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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]

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]

Compositional modification engineering was designed to simultaneously reduce the sintering temperature and improve the dielectric properties of BaTa2V2O11 via in-situ adjusting the V5+/Ta5+ molar ratio. A series of BaTa2-xV2+xO11 ceramics, fabricated by a solid-state reaction method, were characterized for structural evolution and dielectric properties variations. In-situ adjusting V5+/Ta5+ molar ratio significantly lowered the sintering temperature of BaTa2V2O11 and prominently improved the temperature stability of resonance frequency which is explained by the dielectric dilution theory. Competitive microwave dielectric properties with εr = 11.5–25.9, Q × f = 22,172–42,660 GHz, and τf = 42.4–74.6 ppm/ºC were achieved in the BaTa2-xV2+xO11 ceramics sintered at 620–840 oC. All the results indicate that the molar ratio of V5+ is primarily responsible for improving the densification behavior and dielectric characteristics of BaTa2-xV2+xO11, which in turn increases the appropriateness in further practical applications. [ABSTRACT FROM AUTHOR]

Quenching from sintering temperature enhances the depolarization temperature (Td) in Na1/2Bi1/2TiO3-based ceramics without significant deterioration of piezoelectric properties (d33). In this work, quenching effects in an ergodic relaxor 0.97(0.94Na0.5Bi0.5TiO3–0.06BaTiO3)–0.03AgNbO3 (NBT–6BT–3AN) were investigated based on structure, ferroelectric, and dielectric properties. The ergodicity to nonergodicity transition was obtained by quenching NBT–6BT–3AN above 1000 °C. The temperature stability of the quenching-induced nonergodicity was examined by annealing the quenched sample at 300 °C and 600 °C. The effect of oxygen vacancy on ergodicity to nonergodicity transition was investigated by comparing ferroelectric and electrostrain responses of the quenched and nitrogen-atmosphere-annealed samples. The influence of quenching on the structure including the average crystal structure, phase fraction and lattice distortion and the local structure including bond lengths and ordering of ions was analyzed. The ergodicity to nonergodicity transition upon quenching is ascribed to the contribution of the off-centered Bi3+ ions and ordered local structure. [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]

(1–x)K0.5Na0.5NbO3-xLaBiO3 [(1–x)KNN-xLB, x = 0, 0.005, 0.015] lead-free ceramics were prepared via a solid-state reaction route. An orthorhombic symmetry was determined for all samples by the Rietveld refinement of XRD patterns. The 0.995KNN-0.005LB ceramic (KNN-5LB) exhibits an ultrahigh and stable relative permittivity (ε' ~ 2158 ± 15%) with a low dielectric loss tangent (tanδ ≤ 3%) in a very broad operation temperature range from 172 °C to 450 °C due to two close diffuse phase transitions at ~200 °C and ~ 380 °C induced by La and an additional polarization from off-centered Bi ions. The Cole-Cole plot of iso-thermal complex impedance suggests that the high-temperature dielectric response of the KNN-5LB is attributed to the polarizations from grains, grain boundaries and electrode interfaces. Both the imaginary parts of impedance and modulus exhibit the thermally activated process and scaling behavior. The frequency dependent conductivity (σac) of the KNN-5LB follows the Universal Dielectric Response (UDR) law. The conduction mechanism is related to the small polaron hopping. [ABSTRACT FROM AUTHOR]

Two novel garnet-type ceramics Ca3MZrGe3O12 (M = Co and Zn) with pure phase were prepared through a solid-state reaction method. Structure–property relationships were studied by the Rietveld refinement and Raman spectra. The appearance of two weak symmetric stretching vibrational peaks in Ca3ZnZrGe3O12 might be due to the lower ordering. Higher Q × f value in Co-analogue was related to the larger packing fraction and the lower FWHM of A1g mode. The smaller oxygen bond valence in Ca3CoZrGe3O12 indicates a smaller τf value. At the optimized sintering temperature of 1280 °C, Ca3CoZrGe3O12 shows desirable microwave dielectric properties with εr of 10.37, Q × f value of 60,100 GHz, and τf value of −28.5 ppm/oC. The Ca3ZnZrGe3O12 ceramic sintered at 1200 °C has the best microwave dielectric properties with εr of 10.48, Q × f value of 49,700 GHz, and τf value of −35.8 ppm/oC. [ABSTRACT FROM AUTHOR]

A new rock-salt type compound, namely Li3MgNbO5, was synthesized using traditional two-step sintering process for the first time. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermal dilatometer and network analyzer. The Li3MgNbO5 ceramic sintered at 1260 °C adopted a cubic structure with Fm-3 m space group and exhibited excellent microwave dielectric properties (MDPs) of εr = 16.2, Q × f = 96796 GHz, and TCF = − 24.8 ppm/°C. The fitting results of the infrared spectrum indicated that the dielectric polarization of Li3MgNbO5 in microwave frequency band was contributed by phonon absorption in infrared band. Furthermore, the negative TCF value of Li3MgNbO5 ceramic was compensated with a traditional TCF compensator ~ CaTiO3. A near-zero TCF value of + 1.2 ppm/°C was achieved in the composite 0.96Li3MgNbO5–0.04CaTiO3 ceramics with εr = 18.4 and high Q × f = 86625 GHz, exhibiting a great potential to be applied in microelectronics systems. [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]

According to the literature reports, synthesis of Ba 1- x Ca x TiO 3 (BCT) ceramics with good microstructure and satisfactory dielectric property is still a challenge. So, a facile tartaric coprecipitation method in the study is proposed to prepare BCT fine powders with homogeneous morphology, high crystallinity and tetragonality. The effect of Ca2+ doped concentration on microstructure and dielectric property was studied. Results showed that, the characteristics of the raw BCT powders greatly affected the microstructure and site occupancy of Ca2+ in BT ceramics, which subsequently played a crucial rule on the dielectric performance. Owing to the good properties of the raw BCT powders, the as-obtained ceramics demonstrated good microstructure with uniform grain size of ∼1 μm, defined grain boundaries and densely packed without any cracks or pores. In addition, they also demonstrated much improved dielectric properties with good ε r , low tan δ , definite increase of Tc , suggesting they are compatible in application of MLCC with high performance. [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]

(1 − x)K0.5Na0.5NbO3-x(Bi0.5K0.5)ZrO3 [abbreviated as (1 − x)KNN-xBKZ, 0 ≤ x ≤ 0.08] lead-free ceramics have been fabricated by a solid-state processing route. Based on the x-ray diffraction data and temperature-dependent dielectric characteristics, an orthorhombic phase for x ≤ 0.03 and single rhombohedral one for x ≥ 0.05 at room temperature were determined. The cell volume firstly increases, then decreases and finally increases with increasing BKZ, depending on ionic size and crystallographic structure. For the sample of x = 0.05, a temperature-stable high permittivity (~ 1736 ± 15%) along with low dielectric loss tangent (≤ 5%) is recorded from 158°C to 407°C. In addition, the activation energies of dielectric relaxation and dc conductivity at high temperatures were characterized by impedance spectroscopy. A combined effect of lattice distortion and oxygen vacancies on the magnitude of activation energies was discussed. [ABSTRACT FROM AUTHOR]

CaYCuTiO (0 ≤ x ≤ 0.67) ceramics were fabricated by a conventional solid-state reaction method. Lattice parameter of the system increases linearly with increasing x. The high-frequency dielectric loss of CaYCuTiO is suppressed significantly while the dielectric constant decreases slightly. The dielectric, impedance and modulus spectra reveals that the giant dielectric response associates with the Maxwell-Wagner effect. The decrease of dielectric constant is just related to the capacitance of grain boundaries. The dielectric relaxation behavior of the system is independent of Y substitution while the correlation between conductivity and frequency becomes stronger in Y substituted CaCuTiO. It suggests that space charge and long-range hopping of carriers play important roles on the low-frequency dielectric properties. The decrease of grain-boundary activation energy with Y substitution indicates that the concentration of oxygen vacancies increases in grain boundaries. The mechanisms of depressing low-frequency dielectric constant and high-frequency dielectric loss was discussed. [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]

0.4(BaCa)LaTiO-0.6Bi(MgTi)O ( x = 0.00, 0.15, 0.30) ceramics were prepared by a conventional mixed oxide route. Crystal structure of the ceramics was determined using XRD. Dielectric constant of the samples decreases with the increase of La content, however, the temperature stability of dielectric constant was improved. For x = 0.3, a near-plateau dielectric constant 700 ± 80, extended across the temperature range, 30-550 °C (at 1 kHz) was obtained. The corresponding loss tangent, tan δ, was ≤0.025 in the temperature range from 93 to 353 °C. All samples show a relaxor behavior and measurement frequency and the temperature ( T ) corresponding to the maximum of dielectric constant follow the Vogel-Fulcher relationship. Compared the dielectric properties of the samples with other materials, the former has highly attractive for developing capacitors over a wide working temperature range. [ABSTRACT FROM AUTHOR]

Dielectric and ferroelectric properties of multiferroic (1–x)BiFeO3-xBi0.5Na0.5TiO3(BFO-xBNT) (x= 0-0.8) solid solution synthesized by sol-gel route were investigated. XRD patterns revealed that BFO-xBNT is an infinite solid solution with rhombohedral stricture. Lattice parameter and cell volume of the solid solution decrease with the increase of amount of BNT. A possible structure distortion could happen at x = 0.40. BNT makes an influence on grain morphologies and electrical properties. Dielectric permittivity of the solid solution shows dramatic change with the increase in BNT content. Ferroelectric property of BFO is enhanced by introduction of BNT although thePrvalue is very small. [ABSTRACT FROM AUTHOR]

Unfilled tungsten bronze ceramics with general formula KBaRNbO (R = La, Pr, Nd, Sm, Eu, Gd) were prepared by the conventional solid state reaction method. XRD patterns show that all ceramics are pure tungsten bronze phase. Dielectric characterization indicates that the ceramics except KBaGdNbO are relaxors with strong frequency dispersion, while KBaGdNbO shows diffuse phase transition and belongs to classical ferroelectrics. At room temperature, the KBaRNbO compounds (R = La, Pr, Nd) are paraelectrics while the KBaRNbO compounds (R = Sm, Eu, Gd) are ferroelectrics. Among them, KBaGdNbO has the highest remnant polarization (2 P) of 8.2 μC/cm. Phase transition temperature, remnant polarization (2 P) and tetragonality of the compounds increase with the decrease of ionic radius of the rare earths. [ABSTRACT FROM AUTHOR]

BaLa (ZrTi)O (BLZT) ceramics with x = 0.02 (BLZT-1), 0.04 (BLZT-2), 0.06 (BLZT-3) and 0.08 (BLZT-4) were prepared by a solid-state reaction route. Crystal structure of the BLZT ceramics was determined using X-ray diffraction and Raman spectroscopy. While the ceramics for x ≤ 0.04 are pure phase with cubic perovskite structure, pyrochlore LaZrO appears in the samples with x = 0.06 and 0.08. Dielectric properties as function of temperature and frequency showed more than one dielectric anomaly were found at high temperatures during heating but they weakened or disappeared during cooling. Both dielectric relaxation and electrical conductivity were taken into account in point defect mechanism. The double-ionized and short-range hopping of oxygen vacancy should be mainly responsible for the dielectric anomalies and conduction behavior. Activation energy of conductivity E is lower than half of the band gap E obtained by UV-Vis spectroscopy, which results from emergency of oxygen vacancies. In visible light region, the ceramics show a strong absorption with band gap of about 3.57 eV. [ABSTRACT FROM AUTHOR]

Abstract: A/B-site complex perovskite (NaBi(1−x)K x )0.5Ti(1−x)Nb x O3 (also can be written: (1−2x)Na0.5Bi0.5TiO3–xK0.5Bi0.5TiO3–xNaNbO3) (x =0–0.08) lead-free piezoelectric ceramics were fabricated by mechanical alloying technique from their oxide/carbonate mixture. Phase evolvements of the mixture and the influence of x value on crystal structure and microstructure were investigated. The perovskite Na0.5Bi0.5TiO3 phase was progressively formed with passing through the intermediate Bi4Ti3O12 phases with increasing degree of mechanical activation. The Curie–Weiss law and a modified empirical expression were employed to describe the ferroelectric phase transition of (NaBi(1−x)K x )0.5Ti(1−x)Nb x O3 ceramics. The results showed that (NaBi(1−x)K x )0.5Ti(1−x)Nb x O3 ceramics became more relaxor ferroelectric characteristic with the increase in value of x. The enhancement of relaxor characteristic may arise from structural disorder and compositional fluctuation in the crystal structure. [Copyright &y& Elsevier]

Abstract: The intrinsic defects of (Na0.5K0.5)NbO3 (NKN) ceramics fabricated by high-energy ball-milling have been studied. In order to obtain the different amounts of Na/K evaporation, NKN ceramics were sintered in air (NKN exposed samples) and in calcined NKN powder (NKN buried samples), respectively. Compared with the dielectric and piezoelectric properties of the buried samples, the exposed samples exhibited a donor doped behavior at room temperature. A dielectric relaxation, induced by intrinsic oxygen vacancies, was detected in paraelectric phase region. The activity energies of intrinsic oxygen vacancies are 1.04eV and 1.47eV for the exposed samples and buried samples, respectively. The difference of activity energies resulted from singly ionized oxygen vacancies translating into doubly ionized oxygen vacancies with the increase of Na/K evaporation. [Copyright &y& Elsevier]

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]

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]

The present study focuses on the synthesis and characterization of rare-earth titanates, specifically Re 2 TiO 5 (Re La, Nd, Sm), with a particular emphasis on their microwave dielectric properties. The factors influencing the synthesis of La 2 TiO 5 compound through the traditional solid-state method were thoroughly investigated, with a significant finding being the notable impact of moisture absorption in La 2 O 3. The impact of variations in rare-earth cation radii on the structure and dielectric properties was systematically analyzed. Re 2 TiO 5 (Re La, Nd, Sm) ceramics crystallized into an orthorhombic structure with space group Pnam, which was confirmed through Rietveld refinement. The resulting materials demonstrated exceptional microwave dielectric properties characterized by a low permittivity range of 13.72–17.39, high-quality factors ranging from 8331 to 17,795 GHz, and a significantly reduced temperature coefficient of resonance frequency (−33.2∼-12.6 ppm/°C). The correlation between microwave dielectric properties and structural characteristics (including ionic polarizability, packing fraction, and bond valence) was investigated. The exceptional potential of these rare-earth titanates lies in their ability to meet the stringent requirements for low signal transmission delay in wireless communication systems, owing to their advantageous low permittivity within the microwave frequency spectrum. [ABSTRACT FROM AUTHOR]

(1 − x)K0.5Na0.5NbO3-x(Bi0.5Li0.5)ZrO3 (labeled as (1 − x)KNN-xBLZ) lead-free ceramics were fabricated by a solid-state reaction method. A research was conducted on the effects of BLZ content on structure, dielectric properties and relaxation behavior of KNN ceramics. By combining the X-ray diffraction patterns with the temperature dependence of dielectric properties, an orthorhombic-tetragonal phase coexistence was identified for x = 0.03, a tetragonal phase was determined for x = 0.05, and a single rhombohedral structure occurred at x = 0.08. The 0.92KNN-0.08BLZ ceramic exhibits a high and stable permittivity (~ 1317, ± 15% variation) from 55 to 445 °C and low dielectric loss (≤ 6%) from 120 to 400 °C, which is hugely attractive for high-temperature capacitors. Activation energies of both high-temperature dielectric relaxation and dc conductivity first increase and then decline with the increase of BLZ, which might be attributed to the lattice distortion and concentration of oxygen vacancies. [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]

High entropy relaxor ferroelectrics, are a representative type of dielectric with exceptional properties and play an indispensable role in the next-generation pulsed power capacitor market. In this paper, a high-entropy relaxor ferroelectric ceramic (Li 0.2 Ca 0.2 Sr 0.2 Ba 0.2 La 0.2)TiO 3 successfully designed and synthesized using the traditional solid-state reaction method. The microstructure, dielectric properties, and energy storage characteristics of the ceramics were systematically investigated. The ceramic exhibited a dense microstructure with a single-phase perovskite structure and small grain size. The unique microstructure and high insulation not only wides the band gap, but also minimizes residual polarization and resulting in higher energy density (E b) 1.51 J/cm3 and efficiency (η) of 89.6% at a low field strength of 260 kV/cm. Furthermore, the observed anomalous behavior in dielectric relaxation was explained within the context of high entropy ceramics. The material also exhibited excellent temperature/frequency stability and fast charging-discharging speed (∼35 ns). These results demonstrate the effectiveness of high entropy strategy to develop high-performance energy storage capacitors. • High entropy strategy effectively contributes to developing high-performance energy storage capacitors. • Fine grains, wide band gap and high insulation to improve the breakdown field strength. • Combined energy storage performance was achieved under low electric field (∼ 260 kV/cm). • Excellent temperature/frequency stability and fast charging-discharging speed (∼35 ns). [ABSTRACT FROM AUTHOR]

Abstract: 0.92K0.5Na0.5NbO3–(0.08− x)Bi0.5Li0.5TiO3–xBaZrO3 (KNN–BLT–BZ) lead-free piezoelectric ceramics were fabricated by traditional ceramics process. XRD results showed that complete solid solutions with mixed phases of rhombohedra and tetragonal were observed. Diffusion phase transitional behavior, dielectric properties and ferroelectric properties of the KNN–BLT–BZ ceramics were investigated. It was found that the cubic-tetragonal phase transition temperature (T C ) slightly decreased as the amount of BaZrO3 was increased. A morphotropic phase boundary (MPB) between rhombohedral and tetragonal ferroelectric phases was identified in the composition range of 0.04≤ x ≤0.06. Furthermore, good ferroelectric properties were also found in this composition range, with P r of 14.5μCcm−2 and E c of 1.95kVmm−1 for the sample with x =0.04. [Copyright &y& Elsevier]

Abstract: The influence of the microstructure on dielectric properties of Sr0.8(K,Na)0.2Bi2Nb2O9 (SKNBNO) prepared by the solid-state route is reported. The formation of Bi-layer structure was obviously restrained owing to the K and Na ions substituting Sr ions by the X-ray diffraction analysis (XRD) and scanning electron micrograph (SEM). At the same time, some slight secondary phase of bismuth oxide was detected but the structure was not changed. The dielectric constant was restrained by K and Na ions substituting Sr ions, which is mainly attributed to the slight change of lattice constants resulting in a decreased “rattling space” for the cations inside the distorted Nb(V)O6 oxygen octahedron of the perovskite block. A clear enhancement in the stability of frequency and temperature was noticed for SKNBNO sample compared to Sr2Bi2Nb2O9 (SBN) samples. [Copyright &y& Elsevier]

Effect of order/disorder transition on microwave dielectric characteristics is reported to develop a deeper understanding of structure-property relationship in spinel ceramics. Dense x Li 4/3 Ti 5/3 O 4 -(1- x)Mg 2 TiO 4 (0.6≤ x ≤0.9) spinel ceramics were synthesized and characterized for structural and dielectric properties. The critical order/disorder structural transition was induced when x < 0.8, resulting in the ceramic crystallized into a primary cubic spinel phase, while when x > 0.8, the ceramic crystallized into a disordered face-centered cubic phase. The cation occupation caused this order-disorder transition, which directly influenced the variation in microwave dielectric properties. At x = 0.75 the maximum degree of order was achieved resulting in a maximum quality factor of 55,000 GHz and a near-zero τ f = 2.9 ppm/oC. Dielectric properties decreased sharply after x = 0.8 when the disorder face-centered cubic phase started to crystallize. All the results indicated that cation ordering/disordering plays a critical role in determining the optimum microwave dielectric properties in spinel ceramics. [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]

With co-substitution of (Li 0.5 Sm 0.5) at A site and W at B site, the electrical properties of modified Ca 0.92 (Li 0.5 Sm 0.5) 0.08 Bi 2 Nb 2- x W x O 9 [(CLS)BN- x W, x = 0, 0.015 and 0.03] piezoceramics with ultrahigh Curie temperature (T C) of > 930 °C were enhanced dramatically. The increased resistivity induced by the co-substitution ensure them to be polarized under an enough high field. Combined with the increase of spontaneous ferroelectric polarization (P S), the significant enhancements in the piezoelectric, dielectric and ferroelectric properties can be obtained in the composition x = 0.015. Furthermore, the piezoelectric activity (d 33) and bulk resistivity (ρ b) of (CLS)BN-0.015 W can be further enhanced at an appropriate sintering temperature. This optimum composition sintered at 1170 °C shows ultrahigh T C of ∼948 °C, d 33 of ∼17.3 pC/N and ρ b of ∼6.9 MΩ cm at 600 °C, which are comparable to those of the reported high-temperature Aurivillius piezoceramics with T C > 850 °C. [ABSTRACT FROM AUTHOR]

Two novel microwave dielectric materials LiBO 2 (B = Ga, In) were synthesized by a solid-state reaction method. The orthorhombic structured LiGaO 2 sintered at 1075 °C for 4 h exhibits a relative density of 96.1 ± 0.2 % and dielectric properties, namely, ε r ∼ 5.82 ± 0.01 (16.7 ± 0.1 GHz), Q × f = 24,500 ± 2000 GHz, and τ f ∼ -74.3 ± 2 ppm/°C. Meanwhile, the tetragonal structured LiInO 2 sintered at 920 °C for 4 h exhibits a relative density of 85.3 ± 0.2 % and dielectric properties, namely, ε r ∼ 9.6 ± 0.01 (15.2 ± 0.1 GHz), Q × f = 39,600 ± 2000 GHz, and τ f ∼ 9.8 ± 2 ppm/°C. The dielectric properties were investigated by chemical bond theory, and results indicate that the τ f value is closely related to the bond ionicity. The good chemical compatibility of LiInO 2 ceramics with silver electrodes makes it a potential material for LTCC technology. [ABSTRACT FROM AUTHOR]

Ba 2 MGa 11 O 20 (M = Bi, La; called BBG and BLG, respectively) ceramics with monoclinic space group I2/m were prepared through a solid-state reaction method. BBG ceramic sintered at 1150 °C for 6 h has the best microwave dielectric properties with low ε r = 10.68, Q × f = 41,756 GHz, and negative τ f = −61.3 ppm/°C. BLG ceramic sintered at 1440 °C for 6 h exhibits ε r = 13.94, Q × f = 45,592 GHz, and near-zero τ f = −16.3 ppm/°C. The large deviation between ε r and ε th was ascribed to the "rattling" effect of the cations and the existence of lone pair ions of Bi3+. The difference in Q × f of the two ceramics was discussed in terms of packing fraction, and the τ f of BLG was closer to zero than that of BBG due to the smaller τ ε value. Their intrinsic dielectric properties were analyzed through far-infrared reflectivity spectroscopy. [ABSTRACT FROM AUTHOR]

Two garnet-type rare-earth-free ceramics, Ca 3 M 2 SiGa 2 O 12 (M = Sn and Zr), were prepared through a solid-state reaction method. The relationship between crystal structure and microwave dielectric properties was investigated. The larger deviation of ε r from ε theo in Ca 3 Zr 2 SiGa 2 O 12 could be ascribed to the rattling Zr4+. The increase in packing fraction and the decrease in FWHM enhance the Q × f value by substituting Zr4+ with Sn4+. The smaller oxygen bond valence in Ca 3 Zr 2 SiGa 2 O 12 indicates a smaller τ f value. Good microwave dielectric properties are obtained with ε r = 9.14 ± 0.02, Q × f = 106,800 ± 1700 GHz and τ f = -45.8 ± 1.8 ppm/°C for Ca 3 Sn 2 SiGa 2 O 12 and ε r = 11.98 ± 0.03, Q × f = 84,200 ± 1500 GHz, and τ f = -32.8 ± 1.4 ppm/°C for Ca 3 Zr 2 SiGa 2 O 12. Furthermore, near-zero τ f values of +5.7 ± 1.9 ppm/°C and +4.5 ± 1.6 ppm/°C appear in 0.95Ca 3 Sn 2 SiGa 2 O 12 -0.05CaTiO 3 and 0.96Ca 3 Zr 2 SiGa 2 O 12 -0.04CaTiO 3 , respectively. [ABSTRACT FROM AUTHOR]

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]

LiGa 5 O 8 ceramics with inverse spinel structure were prepared in a temperature range of 1200–1300 ℃ by solid-state reaction method. LiGa 5 O 8 ceramics crystallized in cubic structure with space group P 4 3 32, in which Li+ and Ga3+ distributed in the octahedral B sites with 1:3 ordering. The optimal microwave dielectric properties with ε r = 10.51, Q × f = 127,040 GHz, and τ f = – 60.16 ppm/℃ were achieved at 1260 ℃ for 6 h. Microwave dielectric properties were discussed in combination with the intrinsic characteristics of crystal structure by packing fraction, Raman spectra, and infrared reflectivity spectrum. Additionally, CaTiO 3 was used to suppress τ f of LiGa 5 O 8 ceramics to near zero, and optimized performances of ε r = 12.79, Q × f = 109,752 GHz and τ f = +4.07 ppm/℃ were obtained for 0.94LiGa 5 O 8 ‐0.06CaTiO 3 ceramics at 1260 ℃. These bright spots make LiGa 5 O 8 ceramic a potential candidate for 5 G and millimeter wave technology. [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]

Olivine−type structure microwave dielectric ceramics LiYbSiO 4 with near-zero τ f were fabricated by solid-state reaction process for the first time. The relationships among structural parameters, sintering behavior, vibrational modes and microwave dielectric properties for the ceramics were studied. The variation in ε r could be correlated with Raman shift. The variation in Q×f values was inversely correlated to FWMH and average cation covalency. The τ f values were explained with the bond valence sum of cations. Single phase LiYbSiO 4 ceramics could be obtained at the range of 1100–1140 °C and showed promising microwave dielectric properties with ε r = 7.36 – 7.42, Q×f = 19081 – 25276 GHz and τ f = +4.52 – +8.03 ppm/°C. [ABSTRACT FROM AUTHOR]

The effects of Sr2+ substitution for Ba2+ on phase structure, microstructure, dielectric and electric properties for Ba 4-x Sr x SmFe 0.5 Nb 9.5 O 30 (x = 0, 1, 2, 3 and 4) ceramics were systematically researched. X-ray diffraction patterns show that Ba 4-x Sr x SmFe 0.5 Nb 9.5 O 30 (x = 0, 1, 2 and 3) ceramics are tetragonal tungsten bronze compound with a space group of P 4 bm , while the sample for x = 4 is an orthorhombic structure compound. The result can be corroborated by the analysis of Raman spectroscopy. As the Sr2+ contents increase from 0 to 3, the full width at half maximum of Raman lines of all samples increase gradually, indicating that the degree of lattice distortion increase. All tetragonal tungsten bronze ceramics exhibited a broad permittivity peaks, accompanied by frequency dispersion, indicating all samples are relaxor. The electrical properties of BSSFN ceramics were further studied by complex impedance spectroscopy. XPS spectrum shows that Fe2+ and Fe3+ coexist in Ba 4-x Sr x SmFe 0.5 Nb 9.5 O 30 ceramics, and their proportion varies with the concentration of Sr2+. [ABSTRACT FROM AUTHOR]

The microstructure, crystal structure and electrical properties of polycrystalline spinel Li 4 Ti 5 O 12 (LTO) were studied. The Rietveld refinement of the XRD pattern of LTO shows a cubic phase with the space group F d 3 ¯ m. Three dielectric relaxations associated with Li+ ion diffusion through different paths are clear in the temperature dependence of dielectric properties. The relation between dielectric response and local structure is revealed by an in-situ Raman spectroscopy. The variation of β in the KWW function is related to the migration of Li ions, which is in agreement with the universal response law (URL). The scaling behavior of the imaginary part of the electric modulus indicates that three relaxation processes have the same mechanism at each selected temperatures. Combined with impedance and modulus spectra, an insight into the transportation behavior of Li+ at different chemical environments is obtained, meanwhile, it provides an effective tool to probe the relationship between diffuse pathway of lithium ion and dielectric response. • Li+ diffusion leads to three dielectric relaxations with increasing temperature. • The relaxation behaviors associate with diffuse pathway of Li+ ions. • Dielectric spectroscopy LTO was described by the Universal Dielectric Response. • β value in the KWW function reveals the mechanism and path of migration of Li+. • The bulk conduction in LTO is due to the hopping of Li+ ions. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A series of new Ba 4−x Sm 2 Fe 2−x Nb 8+x O 30 TTB was prepared with an adjustable structure that changes from filled to unfilled. • All BSFN ceramics show a more intense dispersion phenomenon as the concentration of Ba2+ decreases. • P-E loops become more slanted and slimmer with the reduced Ba2+ concentration. Abstract Tungsten bronze (TB) structural ceramics with the nominal formula Ba 4-x Sm 2 Fe 2−x Nb 8+x O 30 (BSFN) (x = 0, 0.025, 0.05, 0.075 and 0.1) were prepared using a standard solid-state sintering method. The effects of Ba2+ concentration on the crystallographic phase, microstructure, dielectric and ferroelectric properties were systematically studied. All compounds presented tetragonal tungsten bronze (TTB) structures, where the A1 and A2 sites were exclusively occupied by Sm3+ and Ba2+ ions, respectively, while the Fe3+ and Nb5+ ions were randomly distributed between the B1 and B2 sites. All BSFN ceramics exhibited normal ferroelectric behavior, but the dielectric properties showed an increasing dispersion as the concentration of Ba2+ decreased. The conductive behavior was due to the bulk and grain boundaries, and the direct current conductivity was increased from 0.67 to 0.77 eV with a reduction in the concentration of Ba2+. The polarization-electric field (P-E) and current-electric field (I-E) loops of all the BSFN ceramics showed ferroelectric behavior, and the P-E loops became more slanted and slimmer with reduced Ba2+ concentration. [ABSTRACT FROM AUTHOR]