Route to in situ synthesis of epitaxial Pr2Ir2O7 thin films guided by thermodynamic calculations

TL;DR

This paper combines thermodynamic calculations and experimental methods to identify the challenges in synthesizing Pr2Ir2O7 thin films via PVD and suggests high-pressure CVD as a viable alternative for in situ growth.

Contribution

It provides a thermodynamic analysis of the Pr-Ir-O2 system and demonstrates the limitations of PVD, proposing high-pressure CVD for successful in situ synthesis of Pr2Ir2O7.

Findings

High growth temperatures are necessary for crystallinity.

Conventional PVD cannot achieve the required oxygen partial pressure.

High-pressure techniques like CVD are recommended for synthesis.

Abstract

In situ growth of pyrochlore iridate thin films has been a long-standing challenge due to the low reactivity of Ir at low temperatures and the vaporization of volatile gas species such as IrO3(g) and IrO2(g) at high temperatures and high oxygen partial pressures. To address this challenge, we combine thermodynamic analysis of the Pr-Ir-O2 system with experimental results from the conventional physical vapor deposition (PVD) technique of co-sputtering. Our results indicate that only high growth temperatures yield films with crystallinity sufficient for utilizing and tailoring the desired topological electronic properties. Thermodynamic calculations indicate that high deposition temperatures and high partial pressures of gas species O2(g) and IrO3(g), are required to stabilize Pr2Ir2O7. We further find that the gas species partial pressure requirements are beyond that achievable by any conventional PVD technique. We experimentally show that conventional PVD growth parameters produce exclusively Pr3IrO7, which conclusion we reproduce with theoretical calculations. Our findings provide solid evidence that in situ synthesis of Pr2Ir2O7 thin films is fettered by the inability to grow with oxygen partial pressure on the order of 10 Torr, a limitation inherent to the PVD process. Thus, we suggest high-pressure techniques, in particular chemical vapor deposition (CVD), as a route to synthesis of Pr2Ir2O7, as this can support thin film deposition under the high pressure needed for in situ stabilization of Pr2Ir2O7.