Extreme Materials

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CrTa_0.5Nb_0.5 O₄: A solid solution strategy to enhance the mechanical and thermal properties of rutile structured ternaries

Shuang Zhang, Yize Yao, Xiaohui Wang, Huimin Xiang, Cheng Fang, Hailong Wang, Yanchun Zhou

Extreme Materials, 2025, 1(3): 61-73. DOI: 10.1016/j.exm.2025.08.002

Materials	CrTa_0.5Nb_0.5O₄	CrTaO₄[8]	CrNbO₄[9]
Lattice constants
a	4.644	4.642	4.645
b	4.644	4.642	4.645
c	3.017	3.019	3.014
Atomic positions
Cr/Ta/Nb	(0,0,0)	(0.2990,0.2990,0)	(0,0,0)

Table 1 Crystal structure parameters of CrTaO₄,CrNbO₄ and CrTa_0.5Nb_0.5O₄ obtained by Rietveld refinement.

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Fig. 1. (a) Comparison of the XRD pattern of CrTa_0.5Nb_0.5O₄ powders synthesized at 1150^∘C for 2 h with the theoretical one for CrTa_0.5Nb_0.5O₄. (b) Comparison of the experimental XRD patterns of CrTaO₄,CrNbO₄ and CrTa_0.5Nb_0.5O₄. (c) An enlarged view of the (110) diffraction peak in Fig. 1(b). (d) The experimental (black line) and calculated (red line) XRD patterns of CrTa_0.5Nb_0.5O₄. The difference plot (blue line) is shown in the lower part. Vertical marks indicate the Bragg reflection positions of CrTa_0.5Nb_0.5O₄ (green). (e) SEM image of CrTa_0.5Nb_0.5O₄ powders. (f) particle size distribution of CrTa_0.5Nb_0.5O₄ powders.
Fig. 2. (a) Comparison of the XRD pattern of bulk CrTa_0.5Nb_0.5O₄ material prepared by hot-press sintering at 1400^∘C for 40 min under 30 MPa with the theoretical one. (b) SEM image of the fracture surface. (c) Grain size distribution.
Fig. 3. (a) Compiled data of G/B and Poisson's ratio v of some typical ceramics and Cr,Nb containing RHEAs. (b) Vickers hardness versus indentation load for CrTa_0.5Nb_0.5O₄. (c) SEM image of a representative indent produced under a load of 2.98 N. (d) High magnification SEM image showing crack deflection.
Table 2 Elastic/mechanical properties of CrTa_0.5Nb_0.5O₄together with those of ${\mathrm{C}\mathrm{r}\mathrm{T}\mathrm{a}\mathrm{O}}_{4},{\mathrm{C}\mathrm{r}\mathrm{N}\mathrm{b}\mathrm{O}}_{4},\mathrm{Y}\mathrm{S}\mathrm{Z},{\mathrm{A}\mathrm{l}}_{2}{\mathrm{O}}_{3},\mathrm{C}\mathrm{r}$-Ta-Nb based RHEAs.
Fig. 4. Temperature dependent (a) thermal expansion coefficient, (b) thermal diffusivity, (c) heat capacity, and (d) thermal conductivity of CrTa_0.5Nb_0.5O₄.
Fig. 5. (a) HAADF image of CrTa_0.5Nb_0.5O₄. The red rectangle, blue rectangle and green rectangle mark CrTa_0.5Nb_0.5O₄,CrNbO₄, and CrO, respectively. (b-e) EDS elemental mapping of Cr,Ta,Nb and O. (f) The merged mapping images of Cr,Ta and Nb corresponding to the HAADF in Fig. 5(a).
Fig. 6. (a) HAADF image of rutile-type CrTa_0.5Nb_0.5O₄ in [012] zone axis. (b-e) EDS element mapping of Cr,Ta,Nb and O corresponding to the HAADF in Fig. 6(a). (f) HAADF image of rutile-type CrTa_0.5Nb_0.5O₄ in [101] zone axis. (g-j) EDS element mapping of Cr,Ta,Nb and O corresponding to the HAADF in Fig. 6(f). (k) HAADF image of a grain boundary with the right grain in [101] zone axis, (l-n) EDS element mapping of Cr,Ta, and Nb corresponding to the HAADF in Fig. 6(k). (o) The merged mapping image of Cr,Ta,Nb and O, position of line scanning across the grain boundary is shown in the orange box. (p) Distribution of Cr (red), Ta (green), Nb (blue) and O (yellow) across the grain boundary along the purple line shown in Fig. 6(o).
Fig. 7. (a) HAADF image of rutile structured CrNbO₄ in [001] zone axis. (b-d) EDS element mapping of Cr,Nb and O corresponding to the HAADF in Fig. 7(a). (e-f) The HAADF and the ABF images of rutile structured CrO₂ in [011] zone axis. Atomic resolution EDS mapping of (g)Cr element and (h)O element corresponding to the Fig. 7(e). The atomistic structures are overlaid in Fig. 7(a), (e) and (f).
Fig. 8. GPA images of lattice strain distributions ε_xx,ε_yy and ε_xy in CrO₂[011](a-d),CrNbO₄ in [001] (e-h) and CrTa_0.5Nb_0.5O₄ in [113] (i-l).
Fig. 9. Comparison of thermal conductivity, TEC and Young's modulus of CrTa_0.5Nb_0.5O₄ with those of typical TBCs materials.

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