Disorder-order transitions in Na(x)CoO(2) (x similar to 0.58)

作者：Igarashi Dai^*; Miyazaki Yuzuru; Kajitani Tsuyoshi; Yubuta Kunio

来源：Physical Review B, 2008, 78(18): 184112.

DOI：10.1103/PhysRevB.78.184112

First-order structural transitions have been discovered for a gamma-NaxCoO(2) (x similar to 0.58) sample at T(1)=235 K and T(2)=288 K. Based on the combined results of electron and neutron-diffraction experiments, the compound has been revealed to exhibit a root 7a(0) x root 7a(0)-type (a(0) represents the a-axis length of the hexagonal basic structure) ordered superstructure with the space group of P6(3)/m, being isostructural with K(4)Co(7)O(14), due to the ordering of Na atoms in this temperature range. The Na ordering triggers a cooperative shift of Co-atom trimers parallel to the c axis, leading to an undulated arrangement of the CoO(2) conduction paths. Anomalous change in the magnetic susceptibility, electrical resistivity, and lattice parameters at T(1) and T(2) can be explained by the slight distortion of the CoO(2) layer. Above T(2), in contrast, the compound turns out to possess the gamma-Na(x)CoO(2)-type structure, in which the Na1 and Na2 atoms are randomly distributed.

• 出版日期2008-11