Vibrational and Electronic Properties of Np2O5 from Experimental Spectroscopy and First Principles Calculations

TL;DR

This study combines experimental spectroscopy and first-principles calculations to elucidate the vibrational and electronic properties of Np2O5, a high-valence actinide oxide, providing new insights into its structure and electronic behavior.

Contribution

It presents the first Raman and scanning tunneling spectroscopy studies of Np2O5, along with DFT calculations, to comprehensively characterize its vibrational modes and electronic band gap.

Findings

Raman spectra revealed sharp vibrational features, including low-frequency modes.

STS measurements determined a band gap of 1.5 eV, confirmed by DFT predictions.

DFT calculations assigned vibrational modes and predicted an indirect band gap of 1.68 eV.

Abstract

High-valence actinide oxides are critical to understanding the behavior of 5f-electrons, yet their structural and electronic properties remain poorly understood due to challenges in synthesis and handling. We report the first Raman spectroscopic study of single-crystalline Np2O5 and the first scanning tunneling spectroscopy (STS) measurement on any neptunium-containing material. Hydrothermally synthesized crystals were structurally verified by X-ray diffraction. Raman spectra revealed sharply resolved vibrational features, including previously unreported low-frequency modes. STS measurements revealed a band gap of 1.5 eV. Density functional theory (DFT) enables vibrational mode assignments, reveals neptunium-dominated low-frequency phonons, oxygen-dominated high-frequency modes, and predicts an indirect band gap of 1.68 eV. This predicted value is in excellent agreement with the experimentally measured STS gap. This combined Raman, DFT, and STS approach provides a robust framework for correlating lattice dynamics and electronic structure in actinide materials, providing benchmark data for Np2O5, and opening new avenues for probing structure-property relationships in complex f-electron materials.