Diffusion Of Atoms Research Articles

Unraveling the characteristics of adsorption and diffusion of oxygen atoms on the surface of Zr and ZrO2 crystals with point defects from molecular dynamic simulations

Unveiling the characteristics of adsorption and diffusion of oxygen atoms on the surface of zirconium alloys at microscale is significant during the initial stages of zirconium oxide layer formation in PWRs or LWRs. In this work, Adsorption and diffusion of oxygen atoms on the surface of Zr and ZrO2 crystals have been investigated using molecular dynamic simulations. A special focus of this work is on the diffusion coefficient calculation based on our developed unbiased approach. The results show that a weak effect of temperature on the adsorption rate of ZrO2. The greater influence of grain boundary orientation than the concentration of Frenkel defects on the adsorption rate of oxygen atoms. The number of oxygen atoms that diffuse deep into the studied samples after adsorption on the free surface increases with increasing temperature. Moreover, for crystals that have a certain concentration of Frenkel defects in the volume, the diffusion coefficients are greater than for defect-free crystals. The diffusion coefficient of adsorbed oxygen atoms is smaller for crystal system with grain boundary of Zr/Zr. This distinct feature may be solving the experimental puzzle of oxidation rate of zirconium alloys under neutron irradiation.

Electrical control of the switching layer in perpendicular magnetic tunnel junctions with atomically thin Ir dusting

The use of magnetic tunnel junction (MTJ)-based devices constitutes an important basis of modern spintronics. However, the switching layer of an MTJ is widely believed to be an unmodifiable setup, instead of a user-defined option, posing a restriction to the function of spintronic devices. In this study, we realized a reliable electrical control of the switching layer in perpendicular MTJs with 0.1 nm Ir dusting. Specifically, a voltage pulse with a higher amplitude drives the magnetization switching of the MTJ's bottom electrode, while a lower voltage amplitude switches its top electrode. We discussed the origin of this controllability and excluded the possibility of back-hopping. Given the established studies on enhancing the voltage-controlled magnetic anisotropy effect by adopting Ir, we attribute this switching behavior to the significant diffusion of Ir atoms into the top electrode, which is supported by scanning transmission electron microscopy with atomic resolution.

Study on the impact of hydrogen storage temperature on iron-based thermochemical hydrogen storage technology

Thermochemical hydrogen storage technology based on iron-based materials has received significant attention owing to its low cost, safety features, and high volumetric hydrogen storage density. However, no consensus has been established on the optimal temperature range for hydrogen storage. This study investigated the impact of hydrogen storage temperature on hydrogen consumption capacity, hydrogen release capacity, and hydrogen storage energy consumption. The hydrogen storage temperature was optimized with the objectives of low energy consumption and high hydrogen storage density. The experiments were conducted using thermogravimetric analyzer and gram-scale packed-bed reactor setups, accompanied by thermodynamic and kinetic calculations. The research indicated that at 550 °C, the optimal hydrogen storage temperature, the lowest relative energy demand was 32.30 %, with the hydrogen consumption capacity reaching the theoretical maximum value of 4.8 %, and the hydrogen release capacity reaching 4.04 %. Furthermore, achieving the theoretical maximum value of hydrogen consumption capacity became exceedingly difficult when the hydrogen storage temperature exceeded 570 °C. Microstructural characterization and kinetic calculations revealed that this phenomenon was attributed to the formation of a dense iron layer on the particle surface, which impeded the solid-state diffusion of oxygen atoms. The formation of the intermediate phase wüstite was identified as the cause of the formation of the dense iron layer. Overall, this study provided theoretical support for iron-based thermochemical hydrogen storage processes and offered a perspective into the reaction behavior of the reduction of magnetite with hydrogen.

Enhanced Nanotwinned Copper Bonding through Epoxy-Induced Copper Surface Modification.

For decades, Moore's Law has neared its limits, posing significant challenges to further scaling it down. A promising avenue for extending Moore's Law lies in three-dimensional integrated circuits (3D ICs), wherein multiple interconnected device layers are vertically bonded using Cu-Cu bonding. The primary bonding mechanism involves Cu solid diffusion bonding. However, the atomic diffusion rate is notably low at temperatures below 300 °C, maintaining a clear and distinct weak bonding interface, which, in turn, gives rise to reliability issues. In this study, a new method of surface modification using epoxy resin to form fine grains on a nanotwinned Cu film was proposed. When bonded at 250 °C, the interfacial grains grew significantly into both sides of the Cu film. When bonded at 300 °C, the interfacial grains extended extensively, eventually eliminating the original bonding interface.

Exploration of an atomic‐scale boron additive in SiAlON ceramics

AbstractSiAlON ceramics are of interest for high‐risk applications such as biomedical implants and combustion engine turbines. This work is part of a larger study aimed at leveraging atomic‐ or molecular‐scale additives to control the densification, microstructures, and ultimate structural properties of SiAlONs. Here, we investigate the effects of boron in silicon nitride‐based ceramics. The present work demonstrates a possible chemical method for controlling the microstructural development of SiAlONs by incorporating boric acid (H3BO3) into the starting powder blend. Raman spectroscopy and 11B solid‐state magic angle spinning nuclear magnetic resonance cooperatively indicate that after sintering, boron exists in threefold coordination with nitrogen in the turbostratic boron nitride (t‐BN) structure. The results of this work indicate that the incorporation of boron and generation of t‐BN bonding in the SiAlON system result in a narrower grain size distribution, a suppression of second phases such as yttrium aluminosilicates, and ultimately, increased flexure strength. A separate fractographic study showed that SiAlONs fabricated with 3 wt% boric acid exhibited fracture origins such as subtle surface flaws or cracks, while lower dopant levels and undoped SiAlONs typically failed from flaws such as inclusions or large grains. It is argued that the modification of the intergranular glass chemistry and resulting generation of t‐BN reduces atomic diffusion through the grain boundary phase and inhibits the crystallization of second phases as well as exaggerated grain growth that often characterizes the development of β′‐SiAlON.

Thermally stable Mo-Co-B thin film metallic glass as a potential diffusion barrier in Cu/Si contact system

Thin film metallic glass (TFMG) has demonstrated significant potential for applications in the semiconductor industry. In this work, fully amorphous Mo-Co-B thin films with a smooth surface and dense microstructure were prepared through magnetron sputtering. The thermal stability and diffusion barrier performance of the Mo-based TFMG were evaluated through vacuum annealing at temperatures ranging from 300 to 800 °C for 30 min. Nanoindentation tests were conducted to investigate the evolution of mechanical properties with annealing for the Mo-based thin film. When subjected to annealing at temperatures below 700 °C, the Mo-based thin film retained its fully amorphous structure. It displayed enhanced hardness and Young's modulus due to the annihilation of free volume with annealing. Increasing the annealing temperature to 700 °C and 800 °C resulted in surface oxidation and crystallization of the Mo-based TFMG, respectively, leading to a continuous decline in its mechanical properties. When employed as the diffusion barrier between Cu and Si, the Mo-based barrier layer effectively blocked the diffusion of Cu atoms through the barrier at temperatures below 800 °C. The failure of the barrier occurred at 800 °C due to the crystallization of the amorphous phase. Such excellent diffusion barrier performance of the thermally stable Mo-Co-B TFMG makes it a promising candidate as the barrier material in Cu metallization.

Multi-scale simulation of microstructural evolution for molten U–Zr–O ternary system

The morphological evolution of the molten corium is critical to the success of the “in-vessel retention” (IVR) strategy, which is of great significance for the safety of the nuclear industry under severe accidents. However, the direct observation of microstructural evolution by experiments is impossible in extreme conditions. Herein, a multi-scale simulation approach was employed to investigate the microstructural evolution and related mechanisms for the molten U–Zr–O ternary system. First, based on the reported calculated phase diagram, a simplified free energy formula describing a phase diagram of U–Zr–O was determined, where only liquid phases are focused. Then, the atomic diffusion coefficients were calculated by ab-initio molecular dynamics simulations. Based on such information, a homemade phase-field model was developed, which was coupled with Cahn–Hillard and Navier–Stokes equations. Accordingly, the microstructural evolution of molten U–Zr–O materials was systematically investigated. The results reveal that the evolution of the molten core was driven by both the decreasing free energy and gravity potential, accessing the final morphology of the system as a two-layer structure, including a metallic layer and an oxidized layer. Moreover, diverse intermediate morphologies could be observed from different initial component distributions, although their average compositions were identical. Finally, some intermediate simulated microstructural patterns agreed well with experimental observation, demonstrating the unstable structures captured by experiments and the validity of the simulations. The present study provides an effective approach to investigate the microstructural evolution of molten core and a guideline for optimizing the IVR strategy based on different morphologies in the corium.

Growth of diamond in liquid metal at 1 atm pressure.

Natural diamonds were (and are) formed (thousands of million years ago) in the upper mantle of Earth in metallic melts at temperatures of 900-1,400 °C and at pressures of 5-6 GPa (refs. 1,2). Diamond is thermodynamically stable under high-pressure and high-temperature conditions as per the phase diagram of carbon3. Scientists at General Electric invented and used a high-pressure and high-temperature apparatus in 1955 to synthesize diamonds by using molten iron sulfide at about 7 GPa and 1,600 °C (refs. 4-6). There is an existing model that diamond can be grown using liquid metals only at both high pressure and high temperature7. Here we describe the growth of diamond crystals and polycrystalline diamond films with no seed particles using liquid metal but at 1 atm pressure and at 1,025 °C, breaking this pattern. Diamond grew in the subsurface of liquid metal composed of gallium, iron, nickel and silicon, by catalytic activation of methane and diffusion of carbon atoms into and within the subsurface regions. We found that the supersaturation of carbon in the liquid metal subsurface leads to the nucleation and growth of diamonds, with Si playing an important part in stabilizing tetravalently bonded carbon clusters that play a part in nucleation. Growth of (metastable) diamond in liquid metal at moderate temperature and 1 atm pressure opens many possibilities for further basic science studies and for the scaling of this type of growth.

Effect of Adding Al on the Phase Structure and Gettering Performance of TiZrV Non-Evaporable Getter Materials.

Titanium zirconium vanadium (TiZrV) is a widely used non-evaporable getter (NEG) material with the characteristics of a low activation temperature and a large gas absorption capacity. At present, the research on TiZrV getters mainly focuses on the thin-film state, with little research on the bulk state. In this paper, a TiZrV getter was optimized by adding Al, and the phase structure, activation properties, and gettering performance were studied. With the addition of Al, the α-Zr phase and Ti2Zr phase changed into the Ti-Zr phase and Al-Zr, Al-Ti phase. The newly generated phase promoted the diffusion of hydrogen and oxygen atoms. The activation temperature decreased significantly, as shown in the in situ XPS results. The H2 and CO gettering performance of TiZrVAl samples was promoted to 2073 cm3·s-1 and 1912.8 cm3·s-1, increased by 40.7% and 40.3%. This paper provides valuable ideas for optimizing the properties of bulk TiZrV getters.

Feeling the strain: Enhancing the thermodynamics characteristics of magnesium nickel hydride Mg2NiH4 for hydrogen storage applications through strain engineering

This work is based on density functional theory (DFT) and studies the structural, electronic, thermodynamic properties and dehydrogenation kinetics of the hydride Mg2NiH4 under different uniaxial and biaxial strain applied to Mg2Ni or Mg2NiH4. structural properties are first studied based on generalized gradient (GGA) and local density (LDA). Thermodynamic and electronic properties and dehydrogenation kinetics are then studied using the GGA method based on the Perdew-Burke-Ernzerhor (PPE) approximation. The results obtained show that uniaxial/biaxial tensile and compressive strains are capable of inducing structural deformation by increasing the value of the strain step on both Mg2Ni and Mg2NiH4, and that these strains applied to Mg2NiH4 are capable of reducing the stability of the system more than strains applied to Mg2Ni, due to the contribution of strain energy. More specifically, it lowers the enthalpy of formation to −40 kJ/mol.H2 under compressive strain ε = −7.5% or biaxial tensile strain ε = +7.8%, which corresponds exactly to the ideal value suggested by the US Department of Energy (DOE) for materials suitable for hydrogen storage. And the decomposition temperature fell within the fuel cell operating range (PEM) of 289–393 K. On the other hand, under uniaxial and biaxial strains, the activation energy of hydrogen atom diffusion in Mg2NiH4 varied between 0.40 eV and 0.22 eV, resulting in a remarkable improvement in dehydrogenation properties. Analysis of the total (TDOS) and partial (PDOS) density curves shows that the Mg2NiH4 system has a metallic characteristic, and that this characteristic is maintained by increasing the strain pitch, with a variation in the energy width of the valence band.

Microstructural evolution and mechanisms affecting the mechanical properties of wire arc additively manufactured Al-Zn-Mg-Cu alloy reinforced with high-entropy alloy particles

The mechanical properties of Al-Zn-Mg-Cu alloys produced via wire arc additive manufacturing (WAAM) are often weakened by the presence of continuous and coarse precipitated phases, which significantly limits their practical applications. In this study, high-entropy alloy (HEA) particles were incorporated into Al-Zn-Mg-Cu alloy during the WAAM process, which inhibits the continuity of precipitated phase, and the mechanism of microstructure evolution and macroscopic mechanical properties optimization of the components are explored. The results show that HEA particles promote grain refinement, and disrupt the formation of continuous precipitated phase along the grain boundary by generating plenty of fine spot-like precipitated phases, thus inhibiting grain boundary segregation. The spot-like precipitated phases are connected via a slender second-phase-band. The primary precipitates include the metastable η', stable η, and T phases, and the diffusion of solute atoms forms the Al3Ni and Al3(Ni, Cu)2 phases. The tensile strength increases from 247.4±5.9 MPa to 326.2±19.7 MPa in the horizontal direction and from 273.0±13.7 MPa to 335.4±11.1 MPa in the vertical direction, which correspond to increases of 31.9 % and 22.9 % respectively. The enhancement of mechanical properties is mainly attributed to Hall-Petch, Orowan, load-transfer, solid-solution and dislocation strengthening mechanisms. Only slight variation occurred in the elongation, the increased number of fine spot-like precipitated phases and grain boundaries hinder the crack propagation, while the increased number of pores facilitates the crack propagation, and these effects almost balance each other out in competition. These findings are expected to provide new insights into the microstructure optimization of WAAM components, thereby meeting more practical applications.

Laser shock-enabled optical–thermal–mechanical coupled welding method for silver nanowires

Silver nanowires (AgNWs) are recognized as highly promising materials for flexible and transparent electrode applications. However, existing material-processing methods fail to achieve uniform and reliable AgNWs junctions. In this study, we propose a new method using the laser shock effect combined with the laser heating effect, for creating AgNW junctions within thin films. We explored the welding mechanism of AgNWs through optic-thermal welding, laser shock-enabled mechanical welding, and laser-shock-enabled optical-thermal-mechanical (LS-OTM) experiments, as well as numerical simulations, and the results demonstrate that the innovative mechanism of the LS-OTM process lies in its utilization of laser shock to adjust the gap between the nanowire junctions, which in turn achieves a fine control of the thermal effect of the heating laser localised surface plasmon resonance, and the atomic diffusion in the solid state at intermediate temperature under the action of the impact force is the mechanism of the formation of high-quality junctions. We prepared flexible transparent conductive films and studied their transmittance, conductivity, and thermal properties, the results show that the flexible transparent conductive films prepared by LS-OTM welding method have excellent transmittance, conductivity, and thermal properties, this verifies the feasibility and effectiveness of this processing strategy. The LS-OTM method is a viable solution for manufacturing transparent, conductive films from AgNWs for emerging applications such as flexible heated films, flexible displays, and wearable medical devices.

Plasma activated titanium-based bonding for robust and reliable Si–Si and Si-glass integration

The exceptional biocompatibility of Ti/Ti bonding technology makes it highly significant for the sealing of implantable devices. However, achieving highly reliable Ti/Ti bonding at low temperatures is challenging due to the facile formation of a native oxide film, which hinders the diffusion of interfacial atoms. This paper develops a low-temperature Ti/Ti bonding process based on plasma activation, resulting in a remarkable bonding strength of 17.5 MPa at 300 °C, which can be used for Si–Si homogeneous and Si-glass heterogeneous integration. After optimizing the processes, the surface oxides of Ti can be partially reduced through Ar/H2 plasma activation to form unsaturated chemical bonds, thereby overcoming the limitation of film thickness in Ti/Ti bonding. The results indicate that plasma activation can realize high strength Ti/Ti bonding in the film thickness range of 10–50 nm. It is worth noting that the Ti/Ti bonding area and strength remain stable after immersion experiments in DI water and normal saline for 7 days, which proves that Ti/Ti bonding has good corrosion resistance. In addition, the microcavity structures were prepared using photolithography and etching techniques. The Ti/Ti bonding technology enables direct bonding of microcavity structures with plate Ti, and an intact bonding interface near the microcavity was obtained. This low-temperature Ti/Ti bonding technology is suitable for the three-dimensional integration of various substrate materials, and its excellent corrosion resistance makes it promising for application in the sealing of BioMEMS.

Grain size prediction for stainless steel fabricated by material extrusion additive manufacturing

Most traditional powder melting-based additive manufacturing (AM) technologies generally yield high-performance parts at the expense of additional cost and energy consumption. As an economical and efficient alternative method, material extrusion (ME) that deploys polymer-based filaments with highly filled metal particles offers the possibility of scalable, low-cost fabrication of metal components. As a critical step, sintering governs the mechanical strength and geometry of the final parts. The grain growth behavior induced during sintering should be well controlled to achieve the parts with the desired mechanical performance. Due to the nature of AM, grain growth kinetics could also involve extremely complex grain boundary migration and atomic diffusion mechanisms caused by the heterogeneous pore distribution. In this work, an analytical model was developed to predict and understand the grain growth behavior of stainless steel (SS) 316L built by ME-based sintering-assisted AM. Such a model accounts for anisotropic viscosity parameters calibrated through a three-dimensional dilatometry test, enabling the prediction of grain size evolution during sintering. Grain growth kinetic parameters were further identified by the grain size data at the heating and holding stages. To validate and generalize the model, we also conducted the grain size evolution prediction under different sintering temperature profiles for as-built SS 316L specimens. This work will provide scientific insights into the grain growth behavior of metal parts built by this AM technique and its understanding can be readily transferred to other sintering-assisted AM processes like binder jetting and ink writing for metal structure creation.

Comparative studies on microstructural characteristics and wear behavior of high-speed and low-speed laser cladding graphene/CoCrFeMo0.5NiTi0.5 high-entropy alloy composite layers

To prevent the failure of curved parts due to wear under actual working conditions, a graphene/CoCrFeMo0.5NiTi0.5 high-entropy alloy composite coating was prepared on the surface of a curved part using both high-speed and low-speed laser cladding (LLC). The surface morphology, physical phases, elemental distribution, microstructure, microhardness, and wear behavior of this coating applied via high-speed and LLC were comparatively studied. The results showed that the maximum height difference on the surface of the high-speed laser cladding (HLC) layer was only 44.7 % of that of the LLC layer, and the surface powder was more completely melted. The average microhardness of the HLC layer was about 1.49 times higher than that of the LLC layer and showed a maximum hardness of 666.38 HV0.5, which was about 2.95 times higher than that of the substrate. The internal microstructure of the HLC layer was finer and the diffusion of Fe atoms from the substrate into the coating was significantly reduced. In all three wear environments, abrasive wear occurred in both the low-speed and HLC layers. The total wear rate of the LLC layer was 230.588 μm3 N−1 mm−1, which was about 3.06 times higher than that of the HLC layer (75.395 μm3 N−1 mm−1). The wear surfaces of both cladding layers were oxidized, and the wear rate increased with the oxygen content on the wear surfaces under the same wear conditions. Meanwhile, the oxygen content of the wear surfaces of both cladding layers in sodium chloride solution was significantly higher than that during dry wear.

Effect of Grain Structure of Gold Plating Layer on Environmental Reliability of Sintered Ag-Au Joints.

Gold-plated substrate is widely used in sintering with silver paste because of its high conductivity, stability, and corrosion resistance. However, due to massive interdiffusion between Ag and Au atoms, it is challenging for sintered Ag-Au joints to maintain high reliability. In order to study the effect of grain structure of gold plating layer on the environmental reliability of sintered Ag-Au joints, we prepared four substrates with different gold structures. In addition to the original gold structure (Au substrate), other gold structures were obtained by heat treatment at temperatures of 150 °C (Au-150 substrate), 250 °C (Au-250 substrate), and 350 °C (Au-350 substrate) for 1 h. Compared with the other three gold substrates, the sinter jointed on the Au-350 substrate obtained the highest shear strength. By analyzing the grain structure of the gold plating layer, it is found that the average grain size of the Au-350 substrate is the largest, and the proportion of low-angle grain boundaries is less. Few grain boundaries have a positive impact on inhibiting the excessive diffusion of Ag atoms and improving the bonding performance of the joint. Based on the above study, we further evaluated the environmental reliability of sintered joints. In 150 °C high-thermal storage, the interdiffusion of Ag and Au in the sintered joint on the Au-350 substrate was restricted, retaining stronger bonding until 200 h. In a hygrothermal environment of 85 °C/85% RH, the shear strength of the sintered Ag-Au joint with the Au-350 substrate maintained above 40.2 MPa during 100 h aging. The results indicated that the sintered Ag-Au joint on the Au-350 substrate with the largest grain size has superior high thermal reliability and hygrothermal reliability.

Enhanced Electrical Properties of Bi2−xSbxTe3 Nanoflake Thin Films Through Interface Engineering

The structure–property relationship at interfaces is difficult to probe for thermoelectric materials with a complex interfacial microstructure. Designing thermoelectric materials with a simple, structurally‐uniform interface provides a facile way to understand how these interfaces influence the transport properties. Here, we synthesized Bi2−xSbxTe3 (x = 0, 0.1, 0.2, 0.4) nanoflakes using a hydrothermal method, and prepared Bi2−xSbxTe3 thin films with predominantly (0001) interfaces by stacking the nanoflakes through spin coating. The influence of the annealing temperature and Sb content on the (0001) interface structure was systematically investigated at atomic scale using aberration‐corrected scanning transmission electron microscopy. Annealing and Sb doping facilitate atom diffusion and migration between adjacent nanoflakes along the (0001) interface. As such it enhances interfacial connectivity and improves the electrical transport properties. Interfac reactions create new interfaces that increase the scattering and the Seebeck coefficient. Due to the simultaneous optimization of electrical conductivity and Seebeck coefficient, the maximum power factor of the Bi1.8Sb0.2Te3 nanoflake films reaches 1.72 mW m−1 K−2, which is 43% higher than that of a pure Bi2Te3 thin film.

The nucleation and growth mechanism of solid-state amorphization and diffusion behavior at the W–Cu interface

The W–Cu materials hold vast potential for applications in electronic information, nuclear energy, and aerospace sectors. Here, we report a new occurrence of solid-state amorphization on the Cu side near W–Cu interface. A potential function with accuracy close to density functional theory (DFT) is constructed using machine learning, while the atomic mechanism of solid amorphous nucleation and growth is unveiled through a combination of in-situ transmission electron microscopy (TEM) and molecular dynamics (MD) simulations. Our findings indicate that the Cu near W–Cu interface experiences an amorphous phase transition at 400 °C. This amorphous nucleation is linked to the stress coupling between the W–Cu interface and dislocations within Cu. The lattice distortion arising from dislocations, combined with interfacial stress, results in lattice twisting, leading to the formation of dislocation pileup, HCP and disordered structures. The results of the in-situ TEM show that the dislocation stacking and HCP structures exist for a short period of time, and these structures quickly turn into disordered structures, eventually forming an amorphous band with a width of about 8 nm at the W–Cu interface. However, the amorphous structure is unstable. As temperature rises, the amorphous structure undergoes recrystallization into an ordered structure. Furthermore, we investigated the atomic diffusion behavior of W–Cu. Simulation results reveal that the defect in W significantly impacts diffusion. In summary, our study provides theoretical support for the nucleation mechanism of solid-state amorphization, the understanding of interfacial stress-strain, and the application of W–Cu materials.

Pressureless sintered high-entropy transition metal diboride ceramics doped with yttrium tetraboride

High entropy diborides (HEBs) are new candidates of ultra-high temperature ceramics. However, it is difficult to obtain dense HEB ceramics via pressureless sintering. In this study, yttrium tetraboride (YB4) was introduced to consolidate (Ti0.25Zr0.25Hf0.25Ta0.25)B2 (4TMB2) ceramics and its effects on the microstructures and mechanical properties were studied. YB4 addition facilitates the densification and grain elongation of 4TMB2 ceramics by forming eutectic liquid phases and eliminating oxide impurities. Relative density of 4TMB2 ceramics containing 5 vol% YB4 reaches to 94.4 % after pressureless sintered at 2000 °C for 3 h. The hardness and toughness determined by indention method are 26.9±1.5 GPa and 5.73±1.65 MPa∙m1/2. This ceramics also exhibit excellent four-point bending creep resistance with the strain rate of 1.48×10−7 s−1 at 1900 °C under 20 MPa. The observed creep behavior is attributed to grain boundary sliding, plastic deformation, grain refinement and enhanced atomic diffusion of Y element, all driven by high-temperature stresses.

Luminescence-Monitored Progressive Chemical Pressure Implementation Realized through Successive Y3+ and Mg2+ Doping into Ca10.5(PO4)7:Eu2.

Chemical pressure generated through ion doping into crystal lattices has been proven to be conducive to exploration of new matter, development of novel functionalities, and realization of unprecedented performances. However, studies are focusing on one-time doping, and there is a lack of both advanced investigations for multiple doping and sophisticated strategies to precisely and quantitatively track the gradual functionality evolution along with progressive chemical pressure implementation. Herein, high-valent Y3+ and equal-valent Mg2+ is successively doped to replace multiple Ca sites in Ca10.5(PO4)7:Eu2+. The luminescence evolution of Eu2+ serves as an optical probe, allowing step-by-step and atomic-level tracking of the site occupation of Y3+ and Mg2+, interassociation of Ca sites, and ultimately functionality improvement. The resulting Ca8MgY(PO4)7:Eu2+ displays a record-high relative sensitivity for optical thermometry. Utilization of the environment-sensitive emission of Eu2+ as a luminescent probe has offered a unique approach to monitoring structure-functionality evolution in vivo with atomic precision, which shall also be extended to optimization of other functionalities such as ferroelectricity, conductivity, thermoelectricity, and catalytic activity through precise control over atomic diffusion in other types of substances.