Temperature Time Research Articles

Residual Stress Homogenization of Hybrid Implants

Objectives: Hybrid implants commonly exhibit decreased corrosion resistance and fatigue due to differences in compressive residual stresses between the smooth and rough surfaces. The main objective of this study was to investigate the influence of an annealing heat treatment to reduce the residual stresses in hybrid implants. Methodology: Commercially pure titanium (CpTi) bars were heat-treated at 800 °C and different annealing times. Optical microscopy was used to analyze the resulting grain growth kinetics. Diffractometry was used to measure residual stress after heat treatment, corrosion resistance by open circuit potential (EOCP), corrosion potentials (ECORR), and corrosion currents (ICORR) of heat-treated samples, as well as fatigue behavior by creep testing. The von Mises distribution and the resulting microstrains in heat-treated hybrid implants and in cortical and trabecular bone were assessed by finite element analysis. The results of treated hybrid implants were compared to those of untreated hybrid implants and hybrid implants with a rough surface (shot-blasted). Results: The proposed heat treatment (800 °C for 30 min, followed by quenching in water at 20 °C) could successfully homogenize the residual stress difference between the two surfaces of the hybrid implant (−20.2 MPa). It provides better fatigue behavior and corrosion resistance (p ˂ 0.05, ANOVA). Stress distribution was significantly improved in the trabecular bone. Heat-treated hybrid implants performed worse than implants with a rough surface. Clinical significance: Annealing heat treatment can be used to improve the mechanical properties and corrosion resistance of hybrid surface implants by homogenizing residual stresses.

Effect of Annealing Time on Grain Structure Evolution and Superplastic Response of Al-Mg 5xxx Alloys

The impact of annealing on the recrystallized grain structure and superplastic behavior of two Al-Mg 5xxx alloys used for high-speed blow forming (HSBF) was studied. The results revealed that both alloys demonstrated rapid static recrystallization after only a few minutes of annealing at 520 °C, forming fine and equiaxed grain structures. After four min of annealing, Alloy 2 (Al-4.0Mg-1.18Mn) exhibited a higher fraction of small grains (<10 µm) compared to Alloy 1 (Al-4.5Mg-0.74Mn). Moreover, Alloy 2 displayed enhanced resistance to grain coarsening with increasing annealing times, which was attributed to its higher amount of Al6(Mn,Fe) intermetallic particles and a higher number density of Mn dispersoids. Optimizing the annealing time can effectively develop a fine and stable grain structure in Al-Mg 5xxx alloys. During tensile deformation, Alloy 2 consistently showed higher ductility compared to Alloy 1 at low strain rates (170% vs. 138% at 0.001 s−1 and 163% vs. 134% at 0.01 s−1), whereas at a high strain rate of 1 s−1, both alloys displayed comparable tensile elongation. The high superplastic response of Alloy 2 at low strain rates renders it a superior superplastic alloy for HSBF applications.

Enhancement of superconducting properties of grown FeTe0.65Se0.35 single crystals through air annealing

Abstract This work investigates the annealing effects on the superconducting properties of FeTe0.65Se0.35 single crystals. We examine the impact of varying annealing times on the magnetotransport, magnetic, and vortex pinning properties of the single crystals. The structural analysis shows the single crystalline growth of crystals along the c-axis. X-ray photoelectron spectroscopy results confirm the presence of iron oxides in the annealed samples. Temperature-dependent resistivity and magnetization measurements confirm the superconductivity in the as-grown and annealed samples. However, the as-grown sample shows a broad superconducting transition and low superconducting volume fraction, but after annealing, significant improvement in both is observed. Moreover, the self-field critical current density at 2 K is enhanced by a factor of ~4.5 for the optimally annealed sample compared to the as-grown sample. Experimental observations have been analyzed with the theoretical models to understand the effects of annealing on the vortex pinning mechanisms. Further, the specific heat study confirms the bulk superconductivity in the annealed sample compared to the as-grown single crystal. Overall, our study indicates that the superconducting properties vary with the annealing time, and the best results are obtained at an optimum annealing time.

Rapid Mg substitution to Ga-sites and slow defect recovery revealed by depth-resolved photoluminescence in Mg/N-ion-implanted GaN

Toward p-type GaN formation by Mg ion implantation (I/I) applicable to devices, depth-resolved photoluminescence (PL) revealed key behaviors during activation annealing for precise profile control, such as Mg substitution into Ga-sites (MgGa) and recovery of I/I defects. Depth profiles of the MgGa acceptor concentration were measured for Mg-I/I and Mg/N-I/I samples after ultra-high-pressure annealing at 1300 °C for 1–60 min. The cycle of low-damage dry etching and PL measurement was repeated over the I/I depth, and the MgGa concentration was estimated at each depth based on the calibration curve for the PL intensity ratio between acceptor-bound excitons (A0XA) and free excitons (FXA). In the region deeper than the I/I peak of 0.3 μm, almost all of the Mg atoms rapidly substituted into Ga-sites during the short annealing process. By contrast, the Mg substitution ratios in the shallower region were low when the annealing process was short but were improved by the sequential N-I/I. The low substitution ratio can be explained by MgGa bonding with nitrogen vacancy (VN)-related defects, while the implanted N-ions can compensate them. The PL intensity near the mean implantation depth of Mg/N-I/I was gradually improved as the annealing duration was increased to 60 min, indicating a slow reduction of nonradiative recombination centers. Simultaneously, the green luminescence associated with the VN-related defects decreased in intensity with increasing annealing time. Therefore, the main effect of prolonging annealing is the enhancement of slow defect recovery rather than enhancement of the Mg substitution as a fast process.

Tempering behavior and mechanical properties of tempered AISI H13 steel

Abstract Microstructural evolutions of AISI H13 steel during tempering were quantitatively investigated by scanning electron microscopy (SEM), x-ray diffractometer (XRD), impact test machine, rockwell hardness tester, ball-on-disk tester in order to describe the main mechanism of softening. Under the condition that the tempering time is 2 h, the hardness increases slightly as the tempering temperature increases, but decreases rapidly when the tempering temperature exceeds 500 °C, while the impact energy increases in proportion to the tempering temperature. Friction tests were conducted in dry condition with a load of 30 N, and the friction coefficient and wear rate according to tempering conditions were measured to prove the correlation with hardness and microstructure. In addition, primary tempering from 300 °C to 700 °C was performed at various times to establish a kinetic model to predict hardness under specific tempering conditions.

Non-Arrhenius grain growth in SrTiO3: Impact on grain boundary conductivity and segregation

In this study, a correlation between the conductivity, space charge layers, solute drag and non-Arrhenius grain growth in SrTiO3 was investigated. Strontium titante is known for its non-Arrhenius grain growth where grain growth rates decrease by orders of magnitude with increasing temperatures between 1350°C and 1425°C. Here, undoped SrTiO3 was sintered and annealed at temperatures below and above the grain growth transition. The influence of the annealing temperature and time on the conductivity and space charge layers at grain boundaries (GBs) in SrTiO3 was investigated by electrochemical impedance spectroscopy (EIS). STEM-EDS analysis indicates the presence of GBs with qualitative different cationic segregation in SrTiO3. A distortion of the GB semi-circle in the impedance plots was found which was attributed to the presence of multiple GB types with different electric properties and space charge layers. The presence of two GB types as indicated by impedance analysis corresponds well with previous results, where solute drag and segregation was supposed to cause the non-Arrhenius grain growth behavior of SrTiO3.

Investigation on effect of L12 and B2 phases on tensile properties and mechanisms of Al0.3CoCrFeNi high entropy alloy through aging treatment

Al0.3CoCrFeNi high entropy alloys (HEAs) have excellent mechanical properties due to the large tunability of microstructures, which makes them one of the most promising candidates for engineering application. In the aspect of enhancing tensile properties, precipitation strengthening was verified effective in this HEA and more studies are needed to deepen relative understanding. In this work, Al0.3CoCrFeNi HEAs with coarse-grained single FCC (A) and fine-grained triplex FCC + B2 + σ (B) structures were aged at different temperatures and times to precipitate second phases, and the tensile properties and mechanisms of aged specimens were studied. The results showed that aging of A resulted in the main precipitation of L12 phases throughout FCC matrix and increasing aging temperature obviously increased L12 size, whereas increasing annealing time had minor effect on phase coarsening. At small L12 size of ~2.0nm, stacking fault shearing mechanism was activated during tension and planar dislocation configurations were formed, leading to simultaneous increase of strength and ductility. With increasing L12 size to ~10.0nm, the deformation mechanism was transformed into anti-phase boundary shearing and Orowan bypassing and wavy dislocation configurations predominated, which resulted in the significant increase of yield strength from ~263MPa to ~433MPa without sacrificing notable ductility. On the other hand, aging of B induced the formation of fine B2 phases at residual dislocations and enhancement of tensile yield strength from ~705MPa to ~759MPa. The ductility decreased slightly from ~32% to ~28%, which was related to the plastic deformation of B2 phases. However, it was found that the tensile strengths could not be continuously increased by further increasing aging temperature or time. These findings provide insights into the development of precipitation strengthened HEAs with good mechanical properties.

Thermal Cycling Behavior of Aged FeNiCoAlTiNb Cold-Rolled Shape Memory Alloys

Fe–Ni–Co–Al-based systems have attracted a lot of interest due to their large recoverable strain. In this study, the microstructure and thermal cycling behaviors of Fe41Ni28Co17Al11.5Ti1.25Nb1.25 (at.%) 98.5% cold-rolled alloys after annealing treatment at 1277 °C for 1 h, followed by aging for 48 h at 600 °C, were investigated. From the electron backscatter diffraction results, we see that the texture intensity increased from 9.4 to 16.5 mud and the average grain size increased from 300 to 400 μm as the annealing time increased from 0.5 h to 1 h. The hardness results for different aging heat treatment conditions show the maximum value was reached for samples aged at 600 °C for 48 h (peak aging condition). The orientation distribution functions (ODFs) displayed by Goss, brass, and copper were the main textural features in the FeNiCoAlTiNb cold-rolled alloy. After annealing, strong Goss and brass textures were formed. The transmission electron microscopy (TEM) results show that the precipitate size was ~10 nm. The X-ray diffraction (XRD) results show a strong peak in the (111) and (200) planes of the austenite (⁠⁠γ, FCC) structure for the annealed sample. After aging, a new peak in the (111) plane of the precipitate (⁠⁠γ′, L12) structure emerged, and the peak intensity of austenite (⁠⁠γ, FCC) decreased. The magnetization–temperature curves of the aged sample show that both the magnetization and transformation temperature increased with the increasing magnetic fields. The shape memory properties show a fully recoverable strain of up to 2% at 400 MPa stress produced in the three-point bending test. However, the experimental recoverable strain values were lower than the theoretical values, possibly due to the fact that the volume fraction of the low-angle grain boundary (LABs) was small compared to the reported values (60%), and it was insufficient to suppress the beta phases. The beta phases made the grain boundaries brittle and deteriorated the ductility. On the fracture surface of samples after the three-point bending test, the fracture spread along the grain boundary, and the cross-section microstructural results show that the faces of the grain boundary were smooth, indicating that the grain boundary was brittle with an intergranular fracture.

Statistical analysis of lamellar and Widmannstätten structures obtained in Nb-rich γ-TiAl alloy with varied cooling rate and annealing duration

Nb-rich γ-TiAl alloys are of interest for enhanced mechanical properties and oxidation resistance. The influence of cooling rate and annealing duration on microstructural evolution of Nb-rich γ-TiAl alloy (Ti-45Al-8Nb-0.2B) has been meticulously investigated, with emphasis on phase volume fraction, grain size, and lamellar spacing. The alloy was annealed at 1320 °C for 15 min, and then furnace-cooled, oil-quenched or cryogenic quenched, whereas annealing for 2 h and 26 h was followed by water quenching. The post-anneal microstructures were characterized using X-ray diffraction, optical and scanning electron microscopy, along with energy dispersive spectroscopy and electron backscattered diffraction. Across all samples, a fully lamellar microstructure comprising α2 and γ phases has been consistently achieved, along with sporadically observed small β precipitates, and elongated ribbon-like TiB2. Widmannstätten colonies (WC) have been observed with diverse morphologies, most of which exhibited an angle of around 64° to regular lamellae, supporting the theory of {1‾1‾22} twinning in the α-phase for WC formation. The γ phase fraction has decreased with increasing cooling rate and annealing time. Grain size and lamellar spacing have also declined with cooling rate but increased with annealing time. Additionally, the mean size of equiaxed γ grains has enlarged with annealing duration.

THE EFFECT OF ANNEALING REGIME ON THE PRECIPITATION OF FeCoNiAl0.75Nb0.25 HIGH ENTROPY ALLOY

This paper investigates the effect of the annealing regime on the precipitation of FeCoNiAl0.75Nb0.25 high entropy alloy. The as-cast microstructure consists of coarse dendritic phases that are replaced by equiaxed morphology, and the distribution of the interdendritic phase becomes regularly better with increasing time and annealing temperature up to 825ºC. The precipitated process begins at 700ºC for 8 hours, shortening to 4 hours when the annealing temperature increases. The size of this phase is only a few μm. The fraction of the precipitated phase increases and the size of the dendritic phase is reduced as the annealing temperature is up to 825ºC, while this size rises in the 925ºC/16 hours regime. The microstructure is coarse, and the precipitated phase gradually disappears when the annealing is at 1000ºC. The HV3 hardness of the alloy increases with annealing time when the temperature is lower than 825ºC and reaches the highest value of ~ 614 kg/mm2 at 600ºC/ 24 hours; this value begins to decrease for the 925ºC/16 hours regime. Meanwhile, the hardness gradually decreases with increasing annealing time at 1000ºC. It can be expected due to the rapid coarsening of the dendritic phase, the decrease in the proportion of the precipitated phase in the alloy, and the appearance of plastic flow phenomena at grain boundaries.

Fabrication and Characterization of Aluminum-Doped Nickel Oxide Thin Films for Optoelectronic Applications using the SILAR Method

Study’s Excerpt The effect of varying annealing times on 10% Aluminum-doped Nickel Oxide (ANO) thin films, deposited via the SILAR technique is presented. SEM and RBS analyses were used for detailed correlation between annealing time and the film's microstructural improvements. ANO thin films could be used for advanced technological applications. Full Abstract The effect of varying the annealing time of %10 aluminium-doped Nickel Oxide thin film was studied to understand the possible effect on the optical, structural, and electrical properties of %10 aluminium-doped Nickel Oxide (ANO) for possible application. The thin films were deposited on glass substrates using the successive ionic layer adsorption reaction (SILAR) deposition technique. The samples formed were annealed at 3000C, and the annealing time varied at 1.35 hrs., 1.45 hrs., 1.55 hrs., and 2 hrs, respectively. The deposited films were characterized to obtain the optical, electrical, and structural characteristics and the compositional constituent of the film using the double beam photo spectrometer, Four-Point Probe, Scanned electron Microscope, Energy Dispersion Spectroscopy, and X-ray Diffractometer. The films were observed to have low absorbance in the range of 0.1 to 0.01 and high % transmittance within the range of 80% - 98% in the visible region of the spectrum. The reflectance of the film was observed to decrease with an increase in annealing time in the range of 10% - 2.5%, all in the visible region of the spectrum. The crystallite size of the deposited films decreased with increased annealing time with the structural formation of simple cubic phase NiO thin film. SEM micrograph of the thin films reveals that an increase in annealing time improved the crystallinity of the films with the grain size evenly distributed. The EDS result of the deposited films revealed the presence of nickel, aluminum and Oxygen as the major constituent of the deposited films. The Ruther Ford Backscattering (RBS) analysis of the thickness of the films shows an increase in the thickness with an increase in annealing time. Clearer compositions of the films were also seen from the RBS analysis. Their electrical properties revealed that the films formed had low electrical resistivity and high conductivity, so they could be useful in making optoelectronics devices and corrosion resistance.

Cr2O3–NiO mixed oxides thin films for p-type transparent conductive electrodes

The Cr2O3–NiO mixed oxides’ thin films were formed by means of the layer-by-layer magnetron sputtering deposition of Cr2O3, NiO, and Cr2O3 layers on c-plane sapphire substrates. These thin-film structures, subjected to subsequent annealing, constituted a combination of the monocrystalline (0001) Cr2O3 and nonordered nickel oxide phase, which was a mixture of NiO and Ni2O3. The annealing at 900 and 1000 °С in air facilitated the diffusion of Ni and Cr atoms into the layers. Varying the annealing time allowed us to control the uniformity of the Ni and Cr distribution, the microrelief of the film surface, the transmittance in the visible region, and the sheet resistance of the Cr2O3–NiO thin-film structures. Thus, the films annealed at 900 °C during 30 min were characterized by a uniform distribution, a relatively weakly developed surface, a low sheet resistance, and the highest Haacke's Figure of Merit of 1.49 × 10–9 Ω–1. The formation of mixed Cr2O3–NiO oxides by the proposed approach was found to be an effective way to improve the performances of Cr2O3 based p-type transparent conductive electrodes.

Investigating the effect of Cu underlayer and FTO etching towards photoelectrochemical performance enhancement of Cu2O photoelectrode

Cuprous oxide (Cu2O) exhibits potential as a photoactive material for photoelectrochemical water splitting, owing to its appropriate bandgap, efficient charge carrier separation, and ability to enhance solar-driven hydrogen production. This study investigates the influence of substrate etching, Cu underlayer and Cu2O electrodeposition time, and annealing time on enhancing the photoelectrochemical (PEC) performance. Electrodeposition and thermal oxidation techniques were used to fabricate the Cu2O/Cu/FTOe-A photocathode. It has been observed that FTO etching improves adhesion, light transmission, and efficiency. A Cu underlayer also impacts the PEC performance, wherein an ideal thickness of Cu leads to enhanced PEC performance. This study also focuses on the annealing time that leads to CuO layers and nanowires forming on the Cu2O surface. The structural and chemical changes before and after annealing are confirmed via XRD, XPS, AFM and FESEM analyses. UV–Vis analysis also reveals that the presence of Cu underlayer, FTO etching, and the annealing process affect the electrical properties and light absorption capacities of the Cu2O photoelectrode. Electrochemical impedance analysis (EIS) and Mott-Schottky analysis have provided insights into the enhanced charge transfer properties and band bending in the Cu2O/Cu/FTOe-A, resulting in enhanced PEC performance. Overall, this study provides significant insights into the understanding and enhancement of Cu2O/Cu/FTOe-A photocathodes for potential use in PEC water splitting applications.

Effects of XX catalysts on quantum annealing spectra with perturbative crossings

In adiabatic quantum computation the required run-time to reach a given ground-state fidelity is dictated by the size of the minimum gap that appears between the ground and first-excited state in the annealing spectrum. In general the presence of avoided level crossings demands an exponential increase in the annealing time with the system size which has consequences both for the efficiency of the algorithm and the required qubit coherence times. One promising avenue being explored to produce more favorable gap scaling is the introduction of nonstoquastic XX couplings in the form of a catalyst—of particular interest are catalysts which utilize accessible information about the optimization problem in their construction. Here we show extreme sensitivity of the effect of an XX catalyst to subtle changes in the encoding of the optimization problem. In particular, we observe that a targeted catalyst containing a single coupling can significantly reduce the gap closing with system size at an avoided level crossing. For slightly different encodings of the same problems however, these same catalysts result in closing gaps in the annealing spectrum. To understand the origin of these closing gaps, we study how the evolution of the ground-state vector is altered by the presence of the catalyst and find that the negative components of the ground-state vector are key to understanding the response of the gap spectrum. We also consider how and when these closing gaps could be utilized in diabatic quantum annealing protocols—a promising alternative to adiabatic quantum annealing in which transitions to higher energy levels are exploited to reduce the run time of the algorithm. Published by the American Physical Society 2024

Rapid synthesis and enhanced microwave absorption of carbon-supported high-entropy metal oxide

Complex preparation process and long annealing time of high-entropy metal oxide (HEO) limit its extensive application as microwave absorber at civil and military fields. Herein, a rapid synthesis method of mesocarbon microbeads (MCMB)-loaded spinel structure (FeCoCrNiMnCu)O is studied via plasma flow. In the presence of extreme plasma heating rate, a nanoscale high-entropy phase can be formed while modifying the surface activity of carbon. Simultaneously, due to the short synthesis time, gaseous conversion of carbon under high temperature aerobic conditions is avoided. By appending of carbon, the dual-media absorber exhibits better absorption performance with a maximum peak (-44.7 dB), which achieves over 90 % absorption in 11.2–15.5 GHz with a thickness of only 1.9 mm. Interestingly, the real and imaginary parts of complex permittivity increase remarkably. The former change is attributed to the expansion of heterogeneous hole carrier region and the latter dues to the interfacial polarization of the strongly coupled interface. The increase of dielectric loss and conductance loss leads to great improvement of microwave absorption. Our study injects new vitality into the preparation of HEO for advanced applications and the as-prepared HEOM is promised to be high-efficient microwave absorber based on robust stability and excellent absorbing performance.

A Novel Upside-Down Thermal Annealing Method Toward High-Quality Active Layers Enables Organic Solar Cells with Efficiency Approaching 20.

The emerging non-fullerene acceptors with low voltage losses have pushed the power conversion efficiency of organic solar cells (OSCs) to ≈20% with auxiliary morphology optimization. Thermal annealing (TA), as the most widely adopted post-treatment method, has been playing an essential role in realizing the potential of various material systems. However, the procedure of TA, i.e., the way that TA is performed, is almost identical among thousands of OSC papers since ≈30 years ago other than changes in temperature and annealing time. Herein, a reverse thermal annealing (RTA) technique is developed, which can enhance the dielectric constant of active layer film, thereby producing a smaller Coulomb capture radius (14.93 nm), meanwhile, forming a moderate nano-scale phase aggregation and a more favorable face-on molecular stacking orientation. Thus, this method can reduce the decline in open circuit voltage of the conventional TA method by achieving decreased radiative (0.334 eV) and non-radiative (0.215 eV) recombination loss. The power conversion efficiency of the RTA PM6:L8-BO-X device increases to 19.91% (certified 19.42%) compared to the TA device (18.98%). It is shown that this method exhibits a superb universality in 4 other material systems, revealing its dramatic potential to be employed in a wide range of OSCs.

Unraveling the multistage phase transformations in monolayer MoTe2−x

Monolayer MoTe2 exhibits a variety of derivative structural phases and associated intriguing electronic properties that enable a wealth of potential applications in future electronic and optoelectronic devices. However, a comprehensive study focusing on the complexities of the controllable phase evolution in this atomically thin film has yet to be performed. This work aims to address this issue by systematically investigating molecular beam epitaxial growth of monolayer Mo–Te compounds on bilayer graphene substrates. By utilizing scanning tunneling microscopy, we explored a series of thermally driven structural phase evolutions, including distinct T′-MoTe2, H-MoTe2, Mo6Te6 nanowires, and multistoichiometric MoTe2−x. Furthermore, we carefully investigated the critical effects of the growth parameters—annealing temperature and time and tellurium concentration—on the controllable and reversible phase transformation within monolayer MoTe2−x. The findings have significant implications for understanding the thin film synthesis and phase transformation engineering inherent to two-dimensional crystals, which can foster further development of high-performance devices.

Impact of Irreversible Adsorption on Molecular Ordering and Charge Transport in Poly(3-hexylthiophene) Thin Films on Solid Substrates.

We investigate the irreversible adsorption of poly(3-hexylthiophene) (P3HT) polymer thin films on silicon dioxide/silicon (SiO2/Si) substrates during thermal annealing at a temperature below the melting temperature (Tm) but far above the glass transition temperature (Tg), i.e., Tg ≪ T = 170 °C < Tm, and its effect on their crystalline ordering and charge transport properties. It was found that short-time annealing enhances the molecular ordering of P3HT films, while prolonged thermal annealing gradually disrupts the crystalline structures and reduces the overall crystallinity of the film. Concurrently, thermal annealing at this temperature facilitates the slow irreversible adsorption of P3HT chains at the polymer-solid interface, resulting in the formation of a 1.7 Rg-thick (∼18 nm thick) adsorbed layer on SiO2/Si substrates that is fully amorphous and contains a large fraction of loosely adsorbed chains. We postulate that such irreversible adsorption is responsible for the reduced crystalline packing of P3HT at the polymer-solid interface at Tg ≪ T < Tm, which further disrupts the molecular ordering of the entire 46 nm thick P3HT film by a long-range perturbation effect. Electrical measurements using an organic field-effect transistor (OFET) device reveal that the enhanced charge carrier mobility of P3HT films correlates with an optimized annealing time at Tg ≪ T < Tm, which achieves a balance between maximizing molecular ordering and minimizing the impact of irreversible chain adsorption. These findings provide new insights into the underlying mechanism of thermal annealing in tailoring the structure and property of conjugated polymer thin films prepared on solid substrates.

Mixed equilibrium/nonequilibrium effects govern surface mobility in polymer glasses

Using angle-resolved X-ray photoelectron spectroscopy, sum-frequency generation vibrational spectroscopy, contact angle measurements, and molecular dynamics simulations, we verify that the glass transition temperature (Tg) of polymer glass is lower near the free surface. However, the experimental Tg-gradients showed a linear variation with depth (z) from the free surface, while the simulated equilibrium Tg-gradients exhibited a double exponential z-dependence. In typical simulations, Tg is determined based on the relaxation time of the system reaching a prescribed threshold value at equilibrium. Conversely, the experiments determined Tg by observing the unfreezing of molecular mobility during heating from a kinetically arrested, nonequilibrium glassy state. To investigate the impact of nonequilibrium effects on the Tg-gradient, we reduced the thermal annealing time in simulations, allowing the system to fall out of equilibrium. We observe a decrease in the relaxation time and the emergence of a modified z-dependence consistent with a linear Tg-gradient near the free surface. We further validate the impact of nonequilibrium effects by studying the dependence of the Tg on the heating/cooling rate for polymer films of varying thickness (h). Our experimental results reveal significant variations in the Tg-heating/cooling rate dependence with h below the bulk Tg, which are also observed in simulation when the simulated system is not equilibrated. We explain our findings by the reduction in mass density within the inner region of the system under nonequilibrium conditions, as observed in simulation, and recent research indicating a decrease in the local Tg of a polymer when placed next to a softer material.

Influence of the synthesis route on optical and luminescence properties of glass-ceramic doped with europium ions

The production of transparent glass-ceramic materials often faces challenges, such as inhomogeneities, inclusions, uncontrolled crystallization and other defects that make glass ceramics unsuitable for fiber optics, for example. At the same time, the chosen chemical composition is valuable for its unique properties. The present study investigated the effect of different methods of synthesizing glass-ceramic silica-germanium-antimony matrices on their transmittance optimization and luminescence properties where the conventional melt-quenching route is insufficient in terms of the transparency and homogeneity of the material obtained. The effect of heat treatment on the studied properties was also considered. Full Text: PDF References G.A. Khater, E.M. Safwat, J. Kang, Y. Yue, A.G.A. Khater, "Some Types of Glass-Ceramic Materials and their Applications", Int. J. Res. Stud. Sci. 7(3), 1 (2020). DirectLink J. Deubener, M. Allix, M.J. Davis, A. Duran, T. Höche, T. Honma, et al., "Updated definition of glass-ceramics", J. Non-Crystalline Solids 501, 3 (2018). CrossRef W. Blanc, Y. Gyu Choi, X. Zhang, M. Nalin, K.A. Richardson, G.C. Righini, et al., "The past, present and future of photonic glasses: A review in homage to the United Nations International Year of glass 2022", Progr. Mat. Sci. 134, 101084 (2023). CrossRef P. Golonko, M. Kochanowicz, P. Miluski, M. Kuwik, J. Pisarska, W. Pisarski, J. Dorosz, M. Leśniak, D. Dorosz, A. Basa, J. Żmojda, "Glass-ceramic optical fibers with controlled crystallization of core doped with europium ions", Ceram. Int. S0272884224002955 (2024). CrossRef J. Zmojda, M. Kochanowicz, P. Miluski, A. Baranowska, A. Basa, R. Jadach, M. Sitarz, D. Dorosz, "The influence of Ag content and annealing time on structural and optical properties of SGS antimony-germanate glass doped with Er3+ ions", J. Mol. Struct. 1160, 428 (2018). CrossRef X. Liu, J. Zhou, S. Zhou, Y. Yue, J. Qiu, "Transparent glass-ceramics functionalized by dispersed crystals", Progr. Mat. Sci. 97, 38 (2018). CrossRef T.N.L. Tran, A. Chiasera, A. Lukowiak, M. Ferrari, "Eu3+ as a Powerful Structural and Spectroscopic Tool for Glass Photonics", Materials 15, 1847 (2022). CrossRef Z. Li, L. Tan, C. Chen, D. Zhou, L.R. Jensen, J. Ren, Y. Zhang, J. Qiu, Y. Yue, "The effect of melt-homogenization and heat-treatment on the optical properties of the rare earth doped oxyfluoride glass-ceramics", J. Non-Cryst. Solids 593, 121773 (2022). CrossRef D. Dorosz, M. Kochanowicz, R. Valiente, A. Diego-Rucabado, F. Rodríguez, N. Siñeriz-Niembro, et al., "Pr3+-doped YPO4 nanocrystal embedded into an optical fiber", Sci Rep. 14, 7404 (2024). CrossRef