Thermal expansion performance and intrinsic lattice thermal conductivity of ferroelastic RETaO4 ceramics

Ferroelastic RETaO₄ ceramics are promising thermal barrier coatings (TBCs) because of their attractive thermomechanical properties. The influence of crystal structure distortion degree on thermomechanical properties of RETaO₄ is estimated in this work. The relationship between Young's modulus and TECs is determined. The highest TECs (10.7 × 10⁻⁶ K⁻¹, 1200°C) of RETaO₄ are detected in ErTaO₄ ceramics and are ascribed to its small Young's modulus and low Debye temperature. The intrinsic lattice thermal conductivity (3.94-1.26 W m⁻¹ K⁻¹, 100-900°C) of RETaO₄ deceases with increasing of temperature due to an elimination in thermal radiation effects. The theoretical minimum thermal conductivity (1.00 W m⁻¹ K⁻¹) of RETaO₄ indicates that the experimental value is able to be reduced further. We have delved deeply into the thermomechanical properties of ferroelastic RETaO₄ ceramics and have emphasized their high-temperature applications as TBCs.     

Effect of glassy bonding materials on the properties of LAS/SiC porous ceramics with near zero thermal expansion

Near zero thermal expansion porous ceramics were fabricated by using SiC and LiAlSiO₄ as positive and negative thermal expansion materials, respectively, bonded by glassy material. The coefficient of thermal expansion value of a desired porous composite can be easily controlled by choosing the appropriate ratios of the different phases. It was shown that some of LiAlSiO₄ was decomposed to LiAlSi₂O₆ and LiAlO₂, some of LiAlSiO₄ reacted with SiO₂ to form LiAlSi₂O₆ during sintering. With increasing the content of glassy materials, the reaction between LiAlSiO₄ and SiO₂ was accelerated. The Young's modulus increased due to the neck growth between the SiC grains. The 52.5 vol% LiAlSiO₄ (LAS)/SiC ceramics with ∼36% porosity had a combination of near zero coefficient of thermal expansion ∼0.39 × 10⁻⁶ K⁻¹ at room temperature and relatively high Young's modulus ∼59 GPa.     

New class of high-entropy rare-earth niobates with high thermal expansion and oxygen insulation

Tailoring the structure and properties of materials using the high-entropy (HE) effect is of significant interest in the fields of environmental and thermal barrier coatings (TBCs). In this work, a new class of dense HE rare-earth niobates was successfully prepared by a solid-phase reaction method, including (Sm_1/5Dy_1/5Ho_1/5Er_1/5Yb_1/5)NbO₄ (5HERN), (Sm_1/6Dy_1/6Ho_1/6Er_1/6Yb_1/6Lu_1/6)NbO₄ (6HERN), (Sm_1/7Dy_1/7Ho_1/7Er_1/7Yb_1/7Lu_1/7Gd_1/7)NbO₄ (7HERN), and (Sm_1/8Dy_1/8Ho_1/8Er_1/8Yb_1/8Lu_1/8Gd_1/8Tm_1/8)NbO₄ (8HERN), along with eight single rare-earth niobates (RENbO₄, RE = Sm, Dy, Ho, Er, Yb, Lu, Gd, and Tm). X-ray diffraction analysis showed that 5–8HERN are single-phase solid solutions with a monoclinic structure (space group C12/c1). The thermal expansion coefficients of 7HERN and 8HERN exceed 11 × 10⁻⁶ K⁻¹ at 1200°C and are much higher than those of the RENbO₄ compositions (10.13–10.74 × 10⁻⁶ K⁻¹) and other some HE rare-earth oxides (10.27–10.87 × 10⁻⁶ K⁻¹). Importantly, 5–8HERN have lower oxygen-ion conductivity and higher activation energy than yttrium-stabilized zirconia (YSZ) and the RENbO₄ compositions. The oxygen-ion conductivity of 5HERN (7.52 × 10⁻⁷ S cm⁻¹, 900°C) was 10⁵ times lower than that of YSZ (0.01 S cm⁻¹, 750°C). The hardness of 5–8HERN is ∼7.81–8.46 GPa and these compositions have low intrinsic lattice thermal conductivity at high temperature (1.28–1.69 W m⁻¹ K⁻¹ at 900°C). The mechanism by which the HE effect improved the material properties was elucidated. Young's modulus, hardness, thermal expansion coefficient, and intrinsic lattice thermal conductivity are linearly related to the mass, size, and distortion degree of samples. In contrast, the oxygen-ion conductivity depends on both the degrees of disorder and distortion and the oxygen-ion vacancy concentration. Based on their overall performance, especially their high thermal expansion coefficients and excellent oxygen-barrier performance, HE rare-earth niobates show potential for further development as TBC materials.     

Improved wear resistance and low thermal radiative conductivity of a middle-entropy tantalate Y0.5Gd0.5Ta0.5Nb0.5O4

Ferroelastic YTaO₄ is a promising material for thermal barrier coatings (TBCs), and its thermal and mechanical properties can be further optimized by various methods. In this study, a ferroelastic middle-entropy ceramic Y_0.5Gd_0.5Ta_0.5Nb_0.5O₄ was synthesized by solid-phase sintering, and its microstructures and thermophysical properties were key points. We determined the contributions of phonons and photons to total thermal conductivity, and a low thermal conductivity was obtained by inhibiting high-temperature thermal radiation. The thermal expansion coefficients were improved by introducing of Nb atom into the lattice of the prepared middle-entropy ceramic, which meets the requirements of TBCs. The improved wear resistance originated from relatively high Young's modulus and the hardness of Y_0.5Gd_0.5Ta_0.5Nb_0.5O₄, and it would contribute to the service performance of the corresponding coatings. This work motivates the engineering applications of ferroelastic RETaO₄ and RENbO₄ (RE is rare-earth element) as high-temperature TBCs.     

First-principles study of thermophysical properties of polymorphous YTaO4 ceramics

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.     

Sintering,thermal expansion,and thermal transport properties of A4Ta2O9 (A= Ca,Mg) tantalates

Searching for new oxides with low thermal conductivity and high thermal expansion coefficients (TECs) as thermal barrier coatings (TBCs) is vital for the development of highly efficient gas turbines and aeroengines. We report the densification sintering, high TECs, and low thermal conductivity of A₄Ta₂O₉ (A = Ca, Mg) tantalates. The best sintering temperature of dense A₄Ta₂O₉ ceramics was determined via an optical contact angle tester, and samples with a relative density of 99.8% were synthesized via spark plasma sintering (SPS). The hardness (9–10 GPa), Young's modulus (172.7–211.8 GPa) and fracture toughness (1.5–1.6 MPa m^1/2) of the A₄Ta₂O₉ ceramics are primarily affected by the bonding strength. Furthermore, we studied the thermal transport properties of A₄Ta₂O₉. The low thermal conductivity (1.78–1.93 W m^?1 K^?1 at 900 °C), extraordinary phase stability, and high TECs (11.4–11.8 × 10^?6 K^?1 at 1200 °C) of A₄Ta₂O₉ ceramics make them candidate TBCs with high operating temperatures.     

High-entropy ferroelastic rare-earth tantalite ceramic: (Y0.2Ce0.2Sm0.2Gd0.2Dy0.2)TaO4

In this study, high-entropy rare-earth tantalate ceramics (Y_0.2Ce_0.2Sm_0.2Gd_0.2Dy_0.2)TaO₄ ((5RE_0.2)TaO₄) have been successfully fabricated. The possibility of formation of (5RE_0.2)TaO₄ was verified via first-principles calculations. In addition, the phase structure, ferroelastic toughening mechanism, thermophysical, and mechanical properties were systematically investigated. The (5RE_0.2)TaO₄ ceramics have lower phonon thermal conductivity (1.2–2.6 W·m^–1·K^–1) in the entire temperature range than that of RETaO₄ and YSZ. (5RE_0.2)TaO₄ has a higher fracture toughness and lower brittleness index than YSZ. The thermal expansion coefficients of (5RE_0.2)TaO₄ are as high as 10.3 × 10^-6 K^–1 at 1200°C and Young's modulus is 66–189 GPa, and thus, (5RE_0.2)TaO₄ possesses great potential for application in thermal barrier coatings (TBCs).     

The effect of ZrO2 alloying on the microstructures and thermal properties of DyTaO4 for high-temperature application

High fracture toughness of 8 YSZ (8 wt% yttria-stabilized zirconia) is linked to its ferroelastic toughening mechanism. In this work, the similar ferroelastic domain is detected in monoclinic Dy_1−xTa_1−xZr_2xO₄ ceramics, which derives from the ferroelastic transformation between the high-temperature tetragonal (t) and low-temperature monoclinic (m) phase. The lowest thermal conductivity of Dy_1−xTa_1−xZr_2xO₄ ceramics is reduced by 30% compared with 8 YSZ, and the largest thermal expansion coefficients (TECs) is up to 11 × 10⁻⁶ K⁻¹ at 1200°C, which is comparable to that of 8 YSZ. Notably, the systematic investigations containing phase, microstructure, thermophysical properties of Dy_1−xTa_1−xZr_2xO₄ ceramics will provide guidance for its high-temperature application, especially as thermal barrier coatings.     

High-entropy (Ho0.2Y0.2Dy0.2Gd0.2Eu0.2)2Ti2O7/TiO2 composites with excellent mechanical and thermal properties

High-performance ceramics with low thermal conductivity, high mechanical properties, and idea thermal expansion coefficients have important applications in fields such as turbine blades and automotive engines. Currently, the thermal conductivity of ceramics has been significantly reduced by local doping/substitution or further high-entropy reconfiguration of the composition, but the mechanical properties, especially the fracture toughness, are insufficient and still need to be improved. In this work, based on the high-entropy titanate pyrochlore, TiO₂ was introduced for composite toughening and the high-entropy (Ho_0.2Y_0.2Dy_0.2Gd_0.2Eu_0.2)₂Ti₂O₇-xTiO₂ (x = 0, 0.2, 0.4, 1.0 and 2.0) composites with high hardness (16.17 GPa), Young's modulus (289.3 GPa) and fracture toughness (3.612 MPa·m^0.5), low thermal conductivity (1.22 W·m⁻¹·K⁻¹), and thermal expansion coefficients close to the substrate material (9.5 ×10⁻⁶/K) were successfully prepared by the solidification method. The fracture toughness of the composite toughened sample is 2.25 times higher than that before toughening, which exceeds most of the current low-thermal conductivity ceramics.     

Crystal structure,mechanical and thermal properties of Yb4Al2O9: A combination of experimental and theoretical investigations

The key requirements for a successful thermal and environmental barrier coating (T/EBC) material include stability in high temperature water vapor, low Young's modulus, close thermal expansion coefficient (TEC) with mullite, low thermal conductivity and weak mechanical anisotropy. The current prime candidates for top coat are ytterbium silicates (Yb₂SiO₅ and Yb₂Si₂O₇). A major weakness of these two silicates is the severe anisotropy in mechanical properties and thermal expansion that would lead to cracking of the coating. Thus, searching for new materials with weak mechanical and thermal anisotropy is of signification. In this work, the crystal structure, mechanical and thermal properties of a promising T/EBC candidate, Yb₄Al₂O₉, are investigated theoretically and experimentally. Good ductility, low shear deformation resistance, low Young's modulus (151 GPa) and low thermal conductivity (0.78 W m⁻¹ K⁻¹) is underpinned by heterogeneous bonding characteristic and distortion of the structure. Close TEC (6.27 × 10⁻⁶ K⁻¹) with mullite and weak mechanical anisotropy highlight the suitability of Yb₄Al₂O₉ as a prospective T/EBC.     

Synthesis and thermophysical properties of ATa2O6 (A = Co,Ni, Mg,Ca) tantalates with robust CMAS resistance

A new family of ceramic environmental/thermal barrier coating (E/TBC) materials, that is, ATa₂O₆ (A = Co, Ni, Mg, Ca), for high-temperature applications, are investigated and reported in this study. We focus on the synthesis and features of crystal structures, and on the mechanical and high-temperature properties. ATa₂O₆ oxides have an extraordinary phase stability (up to 1300°C), and their thermal expansion coefficients (6.2–7.3 × 10⁻⁶ K⁻¹) match those of SiC fiber-enhanced SiC ceramic matrix composites (3–7 × 10⁻⁶ K⁻¹). Their low thermal conductivities (min: 1.15 W·m⁻¹·K⁻¹) root in the slow phonon spreading speed and fierce phonon-phonon scattering process, and they will provide exceptional thermal insulation. Moreover, their hardness (5.6–8.8 GPa), toughness (1.4–1.9 MPa·m^1/2), and moduli (100–210 GPa) have good comparability with current E/TBCs. We propose the 33CaO-9MgO-13AlO_1.5-45SiO₂ (CMAS) corrosion mechanisms of ATa₂O₆ ceramics, and their robust CMAS resistance relies on the phase stability of CaTa₂O₆ oxides. The excellent high-temperature properties ensure that ATa₂O₆ can be used as E/TBCs to provide thermal insulation and CMAS corrosion protection.     

High-pressure structural stability,equation of state,and thermal expansion behavior of cubic HfO2

The structural stability, equation of state, and thermal expansion behavior of nanocrystalline cubic HfO₂, an ultra-high-temperature ceramic, have been investigated using X-ray diffraction at extreme conditions of pressures and temperatures. High-pressure studies show that the cubic structure is stable up to 26.2 GPa, while the high-temperature studies show the stability of the cubic structure up to 600°C. The Rietveld structure refinement of the high-pressure data reveals the progressive transition of secondary monoclinic phase to the cubic phase at higher pressures. The phase progression is accompanied by incompressibility along the b axis and a large compressibility along the c axis of the monoclinic structure. The second-order Birch-Murnaghan equation of state fit to the unit cell volume data yielded a bulk modulus of 242(16) GPa for the cubic structure. A linear thermal expansion value of α_a(c) = 8.80(15) × 10⁻⁶°C⁻¹ and a volume thermal expansion value of α_v = 26.5(4) × 10⁻⁶°C⁻¹ have been determined from the in situ high-temperature X-ray diffraction studies. The results are discussed by comparing with the high-pressure and high-temperature behavior of isostructural ZrO₂. To the best of our knowledge, this is the first experimental report on the structural stability of cubic HfO₂ at high pressures.     

Synthesis and thermophysical properties of RETa3O9 (RE = Ce,Nd, Sm,Eu, Gd,Dy, Er) as promising thermal barrier coatings

Thermal barrier coatings (TBCs) are one of the most important materials in gas turbine to protect the high temperature components. RETa₃O₉ compounds have a defect‐perovskite structure, indicating that they have low thermal conductivity, which is the critical property of TBCs. Herein, dense RETa₃O₉ bulk ceramics were fabricated via solid‐state reaction. The crystal structure was characterized by X‐ray diffraction (XRD) and Raman Spectroscope. Scanning electron microscope (SEM) was used to observe the microstructure. The thermophysical properties of RETa₃O₉ were studied systematically, including specific heat, thermal diffusivity, thermal conductivity, thermal expansion coefficients, and high‐temperature phase stability. The thermal conductivities of RETa₃O₉ are very low (1.33‐2.37 W/m·K, 373‐1073 K), which are much lower than YSZ and La₂Zr₂O₇; and the thermal expansion coefficients range from 4.0 × 10^?6 K^?1 to 10.2×10^?6 K^?1 (1273 K), which is close to La₂Zr₂O₇ and YSZ. According to the differential scanning calorimetry (DSC) curve there is not phase transition at the test temperature. Due to the high melting point and excellent high‐temperature phase stability with these oxides, RETa₃O₉ ceramics were promising candidate materials for TBCs.     

Mechanical and thermal properties of δ-RE4Hf3O12 (RE = Yb,Lu)

Rare-earth (RE) hafnates are promising thermal and environmental barrier coating (TEBC) materials for SiC_f/SiC ceramic matrix composites. In this study, pure-phase and dense δ-RE₄Hf₃O₁₂ (RE = Yb, Lu) bulk ceramics have been fabricated via a hot-pressing method. The crystal structure, microstructure, mechanical, and thermal properties of δ-RE₄Hf₃O₁₂ were systematically investigated in order to probe their potential application as TEBCs. The high-temperature elastic moduli of δ-Yb₄Hf₃O₁₂ and δ-Lu₄Hf₃O₁₂ are measured to be 185 and 188 GPa at 1673 K, respectively, which are over 85% values of room temperature. The coefficients of thermal expansion are 7.64 × 10⁻⁶ and 7.46 × 10⁻⁶ K⁻¹ for δ-Yb₄Hf₃O₁₂ and δ-Lu₄Hf₃O₁₂, respectively. The relatively low coefficient of thermal expansion and thermal conductivity as well as their excellent high-temperature stability endow these hafnates as potential TEBC candidates.     

Synergistic modification of properties in Ba[(Zn0.8Mg0.2)1/3Nb2/3]O3 ceramics through ordered domain engineering

The ordered domain engineering was investigated for Ba[(Zn_0.8Mg_0.2)_1/3Nb_2/3]O₃ microwave dielectric ceramics to synergistically modify the physical properties especially the temperature coefficient of resonant frequency τ_f and quality factor Q value together with the thermal conductivity. The ordered domain structure could be tailored and controlled by the post-densification annealing, and the fine ordered domain structures with high ordering degree and low-energy domain boundary were obtained in the present ceramics annealed around 1400°C for 24 h, where the Qf value was improved from 51 000 to 118 000 GHz, τ_f was suppressed from 30 to 25.5 ppm/°C. Moreover, the thermal conductivity at room temperature was increased from 3.79 to 4.30 W m⁻¹ K⁻¹, and the Young's modulus was improved from 98 to 214 GPa. The present work provided a promising approach for synergistic modification of physical properties in Ba-based complex perovskite microwave dielectric ceramics.     

Thermo-mechanical properties of mullite ceramics: New data

Coefficients of elastic stiffnesses and thermal expansion of hot isostatically pressed, reaction-sintered and technical fused-mullite ceramics were measured between 100 and 1673 K in comparison with single crystal mullite employing resonant ultrasound spectroscopy and dilatometry, respectively. Additionally, chemical and phase compositions and the microstructure of the ceramics were studied using X-ray diffraction techniques and scanning electron microscopy. Our studies revealed that despite polycrystallinity and slight porosity of up to 1.6%, the elastic behavior of the hot isostatically pressed ceramics is near to ideal aggregate elastic properties of mullite single crystal, for example, their bulk moduli fit within 0.7% to B = 170.0 GPa of single crystal mullite. On the other hand, with B = 155 GPa, the reaction-sintered mullite behaves significantly softer. The difference can be explained with more tight grain to grain contacts in hot isostatically pressed ceramics as compared to reaction-sintered materials. The thermal expansion of both types of ceramics almost coincides with the corresponding averaged behavior of single crystal mullite. For example, between 573 and 1273 K, the volume expansion coefficients of all these materials are (18.0 ± 0.3)·10⁻⁶ K⁻¹. Obviously, the microstructural features are less important for the macroscopic thermal expansion. Due to heterogeneous microstructure and high α-alumina and zirconia contents, the corresponding properties of fused-mullite refractory deviate strongly from those of the other mullite materials.     

Tailoring thermal and mechanical properties of rare earth niobates by coupling entropy and composite engineering

In this paper, a series of high-entropy rare earth niobates, including fluorite RE₃NbO₇ (HE317), monoclinic RENbO₄ (HE114) and RENbO₄/RE₃NbO₇ composite (HE-composite), are prepared via solid state reaction, following by a study about their thermal and mechanical properties. The high-entropy rare earth niobates exhibit excellent phase stability after thermally exposed to 1300 °C for 100 h, indicating entropy can stabilized high-entropy rare earth niobates. Compared with the single element rare earth niobates, high-entropy rare earth niobates have higher fracture toughness and hardness. The high-entropy RENbO₄/RE₃NbO₇ composite has the best mechanical properties, with a fracture toughness of 2.71 ± 0.17 MPa·m^1/2 and hardness of 9.46 ± 0.24 GPa, respectively. The high-entropy niobates exhibit high coefficients of thermal expansion which is close to 7 wt% Y₂O₃ stabilized ZrO₂. It is also proved that the configurational entropy has little effect on the critical temperature from monoclinic to tetragonal phase transition. The thermal conductivity of HE-composite is lower than HE114, indicating the combination of HE114 and H317 is a more efficient strategy to decrease the thermal conductivity of HE114 than entropy engineering.     

High-temperature mechanical and thermal properties of Ca1−xSrxZrO3 solid solutions

Perovskite oxides are promising thermal barrier coatings (TBCs) materials but their thermophysical properties still need to be further improved before commercial applications. In this work, mechanical/thermal properties of calcium-strontium zirconate solid solutions (Ca_1−xSr_xZrO₃) are investigated. Comparing to the end-compounds CaZrO₃ and SrZrO₃, the solid solutions achieve the enhanced thermal expansion coefficient, decreased thermal conductivity as well as good high-temperature mechanical properties. The experimental thermal conductivities of Ca_1−xSr_xZrO₃ (x = 0.2, 0.4, 0.6, 0.8) are in the range of 1.76-1.94 W·(m·K)⁻¹ at 1073 K, being lower than that of the yttria-stabilized zirconia (YSZ). At the same time, their thermal expansion coefficients (10.75 × 10⁻⁶-11.23 × 10⁻⁶/K at 1473 K) are comparable to that of YSZ. Moreover, the Young's moduli of Ca_0.8Sr_0.2ZrO₃, Ca_0.6Sr_0.4ZrO₃, Ca_0.4Sr_0.6ZrO₃, and Ca_0.2Sr_0.8ZrO₃ at 1473 K are 70.7%, 69.4%, 68.8%, and 71.1% of the corresponding values at room temperature, respectively. The good high-temperature mechanical and thermal properties ensure the potential applications of Ca_1−xSr_xZrO₃ solid solutions as high-temperature thermal insulation materials including TBCs.     

Solvothermal-derived multicomponent rare-earth cerate ceramics toward remarkable thermophysical properties

The multicomponent rare-earth cerate (Y_0.2La_0.2Nd_0.2Sm_0.2Eu_0.2)₂Ce₂O₇ (5RE₂Ce₂O₇) ceramics were successfully fabricated through solvothermal method and the following calcination process. The microstructure and phase composition of the as-obtained products were systematically characterized via SEM, TEM and XRD techniques. The results showed that the as-synthesised 5RE₂Ce₂O₇ has a single-phase fluorite-type crystal structure with the particle size of approximately 200 nm. Furthermore, the as-synthesised 5RE₂Ce₂O₇ demonstrated lower thermal conductivity (1.9–1.26 W m^?1·K^?1 at 25–1000 °C), higher thermal expansion coefficients (CTEs, 12.48 × 10^?6 K^?1 at 1000 °C), and outstanding mechanical properties including large Young's modulus (248.0 ± 0.35 GPa) and high fracture toughness (2.4 ± 0.21 MPam^1/2). The excellent properties of the as-synthesised 5RE₂Ce₂O₇ demonstrates its potential application as a new type of next-generation TBCs.     

Effect of Al3+ doping on mechanical and thermal properties of DyTaO4 as promising thermal barrier coating application

The ceramics of dysprosium tantalate (DyTaO₄) doping with Al³⁺ (the doping content are 0, 2, 4, and 6 mol%, respectively) are successfully synthesized in this work. The results of transmission electron microscopy (TEM) reveal that the DyTaO₄ has the domains within ferroelasticity. The thermal properties indicate that the (Al_xDy_1?x)TaO₄ ceramics have much lower thermal conductivity and better high‐temperature phase stability than that of 8YSZ (yttria‐stabilized zirconia). The elastic properties imply that the (Al_xDy_1?x)TaO₄ have lower elastic properties than that of DyTaO₄. The values of Young's modulus of (Al_xDy_1?x)TaO₄ range from 82 to 135 GPa, and the thermal expansion coefficients (TEC) of (Al_xDy_1?x)TaO₄ vary in the range of (6‐10) × 10^?6 K^?1 when the temperature is below 1200°C.