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Rare earth silicates are promising environmental/thermal barrier coating (E/TBC) materials facing severe CMAS (CaO‐MgO‐Al2O3‐SiO2) corrosion. Previous studies mainly focused on the intrinsic properties of precorrosion coatings, but there were few studies on their CMAS corrosion products that play a crucial role in the performance of coatings in postservice stage. In this work, the mechanical and thermal properties of nine corrosion products between lutetium silicates and CMAS are studied using first‐principles calculations. Their differences of elastic stiffness are attributed to the different crystal structures and bonding strength. The T:O ratio is identified as a factor of the crystal structure for silicate products, and it has a good correlation with their elastic stiffness. Moreover, the divergences of thermal conductivity are dominated by three essential factors, that is, atomic vibration intensity, lattice vibrational anharmonicity, and complexity of crystal structure. Compared with rare earth silicates, six products, that is, the α‐CaSiO3, β‐CaSiO3, Ca2MgSi2O7, Ca2Al2SiO7, CaAl2Si2O8, and Ca2Lu8(SiO4)6O2, showing good damage tolerance and low thermal conductivities, are predicted to be advantageous to E/TBCs. These discoveries reveal the mechanical/thermal properties of corrosion products between lutetium silicates and CMAS and are expected to support the future researches on the performance of E/TBC in the postservice stage. [ABSTRACT FROM AUTHOR]

The increase in operating temperature contributes to improving the performance and fuel utilization efficiency of gas turbines. However, it also places thermal barrier coatings (TBCs) in a more demanding working environment, requiring higher sintering resistance and better mechanical properties. In the present study, HfO2 was introduced into the dual‐phase LaYbZr2O7 system as a doping oxide to form the LaYb(HfxZr1−x)2O7 system. The research concentrated on its phase composition, mechanical properties, and thermophysical properties. The results show that substituting Hf for Zr does not alter the dual‐phase structure of the system. The mutual inhibition between the two phases and the inherent material‐binding capability of Hf further reduce the grain size compared to pure LYZO. Additionally, the presence of Hf reduces the tendency of Frenkel defect formation and cation migration frequency, effectively inhibiting ion diffusion and thereby suppressing the densification and shrinkage trends of the material. The system retains relatively high hardness, fracture toughness, and low elastic modulus of the LYZO matrix, with a decrease in thermal conductivity and an increase in infrared reflectivity. These results suggest that Hf doping enhances the sintering resistance of LYZO material, making them promising for high‐temperature TBCs. Our study presents a viable approach to enhance the sintering resistance of LYZO, and this methodology can be extrapolated to other rare‐earth zirconates. [ABSTRACT FROM AUTHOR]

Ceramic thermal barrier coatings (TBCs) with high toughness and low thermal conductivity are important for developing aero engines with high thrust‐to‐weight ratio and thermal efficiency. In this work, the properties of tantalate Y1/6Yb5/6TaO4 (YYT) were optimized by introducing 8 wt.% yttria‐stabilized zirconia (8YSZ), synthesized using spark plasma sintering, as a second‐phase ceramic. The highest toughness (3.57 MPa m1/2) of the YYT/8YSZ composite ceramics was due to multiple toughening mechanisms. The underlying mechanisms of these processes were revealed based on the microstructures and residual stress of the YYT/8YSZ composite ceramics. A shift from an intergranular fracture to a transgranular fracture was caused by the difference between soft‐grain YYT and hard‐grain 8YSZ, which consumed the fracture energy. Furthermore, the formation of microcracks, crack deflection, bridging, and branching were analyzed based on the differences in Young's moduli and thermal expansion coefficients of YYT and 8YSZ. Internal defects and weak connections between the YYT and 8YSZ grains reduced the thermal conductivity of the composites until it reached its lowest value at 1.4 W m−1 K−1. The studied toughening mechanisms could be applied to various composites. Moreover, herein, we provide a new strategy to design and synthesize TBCs with enhanced performance. [ABSTRACT FROM AUTHOR]

An additively manufactured reaction‐bonded silicon carbide ceramic composite is fabricated using a bimodal powder feedstock and the binder‐jetting printing technique. On fabricating, the ceramic is investigated to report its composition, mechanical, and thermal properties at room temperature and high temperatures (up to 750∘C$^{\circ }C$). The ceramic has a density of 2.76 g/cc, and shows a hardness of 21.74 GPa, and a flexure strength of 207.5 MPa at room temperature. The mechanical property of flexure strength is used to estimate its failure probability under applied stress, using a Weibull distribution. The mechanical properties and failure probabilities are compared with those of conventionally fabricated reaction‐bonded silicon carbide ceramics reported in the literature. These ceramics were fabricated using methods such as slip‐casting, compacting, and tape‐casting. The comparison is used to elucidate the advantages and areas of improvement of the present additive manufacturing technique for reaction‐bonded ceramics. [ABSTRACT FROM AUTHOR]

Recently, CaO‐doped (≤4 mol.%) tetragonal zirconia (CaSZ) ceramic was recommended as a potential alternative to yttria‐stabilized ZrO2 (YSZ). Here, we investigate the limits of starting particle sizes on the stability of tetragonal (t) phase and other associated benefits on measured properties. Synthesized CaSZ powders calcined with different temperatures were used as a mono‐sized or mixed (i.e., two different calcination temperatures) batch fraction for making dense CaSZ ceramic. The mixed‐batch powders were found to be far more efficient in stabilizing the t‐phase in ceramic. Compared to YSZ, CaSZ recorded remarkable enhancement in toughness (up to 8.3 MPa m$\sqrt {\mathrm{m}} $). Contrary to YSZ, CaSZ ceramic demonstrated outstanding thermal stability. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) power devices are attracting significant attention due to their outstanding stability in high-voltage, high-temperature, and highfrequency environments. To replace toxic Pb-based glass, there is an urgent need to develop Pb-free glass for SiC power device encapsulation, considering its superior electrical insulation properties and processing capabilities. Here, we developed a Bi-based glass for effective encapsulation practical of SiC power devices. By increasing the content of glass modifier BaO, the structure of bismuth borate glass can be tuned to reduce glass network density, leading to the transition of structural units from [BO4] to [BO3]. The softened temperature is reduced to 363.4°C with the BaO content increasing to 15 mol%. After encapsulating the SiC power devices using Bi-based glass, the glass demonstrated a reverse breakdown voltage of 650 V and an extremely low leakage current. Therefore, ourwork provided a route for adapting Pb-free-based low-melting glass for encapsulating SiC devices and offered potential for advanced semiconductor packaging. [ABSTRACT FROM AUTHOR]

As ceramics based on magnesium aluminum oxynitrides solid solutions are promising materials as refractories, windows/armors, phosphors, and so forth, it is essential to explore their thermal and thermomechanical properties, owing to the physical requirements on application. In this study, Mg5xAl23−5xO27+5xN5−5x were chosen for the investigation on composition‐dependent thermal and thermomechanical properties by the theoretical calculations. Though the binary system with octahedral bonds contributes more to the thermal expansion coefficient of Mg5xAl23−5xO27+5xN5−5x, the binary system with tetrahedral bonds plays an important role in the variation of the thermal expansion coefficient. The change of heat capacity with the rise of x is mainly attributed to the variation of covalent character of Mg5xAl23−5xO27+5xN5−5x. Moreover, the thermal conductivity is mainly affected by the scattering from atoms in 8a sites. Both thermal and mechanical properties contribute to the variation of thermomechanical properties of Mg5xAl23−5xO27+5xN5−5x. This study can provide guidance to designing spinel materials with desirable thermal and thermomechanical properties for application. [ABSTRACT FROM AUTHOR]

By using the aerodynamic levitation and laser melting technique to well extend the glass‐forming region into the Mg‐rich and peraluminous regime, a series of magnesium aluminosilicate glasses were prepared to investigate the Mg and Al mixed effects on thermal properties, including glass transition temperature (Tg), crystallization behavior, and thermal stability. With the gradual substitution of Mg by Al, Tg exhibits two types of near‐linear rises with different slopes in two compositional regions separated by r = 0.57, where r is equal to the molar ratio of [Al2O3]/([Al2O3] + [MgO]). Moreover, when it comes to other properties, that is, crystallization behavior and thermal stability, this critical point precisely appears at the same r = 0.57. Compared to the slower increase of Tg in Mg‐rich region, the steeper rise of Tg in the peraluminous region is mainly ascribed to the step‐by‐step formation of oxygen triclusters driven by Pauling's second rule. Moreover, the occurrence of the critical point for Tg rise at r = 0.57 rather than the theoretical 0.5 can be seen as a proof of the role of Mg cations partly as a network former. [ABSTRACT FROM AUTHOR]

The densities of molten Y2O3‐Al2O3 compounds, including yttrium aluminum garnet (Y3Al5O12), were determined over a wide temperature range that included an undercooled region, using an electrostatic levitation furnace. The density of the molten Y3Al5O12 varied with temperature according to the relationship 3750 − 0.25(T − Tm) (kg/m3) with Tm = 2240 K and for the range of 1300 K ≤ T ≤ Tm, yielding the thermal expansion coefficient ɑ = 6.7×10−5 K−1. The molar volumes of molten (100‐x)Y2O3‐xAl2O3 (x = 0, 33.3, 50, 55, 62.5, 76.5, 81.5, or 100 mol%) were found to vary with the value of x in a linear manner within the superheated temperature range. However, the molar volumes in the undercooled region deviated from those calculated using an ideal solution model owing to attractive interactions between Y2O3 and Al2O3. [ABSTRACT FROM AUTHOR]

α‐SiAlON is well known for its excellent mechanical properties, but its thermal properties are less investigated. In this work, we investigate the thermal conductivity of Ca α‐SiAlON ceramics with varying m and n values and prepared samples by spark plasma sintering (SPS) at 1600°C or gas pressure sintering (GPS) at 1800°C and 1900°C. The prepared Ca α‐SiAlON ceramics showed thermal conductivities ranging from 4.6 to 10.7 W/(mK) at 25°C. It was found that the thermal conductivity of the α‐SiAlON samples could be reduced by increasing either m or n or both. Besides, the samples prepared by SPS had lower thermal conductivity compared with those by GPS due to their smaller grain size, and the effect of m and n would be minor after m reached 2. These results provide basic knowledge for tuning α‐SiAlON's thermal conductivity for applications concerning thermal management. [ABSTRACT FROM AUTHOR]

Currently, Faraday isolators and rotators for high‐power lasers are popular research topics; therefore, finding magneto‐optical materials with excellent Verdet constants and thermal properties is crucial. In this study, novel holmium scandium aluminum garnet (HoSAG) magneto‐optical ceramics were fabricated using vacuum sintering. This study improved the traditional ball milling method and pre‐synthesized powders with great sinterability after secondary ball milling and sieving. Different pre‐synthesis temperatures were found to have significant effects on the particle size and micromorphology of the synthesized powders. HoSAG ceramics with 0.05 wt% MgO sintering aid and held at 1700°C for 30 h reached a transmittance of 76.7% at 1550 nm. Meanwhile, HoSAG transparent ceramics maintain higher transmittance in the infrared region (>1500 nm) than terbium gallium garnet (TGG) crystals, indicating better application prospects. The Verdet constants of HoSAG magneto‐optical ceramics at 405, 532, 808, and 1064 nm were −421.5, −181.2, −65, and −32.3 rad T−1 m−1, respectively, which are slightly less than those of TGG magneto‐optical ceramics. Moreover, the thermal conductivity of HoSAG ceramics at 300.00 K was 4.89 W m−1 K−1, which is comparable to that of the TGG ceramics. [ABSTRACT FROM AUTHOR]

High‐entropy single‐phase rare earth titanates (RE0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 (RE = Sm, Y, Lu) were designed and synthesized successfully, in which their lattice distortion was quantitatively described by mass disorder and size disorder. It is worth mentioning that (Y0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 could obtain the low thermal conductivity (1.51 W·m−1·K−1, 1500°C), high thermal expansion coefficient (average, 11.69×10−6 K−1, RT ∼1500°C) and excellent high‐temperature stability. In addition, the relationship between the microstructure and thermal transport behaviors has been studied at the atomic scale. Due to the disorder of A‐site ions, severe lattice distortion occurred in specific crystal planes, and the large mass difference between Y3+ and other RE3+ further causes mass fluctuation and results in lower thermal conductivity. Compared with YSZ, the high‐entropy rare earth titanate (Y0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 has lower thermal conductivity, higher thermal expansion coefficient, and excellent high‐temperature stability, which has great potential for application in the thermal protection field. [ABSTRACT FROM AUTHOR]

Terbium aluminum garnet (Tb3Al5O12, TAG) ceramics have become a promising magneto‐optical material owing to the outstanding comprehensive performance, including the magneto‐optical, thermal, and mechanical properties. Fine‐grained TAG ceramics with high optical quality and mechanical properties have attracted much attention. In this study, TAG ceramics with fine grains and high optical quality are fabricated successfully by a two‐step sintering method from co‐precipitated nano‐powders. After pre‐sintered at 1525°C in vacuum and hot isostatic pressed at 1600°C, the in‐line transmittance of TAG ceramics reaches 81.8% at 1064 nm, and the average grain size is 7.1 μm. The Verdet constant of TAG ceramics is −179.6 ± 4.8 rad T−1 m−1 at 633 nm and −52.1 ± 1.9 rad T−1 m−1 at 1064 nm, higher than that of commercial Tb3Ga5O12 crystals. The thermal conductivity of TAG ceramics is determined from 25 to 450°C, and the result is 5.12 W m−1 K−1 at 25°C and 3.61 W m−1 K−1 at 450°C. A comparison of mechanical properties between large‐ and fine‐grained TAG ceramics fabricated under different conditions is conducted. The fine‐grained TAG ceramics possess a bending strength of 226.3 ± 16.4 MPa, which is 9.7% higher than that of the large‐grained ceramics. These results indicate that reducing the grain size on the premise of high optical quality helps improve the comprehensive performance of TAG ceramics. [ABSTRACT FROM AUTHOR]

In this work, Si3N4 and Zr(NO3)4 were used as raw materials to prepare ZrN/ZrO2‐containing Si3N4‐based ceramic composite. The processing, phase composition, and microstructure of the composite were investigated. Hardness and fracture toughness of the ceramics were evaluated via Vickers indentation in Ar at 25°C, 300°C, 600°C, and 900°C. During spark plasma sintering, Zr(NO3)4 was transformed into tetragonal ZrO2, which further reacted with Si3N4, resulting in the formation of ZrN. The introduction of ZrN enhanced the high‐temperature mechanical properties of the composite, and its hardness and fracture toughness reached 13.4 GPa and 6.1 MPa·m1/2 at 900°C, respectively. The oxidation experiment was carried out in air at 1000°C, 1300°C, and 1500°C for 5 h. It was shown that high‐temperature oxidation promoted the formation and growth of porous oxide layers. The microstructure and phase composition of the formed oxide layers were investigated in detail. Finally, it was identified that the obtained composite exhibited a higher thermal diffusivity than that of monolithic Si3N4 in the temperature range of 100°C–1000°C. [ABSTRACT FROM AUTHOR]

Mullite/glass/nano aluminum nitride (AlN) filler (1–10 wt% AlN) composites were successfully fabricated for the low‐temperature co‐fired ceramics applications that require densification temperatures lower than 950°C, high thermal conductivity to dissipate heat and thermal expansion coefficient matched to Si for reliability, and low dielectric constant for high signal transmission speed. Densification temperatures were ≤825°C for all composites due to the viscous sintering of the glass matrix. X‐ray diffraction proved that AlN neither chemically reacted with other phases nor decomposed with temperature. The number of closed pores increased with the AlN content, which limited the property improvement expected. A dense mullite/glass/AlN (10 wt%) composite had a thermal expansion coefficient of 4.44 ppm/°C between 25 and 300°C, thermal conductivity of 1.76 W/m.K at 25°C, dielectric constant (loss) of 6.42 (0.0017) at 5 MHz, flexural strength of 88 MPa and elastic modulus of 82 GPa, that are comparable to the commercial low temperature co‐fired ceramics products. [ABSTRACT FROM AUTHOR]

Temperature limitations in nickel‐base superalloys have resulted in the emergence of SiC‐based ceramic matrix composites as a viable replacement for gas turbine components in aviation applications. Higher operating temperatures allow for reduced fuel consumption but present a materials design challenge related to environmental degradation. Rare‐earth disilicates (RE2Si2O7) have been identified as coatings that can function as environmental barriers and minimize hot component degradation. In this work, single‐ and multiple‐component rare‐earth disilicate powders were synthesized via a sol‐gel method with compositions selected to exist in the monoclinic C 2/m phase (β phase). Phase stability in multiple cation compositions was shown to follow a rule of mixtures and the C 2/m phase could be realized for compositions that contained up to 25% dysprosium, which typically only exists in a triclinic, P1¯${\rm{\bar{1}}}$, phase. All compositions exhibited phase stability from room temperature to 1200°C as assessed by X‐ray diffraction. The thermal expansion tensors for each composition were determined from high‐temperature synchrotron X‐ray diffraction and accompanying Rietveld refinements. It was observed that ytterbium‐containing compositions had larger changes in the α31 shear component with increasing temperature that led to a rotation of the principal axes. Principal axes rotation of up to 47° were observed for ytterbium disilicate. The results suggest that microstructure design and crystallographic texture may be essential future avenues of investigation to ensure thermo‐mechanical robustness of rare‐earth disilicate environmental barrier coatings. [ABSTRACT FROM AUTHOR]

Thermal barrier coatings (TBCs) play an important role in gas turbines to protect the turbine blades from the high‐temperature airflow damage. In this work, we use first‐principles calculations to investigate a specific class of rare‐earth (RE) aluminates, including cubic‐REAlO3 (c‐REAlO3), orthorhombic‐REAlO3 (o‐REAlO3), RE3Al5O12, and RE4Al2O9, to predict their structural stability, bonding characteristics, and mechanical and thermal properties. The polyhedron structures formed by the Al–O bonds are stronger and exhibit rigid characteristics, whereas the polyhedra formed by the RE–O bonds are relatively weak and soft. The alternating stacking of AlO4 tetrahedra, AlO6 octahedra, and RE–O polyhedra, as well as the selection of RE elements, shows intensive influences on the expected mechanical and thermal properties. The B, G, and E of these four types of aluminates decrease in the order of c‐REAlO3 > o‐REAlO3 > RE3Al5O12 > RE4Al2O9. REAlO3 and RE4Al2O9 are brittle and quasi‐ductile ceramics, respectively, whereas RE3Al5O12 is tailorable. The minimum thermal conductivity is in the range of 1.4–1.5 W m−1 K−1 for c‐REAlO3, 1.3–1.4 W m−1 K−1 for o‐REAlO3, 1.25–1.35 W m−1 K−1 for RE3Al5O12, and 0.8–0.9 W m−1 K−1 for RE4Al2O9. RE4Al2O9 with low thermal conductivity and damage tolerance is predicted to be the potential candidates for next‐generation TBC materials. [ABSTRACT FROM AUTHOR]

Bi0.5Na0.5TiO3‐based ceramics with high remnant polarization Pr have shown outstanding potential in the application of high‐power ferroelectric transducers. However, low depolarization temperature Td is an obstacle for their application. Here, a composition design strategy was proposed to simultaneously improve the Td and Pr in BNT‐based materials. Ultrahigh Pr of 40.56 µC/cm2 and relative high Td of 184°C were synergistically achieved in (Bi0.5Na0.5)(Ti0.995Mn0.005)O3 (BNMT) ceramics by adding 1.0 mol% BiGaO3 (BG), which is superior to other reported lead‐free systems. The excellent ferroelectric properties were attributed to strengthen ferroelectric order as evidenced by increased rhombohedral distortion. Meanwhile, the enhanced depolarization temperature, increasing from 168°C for x = 0% to 184°C for x = 1.0%, can be ascribed to the suppression of the thermal‐induced ferroelectric‐relaxor phase transition by adding BG. Those results enable the BNMT‐BG systems ceramics to be an attractive candidate for application in high‐power supplies. [ABSTRACT FROM AUTHOR]

With the increasing service temperature of aeroengines, the development of thermal/environmental barrier coatings (T/EBCs) has been considered to be a great challenge, which requires high‐temperature stability and excellent thermal and mechanical properties. In this work, high‐entropy design was adopted to change the crystal structure of rare‐earth monosilicates used for T/EBCs. The microstructure evolution, thermal and mechanical properties of the plasma‐sprayed (Lu0.25Yb0.25Er0.25Y0.25)2SiO5 and (Lu0.2Yb0.2Er0.2Ho0.2Y0.2)2SiO5 coatings before and after thermal aging at 1350°C for 50 h were investigated. Results showed that the as‐sprayed coatings exhibited dense structure with amorphous and decomposed phases. The change of microstructure like amorphous crystallized and defect healing occurred after thermal aging, which had obvious influence on thermomechanical properties. Compared with single‐component RE2SiO5 (RE = Yb, Er, Y) coatings, the thermal‐aged high‐entropy coatings exhibited lower thermal conductivity, similar thermal expansion coefficient, and better toughness. The work will provide a foundation for the design and application of T/EBCs materials. [ABSTRACT FROM AUTHOR]

The microstructure dependence of thermal radiative properties is critically needed to the design and operation of the thermal barrier coating systems. In this study, different yttria‐stabilized zirconia coating layers are fabricated by air plasma spray with three average porosities 5.9%, 14.5%, and 23.3% at coating thickness from 283 to 955 µm. The room‐temperature, spectral directional–hemispherical transmittance, and reflectance are measured over the wavelength range from 1.35 to 2.5 µm. The radiative properties of absorption and scattering coefficients are reduced by using a hybrid method of the discrete ordinate method and the Kubelka–Munk four‐flux method. Using the image processing tools developed in‐house, the porosity and pore size distribution (PSD) are obtained from SEM images for each coating. A numerical algorithm is used to convert the two‐dimensional PSD into a three‐dimensional PSD assuming that all pores are spheroid. The scattering coefficient is directly computed by the Mie theory based on the PSD. The new approach provides a predictive model of radiative properties based on the PSD, which is extracted from the coating cross‐section images. Comparison of radiative properties obtained by the direct Mie theory computation and those obtained by the reduction from spectral measurement is made and discrepancy is discussed. [ABSTRACT FROM AUTHOR]

The thermal properties of MoW‐HfN, a surrogate cermet for MoW‐UN nuclear thermal propulsion fuel, were characterized over a wide range of elevated temperatures. Thermal diffusivity, coefficient of thermal expansion (CTE), and heat capacity were measured. Optical and scanning electron microscopy were performed to characterize the microstructure and draw structure–property correlations. The thermal diffusivity was obtained using the laser flash method. Diffusivity values ranged from about 0.18 cm2/s at 200°C to 0.15 cm2/s at 1800°C. The CTE was measured using push‐rod dilatometry up to 1600°C, giving values between 6.0 and 9.0 μm/m. A scientific rationalization of the effective material properties is made using the rule‐of‐mixtures and other effective properties models. [ABSTRACT FROM AUTHOR]

In order to explore the temperature‐dependent structural and mechanical/thermal property evolution of pyrochlores, multicomponent rare‐earth zirconates (4RE1/4)2Zr2O7 (RE = La, Nd, Sm, Eu, and Gd) and corresponding single‐component compounds are investigated by molecular dynamics simulations. The structural parameters and mechanical/thermal properties reported in experiments are well reproduced. With temperature enhancement, the bond lengths become large and polyhedrons tend to deform more, whereas the second‐order elastic constants and polycrystalline mechanical moduli gradually reduce. It can be explained by the obvious change of (ZrO6) polyhedrons originating from the Zr–O bond stretching. Furthermore, thermal conductivities show decreasing tendency owing to a sharp decline of the phonon mean free path related to enhanced phonon scattering. As a big influence of temperature on (ZrO6) polyhedrons occurs, the multicomponent design at the Zr‐site is suggested to be paid more attention. This work is expected to shield light on the design for multicomponent pyrochlores as thermal barrier coatings. [ABSTRACT FROM AUTHOR]

Thermal and electrical properties were measured for TiB2 ceramics containing varying CrB2 contents up to 33 mol%. The room‐temperature thermal diffusivity decreased with increasing Cr content from 0.330 ± 0.003 cm2/s for pure TiB2 to 0.060 ± 0.003 cm2/s for (Ti0.66Cr0.33)B2. The amount of anisotropy in the coefficients of thermal expansion increased with increasing Cr content and the c‐axis had the greatest dependence on Cr addition, with an increase of more than 25% in the thermal expansion for 33 mol% CrB2 compared to TiB2, whereas the a‐axis only increased by about 8%. The electrical conductivity was the lowest for (Ti0.66Cr0.33)B2 at ∼8.5 × 103 S/cm compared to ∼106.1 × 103 S/cm for nominally pure TiB2. Overall, the addition of CrB2 as a sintering aid for TiB2 was shown to have a significant effect on the thermal and electrical properties of TiB2 for additions as small as 5 mol% CrB2. [ABSTRACT FROM AUTHOR]

The effects of site symmetric distortion induced by the phase transition on up‐conversion emission and thermal sensing performance of Gd2(MoO4)3:Yb3+/Er3+ (GMO) crystals were elaborately studied by minimizing interference from many factors. Monoclinic GMO showed a much stronger fluorescence intensity and larger fluorescence intensity ratio under the irradiation of 980 nm laser in comparison to the orthorhombic counterpart. These remarkable up‐conversion properties stemmed from the low site symmetry with large site symmetric distortion in monoclinic GMO. Moreover, the thermal sensing property of the samples was assessed based on the fluorescence intensity ratio technique, where monoclinic GMO exhibited much higher maximum absolute sensitivity (Sa = 0.0257 K−1 at 510 K) due to the site symmetric distortion, which was further explained by the Judd–Ofelt theory and polarizability of the chemical bond volume model. Results opened an efficient avenue for achieving highly sensitive thermometry in many daily scenarios via finely tailoring the local site symmetry. [ABSTRACT FROM AUTHOR]

(Pb, La)(Zr, Ti)O3 antiferroelectric (AFE) materials are promising materials due to their energy‐storage density higher than 10 J cm−3, but their low energy‐storage efficiency and poor temperature stability limit their application. In this paper, the (1 − x)(Pb0.9175La0.055)(Zr0.975Ti0.025)O3–xPb(Yb1/2Nb1/2)O3 (PLZTYN100x) AFE ceramics were prepared via two‐step sintering method and investigated thoroughly. With the doping of Yb3+ and Nb5+, the phase structure transforms from the orthorhombic phase (AFEO) to the coexistence of the orthorhombic‐and‐tetragonal phases. This structure reduces the free energy difference between the AFE and ferroelectric phases and reduces the fluctuation of energy with temperature, improving the energy storage efficiency and temperature stability. When the x = 0.05 (PLZTYN5), the AFE ceramic exhibits excellent temperature stability and ultrahigh energy storage performance, whose recoverable energy density (Wrec) is 6.8–8.2 J cm−3 at 30 kV mm−1 in the temperature range from −55 to 75°C, and efficiency (ƞ) is 78%–86.7%. In addition, the change of Wrec is less than 15%, exceeding the performance of most AFE ceramics. The results demonstrate that the PLZTYN5 ceramic has great potential in pulse power capacitors. [ABSTRACT FROM AUTHOR]

The narrow composition design space of high‐entropy transition metal diborides (HE TMB2) limits their further development. In this study we designed six quaternary and quinary high‐entropy transition metal and rare‐earth diborides (HE TMREB2) and investigated their phase stability using the energy distribution of the local mixing enthalpy of all possible configurations. The results show that both quaternary and quinary HE TMREB2 have higher enthalpic driving forces, which facilitates the formation of single‐phase AlB2‐type structures between TMB2 and REB2. Calculations of elastic constants show that the TMB2 component has the greatest effect on the c44 elastic constant and shear modulus G, while REB2 significantly influences the bulk modulus B. Furthermore, LuB2 and TmB2 substantially affect the elastic modulus anisotropy of HE TMB2. Rare‐earth atoms in HE TMREB2 can enhance the nonharmonic interactions between phonons, which results in a significant hindrance in the thermal transport of low‐frequency phonons as well as an increase in the volume thermal expansion coefficients. Thus, the incorporation of REB2 into HE TMB2 has a significant impact on the phase stability and properties. [ABSTRACT FROM AUTHOR]

Based on alumina ceramics, we employ the phase‐field method to study the effects of thermal conductivity, specific heat, density, thermal expansion coefficient, Young's modulus, and fracture toughness on thermal shock cracks. The results show that increasing thermal conductivity and fracture toughness will reduce thermal shock damage. That is, the long crack length becomes shorter, or the crack density becomes smaller. However, increasing the thermal expansion coefficient and Young's modulus will increase thermal shock damage. It is consistent with the previous thermal shock theory. The effect of material parameters on crack propagation speed was also considered. In addition, we carried out a thermal shock test of the zirconia. The results of the phase‐field calculation are the same as the thermal shock results of the zirconia. This paper verifies that the phase‐field method is suitable for simulating thermal shock cracks in other ceramics. [ABSTRACT FROM AUTHOR]

A “self-permeation” method was used to fabricate a Ca0.9La0.067TiO3-0.01Al2O3 (CLT)-reinforced polysilylaryl-enyne/fiber multilayer board with different volume fractions of CLT (0–40 vol%). The microstructure, dielectric, mechanical, and thermal properties were fully studied. The results showed that the composite with optimal dielectric properties (εr∼8.75, tanδ∼0.0043) could be obtained when the volume fraction of CLT reached 30 vol%. Meanwhile, the thermal conductivity reached a high level of 0.644 W/(m⋅K) and 0.762 W/(m⋅K) at Z and X/Y directions, respectively. Due to the high decomposition temperature of PSAE, Td5 (the temperature corresponding to 5% weight loss) of composite loading with 30 vol% CLT was higher than 900°C, which indicates an excellent thermal resistance. And the bending strength could reach 115.3 MPa indicating excellent mechanical property. The novel polysilylaryl-enyne/fiber/Ca0.9La0.067TiO3-0.01Al2O3 multilayer board with excellent performance is expected to be a candidate material for print circuit boards and widely used in the microwave communication field. [ABSTRACT FROM AUTHOR]

A theoretical calculation combined with experiment was used to study highentropy (Hf0.2Ti0.2Mo0.2Ta0.2Nb0.2)B2 (HEB-HfTiMoTaNb). The theoretical calculation suggested HEB-HfTiMoTaNb could be stable over a wide temperature range. Then, a novel solvothermal/molten salt-assisted borothermal reduction method was proposed to efficiently pre-disperse transitional metal atoms in a precursor and synthesize (Hf0.2Ti0.2Mo0.2Ta0.2Nb0.2)B2 nanoscale powders at 1573 K for 6 h, which is nearly 300 K lower than previous reports. The characterization results indicated that the as-synthesized nanoscale HEB-HfTiMoTaNb powder was hexagonal single-phase with homogeneous elements distribution and uniform size, and the oxygen content of the particles is 0.97 wt%. Simultaneously, the mechanical properties, anisotropic nature, and thermal properties of HEB-HfTiMoTaNb were investigated by density functional theory (DFT) calculations. The Cannikin’s law was adopted to explain the improvement of comprehensive mechanical properties. In addition, a significant reduction of thermal conductivity was observed for HEB-HfTiMoTaNb and it only was 1/15 of the value of HfB2. This work suggests a reliable technique for synthesis of nanosized HEB powders and discovery of high-entropy materials under the guidance of first-principle theory. [ABSTRACT FROM AUTHOR]

A “self-permeation” method was used to fabricate a Ca0.9La0.067TiO3-0.01Al2O3 (CLT)-reinforced polysilylaryl-enyne/fiber multilayer board with different volume fractions of CLT (0–40 vol%). The microstructure, dielectric, mechanical, and thermal properties were fully studied. The results showed that the composite with optimal dielectric properties (εr∼8.75, tanδ∼0.0043) could be obtained when the volume fraction of CLT reached 30 vol%. Meanwhile, the thermal conductivity reached a high level of 0.644 W/(m⋅K) and 0.762 W/(m⋅K) at Z and X/Y directions, respectively. Due to the high decomposition temperature of PSAE, Td5 (the temperature corresponding to 5% weight loss) of composite loading with 30 vol% CLT was higher than 900°C, which indicates an excellent thermal resistance. And the bending strength could reach 115.3 MPa indicating excellent mechanical property. The novel polysilylaryl-enyne/fiber/Ca0.9La0.067TiO3-0.01Al2O3 multilayer board with excellent performance is expected to be a candidate material for print circuit boards and widely used in the microwave communication field. [ABSTRACT FROM AUTHOR]

Carbon fiber/phenolic (C/Ph) composites were modified with different weight ratios of hafnium diboride (HfB2) nanofibers to apperceive thermomechanical properties of C/Ph–Hf nanocomposites. Mechanical properties, thermal stability, and ablation resistance of C/Ph–Hf nanocomposites were found to be optimum when the weight percentage of HfB2 was equal to one. Maximum flexural strength and modulus were obtained with 118 MPa and 1.9 GPa for C/Ph–1%Hf nanocomposite, respectively. Increasing the proportion of HfB2, by delaying the temperature of thermal degradation of nanocomposites, enhanced the thermal stability and residual of C/Ph–Hf relative to C/Ph in both nitrogen and air environments. In the oxyacetylene flame test at 2500°C for 160 s, the optimum mass ablation rate of C/Ph–1%Hf nanocomposites was found to be 0.0150 g/s compared to 0.068 g/s for blank C/Ph, along with reducing the back surface temperature by 51%. The ablation mechanism of C/Ph–Hf nanocomposites after the oxyacetylene torch test was concluded from the derivations obtained from X‐ray diffraction, energy dispersion spectroscopy, and microstructure analyses. These clarified that the formation of high‐temperature species, such as HfO2, HfC, and B4C owing to oxidation of HfB2 and subsequent reaction products with char, resulted in an increased ablation resistance of the nanocomposites. [ABSTRACT FROM AUTHOR]

Although KNN‐based ceramics with high electrical properties are obtained through a variety of strategies, the temperature sensitivity is still one of the key technical bottlenecks hindering practical applications. Here, we use a new strategy, meticulously tailoring phase boundary, to refine the ferroelectric boundary of KNN‐based ceramics, leading to high piezoelectricity companied with improving temperature stability. The highest d33 value in this system reaches 501 pC/N with a TC ∼ 240°C, whereas a large strain of ∼0.134% can be kept with 10% lower deterioration until 100°C. The origin of high piezoelectricity is mainly attributed to the well‐preserved multiphase coexistence and the appearance of nanodomains, which greatly facilitate the polarization rotation. Instead of the changed intrinsic thermal insensitivity, the precision phase boundary engineering plays an important role in strengthening the temperature stability of electric‐induced strain. This work provides a simple and effective method to obtain both high electrical properties and excellent thermal stability in KNN‐based ceramics, which is expected to promote the practical applications in the future. [ABSTRACT FROM AUTHOR]

In order to find a kind of MAX phase material suited for thermal barrier coating (TBC) field, the structural properties, mechanical properties, electronic structure, and thermal properties of Nb2AN (A = Si, Ge, and Sn) MAX phase compounds were studied by density functional theory. The results of cohesive energy, formation enthalpy, elastic constants, and lattice dynamics show that the Nb2AN (A = Si, Ge, and Sn) possess good structural stability, mechanical stability, and dynamical stability. Especially in Nb2SnN phase, although its calculated melting point is not the largest one among them, it possesses the best thermal shock resistance. Its coefficient of thermal expansion fits most suitably to the Ni‐based alloy in 300–1452 K and lowest lattice thermal conductivity force it to be an application prospect TBC material. Its mechanical performance is also good for its own smallest deformation of octahedron structure, highest ductileness, and lowest anisotropy. Electronic structure analysis shows that its lowest Debye temperature ΘD${\Theta _{\bf{D}}}$ comes from its highest ionic degree and lowest covalency. Thus, our research provides a deep theoretical basis for the development of new MAX phase materials. [ABSTRACT FROM AUTHOR]

Through the magnetic/thermal transport measurements combined with the analyses of magnetocaloric effect and critical behavior of Co3Sn2S2 single crystal, the main results we obtained are as follows: in the case of the magnetic field H//c‐axis, Co3Sn2S2 exhibits the phase‐separation state below Tc in the low‐field region (H < 500 Oe). Tc increases slightly from 174 to 177 K with an increase in H from 100 to 10 kOe. The second‐order magnetic phase transition near Tc and the itinerant ferromagnetism below Tc are identified. The magnetization below Tc matches well with the three‐dimensional Ising model, instead of the mean‐field model. In the case of H//ab, Tc changes between 175 and 178 K with varying H. Noticeably, M above Tc exhibits a small positive value, instead of the null M as commonly expected in the paramagnetic region. An extra phase transition below 166 K is observed. The magnetic transition near Tc seems not to be the second‐order phase transition. All results show a significant characteristic of anisotropic magnetic phase transition for the Co3Sn2S2 single crystal. They support mutually those in previous reports, moreover, some new phenomena are also observed. They also provide the experimental evidences for the deep insight into the magnetic phase–transition behavior of Co3Sn2S2. [ABSTRACT FROM AUTHOR]

We prepared the novel high‐entropy (xRE1/x)2Si2O7 (RE = Y, Yb, Er, Sc, Gd and Eu, x = 2–6) ceramics by a two‐step method for the application of thermal environmental barrier coatings (TEBCs), and the effect of configuration entropy and lattice distortion on microstructures and thermal properties at high temperature were investigated. The results showed that the configuration entropy resulted from mass disorder can only contribute to the stability of thermal properties and microstructure. Lattice distortion should be responsible for reduction in thermal properties, which may be due to the enhancement of atomic nonharmonic vibration, resulting in intensified phonon scattering and hindering atomic amplitude oscillation. As‐prepared high‐entropy (Y1/6Yb1/6Er1/6Sc1/6Gd1/6Eu1/6)2Si2O7 ceramic exhibited the relatively low thermal diffusivity, thermal conductivity and coefficient of thermal expansion, which were 0.89–0.50 mm2 s–1, 1.99–2.50 W m–1 K–1 and (3.01–3.78) × 10–6 K–1 in the temperature range of 293–1373 K, respectively. This work provides a solid guarantee for the application of TEBC materials. [ABSTRACT FROM AUTHOR]

The thermal and electrical properties were measured for a high entropy carbide ceramic, consisting of (Hf, Ta, Zr, Nb)C. The ceramic was produced by spark plasma sintering a mixture of the monocarbides and had a relative density of more than 97.6%. The resulting ceramic was chemically homogeneous as a single‐phase solid solution formed from the constituent carbides. The thermal diffusivity (0.045–0.087 cm2/s) and heat capacity (0.23–0.44 J/g•K) were measured from room temperature up to 2000°C. The thermal conductivity increased from 10.7 W/m•K at room temperature to 39.9 W/m•K at 2000°C. The phonon and electron contributions to the thermal conductivity were investigated, which showed that the increase in thermal conductivity was predominantly due to the electron contribution, while the phonon contribution was independent of temperature. The electrical resistivity increased from 80.9 μΩ•cm at room temperature to 114.1 μΩ•cm at 800°C. [ABSTRACT FROM AUTHOR]

Borosilicate glass has been adopted internationally for the treatment of nuclear waste with the object of long‐term stabilization through vitrification. Aiming to facilitate experimental comparisons across laboratories, the six‐component international simple glass (ISG) was developed as benchmark. The original ISG produced by Mo‐SCI Corporation (Rolla, MO) was distributed and characterized for different physical properties thus serving as reference for further studies. Still, photoluminescence (PL) properties, which may be useful for scrutinizing radiation‐induced damage, have not been reported. Further, the original ISG contained significant iron impurities, which may present interference in various studies (e.g., optical). Consequently, two new ISG analogs lacking iron impurities (labeled ISG‐1 [closest composition to original ISG] and ISG‐2 [some MgO added at expense of CaO]) were synthesized by Corning Inc. (Corning, NY) (also doped with lanthanum for subsequent corrosion tests involving atom probe tomography), which remain to be fully characterized. Accordingly, this work was undertaken to perform a comprehensive study comparing the three ISG specimens. Various characterizations were then performed on the pristine glasses: X‐ray diffraction and vibrational spectroscopy (structural properties); static‐leach product consistency test (PCT, dissolution behavior); dilatometry and calorimetry measurements (thermal properties); and optical absorption with Tauc and Urbach plots analysis, followed by PL spectroscopy with decay kinetics assessment (optical properties). While the general structural features appeared similar among the glasses, the deconvolution of Raman spectra suggested a lower degree of connectivity in the silica network for ISG‐2. In addition, some differences were indicated from the PCT results and thermal properties assessed, which were discussed based on compositional variations. Further on, the optical properties were shown to be the most distinct. The optical absorption of the original ISG was characterized by Fe2+/Fe3+ impurities not detected for ISG‐1 and ISG‐2. The glasses all exhibited two main PL features (∼1.8 and 2.5 eV) with multiexponential decay behavior apparently of intrinsic origin. In addition, ISG‐1 and ISG‐2 showed a third high‐energy (∼3.4 eV) fast‐decaying contribution tentatively credited to tin impurities, which appeared most significantly for ISG‐1. The results are expected to serve as baseline for future studies simulating the effects of radioactive element decay. [ABSTRACT FROM AUTHOR]

Bioactive glass coatings can improve the osteo integration of metallic implants with the host tissue, thereby increasing their lifespan and overall success rate. However, complex composition‐structure‐property relations in phosphosilicate‐based bioactive glasses make experimental determination of these relations and related composition design of bioactive coatings challenging. By applying molecular dynamics (MD)‐based atomistic simulations with recently developed effective potentials, this work addresses the challenge by using a material genome approach to obtain the composition and structure effects on various key properties for bioactive coating applications. A series of potential bioactive glass compositions were studied and the composition effects on the mechanical and thermal properties that are critical to these bioactive glasses as a coating to metallic implants were calculated. Particularly, by varying the level of B2O3 to SiO2 substitutions, the effect of composition on various key properties was elucidated. It was found that by using cation in a 1 to 1 ratio (BO3/2 to SiO2) instead of the commonly used substitutions (B2O3 to SiO2), the composition effect can be more clearly expressed and, hence, recommended in future composition designs. Together with careful structural analysis, the origin of property changes can be elucidated. The atomistic computer simulation‐based approach is, thus, an effective way to guide future bioactive glass designs for bioactive coatings and other applications. [ABSTRACT FROM AUTHOR]

In this work, resin‐derived carbon coating was prepared on carbon fibers by polymer impregnation pyrolysis method, then silicoboron carbonitride powder was prepared by mechanical alloying, and finally carbon fiber‐reinforced silicoboron carbonitride composites were prepared by hot‐pressing process. The effects of sintering densification and fiber coating on microstructure, mechanical properties, thermal shock resistance, and failure mechanisms of the composites were studied. Fiber bridging hinders the sintering densification, causing more defects in fiber‐dense area and lower strength. However, higher sintering temperature (1800–2000°C) can improve mechanical properties significantly, including bending strength, vickers hardness, and elastic module, because further sintering densification enhances matrix strength and fiber/matrix bonding strength, while the change of fracture toughness is not obvious (2.24–2.38 MPa·m1/2) due to counteraction of higher debonding resistance and less pull‐out length. However, fiber coating improves fracture toughness greatly via protecting carbon fibers from chemical corrosion and damage of thermal stress and external stress. Due to lower coefficient of thermal expansion, lower fiber loading ratio, less stress concentration at the fiber/matrix interface, and better defect healing effect, lower sintering temperature favors thermal shock resistance of composites, and thermal shock recession mechanisms are the damage of interface. [ABSTRACT FROM AUTHOR]

This study examines the incorporation of TiO2 into sodium borosilicate glasses and its effect on the formation of glassy and crystalline microphases. Glasses in the composition range: 7Na2O–23B2O3–(70 ‐ X)SiO2–XTiO2 (where X = 0–14.6 mol.% TiO2) which exhibit phase separation were investigated. Raman studies confirm the formation of two different TiO2 coordinations depending on the molar content of TiO2. Thermal properties of glasses are unaffected by TiO2 addition. The domain size of microphase development in TiO2‐containing glass indicates competition between phase separation and crystallization. Enrichment of titanium on the interphase between glassy microphases reduces the mass transfer and consequently limits the growth rate of glassy phases. This competes with the formation of anatase for which a nucleation‐controlled mechanism is proposed. [ABSTRACT FROM AUTHOR]

Here we report the study temperature dependencies of the Seebeck coefficient, the electrical resistivity (T = 300–750 K), the total thermal conductivity (T = 300–973 K), and the thermoelectric figure of merit (T = 300–750 K) of ceramic samples of γ‐Ln0.8Yb0.2S1.5‐y (Ln = Gd, Dy) solid solutions. It was found that Yb3+ ions in γ‐Ln0.8Yb0.2S1.5‐y act as the promoters of higher crystallite nucleation rate during the formation of solid solutions. This results in the sample dispersion increase and the formation of the additional phonon scattering centers (dislocations and strain stresses along the crystallites semi‐coherent boundaries). These features of the real structure determined the low value of thermal conductivity of γ‐Ln0.8Yb0.2S1.5‐y solid solutions. The lowest electrical resistivity 20 μΩ m at 750 K and the thermal conductivity 0.58 W/m K at 973 K, the highest Seebeck coefficient 125 μV/K at 700 K and the maximum thermoelectric efficiency, ZT = 0.60 (at 770 K) were obtained for γ‐Dy0.8Yb0.2S1.5‐y. [ABSTRACT FROM AUTHOR]

Fluoindinate glass (FIG) is considered an ideal material for fiber laser devices and mid‐infrared bulk optics components owing to its ultra‐low phonon energy and broad transparency window. However, the heat generated by devices fabricated with FIG during their operation limits its application. Therefore, there is an urgent need to study its high‐temperature properties. In this study, the thermal properties, microstructure, crystal phase behaviors, and optical and luminescent properties of high‐temperature FIG were comprehensively evaluated. We also attempted to reveal the changes in its structure at high temperatures using variable‐temperature Raman spectroscopy. We first found that the stretching vibration intensity of nonbridging F(Fnb) decreases, and the bending vibration of FIG increases with an increase in temperature, indicating that high temperatures could lead to the fracture of bridge bonds between some [InF6]3− octahedrons. Certainly, this will lead to glass structural instability, which will further increase the tendency of FIG to undergo devitrification in high‐temperature conditions. We believe that this work will provide a reference for the performance improvement and application of fluoride glass at high temperatures. [ABSTRACT FROM AUTHOR]

This study aims to investigate the effect of the phase transition of CuMn1−xCrxO2 compound on the Jahn–Teller effect which in turn affects the optical, thermal, and thermoelectric power factor properties. The CuMn1−xCrxO2 samples were synthesized by a solid‐state reaction method. The ab initio computation was applied to evaluate the electronic and optical properties in order to confirm the experiment data. The appearance of the phase transition from crednerite CuMnO2 to delafossite CuCrO2 was confirmed by X‐ray diffraction (XRD) and the ab initio computation through displaying the mixed crednerite/delafossite phase; and, the existence of the Jahn–Teller effect was confirmed by the X‐ray photoelectron spectroscopy (XPS) technique exhibiting the occurrence of mixed‐state Mn3+/Mn4+ ions. The results obtained from XRD, XPS, and the ab initio computation implied the decrease of the Jahn–Teller behavior with increased x content under the influence of the phase transition from the crednerite phase to the delafossite phase of CuMn1−xCrxO2. Surprisingly, the Jahn–Teller distortion reduction caused an increase in the energy gap of the optical property, electrical resistivity, and activation energy in thermally activated band conduction. The effect suffered the specific heat behavior by being separated into two groups of crednerite and delafossite, and enhanced the small polaron behavior by increasing the activation energy of thermally activated band conduction. The phase transition reduced the results of thermal conductivity, thermopower, and thermoelectric power factor properties. In other words, the effect of the phase transition from the crednerite CuMnO2 phase to the delafossite CuCrO2 phase on CuMn1−xCrxO2 compound reduced the Jahn–Teller effect with increased Cr content which in turn caused changes in the optical, thermal, and thermoelectric power factor properties. The effect of the phase transition is advantageous for the improvement of material properties. [ABSTRACT FROM AUTHOR]

In this work, we study the structure–topology–property relations of a series of melt‐quenched lithium germanate glasses. These glasses exhibit the so‐called germanate anomaly, that is, the germanium atoms feature a distribution of four‐coordinated and higher coordinated germanium species, manifesting itself as anomalies in several material properties. Here, we couple variations in the number of atomic bond constraints with measured variations in thermal and mechanical properties, including thermal conductivity, Vickers hardness, and fracture toughness. For thermal conductivity, a strong correlation is found with sound velocity as well as with the volumetric constraint density. For hardness, a good correlation with volumetric constraint density is found, whereas, for fracture toughness, variations in network topology alone are insufficient to explain the composition–property relation. To account for this, we apply a recent model which incorporates knowledge of local structure, mechanical properties, and fracture patterns to predict the fracture toughness, showing a good qualitative agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The effects of substituting the B cation in A3BO7 ceramics on their thermal physical properties were investigated by applying a large mass difference. Y3(Nb1‐xTax)O7 (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) ceramics were synthesized, and their structural characteristics were determined. All the fabricated Y3(Nb1‐xTax)O7 ceramics showed defective fluorite structures and glass‐like low thermal conductivity (1.18−2.04 W/m∙K at 25°C) because of the highly distorted crystal structure and significant mass difference. Substitution with Ta5+ enhanced the sintering resistance, leading to superior thermal‐insulating performance via grain boundary scattering. Furthermore, the ceramics exhibited excellent coefficients of thermal expansion, implying the promising applicability of Y3(Nb1‐xTax)O7 as new thermal barrier materials. The effect of mass difference on the thermomechanical properties of the ceramics was examined, suggesting a simple strategy for engineering the chemical composition of new thermal barrier materials. [ABSTRACT FROM AUTHOR]

Zirconium diboride ceramics were densified by hot pressing and spark plasma sintering with heating rates varying from 5 to 300℃/min. Slower heating rates produced larger grains due to the longer times spent at temperatures between 1500 and 1900℃, which is the temperature range in which ZrB2 grains coarsen. Heating rates above 50℃/min resulted in rapid densification, but this led to the retention of up to 3.3 vol.% of ZrO2 particles in the ceramics. After densification, changes to the microstructure were evaluated to interpret the effects of heating rate on thermal and mechanical properties. The flexure strength of ceramics processed by hot pressing up to 80℃/min was proportional to the inverse square root of the maximum grain size based on the Griffith criteria. Conversely, densification by spark plasma sintering, which had heating rates of up to 300℃/min, resulted in microcracks that decreased the elastic modulus from >500 GPa for pristine specimens to <485 GPa for microcracked materials. The use of heating rates >20℃/min also reduced the thermal conductivity due to the presence of retained ZrO2, but improved the strength by reducing the maximum grain size. [ABSTRACT FROM AUTHOR]

Direct mechanical characterization of silicon carbide fibers in extreme hypersonic aerothermal environment is critical to the development of next‐generation inflatable thermal protection systems that could enable delivery of large payloads to planetary surfaces. In this article, we report direct measurements of tensile properties in Hi‐Nicalon silicon carbide fibers exposed to high‐temperature argon plasma exceeding 1100°C using an in situ mechanical testing system integrated into a 30‐kW inductively coupled plasma torch chamber simulating the hypersonic atmospheric entry conditions. As a comparison, ex situ tensile tests were performed on virgin Hi‐Nicalon silicon carbide fibers in both ambient air and vacuum conditions. In situ thermal and optical imaging was used to obtain a real‐time resolution of the thermo‐mechanical events occurring on the fibers during the high‐temperature argon plasma exposure. It is found that the high‐temperature tensile strength of Hi‐Nicalon fiber tows exposed to argon plasma is 0.74 ± 0.19 GPa, which denotes a 59% reduction from the virgin fiber strength in ambient air (1.81 ± 0.19 GPa). Fractographic characterization by scanning electron microscopy shows that the substantial degradation of tensile strength in Hi‐Nicalon fibers results from a reduction of fiber cross‐section due to active surface attack from high‐temperature argon plasma. [ABSTRACT FROM AUTHOR]

Zirconium diboride ceramics were densified by hot pressing and spark plasma sintering with heating rates varying from 5 to 300℃/min. Slower heating rates produced larger grains due to the longer times spent at temperatures between 1500 and 1900℃, which is the temperature range in which ZrB2 grains coarsen. Heating rates above 50℃/min resulted in rapid densification, but this led to the retention of up to 3.3 vol.% of ZrO2 particles in the ceramics. After densification, changes to the microstructure were evaluated to interpret the effects of heating rate on thermal and mechanical properties. The flexure strength of ceramics processed by hot pressing up to 80℃/min was proportional to the inverse square root of the maximum grain size based on the Griffith criteria. Conversely, densification by spark plasma sintering, which had heating rates of up to 300℃/min, resulted in microcracks that decreased the elastic modulus from >500 GPa for pristine specimens to <485 GPa for microcracked materials. The use of heating rates >20℃/min also reduced the thermal conductivity due to the presence of retained ZrO2, but improved the strength by reducing the maximum grain size. [ABSTRACT FROM AUTHOR]

Yttrium tantalate ceramics with ferroelasticity are potential candidates for thermal barrier coating (TBC) ceramics. During the phase transition process, there are three main phases with monoclinic (I2/a), monoclinic‐prime (P2/a), and tetragonal structures (I41/a), and a comprehensive understanding of their thermophysical properties is required. In this study, the thermal and mechanical properties of polymorphous yttrium tantalate (YTaO4) ceramics are systematically investigated under finite temperature by performing first‐principles calculations combined with quasi‐harmonic approximation. The first‐principle study results show that the volume change from M' to T phase is 12.85 Å3 to 12.95 Å3 per atom, whereas the T to M is 12.95 Å3 to 12.84 Å3 per atom, and the change is less than 1%, showing that this process produces almost no volume change. However, the thermal expansion coefficients (TECs) and Young's modulus vary greatly, the TECs value of M YTaO4 is about 11.13 × 10−6 K−1, which is smaller than T YTaO4 as the value 12.01 × 10−6 K−1, and the Young's modulus values of M, M', and T phases are 140.34, 156.68, and 123.29 GPa, respectively. Lastly, the calculated O–Ta bond is stronger than the O–O and O–Y bonds according to the mean bond population and average bond length, resulting in a higher modulus. This work will not only expand the internal mechanism of the thermophysical properties of YTaO4, but also provides support for the design and application of TBC systems. [ABSTRACT FROM AUTHOR]

Spinel‐structured NiMn2O4 ceramics, with different valence Ni sources, were originally prepared using Ni2O3 and NiO as raw materials, and the effects of different valence Ni sources on their electrical properties were first investigated. XRD patterns show that both Ni2O3‐based and NiO‐based NiMn2O4 ceramics are single cubic spinel structures. SEM/EDS images indicate that the NiMn2O4 ceramics exhibited high density at the experiment‐determined sintering temperatures. XPS results and Raman drifts prove that the Ni valence‐induced changes in Mn ions at B sites played a significant role in the electrical properties and thermal stability of NiMn2O4 ceramics. Compared with NiO‐based NiMn2O4, the resistivity at 25°C (ρ25°C) of Ni2O3‐based NiMn2O4 increased dramatically from 3109 to 106958 Ω cm, the thermal constant (B25/50) increased from 3264 to 4473 K, and the resistance shifts after annealing for 1000 h at 150°C decreased from 0.80% to 0.74%. The investigation of the relationship between the material properties and valence of Ni sources has provided a new and effective way for designing the spinel‐structured negative temperature coefficient (NTC) materials by modulating the valence of ions at A sites in the raw materials. [ABSTRACT FROM AUTHOR]