6533b823fe1ef96bd127e9be

RESEARCH PRODUCT

Alkaline cavities and tetrahedra in and solid solutions

subject

description

Seven different crystals were grown with 0 < x < 2 while seven different crystals were grown with , the limit value x = 1 corresponding to the clearly defined compound. A crystallographic study of these solid solutions was performed by comparison with the pure crystal. Structures were solved in the Pnma space group for the rubidium solid solutions and in the space group for the potassium ones. It was shown that the distribution of Cs and Rb, or Cs and K, among the two cationic sites called and was not random: Rb and K exhibit a higher affinity for the smallest cavity, the site. While the phase transition of and can be interpreted as rotations of the rigid tetrahedra mainly around the a direction, the substitution of Cs by Rb or K not only supplies the a rotation of tetrahedra but, as shown by a first-order approximation model, also changes their size and shape.