Formation Of Secondary Phases Research Articles

Research Progress on the Relationship Between Microstructure and Properties of AISI 321 Stainless Steel

AISI 321 stainless steel is widely used in chemical pipelines and nuclear power, prompting research on its high-temperature performance and corrosion resistance. This review focuses on the effects of alloy elements, second-phase particle formation, and heat treatment processes on the microstructure and properties of AISI 321 stainless steel. Fine tuning of alloying elements can affect the mode and effect of dynamic recrystallization, altering the high-temperature flow deformation of AISI 321 stainless steel. In order to achieve phase equilibrium, the relationship between corrosion resistance and high-temperature creep behavior and high-temperature mechanical behavior in the presence of second-phase particles was also analyzed. This review outlines the basic heat treatment procedures for improving material properties, providing a new perspective for solution treatment and improving corrosion resistance. In addition, the latest research progress on other factors affecting the high-temperature performance of AISI 321, such as coatings, was briefly introduced.

The Gypsum Influence on the Formation of Secondary Phases During Autoclave Leaching of Gold-Bearing Concentrates and the Silver Recovery Using Cyanidation

Autoclave leaching of sulfide concentrates may produce various ferric secondary phases, depending on the arsenic content and temperature. Silver is converted to argentojarosite, from which it is not recoverable by standard cyanidation methods. To increase silver recovery, it is necessary to reduce the argentojarosite formation during autoclave leaching. This study was devoted to the influence of gypsum on the formation of secondary phases of ferric arsenate and the subsequent recovery of gold and silver by cyanidation. The addition of gypsum at a consumption of 0.1 g/g(concentrate) helped to increase silver extraction from 13.4 to 98% at cyanidation. Gold recovery was 99%. An increase in gypsum consumption contributed to the ferric arsenate sulfate formation with an increased sulfate sulfur content, and a decrease in the As/S(sulfate) molar ratio in the cake from 3.7 to 0.88 contributed to an increase in silver extraction at cyanidation of up to 98%. Basic ferric sulfate is not formed in this case, since according to EDS mapping, the distribution of arsenic and sulfur over ferric-containing particles is uniform. According to TCLP, stable, sparingly soluble ferric arsenate phases are formed and the cake obtained after cyanidation is stable and suitable for disposal, since the final arsenic concentration in the solution was 0.45 mg/dm3.

Br-Induced Suppression of Low-Temperature Phase Transitions in Mixed-Cation Mixed-Halide Perovskites.

Mixed-cation mixed-halide lead perovskites have been shown to be excellent candidates for solar energy conversion. However, understanding the structural phases of these mixed-ion perovskites across a wide range of operating temperatures, including very low temperatures for space applications, is crucial. In this study, we investigated the structure of formamidinium-based Cs y FA1-y Pb(Br x I1-x )3 using low-temperature in situ synchrotron powder X-ray diffraction. Our findings revealed that substituting the I anion with Br in mixed-cation (Cs,FA) perovskites suppressed the phase transformation from tetragonal to orthorhombic at low temperatures. The addition of Br also prevented the formation of nonperovskite secondary phases. We gained fundamental insights into the structural behavior of these materials by creating a low-temperature phase diagram for the compositional set of mixed-cation mixed-halides. This understanding of the structural properties lays the groundwork for designing more robust and efficient energy materials capable of functioning under extreme temperature conditions, including space-based solar energy conversion.

Investigation on electronic and magnetic properties of Cr doped V2O5 thin films prepared by chemical solution deposition method

The present study examines the role of Cr doping on the electronic and magnetic behaviour of V2O5i.e. V2-xCrxO5 (x = 0, 0.05, and 0.10) thin films, prepared by chemical-solution deposition technique on Si (111) substrate. X-Ray diffraction technique shows the purity of the films and confirms no secondary phase formation. The atomic force microscopy was used to confirm the roughness of the films. A morphological investigation is done using High-resolution scanning electron microscopy associated with Energy dispersive X-Ray mapping of each element of the film. Fourier transform Infrared spectroscopy is utilised to identify functional groups that are present in obtained samples. The band-gap of these obtained samples is in the range of 0.8–0.6 eV, as examined by UV–Vis i.e., its value is decreasing with Cr doping. Using vibrating sample magnetometer, it is clear that samples shows ferromagnetic (FM) behaviour with saturation magnetization 0.3–0.6 μB/cc consistent with Langevin function fitting. It concludes the presence of FM behaviour of films and magnetization increases with carrier density, consistent with the carrier-induced origin of the ferromagnetism. X-ray photoemission spectroscopy (XPS) is utilised to understand its electronic properties. Core level spectra measurements suggest that V is in mixed state of 5+ and 4+. However Cr is in 3+ states. XPS and UV–Vis measurements imply that oxygen vacancies significantly contribute to the declination of the band gap and the promotion of FM-like behaviour. This discovery offers a promising pathway for engineering novel devices.

Programmable mechanical properties of additively manufactured novel steel

Abstract Tailoring thermal history during additive manufacturing (AM) offers a feasible approach to customise the microstructure and properties of materials without changing alloy compositions or post-heat treatment, which is generally overlooked as it is hard to achieve in commercial materials. Herein, a customised Fe-Ni-Ti-Al maraging steel with rapid precipitation kinetics offers the opportunity to leverage thermal history during AM for achieving large-range tunable strength-ductility combinations. The Fe-Ni-Ti-Al steel was processed by laser-directed energy deposition (LDED) with different deposition strategies to tailor the thermal history. As the phase transformation and in-situ formation of multi-scale secondary phases of the Fe-Ni-Ti-Al steel are sensitive to the thermal histories, the deposited steel achieved a large range of tuneable mechanical properties. Specifically, the interlayer paused deposited sample exhibits superior tensile strength (~1.54 GPa) and moderate elongation (~8.1%), which is attributed to the formation of unique hierarchical structures and the in-situ precipitation of high-density η-Ni3(Ti, Al) during LDED. In contrast, the substrate heating deposited steel has an excellent elongation of 19.3% together with a high tensile strength of 1.24 GPa. The achievable mechanical property range via tailoring thermal history in the LDED-built Fe-Ni-Ti-Al steel is significantly larger than most commercial materials. The findings highlight the material customisation along with AM’s unique thermal history to achieve versatile mechanical performances of deposited materials, which could inspire more property or function manipulations of materials by AM process control or innovation.

Porous titanium/hydroxyapatite interpenetrating phase composites with optimal mechanical and biological properties for personalized bone repair

This study introduces the first fabrication of porous titanium/hydroxyapatite interpenetrating phase composites achieved through an innovative processing method. The approach combines additive manufacturing of a customized titanium skeleton with the infiltration of an injectable hydroxyapatite foam, followed by in situ foam hardening at physiological temperature. This biomimetic process circumvents ceramic sintering and metal casting, effectively avoiding the formation of secondary phases that can impair mechanical performance. Hydroxyapatite foams, prepared using two foaming agents (polysorbate 80 and gelatine), significantly reinforce the titanium skeleton while preserving the microstructural characteristics essential for osteoinductive properties. The strengthening mechanisms rely on the conformation of the foams to the titanium surface, thereby enabling a stable mechanical interlocking and effective interfacial stress transfer. This, combined with the mechanical constriction of phases, enhances damage tolerance and mechanically reliability of the interpenetrating phase composites. In addition, the interpenetrating phase composites feature a network of concave pores with an optimal size for bone repair, support human osteoblasts proliferation, and exhibit mechanical properties compatible with bone, offering a promising solution for the efficient and personalized reconstruction of large bone defects. The results demonstrate a significant advancement in composite fabrication, integrating the benefits of additive manufacturing for bone repair with the osteogenic capacity of calcium phosphate ceramics.

Comparative Study on Mechanical Properties and Microstructure Evolution of Mg-3Zn-1Mn/Sn Alloy through Ca-La-Ce Addition.

This study systematically investigates the influence of the composite addition of Ce, La, and Ca elements on the microstructure evolution and mechanical properties of Mg-3Zn-1Mn/Sn (wt.%) alloys. It indicates that the strength of Mg-Zn-Mn series alloys is superior to that of Mg-Zn-Sn series alloys, due to the stronger restriction of nanosized Mn particles on the recrystallization process and grain growth compared with Mg2Sn phases. The addition of the Ca-La-Ce elements significantly enhances the strength of the Mg-3Zn-1Sn alloy (YS increased by approximately 92.5%, UTS increased by approximately 29.2%, and EL decreased by nearly 52.2%), while for the Mg-3Zn-1Mn alloy, a balanced effect on both the strength and performance can be achieved. This difference mainly lies in the more pronounced refined effect on the grain size and the formation of a bimodal grain structure with strip-like un-DRXed grains and surrounding fine DRXed grains for the Mg-3Zn-1Sn alloy. In contrast, the addition of the Ca-La-Ce elements has a less obvious hindrance on the recrystallization process in the Mg-Zn-Mn series alloy, while significantly weakening the extrusion texture while refining the grains. Through in-depth characterization and experimental analysis, it is found that Sn and Ca can promote the formation of brittle and fine secondary phases. A nanoscale Sn phase (Mg2Sn phase) is more likely to accumulate at the grain boundaries, and the size of the nanoscale Ca2Mg6Zn3 in Mg-Zn-Mn series alloys is finer and more dispersed than that in Mg-Zn-Sn series alloys, thus strongly hindering recrystallization and refining the recrystallized structure of the alloy.

Mechanism of praseodymium yttrium regulating the absorption properties of M-type strontium ferrite: From single phase to multi phase mixed system

When Pr and Y ions are added to M-type strontium ferrite, a portion of the ions will enter the main phase lattice, while the excess ions will aggregate at the grain boundaries to form a secondary phase. The occupancy of rare earth ions in the main phase lattice and the formation of secondary phases are two key factors affecting the material's absorbing properties. The difference in ultimate solid solubility between rare earth ions Pr and Y in M-type strontium ferrite is significant, and they also form different secondary phases at grain boundaries. Consequently, the synthesized SrFe12-2xPrxYxO19 (0 < x ≤ 1.5) demonstrates its potential as a microwave absorbing material across a wide range of substitutions. Moreover, the performance changes have their own characteristics at different substitution levels. XRD results show that the samples include pure M phase and the coexistence of M phase and heterogeneous phases, with the heterogeneous phases being perovskite-type and garnet-type. SEM and EDS results indicate that Pr and Y co-substitution can refine grain size and reduce oxygen content. XPS results suggest that the valence change of Pr ions leads to the generation of Fe2+ ions and oxygen vacancies (Od). PPMS results reveal that saturation magnetization and coercivity are mainly affected by anisotropy field and particle size. Co-substitution of Pr and Y increases the dielectric and magnetic losses of the M phase, and the generated heterogeneous phases also enhance the dielectric and magnetic losses through interface polarization and magnetic exchange coupling effects, both cooperatively improving the wave-absorbing performance, with the minimum reflection loss (RLmin) reaching −51.57 dB (x = 0.1, d1 = 4.0 mm, EAB = 2.57 GHz).

Ga-ion migration during co-sintering of heterogeneous Ta- and Ga-substituted LLZO solid-state electrolytes

Li7La3Zr2O12 (LLZO) is an attractive solid-state electrolyte for next-generation lithium solid-state batteries (SSB) because of its high ionic conductivity, and safety properties. Only the cubic LLZO phase has sufficient ionic conductivity, which is stabilized by substitution with elements like Ta or Ga. Ga-substituted LLZO has the highest ionic conductivity but is not stable towards metallic Li anodes, while Ta-substituted LLZO has a slightly lower conductivity but excellent reduction stability towards Li anodes. The combination of LLZO:Ga as a catholyte and LLZO:Ta as a ceramic separator for Li anodes would significantly enhance the performance of SSBs, but both materials have different processing parameters. In this work, the possibility of co-sintering LLZO:Ga|LLZO:Ta components is investigated with varying Li-excess of the LLZO:Ta phase, while the results are compared with pure references. The experiments showed a changed sintering activity, secondary phase formation, Ta- and Ga-ion diffusion, and a changed ionic conductivity when co-sintering LLZO:Ga|LLZO:Ta.

Direct Precursor Route for the Fabrication of LLZO Composite Cathodes for Solid-State Batteries.

Solid-state batteries based on Li7La3Zr2O12 (LLZO) garnet electrolyte are a robust and safe alternative to conventional lithium-ion batteries. However, the large-scale implementation of ceramic composite cathodes is still challenging due to a complex multistep manufacturing process. A new one-step route for the direct synthesis of LLZO during the manufacturing of LLZO/LiCoO2 (LCO) composite cathodes based on cheap precursors and utilizing the industrially established tape casting process is presented. It is shown that Al, Ta:LLZO can be formed directly in the presence of LCO from metal oxide precursors (LiOH, La2O3, ZrO2, Al2O3, and Ta2O5) by heating to 1050°C, eliminating the time- and energy-consuming synthesis of preformed LLZO powders. In addition, performance-optimized gradient microstructures can be produced by sequential casting of slurries with different compositions, resulting in dense and flat phase-pure cathodes without unwanted ion interdiffusion or secondary phase formation. Freestanding cathodes with a thickness of 85µm, a relative density of 95%, and an industrial relevant LCO loading of 15mg show an initial capacity of 82 mAh g-1 (63% of the theoretical capacity of LCO) in a solid-state cell with Li metal anodes, which is comparable to conventional LCO/LLZO cathodes and can be further improved in the future.

Processing and characterization of Ultra High Temperature High‐Entropy (Ti0.2Zr0.2Hf0.2Mo0.2W0.2)B2-based Ceramics: Effect of W granulometry, graphite, and SiC addition

A highly dense and single phase (Ti0.2Zr0.2Hf0.2Mo0.2W0.2)B2 ceramic product is obtained in this work at 1950°C (20 min, 20 MPa) by Spark Plasma Sintering (SPS) from powders prepared by Self-propagating High-temperature Synthesis (SHS). The formation of the (W,Mo)B2 secondary phase is avoided using fine W precursors and adding 1 wt% graphite to the SHS powders before SPS. Kinetic limitations responsible for hindering the synthesis of the high entropy boride are correspondingly eliminated. The resulting 98.5 % dense sample exhibits a homogeneous microstructure, with Vickers hardness of 26.8 GPa. The introduction of 20 vol% SiC produces an increase of the KIC values from 2.32 to 5.11 MPa m1/2. Very relevant is that the volatilization of Mo- and W-oxides occurring during sample oxidation at high temperature, which leads to its rapid degradation with the formation of a very porous oxide scale, can be strongly inhibited by the silicate phases generated in the composite ceramic.

Lithium Volatilization and Phase Changes during Aluminum-Doped Cubic Li6.25La3Zr2Al0.25O12 (c-LLZO) Processing

Stabilized Li6.25La3Al0.25 Zr2O12 (cubic LLZO or c-LLZO) is a Li+-conducting ceramic with ionic conductivities approaching 1 mS-cm. Processing c LLZO so that it is suitable for use as a solid state electrolyte in all solid state batteries, however, is challenging due to the formation of secondary phases at elevated temperatures. The work described in this manuscript examines the formation of one such secondary phase La2Zr2O7 (LZO) formed during sintering c LLZO at 1000 °C. Specifically, spatially resolved Raman spectroscopy and X-ray Diffraction (XRD) measurements have identified gradients in Li distributions in the Li ion (Li+)-conducting ceramic Li6.25La3Al0.25 Zr2O12 (cubic LLZO or c-LLZO) created by thermal processing. Sintering c-LLZO under conditions relevant to solid state Li+ electrolyte fabrication conditions lead to Li+ loss and the formation of new phases. Specifically, sintering for 1 h at 1000 °C leads to Li+ depletion and the formation of the pyrochlore lanthanum zirconate (La2Zr2O7 or LZO), a material known to be both electronically and ionically insulating. Circular c-LLZO samples are covered on the top and bottom surfaces, exposing only the 1.6 mm-thick sample perimeter to the furnace’s ambient air. Sintered samples show a radially symmetric LZO gradient, with more LZO at the center of the pellet and considerably less LZO at the edges. This profile implies that Li+ diffusion through the material is faster than Li+ loss through volatilization, and that Li+ migration from the center of the sample to the edges is not completely reversible. These conditions lead to a net depletion of Li+ at the sample center. Findings presented in this work suggest new strategies for LLZO processing that will minimize Li+ loss during sintering, leading to a more homogeneous material with more reproducible electrochemical behavior.

Simultaneous effect of microwave sintering and TiO2 addition on sinterability, mechanical properties, and scratch resistance of zirconia toughened alumina ceramics

This paper delves into the transformative impact of varying titanium dioxide (TiO2) content on the sinterability, physical, and mechanical properties, as well as scratch behavior, of zirconia-toughened alumina (ZTA) ceramic composites. By adjusting TiO2 content from 0 wt% to 5 wt% and employing advanced microwave sintering at 1150 °C, the study aims to lower the sintering temperature of ZTA. Microwave sintering, known for its efficiency and rapid processing, enables significant enhancements in material properties at reduced temperatures. Notably, incorporating TiO2 into ZTA yields remarkable improvements in physical and mechanical attributes, with the optimal TiO2 content determined to be 3 wt%. At this concentration, the composite achieves exceptional properties: a relative density of ∼99 %, microhardness of ∼2002 HV, and an indentation fracture toughness of ∼6.13 MPa m0.5. These enhancements represent increases of over 120 % in hardness and 61 % in toughness compared to TiO2-free ZTA. Additionally, the highest scratch resistance is observed at 3 wt% TiO2, evidenced by a minimal scratch depth of ∼7.53 μm. However, exceeding the 3 wt% solubility limit results in the formation of secondary phases, such as tialite (Al2TiO5) and zirconium titanate (ZrTiO4), which degrade the composite's properties. This research underscores the potential of TiO2 doping and microwave sintering to elevate the performance of ZTA ceramics, offering a pathway to superior materials for advanced applications.

Coating Robust Layers on Ni-Rich Cathode Active Materials while Suppressing Cation Mixing for All-Solid-State Lithium-Ion Batteries.

This study focused on addressing the challenges associated with the incompatibility between sulfide solid electrolytes and Ni-rich cathode active materials (CAMs) in all-solid-state lithium-ion batteries. To resolve these issues, protective layers have been explored for Ni-rich materials. Lithium lanthanum titanate (LLTO), a perovskite-type material, is recognized for its excellent chemical stability and ionic conductivity, which render it a potential protective layer in CAMs. However, traditional methods of achieving the perovskite structure involve temperatures exceeding 700 °C, resulting in challenges such as LLTO agglomeration, secondary phase formation between LLTO and CAM, and cation mixing within the CAM. In this study, a rapid technique known as flash-light sintering (FLS) was employed to fabricate a uniform and pure perovskite protective layer without inducing cation mixing within the CAM. The LLTO-coated LiNi0.8Co0.1Mn0.1O2 (NCM811) with FLS treatment demonstrated minimal cation mixing and formed a fully covered dense layer. This resulted in a high initial capacity and effectively addressed the incompatibility issues between the sulfide electrolytes and CAM. The rapid FLS method not only streamlines the fabrication of LLTO-coated NCM811 but also provides opportunities for its broader application to materials that were previously deemed impractical because of high sintering temperatures.

The Effects of the Secondary-Phase Distribution on the Dissolution Rate and Mechanical Properties of Soluble Al-Mg-Ga-In-Sn Alloys

The relationships between microstructure, dissolution, and mechanical properties of a soluble Al-Mg-Ga-In-Sn alloy are investigated in the present study. The findings demonstrate that the influence of low-melting-point elements on the dissolution of aluminum alloys can be attributed to the formation of secondary phases composed of Mg2Sn and In3Sn at grain boundaries and their participation in the Al–water reaction. After annealing, the secondary phases at grain boundaries transform from point-like and block-like discontinuous particles to strip-like continuous intergranular phases which envelop the Al matrix, resulting in a 29.8% reduction in the volume. These transformations increase the total contact area of the Al–water interface, amplifying the corrosion current of the annealed alloy to more than 30 times that of the as-cast alloy, thereby accelerating the dissolution rate. Unlike magnesium–lithium alloys, the soluble Al-Mg-Ga-In-Sn alloy exhibits a balanced strength, ductility, and dissolution rate, which presents it as a cost-effective, lightweight, structurally and functionally integrated material for the realm of petroleum exploration.

Structural stability and electrochemical response of 3D printed and reactively sintered Ga-doped Li7La3Zr2O12 electrolytes

Cubic Ga-doped Li7La3Zr2O12 (LLZO) tubes with one closed end were produced by a 3D printing-reactive sintering process. For the first time, the structural stability of Ga-doped LLZO tubes (relative density: ∼88 %, cubic LLZO fraction > 90 %) was evaluated after immersion in eutectic PbLi, a candidate molten breeder, at 350 and 450 °C. The high ionic conductivity cubic LLZO phase was maintained after immersion at 350 °C for 100 h, while secondary phase formation and conversion of cubic LLZO to the tetragonal polymorph was observed after 6 h at 450 °C. Li was successfully pumped through the tubes during linear voltage sweeps at 350 °C, indicating that Ga-doped LLZO is a possible candidate for hydrogen isotope extraction in PbLi via direct electrolysis.

Microstructural evolution and mechanical behavior of WC–4wt.%TiC–3wt.%TaC–12wt.%Co refractory cermet consolidated by spark plasma sintering of mechanically activated powder mixtures

The paper studied the structural features and physicomechanical properties of the WC–4wt.%TiC–3wt.%TaC–12wt.%Co composite refractory hard alloy system obtained by spark plasma sintering (SPS) from a preliminarily mechanically activated powder. It has been shown that preliminary mechanical activation in a planetary mill contributed to the comminution of agglomerates and the formation of a monomodal particle size distribution with a predominance of the submicron fraction, which intensifies the densification processes during subsequent consolidation by the SPS method. Kinetic analysis of the SPS process showed a two-stage sintering pattern with intense densification at temperatures above 790 °C due to rearrangement of WC, TiC, TaC particles and melting of the cobalt binder. It has been found that the SPS method does not lead to the formation of undesirable secondary phases in the entire sintering temperature range. A sintering temperature of 1200 °C is optimal for achieving the best structural homogeneity, density and mechanical properties, providing optimal distribution of carbide phases and the cobalt binder. The microstructure of the sample obtained at 1200 °C represents a refractory skeleton of WC grains with TiC and TaC carbide particles uniformly distributed throughout the volume. Improved fluidity of the melted cobalt binder and its mobile redistribution contribute to increased compactness of the structure and reduced porosity of the material. Samples sintered at 1200 °C possess high physicomechanical characteristics: relative density 99.99 %, hardness HV30 1623.2, bending strength 1125.1 MPa, fracture toughness 10.5 MN⋅m1/2. The abrasive wear resistance of a newly synthesized hard material was evaluated through a turning operation. Results showed durability, indicating promise for cutting tool applications and the need for further research to fully characterize the performance of this novel material.

Probing Interfacial Degradation in Solid-State Batteries Using Machine Learning Force Fields

Solid-state batteries (SSBs) are next-generation energy storage technologies with improved safety and potentially higher energy densities compared to conventional Li-ion batteries, which is enabled by using fast ion-conducting solid electrolytes (SEs). However, practical applications of SSBs are hindered by the electro-chemo-mechanical instabilities at interfaces within the SEs (grain boundaries (GBs)) and between SEs and the electrodes, which deteriorates Li transport and the chemical and mechanical integrity of the cell. To mitigate, fundamental understanding of the intrinsic physico-chemical properties at interfaces is required. To this end, we directly probe atomic structures of the interfaces and GBs by performing large-scale atomistic simulations, enabled by validated machine-learning force fields (MLFFs) and resolve the structure-property relationship at complex interfaces that governs Li-ion transport and stability of SSBs.In this talk, we will discuss the characteristics of garnet Li7La3Zr2O12 (LLZO) SE/LiCoO2 (LCO) cathode interfaces as well as the internal interfaces within the LLZO (GBs). It is observed from our simulations that the propensities for interfacial degradation strongly depend on the surface chemistry of LLZO and LCO. Doping LLZO is found to have a segregation effect at the LLZL GBs, here we will discuss its implication towards secondary phase formation and Li transport kinetics. At last, we will address the impact of interfaces on micro-crack propagation behavior in the LLZO-LCO system. In summary, our results reveal how atomic details of the dynamically evolving interfaces dictate the performance of SSBs, and provide guidance for processing and interface design to achieve desired performance .This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract number DEAC52-07NA27344. Authors acknowledge funding support from the Vehicle Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy and computational resource support from the Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program. This research used resources of the Argonne Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC02-06CH11357.

Effects of B- and A/B-sites Codoping on lattice distortion and defect concentration for high electromechanical response of lead-free piezoelectrics

Effects of different thermal conditions on lead-free (Bi0.65Ba0.35)(Fe0.65Ti0.35)O3 ceramics were studied to reduce secondary phase formation, regulate bismuth vacancies and resulting oxygen vacancies, and Fe ions valence transition during the heat treatment process. The optimal thermal conditions led to a higher d33 = 200 pC/N and a d33* = 420 pm/V. A/B-sites ions replacement in BF35BT, BF35BT-Zr, and BF35BTSZ ceramics were prepared to reveal the effects of different Zr or Sr-Zr-contents. A maximum tetragonality (cT/aT) was estimated for the single doping (Zr) and co-doping (Sr and Zr) cases. For Zr = 0.02, the electric field-induced strain reached its maximum value of d33* = 562 pm/V. Similarly, a strain of d33* = 701 pm/V was observed for Sr-Zr = 0.02. Additionally, the d33* improved to 870 pm/V (90 °C) in Zr = 0.02 and 1130 pm/V (120 °C) in Sr-Zr=0.02. The presence of local structural heterogeneity causes the domain size to decrease as it moves from the micro to the nanoscale. The results demonstrate that improved performance can be associated with reduced concentration of oxygen vacancies, nanodomains by local structural heterogeneity, high lattice anisotropy, higher relative density, and appropriate grain size.

Structure Investigation of highly porous bioceramics based on biogenic hydroxyapatite with graphene oxide coating

Highly porous bioceramics (porosity equal to 93–94 %) based on biogenic hydroxyapatite and sodiumborosilicate glass (40wt% of glass) was prepared by foam replication method at 700 °C and coated by graphene oxide using CVD method. Obtained bioceramics samples were studied by SEM, XRD and Raman spectroscopy. Phase composition, morphology, skeleton density, porosity and compression strength were evaluated. It was shown that biogenic hydroxyapatite in highly-porous bioceramics composition is stable and keeps hydroxyapatite phase without secondary phase formation after sintering with sodiumborosilicate glass as well as after application of CVD method for graphene oxide coating. Formation of graphene oxide for coated bioceramics was confirmed by XRD, SEM and Raman spectroscopy. Significant effect of graphene oxide coating on the porosity and skeleton density was not detected due to thin layer and low content of graphene oxide, but it allows 30 % increasing the compression strength of highly porous bioceramics.