Influence of chemical disorder on mechanical and thermal properties of multi-component rare earth zirconate pyrochlores (nRE1/n)2Zr2O7

Abstract

To explore the underlying mechanism of chemical disorder in high-entropy pyrochlores, ten rare earth zirconates ( nRE1/ n)2Zr2O7 ( n = 1, 2, and 4, RE = La, Nb, Sm, Eu, and Gd) are studied by using first-principles calculations. The mechanical and thermal properties are carefully analyzed with a special focus on local structural evolution and interatomic interaction. It is found that all three kinds of bond lengths increase linearly with lattice parameters whether the pyrochlore involves chemical disorder or not. Compared with the single-component counterparts, the multi-component pyrochlores are recognized to exhibit higher elastic constants and moduli but lower elastic anisotropy. Meanwhile, (LaSmEuGd)2Zr2O7 shows the lowest thermal conductivity, which can be attributed to the larger La atoms and the weaker La–O bonding. Furthermore, the abnormal strengthening of phonon anharmonicity in (SmEu)2Zr2O7 emphasizes the significance of fluctuation in local distortion rather than enhancement in chemical disorder on decreasing thermal conductivity for high-entropy ceramics. This work uncovers the physical origins of the chemical disorder effect on mechanical and thermal properties for pyrochlores and further shed some lights on the design of high-performance high-entropy ceramics with great potential applications including thermal barrier coatings.

Temperature effect on mechanical and thermal properties of multicomponent rare‐earth zirconate pyrochlores

“…In this work, the mechanical and thermal properties (i.e., the elastic constants, bulk, shear and Young's moduli, and thermal conductivity) of (LaSmEuGd) 2 Zr 2 O 7 are lower than those of (NdSmEuGd) 2 Zr 2 O 7 . As La lacks f electrons and has large ionic radius, the bond length of (LaSmEuGd) 2 Zr 2 O 7 is longer than that of (NdSmEuGd) 2 Zr 2 O 7 , 36 which indicates the relatively weaker atomic interaction in this compound. Intuitively, it is believed that these mentioned earlier may be the critical points as the key to dominate the influence of chemical disorder on properties and performance for the high‐entropy pyrochlores.…”

“…In recent decades, theoretical studies are widely adopted in pyrochlore investigations. [33][34][35][36] It can not only predict the thermal and mechanical properties of the materials Their structures, mechanical properties, and thermal properties at different temperatures are calculated. It is found that (ZrO 6 ) polyhedrons and phonon mean free path play major roles in the variation of mechanical properties and thermal properties with temperature, respectively.…”

“…In recent decades, theoretical studies are widely adopted in pyrochlore investigations 33–36 . It can not only predict the thermal and mechanical properties of the materials but also expose the underlying mechanism.…”

“…The role of the La–O and Zr–O bonds in thermal expansion coefficient is revealed 35 . For multicomponent pyrochlores, Li et al 36 . researched ( nRE 1/ n ) 2 Zr 2 O 7 ( n = 1, 2, and 4, RE = La, Nb, Sm, Eu, and Gd) by first‐principles calculations and uncovered that the local distortion rather than chemical disorder plays a key role in decreasing thermal conductivity in multicomponent pyrochlores.…”

Simultaneous manipulations of thermal expansion and conductivity in symbiotic ScTaO 4/SmTaO 4 composites via multiscale effects

“…Furthermore, the correlation between the phonon scattering coefficient and the thermal conductivity is given by Eqs. ( 24) and ( 25) [74][75][76][77][78][79]:…”