Features of crystal structures and thermo‐mechanical properties of weberites RE₃NbO₇ (RE=La, Nd, Sm, Eu, Gd) ceramics

Abstract

Abundant oxides are studied to replace present thermal barrier coatings (TBCs), yttria-stabilized zirconia (YSZ), to perfect the application performances. 1-8 YSZ displays relatively high thermal conductivity (2.5 W•m −1 •K −1 , 1000°C), high Young's modulus (~230 GPa), low application temperature (≤1200°C), and weak CaO-MgO-Al 2 O 3-SiO 2 corrosion resistance. 1,2,9-12 To conquer the weaknesses, multifarious means are applied to perfect YSZ properties, and diverse oxides are researched as novel TBCs. 3,6,13-20 RE 3 NbO 7 oxides (RE is rare earth) are considered as structural materials, as that they display low thermal conductivity (1.0-2.0 W•m −1 •K −1 , 25-900°C), high thermal expansion coefficients (11 × 10 −6 K −1 , 1200°C), and exceptional corrosion resistance. 16,21 The thermal transport mechanism and mechanical properties of fluorites RE 3 NbO 7 are well documented, and the thermal properties of weberites RE 3 NbO 7 are reported. 16,21,22 Besides thermal properties, hardness, toughness, and modulus are vital, nevertheless, the dominant mechanisms of mechanical properties of weberites RE 3 NbO 7 are not clear. The critical factors of hardness, toughness and modulus of ceramics include lattice distortion degree, bond length, microstructure features, and others. Suitable hardness, toughness, and modulus are demanded, and their mutual relations are connective. 23-26 To obtain TBCs with excellent working performance, the mechanical properties and corresponding dominant mechanisms are of great importance. The correlations among crystal structures, surface appearances and mechanical properties of weberites RE 3 NbO 7 are researched. The influences of bond length, lattice distortion degree, crystal structures and microstructures on mechanical properties are studied. Furthermore, the correlations between thermal and mechanical properties are connected. The dominant

Structures, and Thermophysical Properties Characterizations of (La1-xHox)3NbO7 Solid Solutions as Thermal Barrier Coatings

“…where V a was a constant, and it indicated that the temperature dependence of l relied on λ (Bruls et al, 2005). More details about sample preparations, structures identifications, and properties measurements could be found in our previous articles (Chen et al, 2018b;Chen et al, 2019b;Chen et al, 2021a).…”

“…Figures 5A,B,D exhibit that thermal diffusivity and conductivity, and phonon mean free path of (La 1-x Ho x ) 3 NbO 7 solid solutions have the similar temperature dependences because they are dominated by phonons. At room temperature, Ho 3 NbO 7 has the lowest thermal diffusivity (0.34 mm 2 /s), and conductivity (0.96 W • m −1 • K −1 ) contributed to its disorder cubic fluorite lattice (Chen et al, 2021a;Yang et al, 2019;Chen et al, 2018b). Amorphous thermal conductivity is found in Ho 3 NbO 7 , when the remaining prepared samples exhibit different temperature dependences of thermal conductivity.…”

“…, and other candidate oxides (Vassen et al, 2000;Feng et al, 2013;Zhao et al, 2016;Chen et al, 2018b;Li et al, 2018;Liu et al, 2019;Ren et al, 2019;Liu et al, 2020a;Liu et al, 2020b;Chen et al, 2020;Ren et al, 2020;Wu et al, 2020;Chen et al, 2021a;Chen et al, 2021b).…”

“…To study the variations of properties of RE 3 NbO 7 along with the changes of lattice structures and to provide good understanding on these series niobates, the relevant study should be performed. The lowest thermal conductivity of weberite niobates is detected in La 3 NbO 7 , and the minimum thermal conductivity of fluorite niobates is found in Ho 3 NbO 7 oxides (Chen et al, 2018b;Chen et al, 2019b;Yang et al, 2019;Chen et al, 2021a;Chen et al, 2021b). Dense (La 1-x Ho x ) 3 NbO 7 solid solutions are fabricated in this work, and their lattices, thermal conductivity, hardness, and other properties are characterized.…”

“…A 3 BO 7 -type rare earth niobates (RE 3 NbO 7 ) have been studied in the past several years, and they have orthorhombic weberite and cubic fluorite lattices, which rely on RE 3+ ionic size (Ma et al, 2008;Zhang et al, 2017;Yang et al, 2019;Chen et al, 2021a;Chen et al, 2021b;Xiang et al, 2021). The crystal structures of RE 3 NbO 7 derive from fluorite A 4 O 8 , when the four A 4+ ions are substituted by three RE 3+ and one Nb 5+ cation, and one oxygen vacancy is produced in the lattice to maintain charge balance (Wang et al, 2012;Chen et al, 2018a;Chen et al, 2021a;Chen et al, 2021b Different structural and thermophysical property features are documented in weberite and fluorite RE 3 NbO 7 oxides, and they display good thermal insulation performance (Chen et al, 2018b;Yang et al, 2019;Chen et al, 2021a;Chen et al, 2021b). The advantages of RE 3 NbO 7 as TBCs include ultralow thermal conductivity, high TECs, and competitive modulus.…”