Heat capacity and X-ray scattering studies on phase transitions of Rb2MoO4

The structural phase transitions of Rb2MoO4 have been reinvestigated using heat capacity measurement and X-ray scattering technique. In as-grown single crystals of Rb2MoO4, the crystal structure is a monoclinic one isomorphous to β-K2MoO4 (α-sequence) at room temperature. The α-sequence transforms into the β-sequence (isomorohius to β-K2SO4, space group Pnam) at a temperature range from 400 to 500 K. This α-β transition is reconstructive and depends on both temperature and time, especially with accompanying the temperature-dependent incubation time. In the β-sequence, an incommensurate phase characterized by wave vector qx = 1/3 ∼ 2/5 was observed below T3 = 223 K.