Hidden Charge‐Order in the Mixed‐Valent K 0.75 Li 2 Cr 6 O 12 High‐Pressure Oxide
Year: 2025
Type: article
Abstract: The mixed valent high‐pressure oxide K₀.₇ 5 Li 2 Cr₆ 3.54 +O 12 is synthesized at 12 GPa and 1373 K. Synchrotron X‐ray and powder neutron diffraction (PND) reveal a P6 3/m average structure. Analogous to hollandites, CrO 6 octahedra form a corner‐sharing double‐chain framework, this creates two types of channels respectively occupied by Li + and K + . However, electron microscopy and pair distribution function analysis suggest the loss of correlation in and between the K + partially occupied channels. A magnetostrictive paramagnetic‐to‐antiferromagnetic transition occurs at T N = 75 K, where low temperature PND reveals a propagation vector k = [⅓ ⅓ ¼] realising a commensurate helical structure with 45° rotation between Cr 3 ⁺ and Cr⁴⁺ spins in zig‐zag ladders, stabilized by competing ferromagnetic and antiferromagnetic exchanges. Density functional theory calculations highlight the critical role of the c ‐axis compression in determining the magnetic direct exchange interactions thus revealing the ferromagentic‐correlated paramagnet → charge‐ordered antiferromagnetic transition, reminiscent to the pressure induced FM to AFM transition in the related K 2 Cr 8 O 16 hollandite. Despite hidden long‐range charge order due to K⁺ disorder, K₀.₇ 5 Li 2 Cr₆ 3.54 +O 12 exhibits strong spin‐lattice coupling, where a slight change in the structure has a huge impact in the properties.
Source: Advanced Science
Language: English
Field: Materials Science
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $6,730
OpenAlex ID: W4417036404