Ultrahigh Thermal Stability Research Articles

Ag-Pd nanoalloy film with ultra-high thermal and electrochemical stability for power electronic packaging

Nano-Ag paste is a popular material in power electronic packaging, while its microstructure is unstable at high temperatures and suffers from electrochemical migration. In this work, Ag-Pd nanoalloy film has been prepared by the pulsed laser deposition, and been sintered at low temperature for packaging. The thermal stability is significantly improved at 300 ℃ when Ag is alloyed with Pd. The Pd addition significantly increased the diffusion activation energy of Ag atoms and reduced the diffusion coefficient. The Ag-Pd sintered layer exhibited a stable microstructure at 300 °C or even 500 °C, which indicated that Ag-Pd nanoalloy had the potential to serve at high temperatures. Ag-Pd nanoalloy will preferentially generate a PdO passivation film and cover the anode surface, thereby slowing down the dissolution of the Ag and improving its resistance to electrochemical migration. This work provides theoretical studies and insights into the applications of Ag-Pd nanoalloys in high-reliability power electronics.

Ultrahigh thermal stability and piezoelectricity of lead-free KNN-based texture piezoceramics

The contradiction between high piezoelectricity and uniquely poor temperature stability generated by polymorphic phase boundary is a huge obstacle to high-performance (K, Na)NbO3 -based ceramics entering the application market as Pb-based substitutes. We possess the phase boundary by mimicking Pb(Zr, Ti)O3’s morphotropic phase boundary structure via the synergistic optimization of diffusion phase boundary and crystal orientation in 0.94(Na0.56K0.44)NbO3−0.03Bi0.5Na0.5ZrO3−0.03(Bi0.5K0.5)HfO3 textured ceramics. As a result, a prominent comprehensive performance is obtained, including giant d33 of 550 ± 30 pC/N and ultrahigh temperature stability (d33 change rate less than 1.2% within 25-150 °C), representing a significant breakthrough in lead-free piezoceramics, even surpassing the Pb-based piezoelectric ceramics. Within the same temperature range, the d33 change rate of the commercial Pb(Zr, Ti)O3−5 ceramics is only about 10%, and more importantly, its d33 (~ 350 pC/N) is much lower than that of the (K, Na)NbO3-based ceramics in this work. This study demonstrates a strategy for constructing the phase boundary with MPB feature, settling the problem of temperature instability in (K, Na)NbO3-based ceramics.

Ultrafine-grained Al-La-Mg-Mn alloy fabricated by melt spinning and hot extrusion with ultrahigh strength and thermal stability

To enhance the mechanical properties of Al–(La, Ce) alloys, melt spinning and hot extrusion were employed to fabricate Al-La-Mg-Mn alloy with an ultrafine-grained structure (∼0.56 μm). The as-extruded alloy exhibits the highest tensile strength of 621 ± 4 MPa among Al–(La, Ce) alloys fabricated by various methods while retaining an appreciable elongation of 6.8 ± 1.1 %. The high strength is mainly ascribed to the ultrafine grains and high-volume intermetallics, conferring robust grain boundary strengthening and Orowan strengthening effects. Additionally, this study delved into the high-temperature (400°C) coarsening behavior of the intermetallic and grain size. The findings unveil an exceptionally low coarsening rate of the intermetallic at 400°C (3.19×10−33 m4 s−1), accompanied by only slight grain coarsening, underscoring the remarkable thermal stability of the ultrafine-grained structure.

Achieving Ultrahigh Thermal Stability in Cr3+-Activated Garnet Phosphors through Electron Migration between Thermally Coupled Levels.

Recently, Cr3+-activated near-infrared (NIR) phosphors have received much more attention due to their excellent photoluminescence (PL) properties. However, most of them suffer from poor thermal stability which limits further application. Herein, a novel Lu2CaGa4SnO12:Cr3+ phosphor with broadband NIR emission (λem = 750 nm) is synthesized successfully. Despite the good luminescence property, its PL intensity decreases obviously with temperature (I425K = 79%). To improve the thermal stability, a series of Lu2+xCa1-xGa4+xSn1-xO12:Cr3+ (x = 0-1.0) solid solutions with tunable thermal quenching performance have been designed. It is found that the fluorescence intensity ratio (FIR) of 4T2 → 4A2 to 2E → 4A2 [I(4T2)/I(2E)] transitions (i.e. electron occupation) decreases monotonously with increasing [Lu3+-Ga3+] co-substitution, resulting from a strengthened crystal field strength and increased energy difference between 4T2 and 2E energy levels. Benefiting from the various thermal population and energy difference Δ', the PL thermal quenching behavior of Lu2+xCa1-xGa4+xSn1-xO12:Cr3+ can be adjusted easily, and the corresponding mechanism is explored in detail. Most notably, the emission intensity of Lu2+xCa1-xGa4+xSn1-xO12:Cr3+ at 425 K can reach up to 142% compared with that at 300 K, which may be the best for Cr3+-activated NIR phosphors. This work may provide an alternative path for the development of thermally stable broadband NIR phosphors.

Adsorptive separation of Xe/Kr mixtures by microporous lanthanide metal-organic frameworks with high thermal stability

Efficient separation of Xenon (Xe) and Krypton (Kr) is a significant process for their wide industrial applications and potential environmental concerns. Owing to the inert atomic gases (Xe and Kr) nature with similar physical and chemical properties, it is a great challenge to achieve efficient separation of the Xe/Kr mixture. Herein, we report a series of microporous lanthanide based metal-organic frameworks Ln (BTC) (H2O)·(DMF)1.1 (Ln-MOF) (Dy-BTC (1), Er-BTC (2), and Yb-BTC (3)) with ultrahigh thermal stability for adsorptive Xe/Kr separation. These three isostructural Ln-MOFs consisted of lanthanide metal ions and 1,3,5-benzene dicarboxylate ligands that possess a square channel with pore sizes of 6–7 Å. By substitution of Ln ions, Yb-BTC shows the smallest pore size among the three compounds which enables its obvious higher Xe/Kr selectivity compared with the other two Ln-MOFs. Yb-BTC exhibits a moderately high Xe uptake of 2.5 mmol/g (298 K and 1 bar), and a significantly high Xe/Kr uptake ratio of 3.8, indicative of its great potential for separation of Xe/Kr mixture. The effective Xe/Kr separation ability of Yb-BTC was also confirmed by a breakthrough experiment.

Ultrahigh thermal stability of lead-free Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3-BaTiO3 ternary piezoceramics upon quenching treatment

The Bi0.5Na0.5TiO3-based system is one of the most competitive candidates for lead-free piezoelectric materials. However, the relatively low thermal depolarization temperature (Td) hinders the practical application of the materials, making effectively improving Td an urgent challenge to be overcome. Herein, excellent thermal stability with ultrahigh Td value (251 ℃) is obtained in Mn-doped 0.79Bi0.5Na0.5TiO3-0.14Bi0.5K0.5TiO3-0.07BaTiO3 (79BNT-14BKT-7BT:Mn) ternary ceramics by quenching strategy. It is found that the quenching treatment increases the phase proportion and enhances the lattice distortion of tetragonal structure. By utilizing piezoelectric force microscopy (PFM) and autocorrelation function method, it is revealed that the quenching process can induce an increase in the length of correlation polarization, ferroelectric long-range ordering and domain size. The domain switching is significantly suppressed, which contributes to the improvement of Td. This study provides a feasible avenue to achieve BNT-based piezoelectric ceramics with high thermal stability and facilitates their development and application.

Microstructure, mechanical properties and ultra-high temperature thermal stability of GdB6 ceramics fabricated by reactive spark plasma sintering

In this study, a highly dense GdB6 bulk ceramic material was fabricated using one-step in-situ reaction spark plasma sintering technology. The sample with a relative density of 96.7 % and a purity of 96.9 wt% was successfully obtained by sintering at 1800 °C for 30 min under a uniaxial pressure of 50 MPa. The Vickers hardness, elastic modulus and fracture toughness of the as-obtained GdB6 bulk ceramics were 18.9 GPa, 209 GPa and 1.6 MPa·m1/2, respectively. The thermal conductivity of GdB6 at room temperature was 28.68 W·m−1·K−1, 70 % of which was mainly attributed to phonon vibration, while the remaining 30 % to the electrical thermal conductivity. In addition, the as-obtained GdB6 ceramics showed no phase transformation after heat treatment at a relatively high temperature of 2100 °C for 20 min in Ar atmosphere. The highly covalent octahedral boron framework played a critical role in maintaining the phase stability of the GdB6 crystal lattice. This suggested that GdB6 ceramics could be used as potential ultra-high temperature ceramics for aerospace applications and high-power vacuum electronic devices operated at high temperatures.

Garnet Structure-Activated Warm White Light Phosphors Ca3Al2Ge3O12: Dy3+, Eu3+ with Ultrahigh Thermal Stability and Tunable Luminescence.

A series of Ca3Al2Ge3O12: xDy3+, yEu3+ phosphors were successfully prepared by the high-temperature solid-phase method. The phase and morphology of the phosphors were studied by means of Rietveld refinement and scanning electron microscopy. The results show that the phase is pure, and the crystal structure is the Ia3̅d space group. In the Ca3Al2Ge3O12: xDy3+ phosphors, using 380 nm excitation, phosphors showed blue (4F9/2 → 6H15/2) and yellow (4F9/2 → 6H13/2) emission peaks at 481 and 581 nm, respectively. In Ca3Al2Ge3O12: xDy3+, yEu3+ phosphors, the energy transfer was inferred by the spectrum overlap of Dy3+ and Eu3+, and the lifetime attenuation was analyzed from the perspective of dynamics; finally, the band gap structure of the phosphors was analyzed by combining diffuse reflection spectra with the first principle, and the energy transfer mechanism and luminescence mechanism were elaborated by combining theory and practice. The transition from blue white light to red light can be achieved by tuning the range of y in Ca3Al2Ge3O12: 0.015Dy3+, yEu3+. Wherein, when y = 0.07, phosphors, the chromaticity coordinate of warm white CIE is (0.3932, 0.3203), the color temperature is 3093 K, and the warm white light is synthesized. The thermal stability of the synthesized warm white phosphors is 90.1% (423 K), the thermal sensing factors are Samax = 5.51 × 10-4 K-1 (303 K) and Srmax = 0.0359% K-1 (303 K), and the actual quantum efficiency is IQE = 52.48%. These results prove that Ca3Al2Ge3O12: Dy3+, Eu3+ have good application prospects as single-component warm w-LED devices.

High efficient and ultrahigh thermal stability in a rigid rare-earth hybrid molecular crystal: [(CH3CH2)4N]Tb[CH2(SO3)2

Organic-inorganic hybrid molecular fluorescent materials have attracted much attention due to their application potential in white LEDs and high-definition displays. However, achieving high thermal stability for the fields of lighting/displays remains greatly challenging based on the hybrid molecular materials. Herein, we reported a crystalline state 1D rigid rare-earth hybrid coordinate polymer molecular crystal [(CH3CH2)4N]Tb[CH2(SO3)2] (1) along with high quantum yield (QY) 75.2%. Interestingly, this hybrid molecular crystal remains stable up to 728 K (∼455 °C). Remarkably, it exhibits excellent fluorescence thermal stability at high temperatures (150 °C, >95% and 150–200 °C, >82%) and a high thermal activation energy of 568.7 meV. Besides, the fabricated n-UV chips based white-LED by 1, commercial red Y2O3:Eu3+ and blue BaMgAl10O17:Eu2+ phosphor emits white light with color coordinates (CIE, 0.33, 0.32), high color rendering index (CRI) of 91.2, and correlated color temperature (CCT) 5623 K. These results reveal that this ultrahigh thermal stability hybrid molecular crystal as a green phosphor has great potential applications for displays or WLEDs. Therefore, this study opens a new avenue to develop novel rare-earth phosphors and gives new visions for hybrid molecular fluorescent materials.

Construction of a novel nickel-based MOF with accessible oxygen sites for efficient CH4/N2 separation

A novel Ni-based MOF material, TUTJ-201Ni, with accessible oxygen sites, was constructed. The material displayed ultrahigh thermal stability, showing a high separation performance for CH4/N2 mixture.

Precursor-derived SiHfBCN ceramics with ultrahigh temperature stability: Facile preparation, phase evolution behavior, and mechanism of ultrahigh temperature thermal stability

SiHfBCN ceramics are the most promising candidates as ultrahigh temperature ceramics for aerospace applications. In this work, PHSNB precursors were synthesized by hydrosilylation reaction of polyborosilazane (PSNB) and polyhafnocenecarbosilane (PHCS), and then the SiHfBCN ceramics can be obtained from the PHSNB precursors through the precursor-derived ceramics (PDC) strategy. The structure, composition, pyrolysis process, and phase evolution behavior at high temperatures of the SiHfBCN ceramics were systematically investigated. The results show that the optimum SiHfBCN ceramic prepared in this study can remain stable until 1780 °C, and the weight loss at 1800 °C is only 0.8 wt%, demonstrating the excellent high temperature thermal stability of the SiHfBCN ceramics. The outstanding high temperature thermal stability of the SiHfBCN ceramics can be attributed to two reasons. Firstly, the formation of HfCxN1-x solid solution at high temperatures can greatly inhibit the formation of SiNx, so the carbothermal reduction reaction and thermal decomposition reaction of SiNx can be greatly inhibited. Secondly, the generated crystal phases at high temperatures are surrounded by the chaotic layered structures of B–C–N phase, which greatly restricts the decomposition process of the SiHfBCN ceramics. This work presents a convenient strategy in preparing multiphase ceramics (not only SiHfBCN) that can be applicable in various harsh environmental conditions.

Optical fiber links based A thermal planar AWG for ultrahigh thermal stability and ultralow thermal sensitivity

Optical fiber links based A thermal planar AWG for ultrahigh thermal stability and ultralow thermal sensitivity

N-heterocyclic carbenes – The design concept for densely packed and thermally ultra-stable aromatic self-assembled monolayers

Self-assembled monolayers (SAMs) of N-heterocyclic carbenes (NHCs) on metal substrates are currently one of the most promising systems in context of molecular-scale engineering of surfaces and interfaces, crucial for numerous applications. Interest in NHC SAMs is mainly driven by their assumingly higher thermal stability compared to thiolate SAMs most broadly used at the moment. Most of the NHC SAMs utilize imidazolium as an anchoring group for linking molecules to the metal substrate via carbene C atom. It is well established in the literature that standing up and stable NHC SAMs are built only when using bulky side groups attached to nitrogen heteroatoms in imidazolium moiety, which, however, leads to monolayers exhibiting much lower packing density compared to thiolate SAMs. Here, by combined X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and temperature-programmed secondary ion mass spectrometry analysis, we demonstrate that using NHCs with small methyl side groups in combination with simple, solution-based preparation leads to the formation of aromatic monolayers exhibiting at least doubled surface density, upright molecular orientation, and ultra-high thermal stability compared to the NHC SAMs reported before. These parameters are crucial for most applications, including, in particular, molecular and organic electronics, where aromatic SAMs serve either as a passive element for electrode engineering or as an active part of organic field effect transistors and novel molecular electronics devices.

Small Stokes shift and high thermostability in Ce3+ doped K2BaPO4F phosphors

Novel K2BaPO4F:Ce3+ phosphors with strong violet-emission and high thermostability were synthesized by a traditional high-temperature solid-state reaction method. The phase composition and crystal structure were investigated in detail by XRD refinement. DFT calculations based on refined crystal structure were performed. A bright emission in the range of 340–390 nm with a small Stokes shift has been observed when excited at about 323 nm in K2BaPO4F:Ce3+ phosphors. The temperature-dependent PL spectra from 80 to 500 K were investigated systematically. The best doping concentration of K2BaPO4F:xCe3+ phosphors was verified and the concentration quenching mechanism was also confirmed. When the temperature increased from 80 K to 500 K, the emission intensity still remains 53 %. The thermal quenching mechanism was explained using the crystal structure investigation and DFT calculation. The strong near-ultraviolet emission intensity and ultra-high thermal stability indicating that the prepared K2BaPO4F:Ce3+ phosphors have potential applications in anti-counterfeiting and solid-state lighting.

Ultra-high thermal stability InAs/GaAs quantum dot lasers grown on on-axis Si (001) with a record-high continuous-wave operating temperature of 150 °C.

Direct epitaxial growth of group III-V light sources with excellently thermal performance on silicon photonics chips promises low-cost, low-power-consumption, high-performance photonic integrated circuits. Here, we report on the achievement of ultra-high thermal stability 1.3 µm InAs/GaAs quantum dot (QD) lasers directly grown on an on-axis Si (001) with a record-high continuous-wave (CW) operating temperature of 150 °C. A GaAs buffer layer with a low threading dislocation density (TDD) of 4.3 × 106 cm-2 was first deposited using an optimized three-step growth method by molecular beam epitaxy. Then, an eight-layer QD laser structure with p-type modulation doping to enhance the temperature stability of the device was subsequently grown on the low TDD Si-based GaAs buffer layer. It is shown that the QD laser exhibits the ultra-high temperature stability with a characteristic temperature T0=∞ and T1=∞ in the wide temperature range of 10-75 °C and 10-140 °C, respectively. Moreover, a maximum CW operating temperature of up to 150 °C and a pulsed operating temperature of up to 160 °C are achieved for the QD laser. In addition, the QD laser shows a high CW saturation power of 50 mW at 85 °C and 19 mW at 125 °C, respectively.

Ultrahigh thermal stability of dielectric permittivity in 0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Ti0.875Nb0.125)O3

0.6Bi(Mg1/2Ti1/2)O3–0.4Ba0.8Ca0.2(Nb0.125Ti0.875)O3 ceramics with a pseudo-cubic structure and re-entrant dipole glass behavior have been investigated via x-ray diffraction and dielectric permittivity–temperature spectra. It shows excellent dielectric–temperature stability with small variations of dielectric permittivity (±5%, 420–802 K) and dielectric loss tangent (tanδ < 2.5%, 441–647 K) in a wide temperature range. Three dielectric anomalies are observed from 290 to 1050 K. The low-temperature, weakly coupled re-entrant relaxor behavior was described using the Vogel–Fulcher law and the new glass model. The mid- and high-temperature dielectric anomalies are characterized by isothermal impedance and electrical modulus. The activation energy of both dielectric relaxation and conductivity follows the Arrhenius law in the temperature ranges of 633–753 and 833–973 K, respectively. The ultrahigh thermal stability of dielectric permittivity is attributed to the weak coupling of polar clusters, the formation of diffuse phase transition, and the local phase transition of calcium-containing perovskite. The results provide new insights into the defects behavior and the modification way of re-entrant relaxor behavior.

The Pivotal Role of Benzimidazole in Improving the Thermal and Dielectric Performance of Upilex-Type Polyimide.

Polyimide (PI) with ultra-high thermal resistance and stability is essential for application as a flexible substrate in electronic devices. Here, the Upilex-type polyimides, which contained flexibly "twisted" 4,4'-oxydianiline (ODA), have achieved various performance improvements via copolymerization with a diamine containing benzimidazole structure. With the rigid benzimidazole-based diamine bearing conjugated heterocyclic moieties and hydrogen bond donors fused into the PI backbone, the benzimidazole-containing PI showed outstanding thermal, mechanical, and dielectric performance. Specifically, the PI containing 50% bis-benzimidazole diamine achieved a 5% decomposition temperature at 554 °C, an excellent high glass transition temperature of 448 °C, and a coefficient of thermal expansion lowered to 16.1 ppm/K. Meanwhile, the tensile strength and modulus of the PI films containing 50% mono-benzimidazole diamine increased to 148.6 MPa and 4.1 GPa, respectively. Due to the synergistic effect of rigid benzimidazole and hinged, flexible ODA, all PI films exhibited an elongation at break above 4.3%. The electrical insulation of the PI films was also improved with a dielectric constant lowered to 1.29. In summary, with appropriate mixing of rigid and flexible moieties in the PI backbone, all the PI films showed superior thermal stability, excellent flexibility, and acceptable electrical insulation.

The co-optimization of efficiency and emission bandwidth in GSAGG:Cr3+ NIR ceramic phosphors

The NIR phosphor-converted light-emitting diode (NIR pc-LED) is a new near-infrared light source that has been widely studied. Among various NIR phosphors, Cr3+ doped gadolinium aluminum gallium garnet (GAGG:Cr3+) ceramic phosphor has shown great potential due to its ultra-high efficiency and thermal stability. Despite its capabilities, its detection range may be limited due to a relatively narrow emission bandwidth. To make the GAGG:Cr3+ ceramic phosphors achieve both high efficiency and broadband emission, a series of Gd3Al2-x-yScxGa3O12:yCr3+ (GASGG:Cr3+) ceramic phosphors were prepared. Thanks to the decrease of crystal field strength with the doping of Sc3+, the full width at half maximum (FWHM) of GASGG:Cr3+ ceramic phosphors were extended from 84 nm to 117 nm, and the emission peak exhibited a red-shift of 46 nm. Meanwhile, it still retained extremely high external quantum efficiency (EQE = 47%) and excellent thermal stability (90.7%@150 °C). Then, a NIR pc-LED prototype device was fabricated by combining GASGG:Cr3+ ceramic phosphor with a blue LED chip. The NIR light output power and the photoelectric conversion efficiency of this device achieved 646 mW and 19.2%, respectively. Finally, the application effect in night vision and venography of this prototype device was demonstrated.

YB2C2: The first damage tolerant ceramic with melting point over 2500 oC

The ultra-high temperature thermal stability of YB2C2 between 2300 oC and 2550 oC in argon was systematically investigated by induction heating method. The phase composition and microstructure of the samples after heat treatment at different temperatures were characterized with X-ray diffractometry, scanning electron microscopy and transmission electron microscopy. The results show that YB2C2 has excellent ultra-high temperature thermal stability, and it can maintain the structure and phase stability after heat treatment at 2500 oC for 20 min. It would melt rather than decompose with the rising of the temperature. The melting point of YB2C2 is between 2500 oC and 2550 oC, and it has great potential for future ultra-high temperature applications.

Highly Luminescent Earth‐Benign Organometallic Manganese Halide Crystals with Ultrahigh Thermal Stability of Emission from 4 to 623 K (Small 8/2023)

Highly Luminescent Earth‐Benign Organometallic Manganese Halide Crystals with Ultrahigh Thermal Stability of Emission from 4 to 623 K (Small 8/2023)