Structural phase transition in two-dimensional tetramer-cuprate Na₅RbCu₄(AsO₄)₄Cl₂

Abstract

Using Raman scattering and optical birefringence we have investigated a low-temperature phase transition in single crystal of the two-dimensional Na₅RbCu₄(AsO₄)₄Cl₂. Phonon anomalies point to a first order nature of the transition. The observed transition is most probably related to a order-disorder transition of the Rb ion positions along the z axis within the ionic framework of mixed alkali metal chloride lattices.