Average Thermal Expansion Coefficient Research Articles

Feasibility research of perovskite‐type PrAlO3+δ as high‐temperature infrared radiation coating

AbstractThermal radiation coating with low thermal conductivity and high infrared emissivity are desirable. In this work, a novel rare‐earth aluminate (PrAlO3+δ with rhombohedral structure) was synthesized via solid‐state reaction method, and the corresponding coating was fabricated using atmospheric plasma spraying (APS). The study encompassed an investigation into the phase structure, high‐temperature phase stability, thermo‐mechanical characteristics, and infrared properties. The results illustrate that as‐deposited coating contained amorphous phase, but recrystallized coating presented phase stability up to 1600°C. Furthermore, the recrystallized coating exhibited low thermal conductivity of 1.35 W/m K at 900°C as well as an average coefficient of thermal expansion of 10.36 × 10−6/K. Also, the coating exhibited high infrared emissivity related to high valance state (Pr4+) and oxygen vacancies. And the average infrared emissivity within 2–14 µm was 0.822 at 1300°C and presented slight decrease with the increase of temperature (the average infrared emissivity of 0.795 at 1800°C).

Ultralow-Permittivity and Temperature-Stable Ba1-xCaxMg2Al6Si9O30 Dielectric Ceramics for C-Band Patch Antenna Applications.

Ca-substituted Ba1-xCaxMg2Al6Si9O30 ceramics were prepared to explore the relationships among their crystal structural parameters, phase compositions, dielectric properties, and coefficients of thermal expansion and applications in C-band antenna. The maximum solubility of Ba1-xCaxMg2Al6Si9O30 was located at x = 0.25, and Ba1-xCaxMg2Al6Si9O30 ceramics (0 ≤ x ≤ 0.25) crystallized in the space group P6/mcc. In Ba1-xCaxMg2Al6Si9O30 single-phase ceramics, εr was dominated by ionic polarizability and "rattling effects" of Ba2+ and Al(2)3+; Q × f was controlled by the roundness of [Si4Al2O18] inner rings and total lattice energy; and τf was affected by the bond valence of Si/Al(1)-O(1). Notably, the low average coefficients of thermal expansion (2.668 ppm/°C) at -150 °C ≤ T ≤ 850 °C and near-zero coefficients of thermal expansion (1.254 ppm/°C) at -150 °C ≤ T ≤ 260 °C were achieved for the Ba1-xCaxMg2Al6Si9O30 (x = 0.1) ceramic. Optimum microwave and terahertz dielectric properties were obtained for the Ba1-xCaxMg2Al6Si9O30 (x = 0.1) ceramic with εr = 5.80, Q × f = 31,174 at 13.99 GHz, τf = -7.10 ppm/°C, and εr = 5.71-5.85 at 0.2 THz ≤ f ≤ 1.0 THz. Also, the Ba1-xCaxMg2Al6Si9O30 (x = 0.1) ceramic substrate had been designed as a C-band patch antenna with a high simulated radiation efficiency (87.76%) and gain (6.30 dBi) at 7.70 GHz (|S11| = -38.41 dB).

Ultra-high cross-linked active ester-cured epoxy resins: Side group cross-linking for performance enhancement

Active ester hardeners are a unique class of epoxy hardeners that undergo a curing reaction without generating secondary hydroxyl groups. This characteristic enables the production of low dielectric and low moisture absorption epoxy resins. In this study, two active ester hardeners, bisphenol A diisobutyrate (DIB) and bisphenol A dimethacrylate (DMA), were used to prepare epoxy resins by reacting with a resveratrol-based epoxy monomer (REP). By cross-linking the double bonds in the resin (using dicumyl peroxide, DCP), the properties of the resin can be dramatically changed. Among the resins prepared, REP/DMA/DCP exhibited the highest cross-linking density, approximately 48 times that of REP/DIB. Its storage modulus at 300 °C remained at 600 MPa, indicating an equivalent glass transition temperature (Tg) higher than 300 °C. Additionally, the cross-linking of the ester side groups increased the initial degradation temperature by 12–13 °C, reaching 395–396 °C. Regarding the coefficient of thermal expansion (CTE), the cross-linking of ester side groups had no significant effect on the CTE in the glassy state. However, it drastically reduced the CTE above the glass transition temperature. The average CTE (30–300 °C) of REP/DMA/DCP was only 106 ppm/°C. Furthermore, the cross-linking of the ester side groups appeared to reduce the dielectric constant but increased the dielectric loss and the water absorption rate. Nevertheless, REP/DMA/DCP's dielectric constant at 10 MHz of 3.07, dielectric loss of 0.01, and saturated water absorption of 0.77 wt% remain in the low range.

Development and investigation of a porous metal-ceramic substrate for solid oxide fuel cells

The process of creating a porous metal-ceramic material based on Ni-Al alloy and gadolinium-doped cerium oxide (CGO) using the thermal explosion method has been investigated. This study aims to analyze the effect of CGO on the thermal explosion parameters and the architecture of the resulting Ni-Al-CGO materials. In this regard, the influence of adding CGO powder to the Ni-Al system on the synthesis process and structure formation during controlled heat loss thermal explosion has been studied. Dependencies of temperature and time characteristics of the thermal explosion on initial parameters have been measured. It has been demonstrated that the concentration of CGO in the initial mixture and heat dissipation from the sample significantly affect the rate of the exothermic reaction. The phase composition of the obtained porous materials, depending on the CGO content and the temperature of subsequent vacuum annealing, was analyzed using X-ray diffraction. The chemical composition and microstructure of the synthesis products were examined through electron microscopy and energy-dispersive X-ray spectroscopy. The possibility of forming metal-ceramic composites with a porosity of 60–65 % for use as supporting substrates for solid oxide fuel cells with a NiO/CGO anode has been shown. An anodic layer of NiO/CGO was applied to a metal-ceramic base of the composition (Ni+25 %Al)+5 %CGO using screen printing, which was then annealed in an air atmosphere at 1300 °C and reduced at 900 °C in a hydrogen atmosphere. The dilatometric method determined that adding 40 wt.% Cr to a mixture of Ni-Al powders reduces the average coefficient of thermal expansion of the new material.

Investigation of the anisotropic thermal expansion of PbIn6Te10 crystal by high temperature x-ray diffraction measurements

The PbIn6Te10 crystal, an IR laser frequency conversion material, grown via the Bridgman method with dimensions ϕ35 mm × 90 mm in a four-zone furnace, was subject to the investigation of its thermal expansion behavior using high-temperature x-ray diffraction in the range of 25–450 °C. Based on the obtained data, the average thermal expansion coefficients of 15.21 × 10−6 K−1 for α a and 6.44 × 10−6 K−1 for α c were determined utilizing the least square method. The study revealed that the linear and volume thermal expansion coefficients of PbIn6Te10 crystals satisfy the relationships α a > α c > 0, α V = 2α a + α c , and α a increased while α c decreased with increasing temperature, accentuating a substantial anisotropy in thermal expansion between the crystal’s principal axes. A detailed exploration pinpointed that the variations in the PbTe6 octahedron primarily governed the changes in the PbIn6Te10 unit cells, with further investigation uncovering its association with variations in the nearest neighboring bonds, which is mainly related to Pb-Te4 and Pb-Te2 bonds. Additionally, the determination of temperature-dependent anisotropic thermal expansion coefficient α was complemented by calculating Grüneisen parameter γ using Quasi-harmonic Debye model. Remarkably, these parameters also exhibited anisotropic behaviors ( γ⊥ increases with temperature whereas γ// decreases, α ⊥ > α ∥), contributing additional insights into the crystal thermal characteristics.

Contactless Scanning Near‐Field Optical Dilatometry Imaging at the Nanoscale

AbstractTo date, there are very few experimental techniques, if any, that are suitable for the purpose of acquiring quantitative maps of the thermal expansivity of 2D materials and nanostructured thin films with nanoscale lateral resolution in spite of huge demand for nanoscale thermal management, for example in designing integrated circuitry for power electronics. Besides, contactless analytical tools for determining the thermal expansion coefficient (TEC) are highly desirable because probes in contact with the sample significantly perturb any thermal measurements. Here, ω‐2ω near‐field thermoreflectance imaging is presented as a novel, all‐optical, and contactless technique to map the TEC at the nanoscale with precision. Testing of this technique is performed on nanogranular films of gold and multilayer graphene (ML‐G) platelets. With ω‐2ω near‐field thermoreflectance, it is demonstrated that the TEC of Au is higher at the metal‐insulator interface, with an average of (17.12 ± 2.30) ×10−6 K−1 in agreement with macroscopic techniques. For ML‐G, the average TEC is (−5.77 ± 3.79) x10−6 K−1 and is assigned to in‐plane vibrational bending modes. A vibrational‐thermal transition from graphene to graphite is observed, where the TEC becomes positive as the ML thickness increases. The nanoscale method here reported demonstrates results in excellent agreement with its macroscopic counterparts, as well as superior capabilities to probe 2D materials and interfaces.

Study of structural, electrical, and electrochemical properties of Sr3-xPrxFe1.8Co0.2O7-δ cathode for IT-SOFCs

Developing new cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) is still challenging. In this study, co-doped Sr3Fe2O7-δ Ruddlesden-Popper (R-P) (Sr3-xPrxFe1.8Co0.2O7-δ x = (0–0.3)) cathode is synthesized by the polymer complex technique as a cathode for IT-SOFCs. The synthesized powders show a desired tetragonal structure of Sr3-xPrxFe1.8Co0.2O7-δ with an I4/mmm space group. The effect of Pr and Co on the physical, thermal, electrical, and electrochemical properties of the cathodes is investigated. The results reveal that Pr/Co co-doping improves electrochemical properties while increasing the electrical resistivity and average thermal expansion coefficients (TECs). To evaluate the long-term thermal stability of the cathode, they are heated at 800 °C for 100 h in the air, and no contaminant is found. In the optimal amount of Pr and Co (Sr2.7Pr0.3Fe1.8Co0.2O7-δ), area-specific resistance (ASR) of 0.058 Ω.cm2 and maximum output power density of 745 mW/cm2 are obtained at 800 °C. Strong oxygen-reducing reaction (ORR) activity and long-term thermal stability make Sr2.7Pr0.3Fe1.8Co0.2O7-δ an appropriate alternative cathode material for IT-SOFC.

Evolution of microstructure and properties of Ba(Mg1/3Ta2/3)O3 thermal barrier material exposed to CMAS corrosion

Calcium-magnesium-alumina-silicate (CMAS) resistance has become a key parameter to evaluate the properties of thermal barrier coating (TBC) materials. The CMAS corrosion behavior of BMT ceramic as a novel candidate material for TBC is poorly understood. In this paper, the solid-state sintering process was used to prepare the BMT bulks, and the evolution of microstructure, phase composition, thermophysical properties, and mechanical properties of the BMT bulks exposed to CMAS corrosion were studied. The results indicate that obvious elemental interdiffusion between the CMAS melt and BMT occurred at 1250 °C, which changed the original phase composition and formed multiple substances including Ba(Al, Ca)Si2O8, Ba2MgSi2O7, BaTa2O6, Ba2Si4O10, etc. The microstructure of BMT also underwent changes due to differences in the diffusion coefficients of different elements. As corrosion time prolongs, an obvious porous columnar reaction layer formed on the sample surface, causing the CMAS melt to sustainably corrode the deep BMT, resulting in intragranular corrosion. In terms of properties, the thermophysical and mechanical properties of the BMT bulks corroded by CMAS deteriorated. The thermal conductivity at 1100 °C increased from 1.43 W m−1 · k−1 to 1.67 W m−1 · k−1. The average coefficient of thermal expansion at 200–1400 °C decreased from 11.60 × 10−6 K−1 to 10.95 × 10−6 K−1. The hardness dropped by 21 % compared to the original BMT bulk. Therefore, it is necessary to improve the CMAS resistance of BMT ceramic in future studies.

Experimental measurement and modeling of lattice thermal expansion and specific heat capacity of C15-Cr2Nb Laves phase intermetallic compound

In order to determine the lattice thermal expansion and specific heat capacity (Cp) of the C15-Cr2Nb Laves phase, an experimental investigation and modeling were carried out in the present paper by employing high-temperature X-ray diffraction (HTXRD) and differential scanning calorimetry (DSC). A thorough analytical model was utilized to predict the temperature-dependent variations of enthalpy and specific heat, and the predicted findings were compared to the experimentally measured data. Arc melting was employed to synthesize Cr2Nb samples with distinct hexagonal (C14/C36) and cubic (C15) Laves phase structures, which were then subjected to the appropriate heat treatment. Room temperature XRD patterns, SEM, and EDAX experiments on homogenized samples at 1273 K for 72 h validated the homogeneity and C15 (Fd-3 m) crystal structure of Cr2Nb. Rietveld refinement was used to determine the lattice parameters and relative phase fractions of the constituent phases. The average thermal expansion coefficient was determined to be αai = 0.659 × 10−5 and αVi = 1.977 × 10−5 K−1 respectively. The Cp of the C15-Cr2Nb Laves phase intermetallic compound was measured employing heat flux DSC, utilizing conventional “three-step” procedures, and being reported for the first time. The measured Cp and enthalpy increment data (HT – H298.15) with varying temperatures reported in the present investigation are being correlated utilizing the theoretical model applying the quasi-harmonic Debye Grüneisen model in the temperature range 0–860 K and illustrated different contributions to the total heat capacity i.e., vibrational, anharmonic, and electronic.

Thermomechanical Properties of Zeta (Ag3In) Phase.

The thermomechanical properties of materials within die-attach joints play an essential role in assessing the reliability of high-power modules. Ag-In transient liquid phase (TLP) bonding serves as an alternative method for die attachment. However, relevant material data for the ζ (Ag3In) phase, one of the Ag-In intermetallic compound (IMC) products of TLP bonding, are limited. This paper proposes an approach to fabricate a densified and pure bulk sample of the ζ (Ag3In) phase. The thermomechanical properties of the ζ (Ag3In) phase were subsequently investigated at elevated temperatures and compared to those of other IMCs frequently observed in die-attach joints. As the temperature increased from 30 °C to 200 °C, the hardness of the ζ (Ag3In) phase decreased linearly from 1.78 GPa to 1.46 GPa. Similarly, the Young's modulus also decreased linearly from 82.3 GPa to 66.5 GPa. These properties rank among the lowest levels compared to those of other IMCs. The average coefficient of thermal expansion within the temperature range of 70 °C to 250 °C was approximately 18.63 ± 0.61 μm/m/°C, placing the ζ (Ag3In) phase at a moderate level. When considering its potential for mitigating thermal stress, these combined properties render the ζ (Ag3In) phase an appropriate material choice for die-attach joints compared to other IMCs.

Thermal expansion properties of three-dimensional relaxor ferroelectric single crystals

Large-size Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) and Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) single crystals have been successfully produced. Nevertheless, the susceptibility of these crystals to cracking substantially hampers their application. This study investigates the thermal expansion characteristics of PMN-PT and PIN-PMN-PT crystals oriented along the 〈100〉, 〈110〉, and 〈111〉 directions, revealing no significant anisotropy. The average thermal expansion coefficients for the PMN-PT and PIN-PMN-PT crystals range from 7.77 to 8.21 × 10−6 K−1 and from 6.59 to 6.79 × 10−6 K−1, respectively, within the temperature range of 20 to 600 °C. Interestingly, the PMN-PT and PIN-PMN-PT crystals demonstrate unusual thermal expansion behavior around the phase transition temperature. The magnitudes of their thermal expansion coefficients are comparable to those of certain commercial crystals but are lower than that of platinum. The main causes inferred for crystal cracking include the pressure exerted by the platinum crucible and the abnormal thermal expansion behavior around the phase transition temperature.

Nd-doping-induced perovskite/Ruddlesden-Popper heterointerfaces boost the ORR activity and CO2 tolerance for SrFeO3-δ-based cathode

The development of cathode materials with high oxygen reduction reaction (ORR) activity is crucial to realize the wide application of solid oxide fuel cells. Nd-doped SrFeO3-δ (SNF) two-phase nanocomposite was fabricated by a dopant-induced in situ self-assembly process. The SNF nanocomposite comprises 63.4 wt% perovskite main phase (P–SNF) and 36.6 wt% Ruddlesden-Popper second phase (RP-SNF). The average thermal expansion coefficient (TEC) of SrFeO3-δ is reduced by 36.5 % and down to 13.9 × 10−6 K−1. At 750 °C, SNF demonstrates an impressive output power of 779 mW cm−2, which is twice that of the single-phase SrFeO3-δ. The superior performance stems from the heterointerface effect of the in situ self-assembled two phases. This effect increases the content of oxygen vacancies, thereby enhancing both chemical oxygen surface exchange coefficient and bulk diffusion coefficient. Moreover, the SNF composite exhibits excellent CO2 tolerance than the single-phase SrFeO3-δ. This work presents a promising avenue for exploring multifunctional materials through interface engineering, offering new possibilities for future energy conversion devices.

Synthesis and characterization of layered quaternary Mo4/3Lu2/3AlB2 ceramics fabricated by spark plasma sintering

A new high-purity i-MAB phase of Mo4/3Lu2/3AlB2 ceramic (95.06 wt% Mo4/3Lu2/3AlB2 and 4.94 wt% MoB) was successfully synthesized with Mo, Al, Lu, and B as raw materials by spark plasma sintering at 1250 °C. The dense sample with a high relative density of 98.9 % possessed good physical and mechanical properties. The average thermal expansion coefficient from room temperature to 1200 °C was determined to be 8.38 × 10−6 K−1. The heat capacity, thermal conductivity, and electrical conductivity were measured to be 0.28 J·g−1·K−1, 9.90 W·m−1·K−1, and 1.22 × 106 Ω−1·m−1 at room temperature, respectively. Additionally, Vickers hardness was tested to be 10.29 GPa under a load of 10 N, fracture toughness was determined to be 5.13 MPa·m1/2, and compressive and flexural strengths were tested to be 1567 MPa and 468 MPa, respectively. Present research adds a new member to the family of structural-functional ceramics.

Synthesis, structure and thermal expansion of new complex phosphates of titanium and metals in the +2 oxidation state

The phosphates of the composition Ca0.5+xMxTi2-x(PO4)3 (M − Ni, Mg) were synthesized by a co-precipitating of salts in aqueous solutions followed by thermal treatment stages. The studied series formed limited NZP solid solutions within the regions 0 ≤ x ≤ 0.5 (Ni) and 0 ≤ x ≤ 1 (Mg). The Rietveld refinement of the Ca1.2Mg0.7Ti1.3(PO4)3 structure showed that its basis is framework formed by TiO6 and (Mg/Ti)O6 octahedra (together with PO4 tetrahedra), and the Ca2+ ions are situated in the cavities. Thermal expansion of the phosphates depending on their chemical composition was characterized in the temperature range from 173 to 473 K. There was a gradual decrease in the linear thermal expansion coefficients with x growth, so that average linear coefficients varied from (11.0–2.6)∙10−6 K−1. Low average thermal expansion coefficient and its low anisotropy allow the studied phosphate ceramics to withstand temperature changes.

Structural and electrical properties of Bi3GaSb2O11 at high temperatures

We have investigated the crystal structure and electrical properties of Bi3GaSb2O11 at high temperatures. Neither phase transitions nor change in oxygen content were observed at 26–800 °C in air. The crystal structure was successfully refined using neutron diffraction data taken at 26–600 °C. The average thermal expansion coefficient between 26 and 600 °C was 10.4614(7) × 10‒6 °C‒1. There are three different (Ga/Sb)–O bonds of (Ga/Sb)–O3b, (Ga/Sb)–O2, and (Ga/Sb)–O3a. It was found that the thermal expansion coefficient of the (Ga/Sb)–O3b bond is lower than those of other bonds. At 916 °C the total DC electrical conductivity in N2 (1.4 × 10‒3 S cm‒1) was higher than that in air (7.1 × 10‒4 S cm‒1), due to electron conduction in N2. In air, oxide-ion conduction was suggested by electrical-conductivity and polarization measurements. Bond-valence-based-energy calculations suggested oxide-ion migration along the O–O edges and on O–O–O faces of (Ga/Sb)O6 octahedra.

Ca and Fe co-doped NdBaCo2O5+δ double perovskites as high-performance cathodes for solid oxide fuel cells

For intermediate-temperature solid oxide fuel cells (IT-SOFCs), high electrochemical catalytic activity and a suitable thermal expansion coefficient (TEC) are essential criteria. In this investigation, simultaneous Ca and Fe co-doped NdBa1-xCaxCoFeO5+δ (NBCCF, x = 0, 0.1, and 0.2) double-perovskites were prepared and investigated as SOFC cathode materials. The introduction of Ca and Fe effectively decreased the TECs and improved the oxygen reduction activity of the cathode. The average TEC of NdBa0.9Ca0.1CoFeO5+δ (NBCCF1) at 30–850 °C was 19.1 × 10−6 K−1, which is decreased by 27.1 % compared to the only Fe-doped NdBaCoFeO5+δ (NBCF). According to the distribution of relaxation time (DRT) analysis, the rate-limiting steps of the oxygen reduction reaction (ORR) include bulk diffusion and surface exchange of oxygen, and Ca doping can improve both steps. The maximum power density of the single cell with NBCCF1 as cathode reached 665 mW cm−2 at 750 °C. The polarization resistance decreased from 0.0722 to 0.0482 Ω cm2 at 800 °C. These findings indicate NBCCF1 is a viable cathode candidate for IT-SOFC.

In-plane thermal expansion behavior of M55J carbon fiber reinforced SiC matrix composite

With the rapid development of high-precision ultra-stable spacecraft, the absolute values of coefficients of thermal expansion (CTE) of carbon fiber reinforced SiC matrix composite (C/SiC) are required to be closer to 10−7 K−1 or even lower. In this work, high-modulus and low-expansion M55J carbon fiber was selected to replace T300 carbon fiber as the reinforcement to decrease the CTE of C/SiC. The interfacial region, pore distribution and microstructure evolution during the densification process were investigated. With the replacement of T300 carbon fiber by M55J carbon fiber as the reinforcement, axial thermal residual stress in SiC matrix can increase to 378 ± 26 MPa, resulting in the generation of matrix microcracks. This can reduce the constraint of matrix to carbon fiber and provide expansion space for M55J-C/SiC. Therefore, the average in-plane technical CTE of C/SiC in the range of −20 to 50 °C can be reduced from 1.09 × 10−6 to 0.34 × 10−6 K−1.

Average and Local Effect of Thermal Fatigue on the Coefficients of the Thermal Expansion of a Complex Continuous Composite Fibre Used for Car Clutch Facing: A Multi-Technique Study.

The clutch facing is a complex organic matrix composite in dry clutch systems. When the clutch engages, there is a sliding contact between the clutch facing and the mating surfaces, resulting in temperature increases of up to 300 °C. These thermal cycles activate several mechanisms that can have consequences on such material: cracking and, more generally, the ageing of the polymer. The thermomechanical properties of the material therefore evolve according to the number of thermal cycles. This study focused on investigating the local and average evolution of the coefficients of thermal expansion (CTE) of clutch facing as a function of thermal cycles. Several techniques were employed, including image stereocorrelation for determining the CTE, Dynamic Mechanical Analysis (DMA) tests for monitoring the ageing of the material and acoustic emission for highlighting the damage. The results showed that the average CTE decreased as a function of the temperature and the number of loading cycles, while locally, it increased in some areas and decreased in others. These differences appear to be the result of material heterogeneity (actual yarn tracing, etc.) and interaction between cracking and ageing mechanisms in the polymer matrix. Indeed, thermal cycling led to cracking and additional crosslinking, which is influenced by ageing conditions.

Influence of Lu3+ addition on the structure, mechanical and thermophysical properties of Gd3TaO7 oxide

To optimise the mechanical and thermophysical properties of Gd3TaO7, Lu3+ doped Gd3TaO7 oxides were synthesised using sol-gel and high-temperature sintering methods. The results show that nanopowders with uniform particle sizes and bulk samples with compact microstructures were successfully obtained. Owing to the decreased order degree of lattice with increasing fraction of Lu3+, the lattice of (Gd1‒xLux)3TaO7 transforms gradually from an ordered pyrochlore (x ≤ 0.5) into a disordered fluorite (x ≥ 0.7). The Young's modulus (174–192 GPa), Vickers hardness (9.9–10.9 GPa), and fracture toughness (2.61–3.68 MPa m0.5) of the bulk samples are superior or comparable to those of Y2O3-stabilised zirconia (YSZ), which can prolong the service life of thermal barrier coating. The thermal conductivity of (Gd1‒xLux)3TaO7 (0.976–1.628 W m‒1 K‒1, 50–1000 °C), first decreases and then elevates with increasing fraction of Lu3+. Owing to the intensive phonon scattering caused by high-concentration point defects, the thermal conductivity of (Gd1‒xLux)3TaO7 is approximately half that of YSZ. Additionally, the excellent lattice steadiness up to 1400 °C and high average thermal expansion coefficient (≥10.71 × 10‒6 K‒1, 1000–1400 °C) of (Gd1‒xLux)3TaO7 oxides will assist in preventing the premature failure of thermal barrier coating.

Computational Design of High-Entropy Rare Earth Disilicates as Next-Generation Thermal/Environmental Barrier Coatings

Development of advanced thermal/environmental barrier coating (T/EBC) materials possessing balanced thermal-mechanical properties is crucial to protect SiC-based ceramic composites from chemical and thermal attack for better performance of components in the hot section of gas turbine engines. In this work we utilize density functional theory (DFT) together with combinatorial chemistry methodology to design high-performance high-entropy rare earth disilicates (β-RE2Si2O7 (RE=Yb, Y, Er, Lu, La, Ce,)) for enhanced phase stability, desired coefficient of thermal expansion (CTE), low lattice thermal conductivity and good mechanical properties. The CTE are determined by phonon calculations at different volumes within the quasi-harmonic approximation. The lattice thermal conductivities are evaluated by the Debye-Callaway model considering three phonon processes. We show that the solid solution of YYbSi2O7 exhibits lowered lattice thermal conductivity than pure cases and a good range of CTE. We also present good EBC candidate materials of Er1/4Lu1/4Y3/4Yb3/4Si2O7 and Er1/2Lu1/2Y1/2Yb1/2Si2O7 with very low lattice thermal conductivity < 0.23 W/m/K at 1500 K and a good match of average CTE (5.1 - 5.2×10−6 K−1) with SiC without compromising mechanical properties. These new EBC with outstanding multi-functional properties are believed to enable significant increases in the performance of protective components in gas turbines. This work also illustrates an efficient and reliable computational framework in accelerating the design of next-generation T/EBC.