High temperature solution growth, chemical depotassiation and growth mechanism of K_xRhO₂ crystals

Single-phase K_xRhO₂ single crystals (x = 0.70, 0.60 and 0.50) have been grown with a spontaneous nucleation method. More potassium deficient K_xRhO₂ single crystals (x = 0.39 and 0.25) were also obtained by chemical de-intercalations from the as-grown crystal but two-phases exist, which is proved by an electrochemical method. Microstructure characterizations by scanning electron, atomic force microscopy and transmission electron microscopy reveal the existence of a growth step, growth terrace and tri-junction on the as-grown K_xRhO₂ crystals. These results suggest that the growth of K_xRhO₂ follows a two-dimensional nuclei layered growth mechanism, which is also consistent with the Jackson factor extracted from the differential scanning calorimetric result. This work provides crucial information to optimize the growth conditions of K_xRhO₂ single crystals.