Temperature and concentration dependence of X-ray diffuse scattering in a random mixture; Rb_1–x(NH₄)_xH₂Po₄

Abstract

Abstract Measurements of X-ray diffuse scattering in Rb1-x (NH4) x H2PO4 for x = 0.15, 0.25, 0.3, 0.5, and 0.7 have been carried out at low temperatures. The diffuse scattering depends on temperature and NH4-concentration. The temperature dependence of the diffuse scattering can be interpreted by the idea of local cluster condensation. The concentration dependence shows the followings; the diffuse scattering with the modulation wave vector q = 0.25 a* and that with q = 0.35 a* coexist for x = 0.3 below 100 K and the concentration dependence of the wave vector q resembles to the “devil's staircase”. The heterogeneous structure of this mixed crystal is discussed.