Abstract
Lattice structure of hole-doped Na 1.6- x Co[Fe(CN) 6 ] 0.90 2.9H 2 O was systematically investigated against doping level ( x ) and temperature ( T ) by means of synchrotron-radiation powder diffraction. We found that the hole-doping procedure on the Co site induces a rhombohedral–cubic structural phase transition. The rhombohedral phase (cubic phase) is observed in x ≤0.02 and 100 ≤ T ≤300 K ( x ≥0.14 and 100 ≤ T ≤300 K), while two lattice structures coexist in the intermediate- x region (0.02 ≤ x ≤0.14). We interpreted the two-phase region of the x – T phase diagram in terms of intrinsic phase separation into large- x (Na + -poor) and small- x (Na + -rich) regions, because the Na + ions can migrate within the crystal to minimize the total free energy.
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