Near-Infrared Dual-Modal Sensing of Force and Temperature in Total Knee Replacement Using Mechanoluminescent Phosphor of Sr3Sn2O7: Nd, Yb.

Knee replacement surgery confronts challenges including patient dissatisfaction and the necessity for secondary procedures. A key requirement lies in dual-modal measurement of force and temperature of artificial joints during postoperative monitoring. Here, a novel non-toxic near-infrared (NIR) phosphor Sr3Sn2O7:Nd, Yb, is designed to realize the dual-modal measurement. The strategy is to entail phonon-assisted upconversion luminescence (UCL) and trap-controlled mechanoluminescence (ML) in a single phosphor well within the NIR biological transmission window. The phosphor is embedded in medical bone cement forming a smart joint in total knee replacements illustrated as a proof-of-concept. The sensing device can be charged in vitro by a commercial X-ray source with a safe dose rate for ML, and excited by a low power 980 nm laser for UCL. It attains impressive force and temperature sensing capabilities, exhibiting a force resolution of 0.5% per 10 N, force detection threshold of 15 N, and a relative temperature sensitive of up to 1.3% K-1 at 309 K. The stability against humidity and thermal shock together with the robustness of the device are attested. This work introduces a novel methodological paradigm, paving the way for innovative research to enhance the functionality of artificial tissues and joints in living organisms.

Interface-Mediated Mechanoluminescence Enhancement from Heterojunction Phosphors: Experiment and Theory.

Mechanoluminescence (ML) phosphors have made significant progress in various fields, such as artificial intelligence, the Internet of Things, and biotechnology. However, enhancing their weak ML intensity still remains a challenge. Here, we report a new series of Na1-xMgxNbO3:Pr3+ (x = 0.00, 0.10, 0.20, 0.40, 0.60, 0.80, and 1.00 mol %) heterojunction systems, which exhibit significant ML enhancement as compared with either the Pr3+-doped NaNbO3 or MgNbO3, and the physical mechanisms behind the ML enhancement have been explored comprehensively from both the experiment and theory points of view. Experimental tests, including thermoluminescence and positron annihilation lifetime measurements, combined with first-principles calculations, consistently indicate that the ML enhancement observed in these newly reported systems is due to the formation of heterojunctions, which plays a crucial role in modulating the defect configuration of the phosphors and facilitating efficient charge transfer. By controlling the Na/Mg ratio in conjunction with Pr3+ doping, continuous changes in the band offset and the concentrations of certain types of traps in the forbidden gap are achieved, leading to the optimum conditions in the 8/2 ratio samples. These findings demonstrate a novel type of ML phosphor and provide a theoretical basis for the design of high-performance ML phosphor.

The endless search for better alloys.

Machine learning narrows down the enormous search space for functional materials.

Design of defected TaN supercells dataset for structural and elastic properties from ab initio simulations and comparison to experimental data.

These data are supplied for supporting their interpretations and discussions provided in the research article "Large influence of vacancies on the elastic constants of cubic epitaxial tantalum nitride layers grown by reactive magnetron sputtering" by Abadias et al. (2020) [doi: 10.1016/j.actamat.2019.11.041]. The datasheet describes the experimental methods used to measure the longitudinal (VL) and transverse (VT) sound velocities of cubic epitaxial TaN/MgO thin films, and their related cubic elastic constants (c11, c12 and c44), by the picosecond laser ultrasonic (PLU) and the Brillouin light scattering (BLS) techniques, respectively. First-principles numerical simulations provide additional data using specifically designed supercells of TaN structures, generated either by hand or using the alloy theoretical automated toolkit (ATAT) method [A. Zunger et al. (1990)], with different configurations (random, cluster and ordered) of defects (Ta and N vacancies). Phonons calculations support discussion of dynamical mechanical stability of defected TaN cubic structures. The data illustrate the huge role of vacancies in elastic properties and phase stability of TaN films.

Cooperative effect of silicon and other alloying elements on creep resistance of titanium alloys: insight from first-principles calculations.

Creep resistance is one of the key properties of titanium (Ti) alloys for high temperature applications such as in aero engines and gas turbines. It has been widely recognized that moderate addition of Si, especially when added together with some other elements (X), e.g., Mo, significantly improves the creep resistance of Ti alloys. To provide some fundamental understandings on such a cooperative effect, the interactions between Si and X in both hexagonal close-packed α and body-centered cubic ß phases are systematically investigated by using a first-principles method. We show that the transition metal (TM) atoms with the number of d electrons (Nd) from 3 to 7 are attractive to Si in α phase whereas those with Nd > 8 and simple metal (SM) alloying atoms are repulsive to Si. All the alloying atoms repel Si in the ß phase except for the ones with fewer d electrons than Ti. The electronic structure origin underlying the Si-X interaction is discussed based on the calculated electronic density of states and Bader charge. Our calculations suggest that the beneficial X-Si cooperative effect on the creep resistance is attributable to the strong X-Si attraction.

Elastic constants of random solid solutions by SQS and CPA approaches: the case of fcc Ti-Al.

Special quasi-random structure (SQS) and coherent potential approximation (CPA) are techniques widely employed in the first-principles calculations of random alloys. Here we scrutinize these approaches by focusing on the local lattice distortion (LLD) and the crystal symmetry effects. We compare the elastic parameters obtained from SQS and CPA calculations, taking the random face-centered cubic (fcc) Ti(1-x)Al(x) (0 ≤ x ≤ 1) alloy as an example of systems with components showing different electronic structures and bonding characteristics. For the CPA and SQS calculations, we employ the Exact Muffin-Tin Orbitals (EMTO) method and the pseudopotential method as implemented in the Vienna Ab initio Simulation Package (VASP), respectively. We show that the predicted trends of the VASP-SQS and EMTO-CPA parameters against composition are in good agreement with each other. The energy associated with the LLD increases with x up to x = 0.625 ~ 0.750 and drops drastically thereafter. The influence of the LLD on the lattice constants and C12 elastic constant is negligible. C11 and C44 decrease after atomic relaxation for alloys with large LLD, however, the trends of C11 and C44 are not significantly affected. In general, the uncertainties in the elastic parameters associated with the symmetry lowering turn out to be superior to the differences between the two techniques including the effect of LLD.

Magnetic effect on the interfacial energy of the Ni(1 1 1)/Cr(1 1 0) interface.

The work of separation and interfacial energy of the Ni(1 1 1)/Cr(1 1 0) interface are calculated via first-principles methods. Both coherent and semicoherent interfaces are considered. We find that magnetism has a significant effect on the interfacial energy, i.e. removing magnetism decreases the interfacial energy of the semicoherent interface by around 50% . Electronic, magnetic and atomic structures at the interface are discussed. An averaging scheme is used to estimate the work of separation and interfacial energy of semicoherent interfaces based on the results of coherent interfaces. The limitations of the scheme are discussed.

Generalized stacking fault energies of alloys.

The generalized stacking fault energy (γ surface) provides fundamental physics for understanding the plastic deformation mechanisms. Using the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation, we calculate the γ surface for the disordered Cu-Al, Cu-Zn, Cu-Ga, Cu-Ni, Pd-Ag and Pd-Au alloys. Studying the effect of segregation of the solute to the stacking fault planes shows that only the local chemical composition affects the γ surface. The calculated alloying trends are discussed using the electronic band structure of the base and distorted alloys.Based on our γ surface results, we demonstrate that the previous revealed 'universal scaling law' between the intrinsic energy barriers (IEBs) is well obeyed in random solid solutions. This greatly simplifies the calculations of the twinning measure parameters or the critical twinning stress. Adopting two twinnability measure parameters derived from the IEBs, we find that in binary Cu alloys, Al, Zn and Ga increase the twinnability, while Ni decreases it. Aluminum and gallium yield similar effects on the twinnability.

The effect of electron localization on the electronic structure and migration barrier of oxygen vacancies in rutile.

By applying the on-site Coulomb interaction (Hubbard term U) to the Ti d orbital, the influence of electron localization on the electronic structure as well as the transport of oxygen vacancies (VO) in rutile was investigated. With U = 4.5 eV, the positions of defect states in the bandgap were correctly reproduced. The unbonded electrons generated by taking out one neutral oxygen atom are spin parallel and mainly localized on the Ti atoms near VO, giving rise to a magnetic moment of 2 µB, in agreement with the experimental finding. With regard to the migration barrier of VO, surprisingly, we found that U = 4.5 eV only changed the value of the energy barrier by ±0.15 eV, depending on the diffusion path. The most probable diffusion path (along [110]) is the same as that calculated by using the traditional GGA functional. To validate the GGA + U method itself, a hybrid functional with a smaller supercell was used, and the trend of the more probable diffusion path was not changed. In this regard, the traditional GGA functional might still be reliable in the study of intrinsic-defect transportation in rutile. Analyzing the atomic distortion and density of states of the transition states for different diffusion paths, we found that the anisotropy of the diffusion could be rationalized according to the various atomic relaxations and the different positions of the valence bands relative to the Fermi level of the transition states.

Trapping of interstitial defects: filling the gap between the experimental measurements and DFT calculations.

We show that any impurity will slow the diffusion of oxygen in Nb. Using a first-principles plane-wave pseudopotential method and the supercell model, we calculated the interaction energies between substitutional atoms (SA) (X = Ti, V, Ta, Zr, and Hf) and interstitial oxygen in a Nb matrix. All impurities act as traps for oxygen: undersized SA (Ti and V) have strongest binding at the nearest octahedral interstice, while for oversized SA (Zr and Hf), the strongest trapping site is the second-nearest octahedral interstice. We evaluated the diffusion coefficients of O in the Nb-X alloys using kinetic Monte Carlo (KMC) modeling based in the transition state theory, using our calculated oxygen migration energies. From this, the effective (average) X-O interaction energies were extracted using the Oriani model (Oriani 1970 Acta Metall. 18 147-57). The effective X-O interaction energies are close to the strongest interaction energies between X and O obtained from the direct supercell calculations. The phenomenological effective diffusion barrier obtained from the KMC modeling is close to the energy difference between the most stable configuration and the highest saddle point along the diffusion path. Both results demonstrate that the weaker trapping site has negligible influence on the diffusion of O.

Magnetic properties and temperature-dependent half-metallicity of Co2Mn(Ga(1-x)Z(x)) (Z=Si, Ge, Sn) from first-principles calculation.

Using the first-principles exact muffin-tin orbitals method in combination with the coherent potential approximation, we investigated the magnetic properties, exchange interactions, and temperature-dependent half-metallicity of the Co2Mn(Ga1-xZx) (Z=Si, Ge, Sn) alloys. The total magnetic moment follows perfectly a previously proposed Slater-Pauling relation, i.e., µ0 = Nt - 24, with Nt being the number of valence electrons. The Co-Mn and Co1-Co2 (inter-sublattice) interactions are dominated by direct exchange, whereas the Co1-Co1 (intra-sublattice) interaction is characterized by superexchange. The Mn-Mn exchange interaction in Co2MnGa is of long-ranged RKKY-type. However, the Mn-Mn exchange interactions in Co2MnZ are relatively localized and can be attributed to superexchange. The Co-Mn, Co1-Co2 and Co1-Co1 total exchange interactions increase with x, whereas the Mn-Mn total exchange interactions show convex behavior. The calculated Curie temperature (TC) increases with x. The ability of Z to enhance TC follows the sequence of Si > Ge > Sn, in agreement with the experimental findings. The temperature dependence of the spin polarization at the Fermi level [P(T)] is investigated based on the disordered local moment model. P(T) drops abruptly at temperatures much lower than TC. At temperatures higher than 200 K, the composition with higher TC generally corresponds to larger P(T).

The effect of long-range order on the elastic properties of Cu3Au.

Ab initio calculations, based on the exact muffin-tin orbitals method are used to determine the elastic properties of Cu-Au alloys with Au/Cu ratio 1/3. The compositional disorder is treated within the coherent potential approximation. The lattice parameters and single-crystal elastic constants are calculated for different partially ordered structures ranging from the fully ordered L1(2) to the random face centered cubic lattice. It is shown that the theoretical elastic constants follow a clear trend with the degree of chemical order: namely, C(11) and C(12) decrease, whereas C(44) remains nearly constant with increasing disorder. The present results are in line with the experimental findings that the impact of the chemical ordering on the fundamental elastic parameters is close to the resolution of the available experimental and theoretical tools.

Predicted suppression of the superconducting transition of new high-pressure yttrium phases with increasing pressure from first-principles calculations.

Structure searches for new high-pressure phases of Y metal have been performed by using evolutionary algorithms in conjunction with a first-principles, pseudopotential plane-wave method based on density functional theory. The oF16-Fddd and hP3-P3(1)21 phases are predicted to be energetically favorable at pressures over 97 GPa. These two phases are shown to be dynamically stable by computing their phonon dispersions. We thus propose that oF16-Fddd and hP3-P3(1)21 are the most probable crystal structures Y may take in the 97-206 GPa range. The superconducting critical temperatures (T(c)) of the new phases are estimated using the Allen-Dynes formula. The T(c) is predicted to decrease with increasing pressure over about 100 GPa, in sharp contrast to its observed monotonic increase under lower pressure. The electronic origins of the stabilities of the proposed high-pressure phases have also been investigated.

Towards an exact treatment of exchange and correlation in materials: application to the "CO adsorption puzzle" and other systems.

It is shown that the errors of present-day exchange-correlation (XC) functionals are rather short ranged. For extended systems, the correction can therefore be evaluated by analyzing properly chosen clusters and employing highest-quality quantum chemistry methods. The XC correction rapidly approaches a universal dependence with cluster size. The method is applicable to bulk systems as well as to defects in the bulk and at surfaces. It is demonstrated here for CO adsorption at transition-metal surfaces, where present-day XC functionals dramatically fail to predict the correct adsorption site, and for the crystal bulk cohesive energy.