Incommensurate-commensurate phase transition in Rb2ZnBr4

The existence of the successive long-period superstructures, or the ''devil's staircase'', in the temperature evolution of the incommensurately modulated structure has been examined in Rb2ZnBr4 by the neutron diffraction method. Detailed measurements of the third order satellite scattering in the temperature region close to the incommensurate-to-commensurate phase transition have shown that the temperature evolution takes place in more complicated manners than previously reported for this compound. At least three different modulations with distinct wave numbers separated by finite gaps coexist and each of them changes continuously with temperature accompanying the change in the population of the domains corresponding to the respective wave numbers. Assignment of some part of the wave number vs temperature curves to the stairs with fractional numbers afforded no positive evidence of the ''devil's staircase''. (author)