Transition from a phase-segregated state to single-phase incommensurate sodium ordering in γ-NaxCoO2 (x≈0.53)
Year: 2010
Type: article
Abstract: Synchrotron x-ray diffraction investigations of two single crystals of sodium cobaltate ${\text{Na}}_{x}{\text{CoO}}_{2}$ from different batches with composition $x=0.525--0.530$ reveal homogeneous incommensurate sodium ordering with propagation vector (0.53 0.53 0) at room temperature. The incommensurate $(qq0)$ superstructure exists between 220 and 430 K. The value of $q$ varies between $q=0.514$ and 0.529, showing a broad plateau at the latter value between 260 and 360 K. On cooling, an unusual reversible phase segregation into two volume fractions is observed. Below 220 K, one volume fraction shows the well-known commensurate orthorhombic $x=0.50$ superstructure while a second volume fraction with $x=0.55$ exhibits another commensurate superstructure, presumably with a $6a\ifmmode\times\else\texttimes\fi{}6a\ifmmode\times\else\texttimes\fi{}c$ hexagonal supercell. We argue that the commensurate-to-incommensurate transition is an intrinsic feature of samples with Na concentrations $x=0.5+\ensuremath{\delta}$ with $\ensuremath{\delta}\ensuremath{\approx}0.03$.
Source: Physical Review B
Authors: R. Feyerherm, E. Dudzik, S. Valencia, A. U. B. Wolter, C. J. Milne, S. Landsgesell, D. Alber, D. N. Argyriou
Language: English
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2017776739