Computationally accelerated discovery of high entropy pyrochlore oxides

Abstract

High entropy ceramics provide enhanced flexibility for tailoring a wide range of physical properties, emerging from the diverse chemical and configurational degrees of freedom. Expanding upon the endeavors of recently synthesized high entropy ceramics in rock salt, fluorite, spinel and perovskite structures, we explore the relative feasibility of formation of high entropy pyrochlore oxides, A2B2O7, with multi-cation occupancy of the B-site, estimated from first principles based thermodynamic descriptors. Subsequently, we used Monte Carlo simulations to estimate the phase composition, oxygen vacancy concentration and local ionic segregation as a function of temperature and oxygen partial pressure. In parallel, we have investigated the synthesis of several multicomponent oxides with a pyrochlore composition, related to our computational investigations, resulting in several high purity pyrochlore oxides, in some cases with minor impurity phases. Ultimately, our approach allows us to evaluate potential impurity phases, ionic disorder and oxygen vacancy concentration in response to the experimental variables, thereby making realistic predictions that can direct and accelerate experimental synthesis of novel multicomponent ceramics.

Investigation of the chemical versatility in high‐entropy pyrochlores

“…The chemical composition of this secondary phase was confirmed by the EDS spectra (Figure 8E). Similar results were obtained by Pitike et al 18 . for Nd 2 (SnZrHfTiSc) 2 O 7 ; however, the quantity of secondary phase, estimated to be lower than 1% using the Rietveld refinement, seems smaller in our compounds.…”

“…spectra (Figure 8E). Similar results were obtained by Pitike et al 18 for Nd 2 (SnZrHfTiSc) 2 O 7 ; however, the quantity of secondary phase, estimated to be lower than 1% using the Rietveld refinement, seems smaller in our compounds. It could indicate that Sc 3+ can be successfully used on the B site without cationic charge compensation, but with a limit close to 20%.…”

“…We already applied this approach recently to form Dy 2 (TiZrHfGeSn) 2 O 7 , leading to the first entropy‐stabilized pyrochlore 8 . To the best of our knowledge, since then the reported high‐entropy pyrochlores with chemical disorder introduced on the B site are RE 2 (TiZrHfSn) 2 O 7 (RE = Sm or Gd) 15,16 ; Y 2 (TiZrHfMoV) 2 O 7 , Y 2 (TiZrHfV) 2 O 7 , and Y 2 (TiZrHfMo) 2 O 7 17 ; RE 2 (ZrHfSnScNb) 2 O 7 and RE 2 (ZrHfSnScTa) 2 O 7 (RE = La or Nd) 18 ; and the two distorted pyrochlores Nd 2 (ZrHfSnScTa) 2 O 7 and Nd 2 (ZrHfSnTiNb) 2 O 7 19 . Very recently, Jia et al.…”

Influence of composition on structural evolution of high‐entropy zirconates—cationic radius ratio and atomic size difference

“…In 2022, Pitike et al successfully performed DFT-and Monte Carlo calculations based on mixing enthalpies to predict the forming ability of high-entropy pyrochlore oxides with various cations on the B-site. 32 However, a simple indicator for single-phase prediction would facilitate and accelerate the search for new single-phase high-entropy materials. Recent studies proposed a correlation of the atomic size difference δ and the ability of PHEOs to form single phases.…”

Discovering the Ultralow Thermal Conductive High-Entropy Pyrochlore Oxides Through the Hybrid Knowledge-Assisted Data-Driven Machine Learning

“…These descriptive parameters could be treated as the genes/basic building-blocks or the so-called key physical parameters (KPPs) addressing the correlations between mechanical and thermal properties, which present a relatively straightforward physics-informed relationship with the target property/performance 4,8,9 , such as lattice distortion for solid-solution strengthen and alloy composition for thermal expansion coe cient and heat capacity 9 . Since the A 2 B 2 O 7 type high-entropy pyrochlore oxides (HEPOs) have emerged as leading candidates for a new generation of TBC with signi cantly lower thermal conductivity and chemical stability at higher temperatures 10 . It is essential to develop a heat transfer model via as few atomic and electronic KPPs as possible from the present various ones 3,11 , thus, proposing a strategy accelerating the development of advanced HEPOs with intrinsically low thermal conductivity.…”