Temperature-driven sodium-ion dynamical-to-static crossover in the zigzag ordered phase of Na 0.5 CoO 2

2026/07/14 by Anonymous, Shangfei Wu, Hengxin Tan +8
Physics and Astronomy · #cond-mat.mtrl-sci #cond-mat.str-el

paper · pdf · doi:10.1103/4w7b-2l3l

published as Phys. Rev. B 114, 105102 (2026) · 17 pages, 12 figures, to appear in Physical Review B

openalex publication_date 2026/07/14 · arxiv created 2026/07/15 · openalex created_date 2026/07/15 · arxiv updated 2026/08/04 · openalex updated_date 2026/08/04

Abstract

We employ polarization-resolved Raman spectroscopy combined with first-principles calculations to study the sodium-ion lattice dynamics in a sodium zig-zag ordered cobaltate compound Na_0.5CoO₂. We detect two sodium phonon modes for the first time, and their mode frequencies are consistent with first-principles phonon calculations based on an orthorhombic unit cell. We find that they appear below around T^*∼300±50K with large linewidth broadening, much lower than the sodium zig-zag ordering temperature T_S∼460K, and then narrow at lower temperatures. We interpret the sodium-phonon anomalies occurring at T^* as a dynamical-to-static crossover involving mainly the motion of sodium ions. Our results suggest that the gradual freezing of the sodium ions and the well-defined static sodium-zigzag order below T^* set the stage for the emergent electronic and magnetic orders in the CoO₂ layer of Na_0.5CoO₂.

Citations

• First principles phonon calculations in materials science
• Geometrical, electronic, and magnetic properties ofNa0.5CoO2from first principles
• First-principles lattice dynamics ofNaCoO2
• Generalized Gradient Approximation Made Simple
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