Search Results (39)

The (1−x)Ba_0.96Ca_0.04TiO₃−xBi(Li_1/3Zr_2/3)O₃ (x = 0.03–0.15) ceramics were fabricated via the traditional solid reaction method. Characterization results revealed that each component exhibited a pure perovskite structure, and the average grain size significantly diminishes with increasing x. The (1−x)Ba_0.96Ca_0.04TiO₃−xBi(Li_1/3Zr_2/3)O₃ ceramics exhibited prominent relaxor ferroelectric behavior, whose characteristic narrow hysteresis loops effectively enhanced the energy storage performance of the material. Most importantly, the composition with x = 0.10 demonstrated exceptional energy storage properties at 150 kV/cm, achieving a high recoverable energy storage density (W_rec = 1.91 J/cm³) and excellent energy efficiency (η = 90.87%). Under the equivalent electric field, this composition also displayed a superior pulsed discharge performance, including a high current density (871 A/cm²), a high power density (67.3 MW/cm³), an ultrafast discharge time (t_0.9 = 109 ns), and a discharged energy density of 1.47 J/cm³. These results demonstrate that the (1−x)Ba_0.96Ca_0.04TiO₃−xBi(Li_1/3Zr_2/3)O₃ ceramic system establishes a promising design paradigm for the creation and refinement of next-generation dielectrics for pulse power applications. Full article

The influence of processing procedures and microstructural features on the functional properties of relaxor ferroelectric ceramics are of fundamental interest and directly relevant to their applications in dielectric capacitors and electromechanical sensors/actuators. In the present work, solid solutions of 0.65(K_0.5Bi_0.5)TiO₃-0.35(Ba_0.94Ca_0.06)(Ti_0.93Zr_0.07)O₃ (0.65KBT-0.35BCZT) were processed by solid-state reaction using two different procedures, distinguished in terms of mixed or separate calcination of the KBT and BCZT components and leading to homogeneous or core-shell-type relaxor ferroelectric ceramics, respectively. Systematic research was conducted on the impact of the processing techniques and air-quenching procedures on the structure and ferroelectric and electromechanical properties. Higher remanent polarization of the separately calcined materials was ascribed to the ferroelectric nature of the core regions, along with the non-ergodic relaxor ferroelectric response in the shell, which was enhanced by the quenching process. It was also demonstrated that the thermal depolarization temperature increased significantly after quenching, from ~100 to ~160 °C for the separately calcined ceramic, and from ~50 to ~130 °C for the mixed material; moreover, these effects are linked to notable improvements in the ferroelectric tetragonal phase content by air-quenching. Full article

Relaxor ferroelectric film capacitors exhibit high power density with ultra-fast charge and discharge rates, making them highly advantageous for consumer electronics and advanced pulse power supplies. The Aurivillius-phase bismuth layered ferroelectric films can effectively achieve a high breakdown electric field due to their unique insulating layer ((Bi₂O₂)²⁺ layer)). However, designing and fabricating Aurivillius-phase bismuth layer relaxor ferroelectric films with optimal energy storage characteristics is challenging due to their inherently stable ferroelectric properties. In this work, lead-free CaBi_4-xLa_xTi₄O₁₅ films were synthesized using the sol–gel technique and a weakly coupled relaxor design. On one hand, the introduction of La³⁺ ions weaken the dipole–dipole interactions, thereby enhancing the relaxor behavior. Alternatively, the expansion of grain size is restricted to enhance the number of grain boundaries, which possess improved insulating properties. This leads to a higher breakdown electric field. The results indicate that CaBi_4-xLa_xTi₄O₁₅ (x = 1.0) films exhibit excellent recoverable energy storage density (70 J/cm³) and high energy efficiency (73%). Moreover, the film exhibited good temperature stability and frequency stability. This study not only identifies a promising material for dielectric film capacitors but also demonstrates that the energy storage capabilities of Aurivillius-phase bismuth layer ferroelectric films can be effectively modulated through a design incorporating weakly coupled relaxor characteristics. Full article

For the first time, density functional theory (DFT) calculations have been employed for the measurement of the structural, mechanical, optical, and electrical properties of a bismuth-layered structure ferroelectrics (BLSFs) family member possessing an orthorhombic structure with Cmc2₁ space group. Based on the exchange–correlation approximation, our calculations show that Pb₂Bi₄Ti₅O₁₈ possesses an indirect band gap, while the materials X₂Bi₄Ti₅O₁₈ (X = Ba, Ca, and Sr) demonstrate direct band gap, where the estimated density functional fundamental band gap values lie between 1.84 to 2.33 eV, which are ideal for photovoltaic applications. The optical performance of these materials has been investigated by tuning the band gaps. The materials demonstrated outstanding optical characteristics, such as high absorption coefficients and low reflection. They exhibited impressive absorption coefficient (α = 10⁵ cm⁻¹) throughout a broad energy range, especially in the visible spectrum (10⁵ cm⁻¹ region). The findings show that the compounds demonstrate lower reflectivity in the visible and UV regions, making them suitable for single-junction photovoltaic cells and optoelectronic applications. The Voigt–Reuss–Hill averaging technique has been employed to derive elastic parameters like bulk modulus (B), Young’s modulus, shear modulus (G), the Pugh ratio (B/G) and the Frantesvich ratio (G/B) at 0.1 GPa. The mechanical stability of the compounds was analyzed using the Born stability criteria. Pugh’s ratio and Frantesvich’s ratio show that all the compounds are ductile, making them ideal for flexible optical applications. Full article

A bottleneck characterized by high strain and low hysteresis has constantly existed in the design process of piezoelectric actuators. In order to solve the problem that actuator materials cannot simultaneously exhibit large strain and low hysteresis under relatively high electric fields, Nb⁵⁺-doped 0.975(Ba_0.85Ca_0.15)[(Zr_0.1Ti_0.9)_0.999Nb_0.001]O₃-0.025(Bi_0.5Na_0.5)ZrO₃ (BCZTNb_0.001-0.025BiNZ) ceramic thick films were prepared by a film scraping process combined with a solid-state twin crystal method, and the influence of sintering temperature was studied systematically. All BCZTNb_0.001-0.025BiNZ ceramic thick films sintered at different sintering temperatures have a pure perovskite structure with multiphase coexistence, dense microstructure and typical dielectric relaxation behavior. The conduction mechanism of all samples at high temperatures is dominated by oxygen vacancies confirmed by linear fitting using the Arrhenius law. As the sintering temperature elevates, the grain size increases, inducing the improvement of dielectric, ferroelectric and field-induced strain performance. The 1325 °C sintered BCZTNb_0.001-0.025BiNZ ceramic thick film has the lowest hysteresis (1.34%) and relatively large unipolar strain (0.104%) at 60 kV/cm, showing relatively large strain and nearly zero strain hysteresis compared with most previously reported lead-free piezoelectric ceramics and presenting favorable application prospects in the actuator field. Full article

Over the past decades, Na_0.5Bi_0.5TiO₃ (NBT)-based ceramics have received increasing attention in energy storage applications due to their high power density and relatively large maximum polarization. However, their high remnant polarization (P_r) and low breakdown field strength are detrimental for their practical applications. In this paper, a new solid solution (1−x)Na_0.5Bi_0.5TiO₃–xCaHfO₃ (x = 0.04, 0.08, 0.12, 0.16) was constructed by introducing CaHfO₃ into NBT, and thus was prepared using a conventional solid-state reaction. With the addition of CaHfO_3, the disorder of the structure increased, A-site vacancies formed, and thus oxygen vacancies were suppressed due to the replacement of the Na⁺ by Ca²⁺, resulting in the enhanced relaxation behavior and the reduced P_r, the refined grain, and improved breakdown strength. Furthermore, an optimal recoverable energy storage density (W_rec) of 1.2 J/cm³ was achieved in 0.92Na_0.5Bi_0.5TiO₃–0.08CaHfO₃ ceramics under the breakdown strength of 140 kV/cm, which is mainly attributed to the resultant defect of Na⁺ vacancy_. Full article

The study of noble metal minerals of the Ural–Alaskan-type (UA-type) complexes has been traditionally focused on their platinum-bearing dunites and chromitites, while clinopyroxenites have been poorly considered. In this study, we report the first detailed data on the noble metal mineral assemblage in clinopyroxenites of the Kachkanar intrusion, which is a part of a UA-type complex and is renowned for its huge Ti-magnetite deposits. High concentrations of Pd, Au and Ag are closely linked to Cu-sulfide mineralization in amphibole clinopyroxenites, in which they form Pd-Ag-Au minerals: keithconnite Pd_3−xTe, sopcheite Ag₄Pd₃Te₄, stutzite Ag_5−xTe₃, hessite Ag₂Te, merenskyite PdTe, kotulskite Pd(Te,Bi), temagamite Pd₃HgTe, atheneite (Pd,Hg)₃As, potarite PdHg, electrum AuAg and Hg-bearing native silver. Among those, six mineral phases are first reported for clinopyroxenites of the Ural platinum belt. Our evidence supports a petrological model, suggesting that during fractionation of high-Ca primitive magmas at high oxygen fugacity, Pt, Os, Ir, Ru and Rh accumulate in early olivine–chromite cumulates, while Pd, Au and Ag reside in the melt until sulfide saturation occurs and then concentrate in sulfide mineralization. Subsequently, this sulfide mineralization is likely affected by cumulate degassing, which results in a partial resorption of the sulfides and Pd, Au and Ag remobilization by fluid. Second-stage concentration of the sulfides and the chalcophile noble metals in the amphibole-rich rocks may occur when H₂O from the fluid reacts with pyroxenes to form amphiboles, and the fluid becomes oversaturated with sulfides and chalcophile elements. Full article

Class II ceramics are a material with high permittivity but low reliability of their capacitance and bias voltage due to high the temperature sensitivity of their dielectric permittivity. In this work, a BST-based (Ba_0.9−xSr_xCa_0.1)TiO₃·0.03(Bi₂O₃·3TiO₂) (x = 0.2, 0.25, 0.3, 0.35, 0.4) composition with Y5U characteristics was investigated through compositional control to develop high-permittivity and voltage-stable ceramic compositions. Sr doping can increase the breakdown strength (E_b) but decreases the Curie temperature (T_c). The composition at x = 0.3 can obtain optimal comprehensive electrical properties, with high permittivity of 4206, low dielectric loss of ~0.009, and moderate breakdown strength (E_b) of 77.6 kV/cm, which meets Y5U specifications. Typically, a low bias-voltage dependence of capacitance is confirmed with a variation rate of 7.64% under 20 kV/cm. This strategy provides a promising candidate for high-permittivity Class II ceramic dielectrics that can be used in this field. Full article

A novel high-entropy perovskite powder with the composition Bi_0.2K_0.2Ba_0.2Sr_0.2Ca_0.2TiO₃ was successfully synthesized using a modified Pechini method. The precursor powder underwent characterization through Fourier Transform Infrared Spectroscopy and thermal analysis. The resultant Bi_0.2K_0.2Ba_0.2Sr_0.2Ca_0.2TiO₃ powder, obtained post-calcination at 900 °C, was further examined using a variety of techniques including X-ray diffraction, Raman spectroscopy, X-ray fluorescence, scanning electron microscopy, and transmission electron microscopy. Ceramic samples were fabricated by conventional sintering at various temperatures (900, 950, and 1000 °C). The structure, microstructure, and dielectric properties of these ceramics were subsequently analyzed and discussed. The ceramics exhibited a two-phase composition comprising cubic and tetragonal perovskites. The grain size was observed to increase from 35 to 50 nm, contingent on the sintering temperature. All ceramic samples demonstrated relaxor behavior with a dielectric maximum that became more flattened and shifted towards lower temperatures as the grain size decreased. Full article

Low-temperature lead-free silver pastes deserve thorough investigation for sustainable development and application of MgTiO₃ ceramics in electronic devices. In this study, a series of Bi₂O₃-B₂O₃-ZnO-SiO₂-Al₂O₃-CaO glasses with suitable softening temperatures were prepared via melt quenching using a type of micrometer silver powder formed by silver nanoparticle aggregates. The composite pastes containing silver powder, Bi₂O₃ glass powder and an organic vehicle were then screen-printed. The effects of glass powder concentration and sintering temperature on the microstructure of the surface interface were also investigated. The results showed that the silver paste for microwave dielectric ceramic filters (MgTiO₃) possessed good electrical conductivity (2.28 mΩ/□) and high adhesion (43.46 N/mm²) after medium temperature (670 °C) sintering. Thus, this glass powder has great application potential in non-toxic lead-free silver pastes for metallization of MgTiO₃ substrates. Full article

The Yanshan intraplate tectonic belt is a tectonic-active area in the central part of the North China Craton that has undergone long-term orogenic evolution. Detailed studies on magmatic activity and metamorphism of this belt are significant for restoring its orogenic thermal evolution process. The Fangshan pluton in the Zhoukoudian area within this tectonic belt is a product of the late Mesozoic Yanshan event. However, there is a lack of detailed research on the metamorphic evolution history of the ancient terrane surrounding the Fangshan pluton subjected to contact thermal metamorphism. To further constrain the metamorphic P–T evolution of contact metamorphism associated with the Fangshan pluton, we collected rock samples in the andalusite–biotite contact metamorphic zone of the Fangshan pluton, and conducted petrographic investigations, geochemical and mineral composition analysis, and phase equilibrium modeling. The phase equilibrium modeling in the MnO–Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–O system indicates that the peak mineral assemblages of andalusite–biotite schists are pl + q + mu + bi + and ± kfs + ilm + mt, formed at 550 to 610 °C, 1 to 3.5 kbar, and the peak mineral assemblage of garnet–andalusite–cordierite–biotite schists is gt + pl + q + bi + and + cord + ilm + mt, formed at 580 to 620 °C, 1.5 to 2.1 kbar. Therefore, we believe that the rocks in the andalusite biotite contact metamorphic zone of the Fangshan pluton underwent low pressure and medium temperature metamorphism, with the peak metamorphic conditions of about 550–610 °C, <3.5 kbar. The results show that the rocks in contact with the thermal metamorphic zone were rapidly heated by the heat released by the Fangshan pluton, and after reaching the peak metamorphic temperature, they were cooled down simultaneously with the cooling of the rock mass, defined in a nearly isobaric P–T trajectory. Full article

NO has caused many serious environmental problems and even seriously threatened human health. The development of a cheap and efficient method to remove NO from the air has become an urgent need. In this paper, a novel nanocomposite metal-semiconductor photocatalyst Bi-Bi₂Ti₂O₇/CaTiO₃ was prepared. Compared to the original Bi₂Ti₂O₇/CaTiO₃, the modification by the metal Bi increased its photocatalytic activity from 25% to 64% under visible light irradiation. The improved photoactivity owns to the SPR effect and the electron capture effect of Bi metals in metal-semiconductor loaded systems improving the separation efficiency of electron-hole pairs and significantly improving the light absorption capacity of the composite photocatalyst. The capture experiment of active species showed that •OH, •O₂⁻, h⁺ and e⁻ are the main active species in the photocatalytic conversion of NO. This work provides new insights into the conformational relationships of Ti-based photocatalysts for NO removal. Full article

Compared to batteries and electrochemical capacitors, dielectric capacitors are widely studied because of their huge advantages in terms of charging/discharging speed and power density. In this work, high-entropy (Bi_0.2Na_0.2Sr_0.2Ba_0.2Ca_0.2)TiO₃ lead-free relaxor-ferroelectric ceramics were prepared by both conventional sintering (CS) and spark plasma sintering (SPS). The results showed that the ceramic prepared by SPS obtained a high energy storage density of 6.66 J/cm³ and a satisfied energy storage efficiency of 77.2% under an electric field of 430 kV/cm. This is directly related to the high density, fine grains, number of oxygen vacancies, and composition uniformity of the SPS samples. This study provides a new path for the preparation of high-entropy dielectric energy storage ceramics with high energy storage properties. Full article

This study aimed to present the differences in the corrosion properties and protective ability of two bi-layer systems obtained on low-carbon steel in a model corrosive medium of 5% NaCl solution. These newly developed systems consist of Zn-Co (3 wt.%) or Zn-Ni (10 wt.%) alloy coatings as under-layers and a very thin TiO₂ sol-gel film as a top-layer. Scanning electron microscopy (SEM) is used for characterization of the surface morphology of the samples indicating that some quantitative differences appear as a result of the different composition of both zinc alloys. Surface topography is investigated by means of atomic force microscopy (AFM), and the hydrophobic properties are studied by contact angle (CA) measurements. These investigations demonstrate that both sample types possess grain nanometric surface morphology and that the contact angle decreases very slightly. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) are used for characterization of the chemical composition and electronic structure of the samples. The roughness R_q of the Zn-Ni/TiO₂ is 49.5 nm, while for Zn-Co/TiO₂, the R_q value is 53.4 nm. The water contact angels are 93.2 and 95.5 for the Zn-Ni/TiO₂ and Zn-Co/TiO₂ systems, respectively. These investigations also show that the co-deposition of Zn and Ni forms a coating consisting entirely of Ni₂Zn₁₁, while the other alloy contains Zn, Co and the intermetallic compound CoZn₁₃. The corrosion resistance and protective ability are estimated by potentiodynamic polarization (PDP) curves, as well as polarization resistance (R_p) measurements for a prolonged test period (35 days). The results obtained are compared with the corrosion characteristics of ordinary zinc coating with an equal thickness. The experimental data presents the positive influence of the newly developed systems on the enhanced protective properties of low-carbon steel in a test environment causing a localized corrosion—lower corrosion current density of about one magnitude of order (~10⁻⁶ A.cm⁻² for both systems and ~10⁻⁵ A.cm⁻² for Zn) and an enhanced protective ability after 35 days (~10,000–17,000 ohms for the systems and ~900 ohms for Zn). Full article

Bismuth-deficient sodium bismuth titanate (nominal Na_0.5Bi_0.49TiO_2.985, NB_0.49T) presents high oxide ion conductivity, which makes it a potential electrolyte material for intermediate-temperature solid oxide fuel cells. Acceptor doping has been proven an effective approach to enhance the bulk conductivity (σ_b) of NB_0.49T. Here, divalent Ca²⁺ ions were selected to partially replace Bi³⁺ on the A-site of NB_0.49T, and the temperature and composition dependences of σ_b and permittivity were investigated. Results showed that Ca²⁺ doping was effective for enhancing σ_b of NB_0.49T by creating oxygen vacancies. The highest σ_b (0.006 S·cm⁻¹ at 500 °C) was achieved by 2% Ca²⁺ doping. Further increase in the doping level decreased σ_b, which was more pronounced at temperatures below ~350 °C. Most importantly, Ca doping increased the temperature at which the activation energy for bulk conduction changed from ~0.80 eV (at low temperatures) to ~0.40 eV (at high temperatures), and reduced the temperature dependence of permittivity of NB_0.49T. Results from the average structural parameters and the local defect associates are discussed. The findings of this work are helpful for understanding the defect and conduction mechanisms for acceptor-doped NB_0.49T, and are also useful for developing NBT-based dielectrics with temperature-independent permittivity. Full article