Hydride-Buffered Absence of Local Distortions in Mixed-Valent EuVO 2 H Films Revealed by X-ray Fluorescence Holography

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Valence transitions in europium compounds, such as EuO and EuNi 2 (Si 1– x Ge x ) 2, usually induce substantial structural distortions because the ionic radius difference between Eu 2+ (1.25 Å) and Eu 3+ (1.06 Å) exceeds the Hume–Rothery tolerance. Here, we conducted valence-specific structural analysis of strained EuVO 2 H thin films using X-ray fluorescence holography (XFH), where intersite charge transfer between Eu 2+ and V 3+ converts ∼30% of Eu 2+ into Eu 3+ (and V 3+ into V 2+ ). XFH measurements at the Eu L -edge revealed that a 15 nm single-crystalline film maintains remarkable structural coherence, with Eu 2+ and Eu 3+ randomly distributed and showing minimal local distortion despite the >15% size mismatch. This unusual stability is attributed to the size flexibility of H – anions in the EuH layers, which act as structural buffers. The ability to accommodate mixed-valence states without introducing structural disorder likely underlies the enhanced magnetic anisotropy in EuVO 2 H.

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