Two-phase Composites Research Articles

Effect of phase composition on the crystal structure and microwave dielectric properties of ZnMg2TiO5 ceramics

Novel microwave dielectric ceramics ZnMg2TiO5 were synthesized by traditional solid-state method. Crystal structure refinement, transmission electron microscopy (TEM), and Raman spectroscopy reveal the coexistence of a secondary phase, MgO, with the predominant cubic spinel phase (Fd-3m) in ZnMg2TiO5 ceramics. The ceramics with dense microstructures exhibit excellent microwave dielectric properties at 1260 °C: εr = 15.6, Q×f = 92,899GHz (at 10.8GHz), and τf = −56.9 ppm/°C. The content of MgO, driven by thermodynamic factors, influences significantly impact the microstructure and microwave dielectric properties of the ceramics, particularly inducing the generation of localized lattice distortions and the formation of dislocations. The εr follows the same trend as the molecular polarizability of the actual individual crystal cells. Notably, a near-zero τf (−7.4 ppm/°C) was realized by two-phase composites and excellent comprehensive properties were obtained (εr = 17.9, Q×f = 57,546GHz).

Broadband dielectric spectroscopy studies of Co3O4 and Co2TiO4 two-phase spinel composites

Broadband dielectric spectroscopy studies of the two-phase composites, (1 – x) Co3O4 + x Co2TiO4, have been reported over a wide range of compositions (0 ≤ x ≤ 1) and temperatures (80 K ≤ T ≤ 573 K). Normal spinel Co3O4 and inverse spinel Co2TiO4 phases are well distinguishable with ∼4.6 % variation in the lattice parameter of the Co3O4 phase with an increase of x from 0 to x = 1. The ac-conductivity (σ) of this composite follows Johnscher's power law (∼Aωs) variation with frequency exponent factor ‘s’ both greater than as well as less than unity. The temperature dependence of ‘σ’ reveals the Arrhenius-like behavior instead of variable range hopping of charge carriers with activation energy in the 2–1800 meV range. Systematic analysis of such conductivity mechanisms for all the compositions is compared with the pristine Co3O4 system.

Machine-learning-assisted deciphering of microstructural effects on ionic transport in composite materials: A case study of Li7La3Zr2O12-LiCoO2

The effective diffusivity of ionic species in multiphase materials is critical for the design and function of composite materials for electrochemical energy storage. In practice, effective diffusivity depends sensitively not only on the intrinsic diffusivities of constituting materials but also on their topological arrangement; nevertheless, these coupled contributions are oversimplified in most analytical models. Here, we combine atomistically informed mesoscale modeling and machine learning (ML) analysis to unravel how such features affect effective diffusivity in two-phase composites. Using the Li7La3Zr2O12-LiCoO2 composite solid-state battery cathode as a model system, we compute effective diffusivity for 600 distinct dense polycrystalline microstructures with different topological configurations of grains, grain boundaries, and heterointerfaces. We verify that in addition to atomic-scale variabilities, microstructural feature diversity can significantly impact effective transport properties. Across the ensemble of test microstructures, this often results in bimodal distributions of effective diffusivity that encompass two qualitatively distinct operating mechanisms, which we identify via flux analysis. An ML approach reveals that the most critical determining factors for effective diffusivity are the connectivity of bulk phases and their heterointerfaces. The role of ionic mobility at the heterointerfaces is also discussed. These insights highlight the combined importance of microstructure and interface engineering in tuning the transport properties of ionic species in composite materials. Our framework can also be extended for understanding generic microstructure-property relationships in other complex multiphase materials.

Nanosheet-interwoven structures and ion-electron decoupling storage enable Fe1-xS fast ion transport in Li+/Na+/K+ batteries

Fe1-xS, known for its high theoretical capacity, abundant resources, and intrinsic safety, has become a focal point as a universal anode for Li+/Na+/K+ batteries. However, its fast-charging capability is unsatisfactory due to sluggish ion transport rate and low electrical conductivity. Furthermore, its Li+/Na+/K+ storage mechanisms are still unclear. Here, we fabricate a single-crystal Fe1-xS/N-doped carbon composite nanosheet interwoven structure, in which N-doped carbon layers onto surface of Fe1-xS nanosheets ameliorate the electrical conduction and the interwoven nanosheets form open pore channels that favor permeation of electrolytes to boost ion transport. In-situ magnetometry reveals that ion-electron decoupling storage and transport occur in two-phase composites of Fe/Li2S, Fe/Na2S, and Fe/K2S, in which Fe phase stores and transports electrons and sulfide phase stores and transports ions in a space-charge form, resulting in extra ion storage and fast ion transport. Consequently, the nanosheet interwoven structure delivers high capacities (1320.1/652.2/350.6 mAh g−1), outstanding fast-charging performances (679.6/295.4/106.4 mAh g−1 at 20 A g−1), and long cycling life over 5000 cycles as Li+/Na+/K+ battery anodes, respectively

Zn promoted GaZrOx Ternary Solid Solution Oxide Combined with SAPO-34 Effectively Converts CO2 to Light Olefins with Low CO Selectivity.

We proposed a new strategy for CO2 hydrogenation to prepare light olefins by introducing Zn into GaZrOx to construct ZnGaZrOx ternary oxides, which was combined with SAPO-34 to prepare a high-performance ZnGaZrOx/SAPO-34 tandem catalyst for CO2 hydrogenation to light olefins. By optimizing the Zn doping content, the ratio and mode of the two-phase composite, and the process conditions, the 3.5 %ZnGaZrOx/SAPO-34 tandem catalyst showed excellent catalytic performance and good high-temperature inhibition of the reverse water-gas shift (RWGS) reaction. The catalyst achieved 26.6 % CO2 conversion, 82.1 % C2 =-C4 = selectivity and 11.8 % light olefins yield. The ZnGaZrOx formed by introducing an appropriate amount of Zn into GaZrOx significantly enhanced the spillover H2 effect and also induced the generation of abundant oxygen vacancies to effectively promote the activation of CO2. Importantly, the RWGS reaction was also significantly suppressed at high temperatures, with the CO selectivity being only 46.1 % at 390 °C.

Synthesis and structure of polycrystals MnCo2O4-GdCrO4

The article discusses the synthesis and structure of polycrystalline nanocomposite MnCo2O4-GdCrO4 material. The sol-gel method was used as a synthesis of the study. Using X-ray phase analysis (XPA), the structure of the synthesized nanomaterial composition was determined: spinel – cobalt manganate and perovskite – gadolinium chromite. Based on the results of the analysis, it was established that the polycrystalline two-phase composite is a system of spinel-cubic and perovskite-tetragonal types. Morphological analysis of the nanocomposite was carried out using a scanning electron microscope (SEM). According to the data obtained as a result of SEM, the elemental composition was confirmed and the average nanosize of the nanomaterial was obtained, and the content of the compound increased to x2000 was determined, the particle size of MnCo2O4 is 383-281 nm, GdCrO4 – 1.63-1.34 µm; increased to x4000, particle size – MnCo2O4 277-219 nm, GdCrO4 – 1.48-1.27 µm; increased to x6000, particle size – MnCo2O4 239-209 nm, GdCrO4 –1.21-1.07 µm.

Exploring the structural, morphological, and multiferroic properties of Al3+ modified (1-x) BCZT-(x) CFO ceramic composites

Multiferroics with strong magnetoelectric coupling can be created by improving the magnetostriction of the ferrite phase and combining it with the best-known piezoelectric. Herein, the ferromagnetic CoFe2O4 was modified with Al incorporation further improve the resistivity, magnetic, and magnetostrictive properties and then combined with (0.5)Ba(Zr0.2Ti0.8)O3−(0.5)(Ba0.7Ca0.3)TiO3 (BCZT) with different weight percentages. XRD results revealed the presence of a mixed spinel cubic phase for CAF (Fd-3m), whereas BCZT crystallized in a tetragonal structure (Amm2) in composite systems. The dielectric response of the materials was studied using impedance spectroscopy and it displayed a typical Maxwell–Wagner polarization of two-phase composites. The magnetic response of the CAF sample improved significantly which is attributed to the preference of Al3+ ions on tetrahedral sites. The magnetization of composites increased as the nonmagnetic BCZT component increased and the (0.75)CAF-(0.25)BCZT system had the highest saturation magnetization. We anticipate that these systems will have significantly improved magnetoelectric characteristics than unmodified CFO-BCZT systems.

Structure and magnetic properties of the spinel-polymer composites

The development of the functional magnetic composites with determined properties is important task for modern material sciences. Control of magnetic and electrodynamic properties realized by the ceramic/polymer composites preparation. Conduction of the investigations of the correlation between chemical composition of the fillers (magnetic powders) and their concentration in the polymer matrix is the best way for solving this task. Two- and tree-component spinel-polymer composites were produced by thermal pressing. As spinels, CoFe2O4 (CF) and Ni0.4Cu0.2Zn0.4Fe2O4 (NCZFO) were used. As a polymer, FEP was used. The concentration of the spinels in the polymer matrix was fixed at 20 mass.%. Investigation of the structural features and magnetic properties were carried out. The impact of the chemical composition and phase ratio of the composites on crystal structure, microstructure, and magnetic properties were established. Magnetic measurements were performed at 300 and 10 K in the fields up to 70 kOe. It was demonstrated that the synergetic effect of ceramic composites violates of the principle of additivity in two-phase ceramic composites. The impact of the polymer matrix on magnetic properties was demonstrated. It opens new perspectives for practical applications of such kind of materials.

Mechanical Properties and Failure Behavior of Epoxy Rubber Powder Composites Reinforced with Hollow Beads

In this paper, new epoxy resin/rubber powder/hollow beads three-phase composites were prepared by designing the incorporation of fly ash hollow beads with different mass fractions (5%, 10%, 15%, and 20%) as new reinforcing phases into epoxy resin/rubber powder two-phase composites with 5% mass fraction of carbon black rubber powder. Quasi-static compression tests were conducted at room temperature to test the compressive properties of the oxygen resin/rubber powder/hollow beads composites. Calculate the energy absorption properties and energy absorption efficiency of the composites from the compression curves. Fracture characteristics of compressed material specimens with microscopic morphology were observed by scanning electron microscopy. By systematically analyzing the effect of fly ash hollow beads content on the mechanical properties of epoxy resin/rubber powder/hollow beads three-phase composites, it was found that fly ash hollow beads as reinforcing materials can effectively improve the brittleness and yield strength of epoxy resin/rubber powder as well as the energy-absorbing properties and efficiency of the composites. The energy absorption properties of the epoxy resin/rubber powder/hollow beads composites increased and then decreased with the increase in the mass fraction of fly ash hollow beads. In the epoxy resin/rubber powder/hollow beads composites, the most significant performance was observed when the mass fraction of fly ash was 10%.

The effect of Ti/Ba ratio on the microstructures and microwave dielectric properties of BaTi4O9–Ba2Ti9O20 composite ceramics

Considering the strengths and weaknesses of the two distinct physical phases of BaTi4O9 and Ba2Ti9O20, we opted to combine them in order to harness the synergistic effects of their properties. In contrast to conventional two-phase composites, we synthesized BaTi4O9–Ba2Ti9O20 microwave ceramics with varying Ti/Ba ratios utilizing the solid-state reaction method. The phase compositions, surface morphologies, microwave dielectric properties and impedance analyses of the composite ceramics with different Ti/Ba ratios were systematically investigated. The X-ray diffractograms showed that the content of BaTi4O9 decreases rapidly as the Ti/Ba ratio increases from 4.15 to 4.35 and Ba2Ti9O20 becomes the main phase when Ti/Ba = 4.25. From complex impedance spectra, it can be seen that the arc gradually compresses as the Ti/Ba ratio increases, representing a decrease in the resistance. The ceramic possessing a Ti/Ba ratio of 4.15 exhibited superior microwave dielectric properties, characterized by Q × f = 16,622 GHz, εr = 38.01, and τf = 10.37 ppm/°C. These results provide guidance for the future design of high-performance microwave ceramics with medium dielectric constant.

Evolution of the structural parameters and magnetic characteristics in “ferrite/polymer” nanocomposites

Binary and ternary composites based on soft magnetic spinels CoFe2O4 (or CFO) and Ni0.4Cu0.2Zn0.4Fe2O4 (or NCZFO) were produced. Binary CFO/NCZFO ceramic composite was consist of two magnetic phases with 1:1 ratio. Ternary CFO:FEP, NCZFO:FEP and [CFO/NCZFO]:FEP composites were produced by the thermal pressing of the initial ceramic powders (20 wt%) and fluorinated ethylene propylene – FEP (80 wt%). XRD, SEM and VSM investigation were carried out. The impact of the chemical composition and phase ratio of the composites on crystal structure, microstructure and magnetic properties were established. Magnetic measurements were performed at 300 and 10 K in the fields up to 70 kOe. It was demonstrated the synergetic effect for ceramic composite with the violation of the principle of additivity in two-phase ceramic composites.

A macro-mesoscopic constitutive model for porous and cracked rock under true triaxial conditions

The complex mechanical and damage mechanisms of rocks are intricately tied to their diverse mineral compositions and the formation of pores and cracks under external loads. Numerous rock tests reveal a complex interplay between the closure of porous defects and the propagation of induced cracks, presenting challenges in accurately representing their mechanical properties, especially under true triaxial stress conditions. This paper proposes a conceptualization of rock at the mesoscopic level as a two-phase composite, consisting of a bonded medium matrix and frictional medium inclusions. The bonded medium is characterized as a mesoscopic elastic material, encompassing various minerals surrounding porous defects. Its mechanical properties are determined using the mixed multi-inclusion method. Transformation of the bonded medium into the frictional medium occurs through crack extension, with its elastoplastic properties defined by the Drucker–Prager yield criterion, accounting for hardening, softening, and extension. Mori–Tanaka and Eshelby’s equivalent inclusion methods are applied to the bonded and frictional media, respectively. The macroscopic mechanical properties of the rock are derived from these mesoscopic media. Consequently, a True Triaxial Macro-Mesoscopic (TTMM) constitutive model is developed. This model effectively captures the competitive effect and accurately describes the stress-deformation characteristics of granite. Utilizing the TTMM model, the strains resulting from porous defect closure and induced crack extension are differentiated, enabling quantitative determination of the associated damage evolution.

Assessment of the load-bearing capacity of a polymer coating of a part, taking into account the crack resistance of a two-phase composite

The conditions for the failure of the adhesive bond between the substrate and the polymer coating are considered on the basis of the fracture mechanics of composites. The relationships between ultimate normal and tangential stresses and linear concentrations of initial cracks are determined. Keywords:polymer coating, Young's modulus, Poisson's ratio, substrate, crack, adhesion skoryagin@kantiana.ru

Fe-enriched two-phase multiferroic composites based on lead ferroniobate - titanate and modified nickel ferrite

Iron-enriched ferroelectrics are of particular interest as piezoactive components of piezoelectric-ferrite ME ceramics. This is due to the phase composition similarity and the reduction of expected interfacial doping effects during high-temperature calcination. This idea seems attractive, but laborious due to the significantly limited number of possible piezoelectric–ferrite combinations. Therefore, there is practically no data on such systems in the literature. ME composite ceramics based on the highly efficient Fe-containing Pb(Fe0.5Nb0.5)0.935Ti0.065O3 (PFNPT) ferroelectric has been studied. (100-х) wt.% Pb(Fe0.5Nb0.5)0.935Ti0.065O3 (PFNPT) + х wt.% Ni0.9Co0.1Cu0.1Fe1.9O4-d (NCCF) composite systems has been obtained by the solid-state method at 1050 °C, with no foreign phases. The specimens densities amounted to ∼80% of the theoretical. It has been shown that the ME conversion efficiency and other composites properties are significantly influenced by the PFNPT precursor pre-treatment method. The maximum value of the ME coefficient ΔΕ/ΔΗ = 75 mV/(cm Oe) has been observed for specimens with x = 50–60 made from PFNPT powder with the addition of Li2CO3. An increase in the ME composites sintering temperature to 1150 °C leads to the formation of Pb2Nb2O7 foreign phase with a pyrochlore structure along the grain boundaries. The ME coefficient ΔΕ/ΔΗ does not exceed 15 mV/(cm⋅Oe). There is an threefold decrease in the composites piezoelectric parameters (piezoelectric coefficients dij, gij), as well as in their magnetic properties (magnetizations MS, MR) due to piezophase degradation, which is presumably associated with a change in the cations distribution over A and B sublattices of the spinel structure.

Study of crack propagation in multi-phase composites embedded with both stiff and compliant particles using phase field method

Abstract Crack propagation in two-phase particle-reinforced composites is extensively studied using
the phase field method. Typically, the particle either has a higher stiffness(stiff) or a lower
stiffness(compliant) than the matrix. However, the crack propagation in multi-phase composites
with both the stiff and compliant particles is not yet understood well. In this work, we report
on the crack propagation characteristics and the resulting enhanced effective fracture toughness
in multi-phase composite materials with both stiff and compliant particles using the phase filed
method. Three different geometric arrangements of particles are considered: a diagonal array,
a cubic array, and a honeycomb array. The honeycomb configuration had the best combination
of strength and effective fracture toughness. We show that apart from the local geometric
arrangement of the individual particles, the ratio of the stiffness of the individual particles is
an important factor in crack propagation. Furthermore, we show that the ratio of the critical
energy release rate of the individual particles can be tuned to increase the effective fracture
toughness.

Significantly Enhanced Balance of Dielectric Properties of Polyvinylidene Difluoride Three-Phase Composites by Silver Deposited on K2Ni0.93Ti7.07O16 Hollandite Nanoparticles.

Three-phase polymer composites are promising materials for creating electronic device components. The qualitative and quantitative composition of such composites has a significant effect on their functional, in particular dielectric properties. In this study, ceramic filler K2Ni0.93Ti7.07O16 (KNTO) with Ag coating as conductive additive (0.5, 1.0, 2.5 wt.%) was introduced into the polyvinylidene difluoride (PVDF) polymer matrix in amounts of 7.5, 15, 22.5, and 30 vol.%. to optimize the dielectric constant and dielectric loss tangent. The filler was characterized by X-ray phase analysis, Fourier-transform infrared spectroscopy and Scanning electron microscopy methods. The dielectric constant, dielectric loss tangent, and conductivity of three-phase composites KNTO@Ag-PVDF were studied in comparison with two-phase composites KNTO-PVDF in the frequency range from 102 Hz to 106 Hz. The dielectric constant values of composites containing 7.5, 15, 22.5, and 30 vol.% filler were 12, 13, 17.4, 19.2 for pure KNTO and 13, 19, 25, 31 for KNTO@Ag filler (2.5 wt.%) at frequency 10 kHz. The dielectric loss tangent ranged from 0.111 to 0.340 at a filler content of 7.5 to 30 vol.%. A significantly enhanced balance of dielectric properties of PVDF-based composites was found with K2Ni0.93Ti7.07O16 as ceramic filler for 1 wt.% of silver. Composites KNTO@Ag(1 wt.%)-PVDF can be applied as dielectrics for passive elements of flexible electronics.

Correlation between surface-to-volume ratio of the particle shape and elastic properties of the particulate composites

This work is motivated by real-world particle shapes, observed using a scanning electron microscopy. The focus of the presented studies was to understand the influence of the particle shapes on the effective elastic properties of the two-phase composites. For this, particles with polyhedral, undulated and other shapes were numerically modeled using analytical functions. Creation of some shapes, like polyhedral, are known from the literature but Laplace’s spherical harmonics, as well as the Goursat’s surface and some others, were used for the first time to create novel particle shapes. Elastic properties of the composites with different particle shapes were calculated using the finite element analysis. The obtained results show good agreement with mean-field homogenization methods such like Mori-Tanaka and Lielens as well as other numerical results available in the literature. Further, the dependence of the effective Young’s moduli of the composite on the shape and the corresponding surface-to-volume ratio of the particles was studied. It was observed that the effective Young’s moduli increase with the surface-to-volume ratio of the particles in the case where particles are stiffer in comparison to the matrix. It was also remarked that, in the case of particles of similar shapes, the particle surface-to-volume ratio and the effective Young’s moduli differ significantly with the surface curvature and the edge sharpness of the particles.

Granular solids transmit stress as two-phase composites.

A basic problem in the science of realistic granular matter is the plethora of heuristic models of the stress field in the absence of a first-principles theory. Such a theory is formulated here, based on the idea that static granular assemblies can be regarded as two-phase composites. A thought experiment is described, demonstrating that the state of such materials can be varied continuously from marginal stability, via a two-phase granular assembly, then porous structure, and finally be made perfectly elastic. For completeness, I review briefly the condition for marginal stability in infinitely large assemblies. The general solution for the stress equationsin d=2 is reviewed in detail and shown to be consistent with the two-phase idea. A method for identifying the phases of finite regions in larger systems is constructed, providing a stability parameter that quantifies the "proximity" to the marginally stable state. The difficulty involved in deriving stress fields in such composites is a unique constraint on the boundary between phases, and, to highlight it, a simple case of a stack of plates of alternating phase is solved explicitly. An effective medium approximation, which satisfies this constraint, is then developed and analyzed in detail. This approach forms a basis for the extension of the stress theory to general granular solids that are not marginally stable or at the yield threshold.

PH-Regulated host-guest architecture in molybdenum Dioxide/Carbon sphere composites for flexible solid-state supercapacitors

Compositing molybdenum dioxide (MoO2) with carbon sphere (CS) can greatly enhance the conductivity and structural instability to achieve its high theoretical capacitances. The controllable regulation of local architecture and host–guest interaction in the two-phase composites is highly desirable, but commonly hindered by the significant difference in formation mechanism between MoO2 and CS. Herein, a pH-regulated pre-intervention strategy was developed to provide control over the MoO2/CS architecture by adjusting the interplay between the precipitation kinetics of MoO2 and the polymerization effect of hydrochar precursor. By varying the pre-synthesis pH from 10.0 to 0.1, the corresponding dominant formation process of precursor changes from inside-out Ostwald ripening to protonation-induced electrostatic interactions, resulting in the structural evolution of MoO2/CS from hollow CS-encapsulating MoO2 nanosheets and solid CS-supporting MoO2 nanoparticles. The electrochemical test proved the former architecture possesses faster electrode kinetics, lower charge/ion-transfer resistance, and better electrochemical stability. An extended oxidation-etching method was further introduced to prepare mesoporous CS with excellent supercapacitive properties. A flexible solid-state asymmetric supercapacitor composed of optimal MoO2/CS structure as the positive electrode and mesoporous CS as the negative electrode delivers a high energy density of 52.3 W h kg−1 and power density of 14500 W kg−1, and good cycling stability with 89.7 % retention of the initial capacitance after 8000 cycles.

Carbon nanotube reinforced LDPE/SAN thermoplastic nanocomposites: thermo-mechanical and electromagnetic interference shielding properties

A prevalent area of research is the development of structural polymer composites with diverse functions. An ingenious material solution is two-phased nanocomposites with distinctive structural and electrical characteristics. This study produced a nanocomposite structure with carbon nanotube-reinforced low-density polyethylene (LDPE) and styrene acrylonitrile (SAN) as a thermoplastic matrix. The injection molding method was used in the production of nanocomposites. Thermo-dynamic and electromagnetic shielding properties of the nanocomposites were investigated. As the LDPE/MWCNT ratio added to pure SAN increased, the storage modulus decreased as expected, and the storage modulus for the MB50 sample was determined as 1.24 GPa with a 50% decrease. The percolation threshold for the two-phase thermoplastic composite was obtained for the MB50 sample containing 10 wt% carbon nanotubes. In addition, the MB75 sample containing 15 wt% carbon nanotubes reached an EMSE value of 37 dB.