Resolving the Metastable Si-XIII Structure through Convergent Theory and Experiment

TL;DR

This paper combines advanced theoretical modeling with experimental data to finally determine the structure of the long-elusive Si-XIII metastable silicon phase, filling a key gap in silicon phase diagram knowledge.

Contribution

It introduces a convergent methodology that integrates computational and experimental approaches to accurately identify complex silicon structures.

Findings

Validated the proposed crystal structure with multiple experimental signatures

Resolved the long-standing structural ambiguity of Si-XIII

Enhanced understanding of silicon's high-pressure phase diagram

Abstract

Silicon is the undisputed cornerstone of modern technology, with applications ranging from micro- and opto-electronics to quantum technologies. Recently, the exploration of its allotropes has emerged as a pivotal frontier for engineering materials with tailored optical and electronic functionalities. High-pressure experiments have revealed several metastable silicon phases, among which is Si-XIII. First observed more than 20 years ago, this phase has remained structurally unidentified, representing a significant gap in our understanding of elemental silicon allotropy. In this work, a convergent methodology is employed combining advanced theoretical modeling with experimental characterization to finally resolve the long-standing structural assignment of Si-XIII. Guided by careful experimental observations, a structural model validated through first-principles optimization and systematically tested against multiple experimental signatures is constructed. All the fingerprints of this phase are rationalized by our proposed crystal structure: interplanar spacings, Raman frequencies, thermodynamic stability, and kinetic pathways. These findings provide a crucial missing piece in the high-pressure phase diagram of silicon and demonstrate the power of integrating computational predictions with experimental validation to resolve complex structural problems in materials science.