Oxide Ceramics Research Articles

Influence of atmosphere-induction and synergistic effect on the dielectric property of rutile-type (Ge0.2Mn0.2Ti0.2Sn0.2Mo0.2)O2 high-entropy oxides

A new high-entropy oxide, (Ge0.2Mn0.2Ti0.2Sn0.2Mo0.2)O2 with rutile structure, was successfully synthesized using solid-state reaction method. The phase structure of the ceramic samples prepared forming a range of binary to quinary phase with increasing entropy were investigated, and the effects of atmosphere-induction and high-entropy synergistic behavior on the dielectric performance were studied. As the type of the cations increases, the temperature required to form a single rutile structure gradually decreases, while the dielectric properties of the ceramics gradually improved. The dielectric constant of the (Ge0.2Mn0.2Ti0.2Sn0.2Mo0.2)O2 high-entropy oxide ceramics sintered in the nitrogen atmosphere at 1350°C is nearly 20 times higher of the ceramics sintered in the air. This significant enhancement can be attributed to the occurrence of two rutile structures and the generation of excessive oxygen vacancies as a result of high-entropy synergistic behavior under the nitrogen sintering atmosphere.

Dislocation Density-Mediated Functionality in Single-Crystal BaTiO3.

Unlike metals where dislocations carry strain singularity but no charge, dislocations in oxide ceramics are characterized by both a strain field and a local charge with a compensating charge envelope. Oxide ceramics with their deliberate engineering and manipulation are pivotal in numerous modern technologies such as semiconductors, superconductors, solar cells, and ferroics. Dislocations facilitate plastic deformation in metals and lead to a monotonous increase in the strength of metallic materials in accordance with the widely recognized Taylor hardening law. However, achieving the objective of tailoring the functionality of oxide ceramics by dislocation density still remains elusive. Here a strategy to imprint dislocations with {100}<100> slip systems and a tenfold change in dislocation density of BaTiO3 single crystals using high-temperature uniaxial compression are reported. Through a dislocation density-based approach, dielectric permittivity, converse piezoelectric coefficient, and alternating current conductivity are tailored, exhibiting a peak at medium dislocation density. Combined with phase-field simulations and domain wall potential energy analyses, the dislocation-density-based design in bulk ferroelectrics is mechanistically rationalized. These findings may provide a new dimension for employing plastic strain engineering to tune the electrical properties of ferroics, potentially paving the way for advancing dislocation technology in functional ceramics.

Development of corrosion-resistant and bioactive ceramic-polymer hybrid coating over Zn-1Mg biodegradable implant material

Zn is an excellent choice for temporary orthopaedic implants since its degradation rate is better than Mg- or Fe-based biodegradable metals and closely matches the healing pace of fractured bones. The current work focuses on modifying the Zn-1Mg surface to slow its corrosion, synchronising it even more closely with patients' recovery phases while enhancing its surface bioactivity for seamless osteointegration. An oxide coating with porous morphology was initially created on Zn-1Mg through plasma electrolytic oxidation (PEO). Subsequently, the PEO-coating pores were sealed with a polymer matrix of polycaprolactone (PCL) to improve corrosion resistance. Finally, PEO-pores were filled with hydroxyapatite (HA) incorporated PCL to enhance corrosion resistance further and impart bioactivity. Raman and X-ray diffraction (XRD) analysis revealed that the phases in the coatings are mainly ZnO, HA, and polymer PCL. Field emission scanning electron microscopy (FESEM) images revealed the porous nature of the PEO coatings, and the PEO coatings with polymer top coats showcased the sealing of the PEO pores. Energy dispersive spectroscopy (EDS) spectra confirmed the species from HA and PCL on the surface of PEO-coated Zn-1Mg. The coatings PEO and PEO with polymer top coating transformed the hydrophobic Zn-1Mg surface into a hydrophilic one, optimising surface roughness for cell adhesion and nutrient absorption. The ceramic oxide layer introduced by the PEO-coating significantly enhanced corrosion resistance, a benefit further amplified by post-processing with the PCL-based matrix. The inclusion of HA into PCL transformed the coated sample into a highly bioactive surface. Consequently, the HA-incorporated PCL top-coated PEO sample displayed superior cell attachment and viability. These findings indicate that ceramic-polymer hybrid coating filled with HA (the inorganic component found in bone) is an optimal choice for temporary orthopaedic implant scenarios.

Digital light processing of sodium-beta-alumina ceramic electrolytes

Solid-state electrolyte structures using sodium-beta-alumina oxide ceramics, have been fabricated for the first time, using digital light processing; a vat photopolymerisation additive manufacturing process. Green bodies were shaped using a high solids loading ceramic resin of 46 vol.% (72 wt.%) and were then thermally binder removed and sintered. Conventionally sintered at 1580 °C for 5 min, additively manufactured electrolyte test samples exhibited an ionic conductivity of σ = 0.18 S·cm-1 at 300 °C, an activation energy of conduction Ea = 0.38 eV and density of ρ = 3.19 ± 0.01 g·cm-3 (relative density 98%) along with a retention of 91 wt.% of the desirable β’’ rhombohedral phase. Results suggest that digital light processing of sodium polyaluminates is a very promising approach for manufacturing geometrically complex monolithic ceramic electrolytes for future applications in electrochemical energy storage.

Inducing Polar Phase in Poly(Vinylidene Fluoride) with a Molecular Ferroelectric Copper(II) Complex for Piezoelectric Energy Harvesting

AbstractPiezoelectric nanogenerators (PENGs), the current pathway to sustainable energy harvesting, are mostly comprised of bulk oxide ceramics which are toxic, rigid, and costly to synthesize. A suitable alternative to them is flexible polar polymers like polyvinylidene fluoride (PVDF), but stabilizing its polar phase is also a daunting task. all these aforementioned issues by employing a biocompatible have been solved, above‐room‐temperature (Tc &gt; 390 K) ferroelectric discrete molecular complex [Cu(L‐His)(bpy)]ClO4.1.5H2O (Cu‐FE) which is not only suitable for piezoelectric energy harvesting due to its large values of piezoelectric co‐efficient (d33 = 17 pm V−1) but also is capable of imparting polar β‐phase in PVDF via hydrogen bonding interactions under mild condition (60 °C). Among the PENG devices prepared with the composite films of PVDF and various weight % (w/V) compositions of Cu‐FE, the highest output voltage of 8 V (peak to peak) has been obtained, a power density of 4 µW cm−2, and an output current of 3 µA from the 1 wt.% composite film. The fabricated PENG device also exhibits swift capacitor charging in 40 s, and acts as an excellent pressure sensor, with exceptional sensitivity to low pressures (7 kPa), giving an output of 0.4 V.

Silver-promoted ceramic conversion treatment of Ti6Al4V alloy and its mechanical performance

In this paper, the Ti6Al4V alloy surface was modified via ceramic conversion treatment (CCT) with or without a pre-deposited silver layer. After characterizing the surface morphologies, microstructure and phase constituents of the ceramic oxide layer formed at 620 °C, we investigated the surface hardness and the cross-sectional nano-hardness profile under the oxide layer. The static load-bearing capacity of the oxide layers was examined by applying discrete loads via a Vickers indenter and observing the indentations. A scratch test was used to evaluate the load-bearing capacity and the adhesion/cohesion of the oxide layers. The wettability of the surface changed due to the incorporation of silver and the change of surface morphology. Reciprocating friction and wear test was used to assess the tribological properties. Small and dispersed silver nanoparticles and clusters were found in the oxide layer of the Ag pre-deposited Ti6Al4V samples, and they had much better tribological properties in terms of reduced coefficient of friction and wear volume. With the assistance of silver, the efficiency of the CCT was significantly improved.

Assessment of Artificial Anisotropic Materials for Transverse Thermoelectric Generators

By alternately stacking layers of two materials that differ in their Seebeck coefficient and electrical and thermal conductivity, a composite material with artificial anisotropy of thermal and electrical transport properties is formed. Due to the transverse Seebeck effect, a thermoelectric (TE) voltage is generated perpendicular to a temperature gradient ΔT, that is applied at a certain angle φ with respect to the stacked layers (0° &lt; φ &lt; 90°). The TE properties of layered artificial anisotropic materials are described analytically using existing concepts and extending the available definitions to develop a consistent image of anisotropic media for TE energy generation. Based on these analytical descriptions, the TE performance of ceramic oxide–metal composites and transverse TE generators (TTEG) made of them are numerically calculated and presented in contour plots. These so‐called micro‐ and macro‐Babin plots map the influence of internal geometric parameters, i.e., the layer thickness ratio and the angle φ of the applied temperature gradient with respect to the stacked layers. Based on these diagrams, the optimal TTEG geometry can be narrowed down in a simple and fast way. In addition, the diagrams are used for a material screening to evaluate the suitability of different oxide ceramics for use in a TTEG.

Enhanced 3D printing and crack control in melt-grown eutectic ceramic composites with high-entropy alloy doping

As a 3D printing method, laser powder bed fusion (LPBF) technology has been extensively proven to offer significant advantages in fabricating complex structured specimens, achieving ultra-fine microstructures, and enhancing performances. In the domain of manufacturing melt-grown oxide ceramics, it encounters substantial challenges in suppressing crack defects during the rapid solidification process. The strategic integration of high entropy alloys (HEA), leveraging the significant ductility and toughness into ceramic powders represents a major innovation in overcoming the obstacles. The ingenious doping of HEA particles preserves the eutectic microstructures of the Al2O3/GdAlO3(GAP)/ZrO2 ceramic composite. The high damage tolerance of the HEA alloy under high strain rates enables the absorption of crack energy and alleviation of internal stresses during LPBF, effectively reducing crack initiation and growth. Due to increased curvature forces and intense Marangoni convection at the top of the molt pool, particle collision intensifies, leading to the tendency of HEA particles to agglomerate at the upper part of the molt pool. However, this phenomenon can be effectively alleviated in the remelting process of subsequent layer deposition. Furthermore, a portion of the HEA particles partially dissolves and sinks into the molten pool, acting as heterogeneous nucleation particles, inducing the formation of equiaxed eutectic and leading primary phase nucleation. Some HEA particles diffuse into the lamellar ternary eutectic structures, further promoting the refinement of eutectic microstructures due to increased undercooling. The innovative doping of HEA particles has effectively facilitated the fabrication of turbine-structured, conical, and cylindrical ternary eutectic ceramic composite specimens with diameters of about 70 mm, demonstrating significant developmental potential in the field of ceramic composite manufacturing.

Plasma electrolytic oxidation based superhydrophobic coatings: fabrication, rudiments, and constraints

AbstractPlasma electrolytic oxidation (PEO) has evolved as a versatile technique for depositing low surface energy organic-based materials useful in fabricating superhydrophobic (SHP) coating materials. The application of silane-based polymeric organic materials atop PEO coating is the most common method to prepare coating materials for wetting and corrosion protection. Herein, the latest developments in PEO-based coatings employing polymeric/silane-based organic materials with the inclusion of ceramic oxides are reviewed, with emphasis on the structure, wettability, and corrosion resistance. The relevant and existing fundamental design theories and strategies for fabricating highly efficient SHP PEO coatings are also outlined and discussed. The systemic design of SHP coatings by deposition from organic particle dispersion and their inclusion into PEO-micropore layers, as well as the most important parameters affecting the properties of PEO-assisted SHP-based coatings, are highlighted. Furthermore, the merits and challenges of the PEO-assisted SHP-based coating fabrication are critically evaluated to identify remaining challenges and future research directions.

Flash luminescence, resistive switching and metal-insulator transitions in ceramic oxides

A combination of voltage-induced, reversible OFF-ON resistive switching and electroluminescence is reported in two materials that are both mixed conductors of oxide ions and electron holes. This occurs at high temperatures, 450–700 °C in cubic, fluorite-structured hafnia, YxHf1-xO2-x/2 and at more modest temperatures, 200–300 °C in Ca-doped BiFeO3 with a cubic perovskite structure. In both cases, a small voltage in the range 2–40 V is applied across mm-thick ceramic samples. Both effects are influenced greatly by oxygen exchange with the surrounding atmosphere and involve a combination of electron injection at the cathode, hole injection at the anode and generation of internal pn junctions. There are strong similarities between these effects and flash sintering but without the significant sintering, thermoluminescence and Joule heating that may be observed with flash sintering.

Improvement of plastic deformation property and current carrying capacity of Bi2212 wires through low oxygen partial pressure post-annealing of precursor

The performance of superconducting magnets is greatly dependent on the size and uniformity of the superconducting filaments within the wire. However, in the fabrication of Bi2Sr2CaCu2Ox (Bi2212) wires using ceramic oxide as the superconducting filaments, we face multiple challenges including filament fragility, poor uniformity, and non-smooth Ag/superconductor interfaces. These challenges primarily stem from the significantly lower plastic deformation capability of ceramic oxide powder filaments compared to metal matrices. To address these challenges, this study focuses on the modification of ceramic oxide precursor powders. Through the utilization of low-temperature, low oxygen partial pressure (pO2) heat treatment, we have observed significant changes in the Cu chemical states and lattice parameters within the Bi2212 grains. These alterations have proven to be highly effective in reducing the energy required for grain sliding and, in turn, enhancing the plastic deformation properties of the Bi2212 oxide filament. Furthermore, post-annealing the oxide powder under low pO2 conditions narrows the gap in plastic deformability between the Ag sheath and the oxide filaments, resulting in improved filament uniformity and a smoother Ag/oxide interface in Bi2212 wires. Notably, the Bi2212 grains exhibit an orderly arrangement within the wires. As a result of these improvements, the critical current density (Jc) of the final wires increases by an impressive 70 %. The outcomes of this study are not only crucial for producing Bi2212 magnets with higher magnetic field strength, improved magnetic field uniformity, and enhanced operational stability, but also offer fresh insights and methodologies for advancing the field of superconducting materials.

An atomistic simulation study on ductility of amorphous aluminum oxide

Aluminum oxide is a widely recognized structural ceramic material known for electrical insulation and wear/corrosion resistance. Recent studies have challenged the conventional perception of brittleness by uncovering remarkable plasticity in amorphous aluminum oxides. To further enhance the fracture toughness of aluminum oxides and expand their applications in fields requiring resistance, it is crucial to analyze the factors influencing the tensile deformation process and investigate the underlying origins of ductility. In this study, molecular dynamics simulations were employed to compare the ductility of amorphous aluminum oxides with crystalline aluminum oxides and other amorphous ceramic oxides. Our findings indicate that the degree of crystallinity significantly influences ductility. Moreover, the simulations revealed that amorphous aluminum oxides exhibit the highest total elongation among binary structural ceramic oxides such as TiO2 and SiO2, underscoring the intrinsic plasticity of aluminum oxide. Furthermore, we discovered that aluminum oxides possess a low bond-dissociation energy (EBD) compared to other structural ceramic oxides, leading to a higher occurrence frequency of plastic deformation mechanisms. Based on these observations, low EBD could be proposed as the probable indicator that enables the estimation of ductility of structural amorphous oxides without resorting to complex atomistic simulations. This quantitative criterion, based on an easily accessible material property, provides valuable guidance for predicting the ductility of newly-designed structural ceramic materials.

Preparation and properties of micro-arc oxidation ceramic coatings using machine vision technology

In this paper, a machine vision system is combined with non-immersion micro-arc oxidation (MAO) technology, using color as a visual feature, and automatically determining the MAO process through a self-developed color image segmentation program for HSV channel. The robotic arm accurately regulates the machining position and duration. Dense ceramic oxide coatings of similar quality to the artificially prepared coatings were successfully prepared on aluminum (Al) surface. The surface morphology and elemental composition of the samples were characterized using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The performance of the coatings was tested through thickness tests, hardness tests, and roughness tests. The tribological properties were tested by friction experiments, and its corrosion resistance was tested by electrochemical corrosion tests. The results confirm the effectiveness of a machine vision system for MAO process control, which is capable of preparing high-quality coatings comparable to manual operations. This not only solves the need for precise film formation in different application scenarios, but also provides a more efficient, controllable and innovative solution for the MAO process.

Fracture toughness and slow crack growth behaviour of metal-proton conducting ceramic composites

The fracture toughness and slow crack growth behaviour of two load-bearing metal ceramic components adopted in negatrode-supported electrochemical devices, namely Ni-BCZY27 and Ni-BCZY442, are investigated via double torsion technique.The investigation showed that the two metal-ceramic composites are considerably less sensitive to slow crack growth when compared to oxide ceramics such as stabilized zirconia and alumina, with KI0/KIC equal to approximately 0.8. On the other hand, they also showed lower fracture toughness than Ni-3YSZ, with Ni-BCZY442 and Ni-BCZY27 having a fracture toughness of respectively 1.74 and 3.04 MPa*m1/2 for porosities equal to 25.8% and 19.1% respectively, compared to Ni-3YSZ reported in previous work with similar Ni content and porosity of approximately 30% having a fracture toughness equal to 3.4 MPa*m1/2. Furthermore, the analysis of samples presenting extensive barium depletion indicated fast fracture propagation upon application of loads significantly lower than the critical fracture load.

Fabrication and mechanical properties of multi-principal cation (Mg,Ti,Cr,Zr,Al,Si) mullite ceramic

Milti-principal cation oxide ceramics with excellent mechanical properties for potential applications in coating materials. A Multi-principal cation mullite (MPCM) ceramic is synthesized with MgO, TiO2, Cr2O3, ZrCl2O·8H2O and Al2O3, SiO2 via solid state reaction at 1600 °C. It is determined that 96.9 % of the sample composition is mullite. MPCM ceramic exhibits higher compressive strength (981 ± 19 MPa) and fracture toughness (3.37 ± 0.05 MPa∙m1/2), the compressive strength has raised by 453 MPa, and the added value of solution strengthening (452 MPa) is gained by using solid-solution strengthening theory. The improvement of compressive strength is mainly due to the solution strengthening effect of the four oxides(Mg, Ti, Zr, Cr), and the improvement of fracture toughness is caused by the grain hindrance during crack propagation. Moreover, its application at the high-temperature resistant coating is verified through experimentation. The interfacial binding force, as an important mechanical property index for ceramics, is researched. In this study, pure mullite powder and MPCM powder are coated onto the refractory TaWNbV alloy matrix by slurry coating method, and the interfacial toughness of the two coatings mingled with the matrix is calculated to be 72.9 and 62.6 J·m−2, respectively. The “shrinking cylinder” model is introduced to interpret the oxidative weight gain mechanism of the two coatings.

Effect of different gamma-ray doses on the structural, optical, and radiation shielding features of the YBa2Cu3Oy ceramic oxide

Effect of different gamma-ray doses on the structural, optical, and radiation shielding features of the YBa2Cu3Oy ceramic oxide

Unveiling thermal stresses in RETaO4 (RE = Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er) by first-principles calculations and finite element simulations

Thermal stress (σ) plays a critical role in regulating the stability and durability of thermal barrier coatings (TBCs) during service. However, its measurements are limited due to technical challenges. Here, thermal stresses in RETaO4 (RE = Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er) TBCs have been evaluated by a cross-scale model, integrating first-principles calculations and finite element simulations (FEM). The isobaric heat capacity, thermal expansion coefficients, density, Young's modulus, and Poisson's ratio of RETaO4 as a function of temperature have been determined by the quasi-harmonic approach (QHA) and the quasi-static approach (QSA). Taking these properties as the input data of FEM, the σ of TBCs with RETaO4 as ceramic coatings is estimated. It indicates that the maximum tensile stress exists at the ceramic and thermal-grown oxide coating interface. Notably, TBCs_NdTaO4 exhibits the highest tensile stress, reaching up to 2093 MPa, while TBCs_GdTaO4 has the lowest value at 1880 MPa. Furthermore, the key factors affecting σ are estimated using interpretable machine learning based on the decision tree algorithm. The RETaO4 with small Poisson's ratio, strong electronegativity, small heat capacity, and thermal expansion coefficients is helpful to achieving low σ in TBCs. GdTaO4, YTaO4 and (Ho0.5Er0.5)TaO4 emerge as more favorable options as ceramic layer due to their lower σ in TBCs. This present cross-scale model provides a successful tool for predicting σ and the reverse design of TBCs materials based on low σ in TBCs.

Oxide ceramics of A2M3O12 family with negative and close-to-zero thermal expansion coefficients: Machine learning-based modeling of functional characteristics

Ceramic materials with negative and close-to-zero coefficients of thermal expansion may open the avenue to the technologies that have so far been constrained by physical limitations concerned with the thermal stress or with the insufficient structural stability. Two important characteristics of NTE materials which could be used for the evaluation of the possible area and limitations of the sphere of application for negative thermal expansion (NTE) materials are the linear thermal expansion coefficient and the transition temperature from monoclinic to orthorhombic phase. In this study, the machine learning methods were involved in the analysis of experimental data for NTE oxide ceramics of A2M3O12 family (where M is Mo6+, W6+, V5+ or P5+ while A position may be accommodated by the wide range of metal cations). The models are characterized by the following statistical coefficients: the determination coefficient R2 = 0.81 and prediction error RMSE = 1.170 for linear thermal expansion coefficient; the corresponding parameters for the phase transition temperature were assessed as 0.81 and 82.239, respectively. Ionic conductivity in this class of compounds has been discussed as a tandem functional characteristic, emphasizing the role of anharmonicity in both characteristics. The role of synthesis route and defect chemistry in NTE was analyzed. A conclusion on the expected enhancement of NTE resulted from the intentional introduction of cation A vacancies has been made. The principal possibility of combining two functional characteristics, - an ion conductor and a phase with negative thermal expansion, with some compromise in the characteristics of each of them is substantiated.

Hybrid Organic–Inorganic Materials Prepared by Sol–Gel and Sol–Gel-Coating Method for Biomedical Use: Study and Synthetic Review of Synthesis and Properties

The need to improve the expectancy and quality of life of subjects affected by disabling pathologies that require the replacement or regeneration of tissues or parts of the body has fueled the development of innovative, better-performing materials that are capable of integrating into and being tolerated by body tissues. Materials with these characteristics, i.e., bio-functionality, bio-safety, and biocompatibility, are defined as biomaterials. One of the many methods for producing such materials is the sol–gel technique. This process is mainly used for the preparation of ceramic oxides at low temperatures, through hydrolysis and polycondensation reactions of organometallic compounds within a hydroalcoholic solution. This study is based on a specific type of biomaterial: organic–inorganic hybrids. The aim of this study is to provide an overview of the advantages and disadvantages of the sol–gel technique, as well as describe the preparation and chemical and biological characterization, uses, and future prospects of these biomaterials. In particular, the use of plant drugs as organic components of the hybrid material is the innovation of this manuscript. The biological properties of plant extracts are numerous, and for this reason, they deserve great attention from the scientific community.

Dielectric and Electrical Behavior of Apraseodymium Based Tungsten Bronze Ceramics

AbstractThe ceramic oxide Na2Ba2Pr2W2Ti4Nb4O30 (NBPWTN) is prepared by a mechanical mixed oxide route. The compound formation and the phase are concluded from the x‐ray diffraction pattern taken at room temperature (XRD). The uniform distribution of grains of various sizes with negligible voids is studied from scanning electron micrograph of the sample pellet. The presence of dielectric dispersion and ferroelectric phase in the material is observed from the temperature‐dependent dielectric parameters at selected frequencies. The existence of ferroelectricity in the material is further confirmed by the room temperature hysteresis loop. Impedance spectroscopic studies informed about the correlation between the microstructure and electrical behavior. The frequency variation of AC conductivity refers to Jonscher's law. The temperature variation of frequency exponent term n indicates OLPT (overlapping large polaron‐tunneling) model of the conduction mechanism in the sample. NBPWTN is a strong candidate for applications involving thermistor‐related devices because of the temperature dependency of resistance. The value of temperature sensitivity coefficient β in our investigation is achieved between 2000 and 11 000 K, confirming that the material has a high‐temperature stability property and is ideal for high‐temperature electronics applications. The high room temperature dielectric constant value of the ceramic (around 500) is useful for dielectric capacitor applications.