First Principles Phase Diagram Calculations for the Octahedral-Interstitial System ZrO$_{X}$, $0 \leq X \leq 1/2$

TL;DR

This study uses first-principles calculations to predict the phase diagram of ZrO$_{X}$ with octahedral interstitials, revealing three stable ordered phases at high temperatures, differing from experimental reports.

Contribution

It provides a theoretical prediction of the phase diagram for ZrO$_{X}$ using cluster expansion, identifying stable phases and their temperature-dependent stability.

Findings

Predicted four ordered ground states at 0 ≤ X ≤ 1/2.

One ground state disproportionates below 20K.

At 420K, three ordered phases are stable, not four.

Abstract

First principles based phase diagram calculations were performed for the octahedral-interstitial solid solution system \alpha ZrOX (\alpha Zr[ ]_(1-X)OX; [ ]=Vacancy; 0 \leq X \leq 1/2). The cluster expansion method was used to do a ground state analysis, and to calculate the phase diagram. The predicted diagram has four ordered ground-states in the range 0 \leq X \leq 1/2, but one of these, at X=5/12, is predicted to disproportionate at T \approx 20K, well below the experimentally investigated range T \approx 420K. Thus, at T \succeq 420K, the first-principles based calculation predicts three ordered phases rather than the four that have been reported by experimentalists.