Phase transition in caesium dihydrogen phosphate crystal with thallium impurities

Abstract

A mixed crystal between two one-dimensional hydrogen bonding crystals of caesium dihydrogen phosphate (CDP) and thallium dihydrogen phosphate (TDP), CDP1-xTDPx, was studied by dielectric constant measurements of phase transition characteristics. Dielectric constant dependence on temperature in the CDP1-xTDPx crystal was best fitted by a power-law equation of the form epsilon' = C(T - T-o)(-gamma) with gamma = 1.43 for CDP, and gamma = 1.39 and gamma = 1.34 for CDP1-xTDPx mixed crystals of x = 0.003 and x = 0.008 respectively. A quasi-one-dimensional Ising model was employed to explain the experimental observations in terms of the decrease in the intrachain interaction constant, J(parallel to)/k(B), and the increase in the interchain interaction constant, J(perpendicular to)/k(B), with increasing TDP impurity concentration x.