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Zhang et al. J. Mater. Inf. 2026, 6, 11 Page 9 of 17

Figure 4. The relationship between lattice thermal conductivity at 300 K by and fracture toughness for RE 3 TaO 7 and RE 2 Zr 2 O 7 with
reported data [10,76,81-83] .

Figure 4. RE Zr O oxides cluster within a region of high K and moderate thermal conductivity, ideal for
7
IC
2
2
applications prioritizing mechanical integrity. In contrast, the orthorhombic C222 -type RE TaO oxides
1
7
3
occupy the low-κ , moderate-K region, which is advantageous for maximizing thermal insulation, albeit
IC
L
potentially at the expense of mechanical robustness. These results, validated against available experimental
data, underscore the effectiveness of the data-driven predictive framework employed.
Atomic and electronic attributes of lattice distortion
To clarify the atomistic origins governing the thermal conductivity and K of RE-based RE TaO and
IC
3
7
RE Zr O oxides, detailed analyses of bonding environments were conducted. These include bonding charge
2
7
2
density distributions and quantitative descriptors related to bond length and charge heterogeneity. Such
atomic-scale characterizations directly inform the macroscopic property trends observed, offering a unified
descriptor-based framework justified by the structural similarities between the two oxide families - both
composed of interconnected BO octahedra (B = Ta or Zr) and distorted RE–O polyhedra, despite differences
6
in nominal RE:O ratios.
As shown in Figure 5, bonding charge density (Δρ) isosurfaces reveal marked differences in electronic
[65]
distribution between the orthorhombic C222 -type RE TaO and pyrochlore RE Zr O oxides. In both cases,
7
3
7
2
2
1
yellow and blue regions around RE and O atoms indicate strong ionic character. However, the RE TaO 7
3
oxides exhibit pronounced anisotropy in charge distribution, consistent with their lower crystal symmetry
and indicative of stronger local lattice distortions. In contrast, the zirconates show more isotropic and
symmetric Δρ patterns, aligned with their higher lattice symmetry and more ordered vacancy configuration.
To quantitatively assess local structural disorder, two descriptors were defined: bond-length variance (D )
b
and Bader charge variance (D ):
e
( ) 2
1 − ¯
∑
= (1)
¯

=1
( ) 2
∑
1 − ¯
= (2)
¯
=1