear dielectric material. Due to progress in tunable dielectrics for 6G, some ferroelectric composites may enable operation of a nonlinear dielectric – superconductor qubit at hundreds of gigahertz. Other nonlinear dielectric materials include quantum paraelectrics and charge density wave materials. These are of interest due to robust collective modes resulting from macroscopically occupied states. Other proposed nonlinear resonators employing nonlinear dielectrics include quarter- and half-wavelength resonators. Voltage tunability is a potential feature of the proposed concepts.

Improved dielectric properties of Ba0.5Sr0.5TiO3–ZnAl2O4 composite ceramics using double sintering

Ba0.5Sr0.5TiO3–ZnAl2O4 composite ceramics were prepared by double sintering and conventional sintering. The results show that the double sintering can effectively reduce the ion diffusion between Ba0.5Sr0.5TiO3 and ZnAl2O4 phases. The double sintered samples exhibit higher density and more uniform grain size distribution than the conventional sintered samples. The dielectric permittivity of double sintered samples is lower than that of conventional sintered samples. Impedance spectrum analysis shows that the oxygen vacancy content and grain boundary resistance of the double sintered samples is lower than that of the conventional sintered samples, which indicates that the Q value of the double sintered samples is higher than that of the conventional sintered samples. The optimum dielectric tunability and Q value of double sintered 60 wt%Ba0.5Sr0.5TiO3-40 wt%ZnAl2O4 sample are 23.4% at 30 kV/cm and 276 at 2.257 GHz, respectively. Therefore, double sintering is a strategy that can effectively adjust the dielectric tunability and Q value of BST-ZA composite ceramics.

Remote Reconfiguration of Microwave Filters Using Dielectric Tuners

The objective of this article is to explore the use of dielectrics to reconfigure remotely microwave filters in rectangular waveguide. To start, we study experimentally the phase shift that is achievable using dielectric tuning elements in a rectangular waveguide. We then compare the results obtained with the performance of standard metallic tuning cylinders and screws. Next, the passive intermodulation (PIM) behavior of dielectric tuning elements is investigated experimentally. The PIM results obtained using dielectrics are then compared with the ones of metallic tuning elements. After that, the measured results for a filter tuned with a number of different dielectric tuning elements are discussed to identify the required relation between cavity size, dielectric constant, and tuner diameter. As a proof of concept, we then design, manufacture, and test two filters, one in WR75 and the other in WR90. Both simulated and measured results are then presented clearly demonstrating that the structures discussed can indeed be reconfigured (or tuned) both in terms of filter center frequency and bandwidth. Finally, computer-driven linear actuators are connected to the dielectric tuners, and the remote tuning capability is successfully demonstrated.

Hygrothermal aging behavior of sandwich-structure Ba0.6Sr0.4TiO3/PVDF composites with high energy storage property and dielectric tunability

Ba0.6Sr0.4TiO3/PVDF composite is a promising material to be applied to manufacture filters, phase shifters, biosensors, and other electronic components due to its excellent dielectric constant, dielectric tunability and good biocompatibility. However, as a polymer material, the PVDF matrix will have a series of aging behaviors during the actual use, which will affect the stability and service life of components. In this work, two sandwich structure BST/PVDF composites with different ceramic morphologies (namely 0D-BPB and 2D-BPB) were prepared, and the effects of hygrothermal aging times on the chemical structure, energy storage properties, and dielectric tunability of the composites were studied. The results show that the physical properties of both 0D-BPB and 2D-BPB will deteriorate with increasing aging time under hygrothermal conditions, which resulted from the PVDF phase transition from β to γ phase. And the 2D-BPB sandwich structure composite has the best anti-hygrothermal aging behavior. When the hygrothermal aging time is 480 h, which is approximately equal to the actual natural environment for 7 years, the energy storage and dielectric properties are still showed a high level: the dielectric constant of 2D-BPB is 27.6, the energy storage density is 12.64 J/cm3, and the dielectric tunability is 78.4 %, respectively. The results provide certain reliability for the application of BST/PVDF in various electronic components.

Research progress of double perovskite ferroelectric thin films

Double perovskite ferroelectric thin films are completely new material systems derived from single perovskite. Their diversity of composition and structure and the tendency for spontaneous atomic ordering broaden the path for the development of ferroelectric thin films. The ordered double perovskite ferroelectric thin films lead to excellent ferroelectric, dielectric, magnetic, and optical properties, promising further applications in photovoltaic cells, information memory, and spintronic and photoelectric devices, where the intrinsic coupling and tuning of multiple properties could also push it into multifunctional intersecting devices. However, complex internal physical mechanisms and difficult preparation conditions have prevented its further development. Based on ordered/disordered ferroelectric thin films of double perovskites, this paper first discusses ordered characterization methods such as superstructure reflection/diffraction peaks, especially for epitaxial thin films, saturation magnetization (macroscopic), and scanning transmission electron microscopy (microscopic). In response to the generally poor ordering of present systems, the paper also reviews the internal structure of the material and the external synthesis conditions that affect the ordering, including the valence and radii of the cations, preparation methods, element substitution and strain engineering, in the hope of triggering further research into ordered double perovskite ferroelectrics. Combined with the current state of research on existing double perovskite ferroelectricity thin film systems, advances in the fields of ferroelectric photovoltaics, magnetoelectric coupling, dielectric tunability, resistive switching, and photoelectric coupling have been presented. Finally, the challenges facing the material system are discussed and an outlook is provided for the development of the field.

64‐3: Invited Paper: Latest Developments Liquid Crystals for RF Applications

Driven by the need for new affordable wireless data communication technologies, special liquid crystals have been developed and optimized for use in microwave components above 10 GHz. As tunable dielectrics, they pave the way for continuously tunable antennas for SATCOM and wireless 5G/6G applications either fixed at home or on‐the‐move. This presentation gives an insight into the current material development with special focus on the application in transparent antennas for fixed 5G access. Sunlight stability tests for an equivalent device lifetime of 5 years were conducted resulting in yellowing index values of &lt; 4, being 2.5 times less than the required threshold.

Preparation and characterization of crystalline Ba0.5Sr0.5TiO3 thin films on FTO transparent electrodes

To achieve an economic advantage, nanocrystalline Ba0.5Sr0.5TiO3 (BST) thin films were prepared on FTO-coated glass substrates using an aqueous sol–gel process. The crystal structures and chemical states of the obtained thin films were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The XRD patterns confirmed the perovskite structure of the BST samples, while XPS analysis demonstrated that Ba element was in its single oxidation state in the film with annealing temperature of 600 °C. In contrast, Ba was present in a mixed oxidation state upon increasing the annealing temperature. It was found that the BST thin film prepared at a relatively low annealing temperature of 600 °C exhibited optimal crystallinity and superior dielectric properties, along with excellent optical transparency. More specifically, this film exhibited a dielectric tunability of 44.81% (1.33 MV/cm), a figure of merit of 56.01, and an average transmittance of 87.2% in the visible region.

Defect-Induced, Ferroelectric-Like Switching and Adjustable Dielectric Tunability in Antiferroelectrics.

Antiferroelectrics, which undergo a field-induced phase transition to ferroelectric order that manifests as double-hysteresis polarization switching, exhibit great potential for dielectric, electromechanical, and electrothermal applications. Compared to their ferroelectric cousins, however, considerably fewer efforts have been made to understand and control antiferroelectrics. Here, it is demonstrated that the polarization switching behavior of an antiferroelectric can be strongly influenced and effectively regulated by point defects. In films of the canonical antiferroelectric PbZrO3 , decreasing oxygen pressure during deposition (and thus increasing adatom kinetic energy) causes unexpected "ferroelectric-like" polarization switching although the films remain in the expected antiferroelectric orthorhombic phase. This "ferroelectric-like" switching is correlated with the creation of bombardment-induced point-defect complexes which pin the antiferroelectric-ferroelectric phase boundaries, and thus effectively delay the phase transition under changing field. The effective pinning energy is extracted via temperature-dependent switching-kinetics studies. In turn, by controlling the concentration of defect complexes, the dielectric tunability of the PbZrO3 can be adjusted, including being able to convert between "positive" and "negative" tunability near zero field. This work reveals the important role and strong capability of defects to engineer antiferroelectrics for new performance and functionalities.

Dual‐Channel Dielectric Tunability in Highly Textured BaTi0.99Fe0.01O3−δCeramics With Micro‐Twin Boundary

AbstractDielectric tunability is widely used in numerous electronic devices, including wavelet filters, lens antennae, and varactors. However, a dielectric device often has only one tunable dielectric constant range, confining the integration of a multi‐frequency electronic circuit. Herein, a new kind of dielectric tunable textured BaTi0.99Fe0.01O3−δceramics with micro‐twin boundaries is proposed for the dual‐channel controllable dielectric constants. The relative tunability with the acceptable figure of merit is as large as 76% in the crossover channel, which is superior to that of the most state‐of‐the‐art BaxSr1 −xTiO3counterparts. This new design strategy offers the possibility of dual‐channel filters in one dielectric device controlled by external electric fields. The required external electric field is moderate with the help of reversible micro twins, which is confirmed by first‐principles studies. The static magnetic field interference on the dielectric constant is also evaluated, showing the frequency stability of dielectric tunability in a range between 5k and 1 mHz.

U-shaped micropores induced dielectric and piezoelectric tunability in bismuth sodium titanate-based ceramics

U-shaped micropores induced dielectric and piezoelectric tunability in bismuth sodium titanate-based ceramics

Grain size-driven effect on the functional properties in Ba0.6Sr0.4TiO3 ceramics consolidated by spark plasma sintering

Dense fine-grained Ba0.6Sr0.4TiO3 ceramics with submicronic grains sizes (GS) have been prepared using nanopowders synthesized via sol-gel route and consolidated by Spark Plasma Sintering (SPS). By changing SPS parameters, the GS was reduced from 214 nm to 74 nm. Diffuse ferroelectric-paraelectric phase transitions and low values of dielectric permittivity (<1000) at the Curie temperature (TC ∼280 K) were revealed by Impedance Spectroscopy in all sintered ceramics. The GS reduction from submicron to nanoscale range reflects in a gradually diminishment of dielectric constant, tunability, polarisation and storage energy properties. Raman spectroscopy investigations pointed out the presence of polar nanoclusters above the TC. The short-range polar order is affected by the GS decrease, but becomes more thermally stable. The observed properties of Ba0.6Sr0.4TiO3 nanostructured ceramics are interpreted by considering the interplay between the GS reduction, the role of low-permittivity grain boundaries and the diffuse character of the ferroelectric-to-paraelectric transformation.

Comparison of structural and dielectric properties of doped (M, R and A) barium strontium Titanate: Review

Barium Strontium Titanate is lead -free, environment friendly compound having high dielectric constant, high dielectric tunability and low dielectric loss which make this perovskite material applicable for various industrial, electronic and microwave tunable device. Recent development in Barium Strontium Titanate by doping modification of (Alkali metal, Transition and Rare earth metal) are reviewed. The A site doping, B site doping and both site co-doping modification are analysed and summarized respectively. By using multiple manufacturing techniques, including the conventional method and sol–gel, the comparison of the dielectric and microstructure properties of barium strontium titanate with different dopants is critically examined. Out of these dopants, Transition metal doped Barium Strontium Titanate show more suitable properties for applications like storage capacitors and phase shifters etc. BST ceramics with transition metal doping shows low dielectric loss and high dielectric constant suitable for DRAM cell capacitor as well as for tunable antennas having large frequency domain, as well as for microwaves devices.