Thermal behaviors of cryptomelane (K
xMn
8O
16 ; 0≤
x≤2) have been examined with DTA and TGA. The differences in thermal decomposition of various cryptomelanes depend on the K-ions occupancy in its one-dimensional tunnels. Arising temperature from 630°C to 860°C, cryptomelane with lower occupancy is gradually converted to one with higher occupancy accompanied by producing bixbyite (Mn
2O
3) . After the tunnels are filled up with K-ions at 860°C, the cryptomelane is converted to bixbyite and K
2Mn
4O
8 phase. Subsequently, the bixbyite is transformed to hausmannite (Mn
3O
4) . According to the above fact, cryptomelanes with various occupancies have been obtained by means of solid state reaction. [J. Cryst. Soc. Jpn.
26,
278 (1984) ] .
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