# X-ray driven first-order phase transition in GeO2 glass under pressure

## TL;DR

This study reveals that intense synchrotron X-ray irradiation can induce a first-order phase transition in GeO2 glass under pressure, highlighting the influence of X-rays as an external stimulus and the need to consider X-ray effects in high-pressure experiments.

## Contribution

It demonstrates that X-ray irradiation can drive a phase transition in GeO2 glass under pressure, providing a new method to study dense matter formation.

## Key findings

- X-ray irradiation induces a tetrahedral to octahedral transition in GeO2 at high pressure.
- The transition occurs progressively from 5.4 GPa to 20.4 GPa under X-ray exposure.
- X-ray effects can alter the interpretation of high-pressure structural experiments.

## Abstract

Unprecedented bright and intense synchrotron X-rays have been widely used to unravel numerous compelling electronic and structural properties using a large variety of physical techniques, while the puzzling phenomenon is the uncertainties of measurements due to X-ray induced considerable electronic and structural changes of a matter under study. Here, we report an X-ray driven first-order tetrahedral-octahedral phase transition in GeO2 glass at high pressure using X-ray absorption fine structure (XAFS) with a nano-polycrystalline diamond anvil (NPD) cell. Upon X-ray irradiation from an undulator device, the XAFS spectrum at 5.4 GPa, which is below the threshold pressure of tetrahedral to pentahedral transition, starts to progressively approach the spectrum of octahedral GeO2 at 20.4 GPa. Detailed analysis indicates that both the nearest distance and coordination number of GeO2 glass at 5.4 GPa increase to those of a fully octahedral glass above 20 GPa, while negligible changes were found at other low pressures. These observations demonstrate that X-ray irradiation can be served as an alternative stimulus for forming dense matter under pressure, as the well-known external stimuli of pressure and temperature. Dense matter formed under external stimuli is crucial for understanding the formation, differentiation and evolution of planet and Earth. Attention for the X-ray induced structural uncertainties is called, especially for addressing metastable states under extreme conditions which may become undetectable in terms of intense synchrotron X-rays as structural tools.

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Source: https://tomesphere.com/paper/1705.02463