Transition from a phase-segregated state to single-phase incommensurate sodium ordering in Na_xCoO_2 with x \approx 0.53

Abstract

Synchrotron X-ray diffraction investigations of two single crystals of Na_xCoO_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 K 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 K and 360 K. On cooling, 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 x 6a x c hexagonal supercell. We argue that the commensurate-to-incommensurate transition is an intrinsic feature of samples with Na concentrations x = 0.5 + d with d ~ 0.03.

arXiv commentCorrected/improved version

References in corpus (18)

• Charge-ordering, commensurability and metallicity in the phase diagram of layered Na(x)CoO(2)
• Patterning of sodium ions and the control of electrons in sodium cobaltate
• Low temperature phase transitions and crystal structure of Na0.5CoO2
• Theory of Sodium Ordering in NaxCoO2
• Magnetic Correlation of NaxCoO2 and Successive Phase Transitions of Na0.5CoO2 -NMR and Neutron Diffraction Studies-
• Series of Bulk Magnetic Phase Transitions in NaxCoO2: a muSR study
• Searching for Stable Na-ordered Phases in Single Crystal Samples of gamma-NaxCoO2
• Structural transition in NaxCoO2 with x near 0.75 due to Na rearrangement
• Sodium vacancy ordering and the co-existence of localized spins and itinerant charges in NaxCoO2
• Electronic texture of the thermoelectric oxide Na0.75CoO2
• Spin correlations and cobalt charge states: A new phase diagram of sodium cobaltates
• NQR and X-ray investigation of the structure of Na${}_{2/3}$CoO${}_2$ compound
• Structural Phase Transitions and Sodium Ordering in Na0.5CoO2: a Combined Electron Diffraction and Raman Spectroscopy Study
• Melting of the Na layers in solid Na0.8CoO2
• Stripe correlations in Na${}_{0.75}$CoO${}_2$
• Crystal-to-stripe reordering of sodium ions in NaxCoO2 (x>=0.75)
• Rearrangement of Sodium ordering and its effect on physical properties in $N{a}_{x}Co{O}_2$ system
• Sodium ion ordering of Na0.77CoO2 under competing multi-vacancy cluster, superlattice and domain formation