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Tunable dielectric materials, serving as key components in microwave electronic application, require both high dielectric tunability and low dielectric loss. However, the trade-off between dielectric tunability and dielectric loss restricts the improvement of the overall dielectric tunability properties. In the present study, we proposed an effective approach to benefit both high tunability and low dielectric loss, i.e., improving intrinsic dielectric response from the lattice polarization and restricting the extrinsic dielectric response from the domain motions at the same time. Experimentally different acceptor dopants were employed, including the introduction of K at the A-site and Mn, Fe and Co at the B-site. On one hand, the different acceptor dopants could adjust the Curie temperature and consequently resulting in the enhanced intrinsic dielectric response at room temperature. On the other hand, the employment of acceptor dopant could introduce the oxygen vacancies and form the acceptor-oxygen vacancy dipoles which may restrict the reorientation of microdomains, resulting in the decrease of extrinsic dielectric response. Herein, both enhanced tunability and reduced dielectric loss were achieved in acceptor doped BZT ceramics at ambient temperature (27 °C). In particular, Fe doped BZT ceramics achieved both high dielectric tunability of 93.8 % and low dielectric loss of 0.0038. Such performance is competitive with that of previous reported dielectric tunable materials. In addition, the dielectric tunability of Fe doped BZT ceramics maintained over 60 % within the wide temperature range from −20 °C to 60 °C. [ABSTRACT FROM AUTHOR]

Due to their responsiveness to modulation by external direct current fields, dielectric tunable materials are extensively utilized in integrated components, such as ferroelectric phase shifters. Barium strontium titanate ceramics have been considered the most potential tunable materials for a long time. However, the significant dielectric loss and high voltage drive have limited their further applications. Recently, Bi6Ti5WO22 ceramic has regained attention for its high dielectric tunability with low loss. In this study, we judiciously introduce Nb5+ with a larger ionic radius, replacing Ti4+ and W6+. This successful substitution enables the modulation of the phase transition temperature of Bi6Ti5WO22 ceramics to room temperature, resulting in superior tunable properties. Specifically, the 0.7Bi6Ti5WO22−0.3Bi6Ti4Nb2O22 ceramics exhibit giant tunability (~75.6%) with ultralow loss (<0.002) under a low electric field (1.5 kV/mm). This tunability is twice that of barium strontium titanate ceramics with a similar dielectric constant and only one-tenth of the loss. Neutron powder diffraction and transmission-electron-microscopy illustrate the nanodomains and micro-strains influenced by ion substitution. Density functional theory simulation calculations reveal the contribution of ion substitution to polarization. The research provides an ideal substitute for tunable material and a general strategy for adjusting phase transition temperature to improve dielectric properties. The authors realize composite optimization in dielectric tunable materials by simultaneously achieving low electric field, large tunability, and low loss through ion substitution design in ferroelectric tunable materials. [ABSTRACT FROM AUTHOR]

A comparative study of biaxial-orientated polypropylene (BOPP) films extracted from one failed HVDC filter capacitor (serving for 10 years) and one fresh capacitor (spare capacitor from the same batch) is reported in this paper. Experimental results show that the 10-year online operation does not bring about molecular changes; however, molecule reorganization and recrystallization was detected using differential scanning calorimetry and dynamic mechanical analysis tests. Electrical measurements including dielectric spectra, DC conductivity measurement, DC breakdown strength and were also performed. The experimental results show that the aging process causes an increase in dielectric constant, dissipation factor, DC conductivity, and the DC breakdown strength. Thermal stimulated current measurements indicate that traps were introduced by aging and are responsible for such abnormal changes. The nano-cavitivies generated by molecule reorganization could possibly act as charge traps. Therefore, homo-charges can accumulate in the vicinity of the electrodes, leading to the degradation of long-term withstand strength but an enhancement of short-term breakdown strength. [ABSTRACT FROM AUTHOR]

In the present study, BaTi 0.8- x Zr 0.2 Mn x O 3 (x = 0, 0.25 %, 0.5 %, 0.75 %) ceramics were prepared via a solid-state reaction process. Results showed that both enhanced tunability of 93.4 % (at 20 kV/cm and 27 °C) and reduced dielectric loss tangent of 0.005 at 10 kHz were achieved in BaTi 0.8- x Zr 0.2 Mn x O 3 ceramics at x = 0.5 %. Such dielectric tunability was higher than that of common materials whose tunability hardly exceeded 85 %. Moreover, the mechanism of enhanced dielectric tunability was discussed. The contribution of the intrinsic polarization to the dielectric tunability increased with the increase of Mn content, leading to a higher tunability. Meanwhile, the "domain pinning" effect of M n Ti ″ − V O ● ● × defect dipoles restricted the reorientation of microdomains, thus decreasing extrinsic contribution and dielectric loss tangent. Furthermore, the tunability for the BaTi 0.8- x Zr 0.2 Mn x O 3 (x = 0 %, 0.25 %, 0.5 %, 0.75 %) samples was measured in the temperature range of − 30 to 85 °C, showing a favorable dielectric tunable performance with good temperature stability. • High tunability of 93.4% and relatively low dielectric loss tangent of 0.005 at 10 kHz were obtained. • Superior thermal stability was obtained in Mn-doped BaTi 0.8 Zr 0.2 O 3 ceramics. • Effect of Mn doping on dielectric tunability and dielectric loss tangent was revealed. [ABSTRACT FROM AUTHOR]

In the present study, pure and donor–acceptor co-doped Ba 0.675 Sr 0.325 TiO 3 (BST) ceramics were prepared by the conventional solid-state reaction method. La was fixed as the donor dopant at A-site while Mn, Cr, and Fe were selected as the acceptor dopants at B-site. The effect of acceptor dopants on the microstructure and electrical properties of BST ceramics was investigated systematically from the view of different ionic radius and electronegativity. Enhanced dielectric tunability and reduced dielectric loss could be realized by co-doping, resulting in a significant improvement in the figure of merit (FOM). The optimum tunable properties were obtained in Mn–La co-doped ceramics with the dielectric tunability of 85.1%, the dielectric loss of 0.0018, and the FOM of 472. Such results could be attributed to the smaller ionic radius and weaker electronegativity of Mn. Compared to pure BST ceramics with the FOM of 40, co-doped BST ceramics exhibited great potential for tunable device applications. The breakdown strength (BDS) of BST ceramics was also studied in this work. Improved breakdown strength by co-doping took better stability for its applications under applied electric field. • High dielectric tunability and reduced dielectric loss were achieved by co-doping. • Significant improvement was realized in the figure of merit from 40 to 472. • The breakdown strength was enhanced by 74%. • Effect of dopants was studied by varied ionic radius and electronegativity. • Co-doped ceramics exhibited great potential for tunable device applications. [ABSTRACT FROM AUTHOR]

In the present study, the doping effect of SiO2 on the dielectric, ferroelectric and piezoelectric properties of the (Ba0.7Ca0.3)(Zr0.2Ti0.8)O3 ?abbreviated as BZT-50BCT hereafter? ceramics sintered at different temperatures were systematically studied. With the SiO2 dopant, the distribution of the grain size became more homogeneous. Besides, the average grain sizes firstly increased with increasing the SiO2 concentrations and then decreased. As the macroscopic properties, the dielectric constant decreased with the addition of SiO2. The remnant polarization Pr firstly increased and then decreased with increasing the SiO2 concentration. While the coercive field monotonically decreased with the SiO2 dopant. And the piezoelectric constant d33 firstly enhanced by the SiO2 and then reduced as further increasing the SiO2 concentrations. The maximum d33 of 500 pC/N has been obtained in the 0.5 mol% SiO2 doped BZT-50BCT ceramics sintered at 1500° from the industry available raw materials. [ABSTRACT FROM AUTHOR]

• Achieve the high dielectric tunability and the reduced dielectric loss by La/Fe co-doping in Ba 0.65 Sr 0.35 TiO 3 ceramics. • Improve the figure of merit to 197 which is nearly 5 time compared to the pure Ba 0.65 Sr 0.35 TiO 3 ceramics. • Enhance the breakdown strength by 86% due to the reduced grain size and dense microstructure. In the present study, (Ba 0.65 Sr 0.35) 1−x La x Ti 1−x Fe x O 3 (x = 0, 0.0025, 0.005, 0.01) ceramics were designed and prepared by the conventional solid-state reaction method. The microstructures and electrical properties of La/Fe co-doped Ba 0.65 Sr 0.35 TiO 3 ceramics were investigated. Enhanced dielectric tunability and reduced dielectric loss were achieved in this system. The acceptor dopant Fe3+ was used to lower dielectric loss while the donor dopant La3+ was added to improve dielectric tunability. The optimum tunable properties took place at x = 0.0025 with the dielectric tunability = 78.8% and the dielectric loss = 0.0040. The figure of merit (FOM) was improved to 197, about five times that of pure BST. The breakdown strength (BDS) enhanced from 59.9 kV/cm to 111.4 kV/cm by La3+ and Fe3+ dopant, which promoted the stability of BST ceramics under high applied electric field. In conclusion, excellent tunable properties and improved breakdown strength made it possible for the La/Fe co-doped BST ceramics to be promising for tunable microwave applications. [ABSTRACT FROM AUTHOR]

We report that an obvious difference in the 'domain stabilization' effect between 1.0 mol. % Mn doped (Ba1-xSrx)TiO3 and (Pb1-xSrx)TiO3 piezoelectrics with a similar c/a ratio and aging treatment, though typically 'increased' stabilization effect occurs with the increase of c/a in each system. The three-time larger microscopic defect dipole field Ei in lead-system from P-E measurements suggests the more aligned defect dipoles through kinetically easier hopping of oxygen vacancy originated from local structure rather than the average structure like c/a may be a primary cause of the strong domain stabilization effect. This may help on the hardening functionality improvement of lead-free systems. [ABSTRACT FROM AUTHOR]

We report a large piezoelectric Pb-free system-Ba(Ti0.8Hf0.2)O3-(Ba0.7Ca0.3)TiO3, designed upon a triple-point morphotropic phase boundary (TMPB) idea. The system shows anomalies of both ac (dielectric and piezoelectric) and dc (P-E hysteresis) properties around TMPB, especially the d33 achieving ∼550 pC/N at room temperature. Moreover, the detected non-zero thermal hysteresis around triple point shows a first order transition nature and non-isotropic polarization state, as well as verified by our theoretical Landau-type deduction, thus being considered as an important factor to influence the piezoelectricity along TMPB. Our work may stimulate the study on triple-point-related critical phenomena in other ferroic systems. [ABSTRACT FROM AUTHOR]

This paper reports a ferroelectric-to-paraelectric (FE-PE) two-step transition in the acceptor-doped ferroelectric systems. In ceramic samples, the DSC peak as well as the dielectric permittivity peak exhibits a split after aging at DSC peak temperature. Such phenomenon also exists in the grain-boundary-free single crystal samples; this excludes the possibility of a grain boundary effect. Moreover, the in-situ optical microscopy observation during heating proves that such peak split is due to a two step FE to PE transition. The microscopic explanation is given based on the symmetry-conforming properties of point defects. [ABSTRACT FROM AUTHOR]

The electrical degradation of four different commercial ZnO-based varistors under the combined DC bias and high temperature condition was investigated with XRD, SEM, I – V , impulse current measurement, and dielectric spectroscopy, respectively. Contrary to the negligible structural changes, the electrical properties vary significantly after the degradation from sample to sample. Those deviations could not be completely ascribed to the differences in fabrication, but instead be consistently explained in terms of the intrinsic defect structure of ZnO ceramics. With a detailed analysis of their dielectric spectra in broad temperature and frequency ranges, it was found that zinc interstitial is the main intrinsic defect species responsible for the observed electrical degradation and its density could be used as a “universal” microscopic parameter to characterize the macroscopic electrical degradation. In addition, depending on the conduction mechanism, the role taken by Zn i also differs correspondingly. [ABSTRACT FROM AUTHOR]