Low dielectric loss of Bi-doped BaZr0.15Ti0.85O3 ceramics for high-voltage capacitor applications

BaZr_0.15Ti_0.85O₃ ceramics are prepared via the conventional solid state reaction method. The effects of Bi₂O₃·3TiO₂ doped on dielectric properties and breakdown strength of BaZr_0.15Ti_0.85O₃ ceramics are systematically discussed. Doping of Bi₂O₃·3TiO₂ can obviously improve the breakdown strength and reduce the dielectric loss of the material. It is attributed to the Bi³⁺ substituted Ba²⁺ is an unequal ion substitution, and two Bi³⁺ substitute three Ba²⁺ to produce an A vacancy, thereby increasing the lattice energy and promoting the diffusion and migration of the particles during the sintering process, promoting the sintering and reducing the sintering temperature. However, the dielectric constant of the material is decreased. When the amount of Bi₂O₃·3TiO₂ is 12 mol%, the minimum dielectric loss tanδ = 0.0009, the maximum breakdown strength is E_b = 15.09 kV/mm, the insulation resistivity is 3.52 × 10¹¹ Ω cm. The energy storage density of the BaZr_0.15Ti_0.85O₃ ceramic samples doped with Bi₂O₃·3TiO₂ varies from 0.008 J/cm³ to 0.012 J/cm³.     

Pyroelectric,ferroelectric, piezoelectric and dielectric properties of Na0.5Bi0.5TiO3 ceramic prepared by sol-gel method

Sodium bismuth titanate (BNT) nanopowder of molar composition 50/50 (Na_0.5Bi_0.5TiO₃) was prepared by a sol-gel processing method. The structure and microstructure of the precursor gel as well as the ferroelectric, pyroelectric, dielectric and piezoelectric properties of the BNT were studied. BNT crystallized in the rhombohedra perovskites structure Na_0.5Bi_0.5TiO₃ was obtained from the precursor gel by heating at 700 °C for 2 h in air. The BNT ceramic at 1100 °C sintering temperature present high crystallinity, good dielectric properties at 1 kHz (ε′=885, tan δ=0.03, T_c=370 °C), piezoelectric properties (k₃₃=0.39, c₃₃=105 GPa, e₃₃=12.6 C/m², d₃₃=120 pC/N), high remnant polarization (P_r=47 μC/cm²) and pyroelectric coefficient ($p$=707 μC/m² K) and low coercive field (E_c=55 kV/cm). Hence, the BNT prepared by sol-gel method could be used for silicon based memory device application where a low synthesis temperature is a key requirement.     

Piezoelectric and ferroelectric properties of lead-free [Bi1−y(Na1−x−yLix)]0.5BayTiO3 ceramics

Lead-free [Bi_1−y(Na_1−x−yLi_x)]_0.5Ba_yTiO₃ (BNLB-x/y) piezoelectric ceramics were prepared by sintering the constituent oxides, and their piezoelectric and ferroelectric properties studied. The results of X-ray diffraction (XRD) suggest that Li⁺ and Ba²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ (BNT) lattices to form a solid solution with a single-phase perovskite structure. The ceramics can be well sintered at 1100–1150 °C. The introduction of Li⁺ and Ba²⁺ into Bi_0.5Na_0.5TiO₃ significantly decreases the coercive field, E_c but maintains the large remanent polarization, P_r of the materials. The ceramics exhibit relatively good piezoelectric properties and very strong ferroelectricity: piezoelectric constant, d₃₃ = 208 pC/N, planar electromechanical coupling factor, k_p = 37.0%, remanent polarization, P_r = 38.5 μC/cm², coercive field, E_c = 3.27 kV/mm. The depolarization temperature, T_d of BNLB-0.075/0.04 ceramics is about 190 °C.     

Studies on electrical and dielectric properties of co-precipitated Aurivillius phase Ca1−xBaxBi2Nb2O9 ceramics

Polycrystalline samples of lead free Ca_1−xBa_xBi₂Nb₂O₉ ceramics has been synthesized by simple chemical co-precipitation method. Single phase layered perovskite structure was confirmed by X-ray diffraction with average crystallite size in the range of 46–57 nm. Randomly oriented grains with inhomogeneous morphology was observed by scanning electron microscopy. Study of dielectric constant and corresponding tangent loss was carried out in the frequency range of 1 Hz to 5 MHz at room temperature. Ca_1−xBa_xBi₂Nb₂O₉ shows maximum value of dielectric constant of 535 at 1 Hz. The highest polarization of 0.026 μC/cm² was obtained at an applied electric field of 10 kV/cm using PE loop measurement.     

Optical,thermal and dielectric properties of Bi4(TiO4)3 ceramic powders

Bismuth titanate (Bi₄(TiO₄)₃) ceramic powders have been synthesized by using a solid state reaction method. Prominently intense blue emission at 480 nm has been measured with an excitation at 418 nm. The reason for the observance of such a blue emission from this ceramic powder has been explained. The phase formation has been investigated by X-ray diffraction analysis (XRD). The morphology and composition of the ceramic powders have been studied from the measurement of SEM and EDS profiles. FTIR and Raman spectra have also been recorded to analyze the presence of functional groups and Raman active modes in the Bi₄(TiO₄)₃ ceramic powders. The sintering temperature has been optimized to be 1100 °C based on the measured TG–DTA profiles of the as prepared material. Besides these, dielectric properties of ceramic powder in the frequency range of 200 Hz–3 MHz at 300 K have also been carried out.     

Synthesis of fine-grain Ba0.96La0.04TiO3 dielectric ceramics by different routes for multilayer ceramic capacitors

Spherical Ba_0.96La_0.04TiO₃ powders were synthesized by a wet chemical method-based on a precipitation process, able of controlling uniformity and particle size. After sintering, fine-grain Ba_0.96La_0.04TiO₃ ceramics with good dielectric properties were obtained. Different synthesis routes of Ba_0.96La_0.04TiO₃ ceramics were used, and their effects on microstructure and dielectric properties were examined. Results showed that the ceramics samples prepared by La³⁺ and Ba²⁺ added together (abbreviated as, BLT-T) resulted in a mixture of large and small grains, sharp permittivity peaks, and high dielectrics loss. By comparison, another ceramics samples prepared by La³⁺ and Ba²⁺ added separately (BLT-S) exhibited uniform grain size and broadened/flattened permittivity peaks. The high value of ε_r (3255) and low tan δ (0.01) at room temperature and negligible temperature coefficient of capacitance from − 35 to 85 °C suggested the suitability of the above materials for multilayer capacitor applications.     

Tuning the ferroelectric-relaxor transition temperature in NBT-based lead-free ceramics by Bi nonstoichiometry

In this study, the Bi-nonstoichiometric 0.99Bi_x(Na_0.8K_0.2)_0.5TiO₃-0.01SrTiO₃ (BNKST) ceramics with x = 0.5–0.535 mol (Bi50-Bi53.5) were prepared by a conventional solid-state reaction method. The effects of Bi excess on structural transition and ferroelectric stability of BNKST ceramics were systematically investigated by the Raman spectra, dielectric analyses and electromechanical measurements. The introduction of excess Bi³⁺ could significantly break the long-range ferroelectric order and favor the presence of relaxor phase, then the ferroelectric-relaxor transition temperature (T_FR) can be effectively tuned to around room temperature by Bi nonstoichiometry, giving rise to an enhanced room-temperature strain property. The positive strain S_pos and dynamic piezoelectric constant d₃₃^* of Bi52.5 critical composition reach 0.33% and 440 pm/V, respectively at 6 kV/mm. The high recoverable strain of Bi52.5 sample can be attributed to the electric-field-induced reversible relaxor-ferroelectric phase transition. The present work may be helpful for further understanding and designing high-performance NBT-based lead-free ceramics for piezoelectric actuator applications.     

Defect chemistry of a high-k ‘Y5V’ (Ba0.95Eu0.05)TiO3 ceramic

The influence of the sintering temperature (T_s) on the structure, dielectric and valence-state properties of (Ba_1−xEu_x)TiO₃ (x=0.05) ceramics was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), Raman spectroscopy, and dielectric temperature measurements. An increase in T_s can increase the solubility limit of Eu in BaTiO₃. When the T_s was increased to 1450 °C, a high-k ‘Y5V’ (ε′_RT=8500) ceramic (C-BE5T) with a single-phase cubic structure was obtained. The dielectric peak shifted rapidly toward lower temperatures with increasing T_s at a rate of −0.46 °C/K. A symmetric (200) XRD peak, exaggerated grain growth (5.6 μm), a mixed valence of Eu²⁺/Eu³⁺, an asymmetric main Raman band at 2494 cm⁻¹ and a weak sharp band at 1516 cm⁻¹ in the high-wavenumber region are characteristics of cubic symmetry of C-BE5T. The formation of a solid solution of C-BE5T and defect chemistry are discussed.     

Influence of Ca substitution on microstructure and electrical properties of Ba(Zr,Ti)O3 ceramics

In the present work, lead-free (Ba_1?xCa_x)(Zr_0.04Ti_0.96)O₃ (x=0.00–0.09) ceramics were fabricated via a solid-state reaction method. The microstructure and electrical properties of the ceramics were investigated. The microstructure of the BCZT ceramics showed a core shell structure at compositions of x=0.03 and 0.06. The substitution of small amount of Ba²⁺ by Ca²⁺ resulted in an improvement of the piezoelectric, dielectric and ferroelectric properties of the ceramics. The orthorhombic–tetragonal phase transition was found in the composition of x≤0.03. Piezoelectric coefficient of d₃₃～392 pC/N and lowest E_c～3.3 kV/cm with highest P_r～14.1 μC/cm² were obtained for the composition of x=0.03 while its Curie temperature (T_C) was as high as 125 °C. However, the ferroelectric to paraelectric transition temperature had slightly shifted towards room temperature with increasing Ca²⁺ concentration.     

Dielectric,pyroelectric, and ferroelectric properties of gadolinium doped Sr0.53Ba0.47Nb2O6 ceramic

Strontium barium niobate doped with gadolinium, with the stoichiometric formula Gd_ySr_{(0.53–3y/2)}Ba_0.47Nb₂O₆ (GSBN) was synthesized using the solid-state reaction method, with varied mol% compositions of Gd (y=0.00, 0.01, 0.03, 0.05 and 0.07). Gadolinium was chosen as a dopant with the goal of enhancing the ferroelectric and pyroelectric properties of SBN. The X-ray diffraction spectra showed that all compositions exhibit a single-phase tetragonal tungsten bronze structure. The influence of Gd as dopant on the microstructure was examined by using field emission scanning electron microscopy. The dielectric characteristics of the samples showed diffuse phase transitions. The Curie temperature of the samples shifted to lower temperature with increasing Gd concentration. The relaxor characteristic of the GSBN (above and below the Curie temperature) was described using the Curie-Weiss Law, a Gaussian distribution, and a quadratic equation. SBN doped with 3 mol% of Gd exhibits the highest remnant polarization, P_r=8.8 μC/cm², while 1 mol% Gd-doped SBN shows the highest pyroelectric coefficient of 285 µC/m² K. These qualities can be useful in security, healthcare, pollution monitoring, fire sensing, and smart energy system applications.     

Electrocaloric effect and pyroelectric energy harvesting of (0.94 − x)Na0.5Bi0.5TiO3-0.06BaTiO3-xSrTiO3 ceramics

Ceramics with the composition (0.94 − x)Na_0.5Bi_0.5TiO₃–0.06BaTiO₃–xSrTiO₃ (NBBSTx) where x = 0.10, 0.15, 0.20, and 0.25 were synthesized by a conventional solid-state reaction method to investigate their electrocaloric effect (ECE) and pyroelectric energy harvesting (PEH) properties. The ferroelectric, dielectric, and pyroelectric properties of the prepared ceramics were measured and discussed. It is found that the strontium titanate (ST) content and bias field greatly affect the ferroelectric–relaxor transition. Increasing ST content lowers the depolarization temperature of the ceramics, and both the ECE and PEH behavior of the ceramics strongly depend on their ST content because of the composition-induced decrease of the ferroelectric–relaxor transition temperature. The present investigation demonstrates that the ECE and PEH properties of NBBSTx ceramics can be tuned by introducing ST. Furthermore, a high PEH density of 425 kJ/m³ is obtained for NBBST0.20, which is much higher than those of conventional Pb-based ferroelectrics.     

Luminescence and structural study of Bi4−xEuxTi3O12 solid solution

The Bi₄Ti₃O₁₂ (BIT) is a well known ferroelectric ceramic within the family of so called Aurivillius phases. The present work shows that when bismuth (Bi³⁺, r = 0.96 Å) is substituted by trivalent europium (r = 0.95 Å), a solid solution, Bi_4−xEu_xTi₃O₁₂ (BIET), is formed. This solid solution was obtained by coprecipitation and characterized by X-ray diffraction, electron microscopy and density measurements. The solubility limit x was determined, and the variation of the lattice parameters was measured through profile fitting of the whole pattern. In order to establish the europium substitution site, we studied the luminescent properties of the material. The excitation spectra, at room temperature, show a broad band associated with a charge transfer state and with the intrinsic absorption of Bi³⁺. We found at least two Eu³⁺ sites, selectively excited. The Eu³⁺ emission spectra reveal a significant rising of the point symmetry at the rare earth site with respect to the Bi C₁, deduced from the crystallographic analysis.     

Bismuth titanates candidates for high permittivity LTCC

Bi₂O₃–TiO₂ composites are known to possess attractive microwave dielectric properties. However, producing LTCC analogues with equally promising dielectric properties is problematic. Here, we show that judicious choice of both TiO₂ starting powders and dopants can produce composites with excellent properties. Three TiO₂ powders were evaluated: 1 μm-anatase, 1 μm-rutile and a nanosized (30 nm) mixture of 75–25 anatase-rutile. The best dielectric properties were obtained by using uncalcined nanosized anatase/rutile with Bi₂O₃ powder. By doping this Bi₂O₃–TiO₂ powder mixture with 0.112 wt.% CuO dielectric properties of Q × f = 9000 GHz, ɛ_r = 80 and τ_f = 0 ppm/K (at 300 K) were obtained at a sintering temperature of 915 °C.     

Dielectric and Magnetic properties of (1 − x)BiFeO3–xBa0.8Sr0.2TiO3 ceramics

The polycrystalline samples of (1 ? x)BiFeO₃–xBa_0.8Sr_0.2TiO₃ (x = 0, 0.1, 0.2, 0.25, 0.3, 0.4 and x = 1) were prepared by the conventional solid state reaction method. The effect of substitution in BiFeO₃ by Ba_0.8Sr_0.2TiO₃ on the structural, dielectric and magnetic properties was investigated. X-ray diffraction study showed that these compounds crystallized at room temperature in the rhombohedral distorted perovskite structure for x ≤ 0.3 and in cubic one for x = 0.4. As Ba_0.8Sr_0.2TiO₃ content increases, the dielectric permittivity increases. This work suggests also that the Ba_0.8Sr_0.2TiO₃ substitution can enhance the magnetic response at room temperature. A remanent magnetization M_r and a coercive magnetic field H_C of about 0.971 emu/g and 2.616 kOe, respectively were obtained in specimen with composition x = 0.1 at room temperature.     

Structural,dielectric, and piezoelectric properties of fine-grained NBT–BT0.11 ceramic derived from gel precursor

(Na_1/2Bi_1/2)TiO₃ doped in situ with 11 mol% BaTiO₃ (NBT–BT_0.11) powders were synthesized by a sol–gel method, and the electrical properties of the resulting ceramics were investigated. The powders consisting of uniform and fine preliminary particles of about 50 nm were prepared by calcining the gel precursor at 700 °C. (Na_1/2Bi_1/2)_0.89Ba_0.11TiO₃ ceramics, sintered at temperatures up to 1150 °C have a rhombohedral symmetry, while the ceramic sintered at 1200 °C exhibits a tetragonal crystalline structure. The ceramics show high dielectric constant (?_r ～ 5456), dielectric loss of 0.02, depolarization temperature T_d ～ 110 °C and temperature corresponding to the maximum value of dielectric constant T_m ～ 262 °C. The dielectric constant (?₃₃) and the piezoelectric constant (d₃₃) attain the maximum values of 924 and 13 pC/N, respectively, while the electromechanical coupling factor (k_p) value is 0.035. The NBT–BT_0.11 ceramics derived from sol–gel present high mechanical quality factor (Q_m ～ 860). The dielectric and piezoelectric properties values of NBT–BT_0.11 ceramics derived from sol–gel are smaller than those of samples produced by the conventional solid state reaction method, due to the grains size and oxygen vacancies that generate dipolar defects.     

Structure stability and microwave dielectric properties of double perovskite ceramics – Ba2Mg1−xCaxWO6 (0.0 ≤ x ≤ 0.15)

The structure stability of double perovskite ceramics – Ba₂Mg_1?xCa_xWO₆ (0.0 ≤ x ≤ 0.15) has been studied by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Raman spectrometry in this paper. The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 8–11 GHz. The results show that small amount of Ca substitution for Mg increases the Mg/CaO bond strength, and hence the stability of the double perovskite. But it cannot completely suppress the decomposition of Ba₂Mg_1?xCa_xWO₆ at high temperature. Although space group Fm?3m is adopted for all compositions, nonrandom distribution of Ca²⁺ and Mg²⁺ on 4b-site within the short range scale is observed due to their large cation size difference. Small level doping of Ca (x ≤ 0.1) increases the dielectric permittivity monotonically, but does not affect the Q × f value greatly. As expected, the substitution of Ca tuned the temperature coefficient of resonant frequency (τ_f value) from negative to positive value. Excellent combined microwave dielectric properties with ?_r = 20.8, Q × f = 120,729 GHz, and τ_f = 0 ppm/°C could be obtained for x = 0.1 composition. However the Q × f value degrades considerably when the sample was stored under ambient conditions for a long time.     

Synthesis,dielectric and relaxation behavior of lead free NBT–BT ceramics

The 0.94(Na_0.5Bi_0.5TiO₃)–0.06BaTiO₃ ceramics have been prepared by the conventional solid state reaction method. Structural analysis of the prepared ceramic was made by means of room temperature XRD, FT-IR and Raman spectra. The formation of perovskite structure is confirmed by XRD and Raman studies. The dependence of dielectric constant on temperature for various frequencies (100 Hz–1.2 MHz) has been determined. The diffuse transition is observed in the variation of dielectric constant and it provides evidence for the relaxor characteristics. The relaxation mechanism of the prepared ceramic is also discussed in detail by using Debye, V–F and Power law relations and the suitable model was predicted by means of goodness of parameter. This is the first time the relaxation process is discussed for the lead free system to the best of our knowledge. High piezoelectric properties with d₃₃=206 pC/N are observed in the present system.     

Relaxor behavior and ferroelectric properties of a new Ba4SmFe0.5Nb9.5O30 tungsten bronze ceramic

Unfilled tungsten bronze ceramics with a composition of Ba₄SmFe_0.5Nb_9.5O₃₀ were prepared by the conventional solid-state sintering method. The phase, microstructure, dielectric and ferroelectric properties were studied. Room temperature XRD results indicated that the ceramic occurs in the tetragonal space group P4bm phase with cell parameters of a=b=12.4712(2) Å and c=3.9430(2) Å. The temperature-dependent dielectric properties, XRD data and Raman spectra data indicated that BSFN ceramics exhibit no phase changes from 35 °C to 450 °C. Fitting of a Vogel-Fulcher relationship with an activated energy E_a of 0.11 eV indicates an unambiguous dielectric relaxor state near room temperature. Furthermore, the BSFN ceramics exhibited residual polarization and coercive field of 3.45 µC/cm² and 24.65 kV/cm, respectively.     

Improved photoluminescence,thermal stability and temperature sensing performances of K+ incorporated perovskite BaTiO3:Eu3+ red emitting phosphors

K⁺ ions incorporated perovskite Ba_(1−x)TiO₃:x Eu³⁺ red emitting phosphors synthesized via facile solid -state reaction method has been investigated in the current study. The photoluminescence and decay time behavior of Ba_(1−x−y)TiO₃:x Eu³⁺,yK⁺ phosphors are investigated as a function of Eu³⁺, K⁺ concentration and temperature. An intense and sharp emission peak at 615 nm was exhibited by the phosphors upon excitation at 397 nm (⁷F₀→⁵L₆). It can be credited to the hypersensitive electric dipole transition ⁵D₀→⁷F₂, which confirms that Eu³⁺ ions are located at non-centrosymmetric site of the host. The incorporation of K⁺ ions in optimized Ba_0.95TiO₃:0.05 Eu³⁺ phosphor resulted in a remarkable enhancement of photoluminescence intensity by 2.33 times as compared to bare one. The Ba_0.89TiO₃:0.05 Eu³⁺, 0.06 K⁺ phosphors were found to observe good temperature sensing along with adequate thermal stability even at 427 K. Furthermore, the photometric parameters have been also studied which are strongly facilitate the prepared ceramic samples as suitable for potential application in lighting.     

Improvement of structural and superconducting properties of Bi-2212 textured rods by substituting sodium

In this paper, the physical and superconducting properties of Bi₂Sr₂Ca_1−xNa_xCu₂O_8+δ with x=0.0, 0.05, 0.075, 0.1, and 0.20 textured superconducting fiber rods prepared by a laser floating zone (LFZ) technique were studied. The effects of Na⁺¹ substitution for Ca²⁺ have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transport measurements, dc-magnetization, magnetic hysteresis and magnetic critical current density. The powder XRD patterns of samples have indicated that Bi-2212 phase is the major one, independently of Na content. The best critical temperature, T_C, has been found as 93.3 K from M–T data for the sample with 0.075 Na substitution. The maximum magnetic J_C value has been calculated as 1.35×10⁵ A/cm² at 10 K for the 0.10 Na sample. The maximum transport critical current density has directly been measured as 1.3×10³ A/cm² at 77 K for the 0.05Na sample.