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0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Nb0.125Ti0.875)O3 ceramics with a pseudo-cubic structure and re-entrant dipole glass behavior have been investigated via x-ray diffraction and dielectric permittivity–temperature spectra. It shows excellent dielectric–temperature stability with small variations of dielectric permittivity (±5%, 420–802 K) and dielectric loss tangent (tanδ < 2.5%, 441–647 K) in a wide temperature range. Three dielectric anomalies are observed from 290 to 1050 K. The low-temperature, weakly coupled re-entrant relaxor behavior was described using the Vogel–Fulcher law and the new glass model. The mid- and high-temperature dielectric anomalies are characterized by isothermal impedance and electrical modulus. The activation energy of both dielectric relaxation and conductivity follows the Arrhenius law in the temperature ranges of 633–753 and 833–973 K, respectively. The ultrahigh thermal stability of dielectric permittivity is attributed to the weak coupling of polar clusters, the formation of diffuse phase transition, and the local phase transition of calcium-containing perovskite. The results provide new insights into the defects behavior and the modification way of re-entrant relaxor behavior. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the effect of processing parameters and composite regulation on the structure and property relationship of lightweight low‐permittivity Li2O–Al2O3–B2O3 dielectric system. Li2BAlO4 ceramic and (1 − x)Li2BAlO4–xSrTiO3 ceramics were synthesized using a conventional solid‐state reaction method. Thermodynamic analysis, sintering temperature, phase formation, crystal structure, and microwave dielectric properties were investigated. Thermal analysis revealed a melting temperature of 847°C, suggesting a comparatively low temperature for the sintering of Li2BAlO4 ceramics. Li2BAlO4 crystalized into a monoclinic structure with P21/c space group, with [Al2B2O8] rings connected by [BO3] triangles and [AlO4] tetrahedra through Al–O–Al bridges. Dense Li2BAlO4 ceramics with a relative density of ∼97.7% were sintered at 750°C and had optimal microwave dielectric properties with relative permittivity (εr) of 5.13, quality factor (Q × f) of 22 610 GHz, and the temperature coefficient of resonance frequency (τf) of −112.5 ppm/°C. The 0.88Li2BAlO4–0.12SrTiO3 composite ceramic has excellent microwave dielectric properties with εr = 8.83, Q × f = 14 000 GHz, τf = 4.6 ppm/°C. The ceramics also demonstrated an inert behavior with silver electrodes proving its application in low‐temperature cofired ceramic (LTCC) technology. [ABSTRACT FROM AUTHOR]

High‐entropy strategy is a design that uses multiple elements to increase configurational entropy. As an emerging research field, high‐entropy was originally applied to metals, but it has shown great potential in inorganic nonmetallic materials. Since the first discovery of colossal dielectric permittivity in high‐entropy ceramics, it indicates that the high‐entropy strategy is feasible in dielectric ceramics. The multi‐ion solid solution will bring a broader space for the material structure and property tailoring. With the research of domestic and foreign scholars in high‐entropy dielectrics, we believe that entropic engineering can effectively regulate dielectric properties. The review paper explores the potential of the high‐entropy strategy in dielectric ceramics. It provides a detailed overview of the structural properties and the potential benefits of utilizing high‐entropy materials in dielectric ceramics. The review also covers the current research advancements in the field and provides insights into future directions for further development of high‐performance dielectric ceramics. [ABSTRACT FROM AUTHOR]

In this work, cyclotetravanadate Na2SrV4O12 was synthesized at a relatively low sintering temperature of ∼500°C using a solid‐state reaction method. X‐ray diffraction and a transmission electron microscope characterization featured a tetragonal structure that was built by a 3D frame of isolated tetracyclic (V4O12)4−. Dielectric measurements demonstrated strong dependence on frequency and temperature. A low relative permittivity of εr ∼ 8 ± 0.2 and a dielectric (loss tanδ) ∼ 0.4 ± 0.01 was achieved at a frequency of 10 kHz and room temperature. ac impedance and conductivity analysis revealed a thermally activated migration behavior of charge carriers with a short‐range hopping feature. XPS analysis validated the existence of oxygen vacancy and reduction in vanadium (from V5+ to V4+), which gave rise to charged lattice defects. The migration or hopping of such charged defects was responsible for the observed electrical behaviors. Owing to the simple composition, inexpensive raw materials and low density (2.99 g/cm3) make Na2SrV4O12 ceramic a potential candidate for lightweight devices and in photocatalytic degradation and all‐solid‐state ion batteries. [ABSTRACT FROM AUTHOR]

(1 − x)K0.5Na0.5NbO3–xLa(Zn0.5Zr0.5)O3 [(1 − x)KNN–xLZZ, x = 0.005, 0.010, 0.015, 0.020] ceramics were synthesized to fulfill the application requirement of high-temperature ceramic capacitors. The influence of LZZ content on the phase structure, microstructure morphology, dielectric and conductivity behaviors of this system was conducted. An orthorhombic phase for 0.005 ≤ x ≤ 0.010 and an orthorhombic-tetragonal coexisting phase for 0.015 ≤ x ≤ 0.020 were determined by the X-ray diffraction, Rietveld refinement, and dielectric spectra. The ceramic with x = 0.015 exhibits an ultrahigh and stable permittivity (ε' ~ 1892, ± 15% variation) and a low dielectric loss (tanδ ≤ 0.05) in a wide temperature region of 82–382 °C owing to the composition heterogeneity-induced shoulder-like peak and diffuse phase transition from tetragonal to cubic. The activation energies from the high-temperature dielectric relaxation and conductivity behaviors initially enhance greatly and then increase slowly, which could be related to the synergy effect of decreased oxygen vacancies and microstructure morphology evolution. [ABSTRACT FROM AUTHOR]

High‐performance colossal‐permittivity (CP) materials have huge potential applications in the miniaturization of electronic components and high‐energy storage applications. Here, we report CP behavior in rare‐earth Ln‐doped BaTiO3 (Ln = La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, and Er) ceramics. CP (>1 × 105) and low loss (<5% at 1 kHz) were achieved. Additionally, all ceramic samples with excellent temperature stability over a wide temperature range (25–250°C). X‐ray photoelectron spectroscopy verified the existence of point defects (Ti3+ and VO••$V_{\rm{O}}^{{\rm{ \bullet \bullet }}}$) in Ln‐doped BaTiO3 ceramic samples annealed in an N2 atmosphere. Electron paramagnetic resonance further demonstrated the existence of Ti3+. The coupling of point defects forms an electron‐pinned defect‐dipoles (EPDD) effect and induces strong hopping polarization. In addition, an internal barrier layer capacitance (IBLC) effect and a surface barrier layer capacitor (SBLC) effect are identified by impedance spectroscopy and DC bias voltage. The CP is attributed to the combined effect of EPDD, IBLC, and SBLC. Furthermore, the high‐temperature stability of CP is related to the strong coupling of defect‐dipole complexes. [ABSTRACT FROM AUTHOR]

In this study, Ba4RCo0.5Nb9.5O30 (R = La, Nd, Sm, Eu) (BRCN) ceramics were synthesized using a high-temperature solid-state reaction. The XRD refinement results show that ceramic samples are tetragonal tungsten bronze (TTB). As the radius of rare-earth ions decreases, the unit cell volume of BRCN ceramics decreases, and the radius difference between Ba2+ and R ions increase, which results in BO6 octahedral distortion and the Raman peaks shift to high frequency. In addition, as the radius of rare-earth ions decreases, the ionic displacements increase and thus the dielectric constant peak temperature goes up. The high-temperature impedance results show that there exists n-type electronic conduction in the samples. The remanent polarization of the P–E curve at low frequencies increases from 0.470 to 1.038 μC cm−2 as the rare-earth ion radius decreases. [ABSTRACT FROM AUTHOR]

Ta-doped 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 [(1 − x)(0.94BNT–0.06BT) − xTa (x = 0.00–0.02)] ceramics were prepared by a solid-state reaction process. X-ray diffraction (XRD) shows a rhombohedral symmetry with space group R3c for all samples. The introduction of Ta moves the low-temperature dielectric anomaly to lower temperature while the high-temperature dielectric anomaly becomes broader, although the dielectric permittivity is depressed slightly. Dielectric permittivity (ɛr) as a function of temperature for the sample x = 0.02 shows a stable and broad relative permittivity ∼ 3500 from 50 °C to 400 °C with low dielectric loss (tanδ) ≤ 0.02 from 80 °C to 340 °C (at 1 kHz). A Debye-like relaxation was found in the paraelectric region. The activation energy of relaxation frequency (Ea) of the samples x = 0, 0.005, 0.01, 0.02 is 0.62 eV, 0.84 eV, 1.15 eV and 1.20 eV and the activation energy of conduction (Econ) is 0.56 eV, 0.72 eV, 0.89 eV and 0.90 eV for x = 0.00, x = 0.005, x = 0.01 and x = 0.02, respectively, which are derived from isothermal impedance spectroscopy and admittance spectroscopy, respectively. The dielectric relaxation behavior is related to the migration of oxygen vacancies and cation vacancies dependence on the concentration of Ta. [ABSTRACT FROM AUTHOR]

The role of B-site ions of Bi0.5Na0.5TiO3 (BNT) on its complex phase transition remains unclear due to its polarization attributing to both Bi and Ti. In this paper, the phase transition of (Bi0.5Na0.5)0.94Ba0.06(Ti1−0.01b/4B0.01)O3 (BNT6BT) (B = Nb, Mn, Fe, and Cu) ceramics was modified by low-concentration donor doping (Nb) and acceptor doping (Mn, Fe, and Cu) in order to determine the origin of phase transition behavior. The phase structure, microstructure, local structure/lattice vibration, phase transition temperature, and dielectric properties of BNT6BT-Nb, Mn, Fe, and Cu ceramics were investigated. Results showed that all samples formed a single perovskite phase at room temperature, and donor (Nb) and acceptor (Mn, Fe, and Cu) doping can regulate the ratio of R3c and P4bm coexisting as nanoscale entities. The grains show polyhedral morphology, and average grain size lies between 1 and 2 μm. The Raman spectroscopy study shows that doping modification can change the phase transition temperature. The relation is in well agreement with the three different dielectric anomalies derived from the dielectric curves of εr versus T. Low concentration of cation (Nb, Mn, Fe, and Cu) doping can tailor the dielectric permittivity, depolarization temperature, and phase transition temperature of BNT6BT. All samples exhibit a large dielectric constant and good frequency stability. [ABSTRACT FROM AUTHOR]

The 0.65Bi(Mg1/2Ti1/2)O3‐0.35PbTiO3 (0.65BMT‐0.35PT) ceramic, nearby morphotropic phase boundary (MPB), between tetragonal and rhombohedral was prepared. Dielectric permittivity dependence of temperature exhibits a re‐entrance dipole glass‐like behavior near room temperature. The behavior was described by the Vogel‐Fulcher law and the new glass model. Furthermore, a phenomenological statistical model was employed to determine the distribution of clusters dependence of temperature. The lattice dynamics of the 0.65BMT‐0.35PT ceramic was estimated by Raman spectroscopy from 298‐723 K. A disruption of ferroelectric long‐range order and an occurrence of local lattice distortion were revealed. The relaxor‐ferroelectric (r‐FE) nature of the 0.65BMT‐0.35PT was characterized by polarization‐electric field P(E). A close relation between the distribution of clusters and ferroelectric properties was established. [ABSTRACT FROM AUTHOR]

Mn contained ceramics with nominal formula Ba4RMn0.5Nb9.5O30 (R = La, Pr, Nd and Eu) were fabricated via a conventional solid−state reaction. The phase structure, microstructure, dielectric and ferroelectric properties of the materials were systematically studied. Ambient temperature XRD patterns indicate that all of the ceramics are single tetragonal tungsten bronze phase with space group P4bm. All of these ceramics present a broad permittivity peak, while only Ba4LaMn0.5Nb9.5O30 exhibits obvious frequency dispersion indicating relaxation. With decreasing A1-site ions size, the maximum dielectric constant temperatures (Tm) gradually increase. The relaxation activation energy and direct current conductivity activation energy of all compounds were obtained by linear fitting with Arrhenius equation. Furthermore, with the increase of the A1-site ions size, the Raman shift moves to a high frequency, indicating that different degrees of lattice distortion. Polarizations versus electric field (P–E) loops measured at ambient temperature show that Ba4EuMn0.5Nb9.5O30 has the highest remnant polarization value. [ABSTRACT FROM AUTHOR]

It has been a challenge to provide a unified description of the dielectric response vs temperature for ferroelectrics with diffuse phase transition (DPT) and relaxor behaviors, which can be used to fit the dielectric response both below and above the peak temperature (Tm). Most of the available functions used in fitting experimental data only provide a description of the dielectric permittivity near and above Tm. In this work, employing a macroscopic and phenomenological statistical model and using Ba(Ti1−x Zrx)O3 ceramics as an example, we revisit the dielectric permittivity's temperature dependence, analyzing their DPT and relaxor behaviors and providing a complete description over the whole temperature range. We show that good agreements between theoretical and experimental results can be achieved. To better understand how Ba(Ti1−x Zrx)O3 ceramics changes from DPT to relaxor with increasing x, we also discuss the relation between the fitting parameters and Ba(Ti1−x Zrx)O3's composition and structure, which suggests that the parameters from the statistical model reflect the size of the correlated Ti ions (small clusters or polar nanoregions), which largely determine the behavior of Ba(Ti1−x Zrx)O3 ceramics. [ABSTRACT FROM AUTHOR]

It has been a challenge to provide a unified description of the dielectric response vs temperature for ferroelectrics with diffuse phase transition (DPT) and relaxor behaviors, which can be used to fit the dielectric response both below and above the peak temperature (Tm). Most of the available functions used in fitting experimental data only provide a description of the dielectric permittivity near and above Tm. In this work, employing a macroscopic and phenomenological statistical model and using Ba(Ti1−x Zrx)O3 ceramics as an example, we revisit the dielectric permittivity's temperature dependence, analyzing their DPT and relaxor behaviors and providing a complete description over the whole temperature range. We show that good agreements between theoretical and experimental results can be achieved. To better understand how Ba(Ti1−x Zrx)O3 ceramics changes from DPT to relaxor with increasing x, we also discuss the relation between the fitting parameters and Ba(Ti1−x Zrx)O3's composition and structure, which suggests that the parameters from the statistical model reflect the size of the correlated Ti ions (small clusters or polar nanoregions), which largely determine the behavior of Ba(Ti1−x Zrx)O3 ceramics. [ABSTRACT FROM AUTHOR]

Unfilled tungsten bronze ceramic Ba3.5Sm1.5Fe0.75Nb9.25O30 was prepared by a conventional solid-state reaction method. Its structure, microstructure, and dielectric properties were investigated. Dielectric behaviors indicate that the ceramics are ferroelectric at room temperature with a remnant polarization ~1.61 μC/cm2 and a coercive field ~13.91 kV/cm. Ba3.5Sm1.5Fe0.75Nb9.25O30 ceramics have temperature stability with a high dielectric constant (ε r) varying from 172 to 202 at the temperature range −55 to 200°C (at 1 MHz). Capacitance change rate of the sample is less than 15%. These results indicate that Ba3.5Sm1.5Fe0.75Nb9.25O30 ceramics might be promising in temperature-stable multi-layer ceramic capacitors. [ABSTRACT FROM AUTHOR]

In order to develop dielectric ceramics with temperature-stable permittivity characteristics, Eu and Ti co-doped KNaNbO [(1 − x)KNaNbO-xEuTiO] ceramics were prepared by a conventional solid state route. The effect of EuTiO on the phase structure and dielectric performance of KNN ceramics were investigated. The temperature dependence of the relative permittivity illustrated that the small amount of EuTiO depressed the dielectric peak of ferroelectric-paraelectric transition. Therefore, the temperature stability and relative permittivity of ceramics were effectively improved. As x = 0.03, the ceramic showed superior dielectric temperature stability (±10 %), very low dielectric loss (0.008 at 250 °C) and a relatively high permittivity (>1500 at 250 °C) over the temperature range from ~100 to 350 °C. It suggests that this ceramic is a promising candidate for high-temperature capacitor application. [ABSTRACT FROM AUTHOR]

Abstract: The influence of copper on the microstructure, electrical properties, resistances of grain and grain boundary of nonstoichiometric CaCu3x Ti4O12 ceramics, with x =0.8, 0.9, 1.0, 1.1 and 1.2) prepared by solid state reaction were investigated. The second phase TiO2 and CaTiO3 are found in copper deficiency samples while CuO appears in the other samples. The grain size changes dramatically with the increase of copper. Frequency dependence dielectric permittivity exhibits that the deficient and excess of copper promote to a decrease of dielectric permittivity. Impedance complex plane shows both copper deficient and copper excess result in the increases of resistances of grain, grain boundary and contact resistance between electrode and ceramics. [Copyright &y& Elsevier]

0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Nb0.125Ti0.875)O3 ceramics with a pseudo-cubic structure and re-entrant dipole glass behavior have been investigated via x-ray diffraction and dielectric permittivity–temperature spectra. It shows excellent dielectric–temperature stability with small variations of dielectric permittivity (±5%, 420–802 K) and dielectric loss tangent (tanδ < 2.5%, 441–647 K) in a wide temperature range. Three dielectric anomalies are observed from 290 to 1050 K. The low-temperature, weakly coupled re-entrant relaxor behavior was described using the Vogel–Fulcher law and the new glass model. The mid- and high-temperature dielectric anomalies are characterized by isothermal impedance and electrical modulus. The activation energy of both dielectric relaxation and conductivity follows the Arrhenius law in the temperature ranges of 633–753 and 833–973 K, respectively. The ultrahigh thermal stability of dielectric permittivity is attributed to the weak coupling of polar clusters, the formation of diffuse phase transition, and the local phase transition of calcium-containing perovskite. The results provide new insights into the defects behavior and the modification way of re-entrant relaxor behavior. [ABSTRACT FROM AUTHOR]

A low temperature fired Na 2 CaV 4 O 12 ceramic was synthesized via a solid-state reaction route at a temperature range of 350–550 °C. The Thermal analysis confirmed the densification and melting temperature of Na 2 CaV 4 O 12 to be 530 °C and 580 °C, respectively. Dielectric properties together with the electrical conductivity were characterized at a broad frequency and temperature range. A super-low relative permittivity of ε r = 7.72 and loss tangent of tan δ = 0.06 were obtained at 1 MHz at room temperature. A dielectric anomaly peak took place around 515 °C, which was associated with the phase transition from P 4/ nbm to P 4 ‾ b 2. Ac impedance spectrum coupled with complex modulus plots unveiled the electrical conduction mechanism, which was dominated by the short-range movement of the charge carriers at low temperatures (T ≤ 220 °C) however long-range migration of charge carriers emerged at higher temperatures. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the effect of processing parameters and composite regulation on the structure and property relationship of lightweight low‐permittivity Li2O–Al2O3–B2O3 dielectric system. Li2BAlO4 ceramic and (1 − x)Li2BAlO4–xSrTiO3 ceramics were synthesized using a conventional solid‐state reaction method. Thermodynamic analysis, sintering temperature, phase formation, crystal structure, and microwave dielectric properties were investigated. Thermal analysis revealed a melting temperature of 847°C, suggesting a comparatively low temperature for the sintering of Li2BAlO4 ceramics. Li2BAlO4 crystalized into a monoclinic structure with P21/c space group, with [Al2B2O8] rings connected by [BO3] triangles and [AlO4] tetrahedra through Al–O–Al bridges. Dense Li2BAlO4 ceramics with a relative density of ∼97.7% were sintered at 750°C and had optimal microwave dielectric properties with relative permittivity (εr) of 5.13, quality factor (Q × f) of 22 610 GHz, and the temperature coefficient of resonance frequency (τf) of −112.5 ppm/°C. The 0.88Li2BAlO4–0.12SrTiO3 composite ceramic has excellent microwave dielectric properties with εr = 8.83, Q × f = 14 000 GHz, τf = 4.6 ppm/°C. The ceramics also demonstrated an inert behavior with silver electrodes proving its application in low‐temperature cofired ceramic (LTCC) technology. [ABSTRACT FROM AUTHOR]

The crystal structure of (1-x)BaTiO3-xBiAlO3 (x = 0, 0.02, 0.05, 0.08, and 0.1) ceramics was determined using X-ray diffraction and Raman spectroscopy at room temperature, which revealed a phase transition from tetragonal to rhombohedral with increasing x. The dielectric properties were studied as a function of temperature at different frequencies, which indicated that the phase transition temperature (Tm) decreased with increasing x. The relaxor behavior was observed by frequency and temperature dependent dielectric permittivity. The Lorenz-type quadratic law was used to characterize the dielectric permittivity peaks near Tm of high-temperature slopes at 1 MHz. The temperatures Tm of dielectric permittivity peaks fit very well with the Vogel-Fulcher law in x = 0.05 and x = 0.1. The polarization hysteresis loops and electrostrictive were displayed at room temperature. The sample for x = 0.1 exhibits a slim loop with negligible hysteresis and a subtle linear feature, which is a promising transducer material for use as an active element. [ABSTRACT FROM AUTHOR]

The miniaturization of electronic components has become a megatrend in the future, making colossal dielectric permittivity materials receive unprecedented attention. In this work, we proposed a universal route to achieve colossal dielectric permittivity, low loss factor and excellent dielectric temperature stability in rare earth doped perovskite oxide SrTiO 3. Sm doped SrTiO 3 ceramics prepared by high-energy ball milling exhibit ultrahigh dielectric permittivity 441,543, low loss factor 0.02, good dielectric temperature stability (<15 %) in the temperature range of −55–200 °C, and very high resistance 109Ω, which meets the EIA X9R standard, XPS and impedance spectra indicate that the electron-pinned defect-dipoles effect is the origin of colossal dielectric permittivity and low loss factor. This work shows that Sm-doped SrTiO 3 activated by high-energy ball milling has broad prospects in the applications of thermally-stable miniaturized capacitors. [ABSTRACT FROM AUTHOR]

In this contribution, the novel double-perovskite La 2 Mg(Mg 1/3 Sb 2/3)O 6 has been successfully prepared by solid-state reaction method, and its structure has been determined for the first time by a combination of X-ray and neutron powder diffraction data analysis. The novel material exhibits a thermal expansion of ∼9.1 ppm/°C and a large optical band gap (4.23 eV). The complex impedance data analysis indicates that La 2 Mg(Mg 1/3 Sb 2/3)O 6 features a Debye-like behaviour, with a bulk conductivity, σ b , varying between 10-7-10-4 S ‧cm-1 within 500–900 °C temperature range, and activation energy (E a) of ∼ 1.36 eV. In addition, the microwave dielectric properties of La 2 Mg(Mg 1/3 Sb 2/3)O 6 sintered at 1625 °C display optimized quality factor (Q× f) of ∼ 28,700 GHz (f = 9.65 GHz), a dielectric constant (ε r) of ∼ 20.2 and temperature coefficient of the resonant frequency (τ f) of ∼ − 89 ppm/°C. This work widen the reduced number of A 3 + B 2 / 3 2 + B 1 / 3 5 + O 3 compounds explored so far. [Display omitted] [ABSTRACT FROM AUTHOR]

Holmium doped BaTiO 3 ceramics were prepared by a solid-state reaction. Colossal dielectric permittivity (≥105) and a very low loss tangent (<1.5%) at 10 kHz were achieved. Furthermore, the ceramics exhibit excellent temperature stability with a broad operating temperature range (25–400 °C). The evolution of the concentrations of oxygen vacancies and reduced Ti3+ was estimated by the XPS. Defect dipole complexes, coupled between the negatively and positively charged defects, are responsible for the observed huge dielectric permittivity. Temperature dependence of dc conductivity demonstrates that the stability of the defect dipole complexes matches the temperature range of stable dielectric properties. The result bridges a relationship between defect dipoles and dielectric behavior to understand the huge permittivity response and low loss mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Dielectric properties and charge compensation of Li and Co co-doped NiO (LCNO) ceramics prepared by a simple sol–gel route have been investigated. The concentration of Co makes a great influence on microstructure, dielectric properties and charge compensation mechanism of the LCNO ceramics. Grain size of the ceramics increases from 5.6μm to 7.2μm with dependence on Co concentration. By using a complex impedance analysis at different temperatures, the samples exhibit an electrically heterogeneous structure, which is responsible for a giant dielectric permittivity. The relationship between the activation energies of dielectric relaxation and conduction and charge compensation mechanism in this system were discussed. [Copyright &y& Elsevier]

Two cubic garnet-structured Sr 3 B 2 Ge 3 O 12 (B = Yb, Ho; called SYG and SHG) ceramics synthesised by the high-temperature solid-phase reaction method were investigated in terms of phase formation, sintering behaviour and microwave dielectric performance. At their optimal sintering temperatures, SYG had low dielectric constant (ε r) = 9.30, high quality factor (Q × f) = 129,360 GHz and negative temperature coefficient of resonant frequency (τ f) =−42 ppm/℃, whereas SHG exhibited low ε r = 9.23, Q × f = 104,600 GHz, and comparatively near-zero τ f =−26 ppm/℃. The difference in microwave dielectric performance of both ceramics was discussed by the packing fraction, full width at half maximum (FWHM) of A 1g Raman mode at 779 cm−1 (775 cm−1) and bond valence. The intrinsic dielectric properties of SYG and SHG ceramics were investigated by the infrared reflectivity spectra, and their negative τ f values were tuned to near-zero. [ABSTRACT FROM AUTHOR]

In this work, compositional modification was proposed to improve the sintering behavior of Li 4 WO 5 via MgO additive. A series of (1- x)Li 4 WO 5 - x MgO ceramics were prepared by a simple solid-state reaction route. Solid solutions between Li 4 WO 5 and MgO were formed due to their same crystal structure and the similar ionic sizes. MgO modification improved the microstructure and densification, which in turn increased the dielectric performances of Li 4 WO 5. A composition with x = 0.075 possessed a combination of optimum dielectric properties with a relative permittivity (ε r) of 10.8, a quality factor (Q×f) of 26,270 GHz, and a temperature coefficient of resonance frequency (τ f) of −8 ppm/°C. The evolutions in dielectric properties with composition were studied from internal effects (ionic polarizability, and packing fraction) and external contributions (density variation). Competing effects from extrinsic and intrinsic contributions give rise to improvements in dielectric properties. [ABSTRACT FROM AUTHOR]

Two garnet-structured microwave dielectric ceramics of A 3 Y 2 Ge 3 O 12 (A = Ca, Mg; called CYG and MYG, respectively) were synthesized. CYG was crystallized in a normal cubic garnet structure with Ca2+ fully occupying the dodecahedral (A) site, whereas MYG was an inverse garnet with mixed distribution of Mg2+/Y3+ at the A site. The difference in ionic occupation resulted in anomalies in microwave dielectric properties, with dielectric constant (ε r) = 14.1, quality factor (Q × f) = 12,600 GHz and positive temperature coefficient of resonant frequency (τ f) =120.5 ppm/°C for MYG ceramic and ε r = 10.8, Q × f = 97,126 GHz and τ f = −40.6 ppm/°C for CYG ceramic. The large deviations in measured ε r from theoretical ε th possibly resulted from the garnet structural constraints leading to 'rattling' Mg2+ and Y3+ in A site of MYG. Infrared reflectivity spectra analysis revealed ion polarization contributed mostly to the permittivity of both ceramics in microwave frequency ranges. [ABSTRACT FROM AUTHOR]

The 0.65Bi(Mg1/2Ti1/2)O3‐0.35PbTiO3 (0.65BMT‐0.35PT) ceramic, nearby morphotropic phase boundary (MPB), between tetragonal and rhombohedral was prepared. Dielectric permittivity dependence of temperature exhibits a re‐entrance dipole glass‐like behavior near room temperature. The behavior was described by the Vogel‐Fulcher law and the new glass model. Furthermore, a phenomenological statistical model was employed to determine the distribution of clusters dependence of temperature. The lattice dynamics of the 0.65BMT‐0.35PT ceramic was estimated by Raman spectroscopy from 298‐723 K. A disruption of ferroelectric long‐range order and an occurrence of local lattice distortion were revealed. The relaxor‐ferroelectric (r‐FE) nature of the 0.65BMT‐0.35PT was characterized by polarization‐electric field P(E). A close relation between the distribution of clusters and ferroelectric properties was established. [ABSTRACT FROM AUTHOR]

Unfilled tungsten bronze ceramic Ba3.5Sm1.5Fe0.75Nb9.25O30 was prepared by a conventional solid-state reaction method. Its structure, microstructure, and dielectric properties were investigated. Dielectric behaviors indicate that the ceramics are ferroelectric at room temperature with a remnant polarization ~1.61 μC/cm2 and a coercive field ~13.91 kV/cm. Ba3.5Sm1.5Fe0.75Nb9.25O30 ceramics have temperature stability with a high dielectric constant (ε r) varying from 172 to 202 at the temperature range −55 to 200°C (at 1 MHz). Capacitance change rate of the sample is less than 15%. These results indicate that Ba3.5Sm1.5Fe0.75Nb9.25O30 ceramics might be promising in temperature-stable multi-layer ceramic capacitors. [ABSTRACT FROM AUTHOR]

In this paper, a new type of lead-free ceramic of Sr 4−x Ba x SmFe 0.5 Nb 9.5 O 30 (x = 0, 0.25, 0.5, 0.75 and 1, abbreviated as SBSFN) was prepared by high-temperature solid-phase synthesis. With the increase of x, the packing fraction in the unit cell increases, the vacancy decreases, and the orthogonal phase transforms into the tetragonal phase. The XRD and refinement results show the distortion in the BO 6 octahedron variety as the vacancy decreases. When x increases from 0.5 to 1, and the peak value of the dielectric constant (ε r) increases from 215 to 665 (10 kHz). With the fluctuation of the composition, the relaxation phenomenon is obvious. The impedance data show that there are crystal grains and grain boundaries at high temperature, and all samples undergo a relaxation thermal activation process. The breakdown field strength and remnant polarization of the ceramics increase with increasing x, which indicates that the ferroelectric properties of these ceramics improve. • The decrease of A-site vacancy make phase transform and decreases the BO6 octahedron distortion. • The decrease of A-site vacancy increases the relaxation ferroelectricity. • The decrease of A-site vacancy increases the dielectric constant. [ABSTRACT FROM AUTHOR]

AC 3 B 4 O 12 -type perovskite CaCu 3 Ti 4 O 12 (CCTO), □ 0.34 Pr 0.67 Cu 3 Ti 4 O 12 (PCTO), □ 1 Cu 3 Ta 2 Ti 2 O 12 (CTTO), □ 2 Cu 2 Ta 4 O 12 (CTO) ceramics with different concentration cation vacancies were prepared through traditional solid state reaction method. X-ray diffraction analysis indicated that CCTO and PCTO are perovskite cubic with space group Im -3 (no. 204) while CTTO and CTO are Pm -3 (no. 200). Cell parameter of the samples dramatically increases with the increase of cation vacancies. Dielectric permittivity of them maintains very high value of ∼10 4 from room temperature to 550 K but the dielectric loss is depressed with the increase of cation vacancies in the same space group. The dielectric properties and conductivity behavior were described by the Debye relaxation and the universal dielectric response, respectively. The effect mechanism of cation vacancy and crystal structure on carrier transposition were discussed. [ABSTRACT FROM AUTHOR]

Abstract: Two new tungsten bronze ferroelectrics Sr6−n Pr n Ti n Nb10−n O30 (n =1, 2) were synthesized and characterized. Sr5PrTi3Nb7O30 and Sr4Pr2Ti4Nb6O30 had tetragonal filled tungsten bronze structure at room temperature, and exhibited weak ferroelectric nature with remnant polarizations (P r ) of 0.81 and 0.8μCcm−2, respectively. Sr5PrTi3Nb7O30 showed diffused relaxor behavior with the Curie temperature T c at around 70°C (at 1MHz), while Sr4Pr2Ti4Nb6O30 showed diffused normal ferroelectric transition with T c at 182°C. Their dense ceramics had dielectric constant of 550 and 325, and dielectric loss (tan δ) of 0.05 and 0.006 for Sr5PrTi3Nb7O30 and Sr4Pr2Ti4Nb6O30 at 1MHz, respectively. Heterogeneous mixtures of the two compounds might be used to fabricate temperature-stable dielectrics. [Copyright &y& Elsevier]

A low-permittivity and low-loss ceramic, Li 4 GeO 4 , was fabricated via solid state reaction route. XRD showed that a single orthorhombic Li 4 GeO 4 phase with olivine structure was prepared over the sintering temperature range of 660–740 °C. Dense ceramic sintered at 720 °C revealed excellent microwave properties, with ε r ~6.99, Q × f ~47,813 GHz (at 15.5 GHz), and τ f ~ − 159.2 ppm/°C. The microwave dielectric performances were analyzed with the intrinsic characteristics of crystal structure by ionic polarizability and Raman spectra. Additionally, the Li 4 GeO 4 ceramic showed good chemical compatibility with Ag sintered at 720 °C. In the low-temperature cofired ceramic (LTCC) application, aforesaid results manifested that Li 4 GeO 4 ceramic was considered as a potential candidate. • A low-permittivity and low-loss ceramic, Li 4 GeO 4 , was fabricated via solid state reaction route. • Dense ceramic sintered at 720 °C revealed excellent microwave properties, with εr ~ 6.99, Q × f ~ 47,813 GHz (at 15.2 GHz), and τ f ~ –159.2 ppm/°C. • The microwave dielectric performances were analyzed with the intrinsic characteristics by ionic polarizability, packing fraction, and Raman spectra. [ABSTRACT FROM AUTHOR]

Capacitance change for all ceramics at 10 kHz. • In the titled "Origin of ultrahigh thermal stability on dielectric permittivity and dipole glass-like behavior of 0.4Ba0.8Ca0.2TiO3-0.6Bi(Mg0.5Ti0.5)O3 (BCT-BMT) based ceramics" of manuscript, the ultrahigh thermal stability on dielectric permittivity of BCT-BMT based ceramics with a pseudo-cubic crystal structure was prepared. • The dipole glass-like behavior behavior of all ceramics were characterized by a phenomenological statistical model. • The origin of ultrahigh thermal stability on dielectric permittivity is attributed by the weaker interaction between active dipoles and less ferroelectric long-rang order. • The 5 mol% Si doped BCT-BMT ceramics shows that the capacitance variation are lower than ± 5 % (1209 ± 60) between a wide temperature range from 437 K to 796 K with a low dielectric loss (tan δ < 0.025) from 443 K to 714 K, indicating a promising material for use in high-temperature capacitors. The 0.4Ba 0.8 Ca 0.2 TiO 3 -0.6Bi(Mg 0.5 Ti 0.5)O 3 (BCT-BMT) and 5 mol% Si doped 0.4Ba 0.8 Ca 0.2 TiO 3 -0.6Bi(Mg 0.5 Ti 0.5)O 3 (BCST-BMT) ceramics with a pseudo-cubic crystal structure were prepared. Both as-prepared and O 2 annealing ceramics (BCT-BMT-O 2 and BCST-BMT-O 2) exhibit a typical re-entrant dipole-glass-like relaxor behavior and excellent thermal stability of dielectric permittivity above T m. A statistical model was employed to describe the temperature dependence of dielectric permittivity, which reveals the origin of the special dielectric properties. The large dielectric permittivity is attributed to the weakly interacting polar nanoregions (PNRs) associated with complex ionic substitution of both the A-site and B-site. The ultrahigh thermal stability is related to the thermal distribution of active dipoles. The Si doped BCT-BMT ceramic shows that the capacitance variation are lower than ± 5 % (1209 ± 60) in a wide temperature range from 437 K to 796 K with a low dielectric loss (tan δ < 0.025) from 443 K to 714 K, indicating a promising material for use in high-temperature capacitors. [ABSTRACT FROM AUTHOR]