STRUCTURE-ANALYSIS OF K(X)RB(1-X)X(X=BR, I) MIXED-CRYSTALS BY RB-87 AND K-39 NMR AND X-RAY-DIFFRACTION METHODS

X-ray diffraction profiles indicated that K(x)Rb(1-x)X(X = Br, I) crys tals as prepared by the melt-annealing method are a face-centered cubi c structure and the method produced a complete solid-solution. The lin ear relation between the lattice constants and K (or Rb) concentration s of the crystals by X-ray diffraction corresponded fairly well to the result of an eighth unit lattice of NaiK4-i(i = 0-4) as calculated by the energy-gradient optimization method using a semi-empirical MO PM3 program. Rb-87 and K-39 MAS NMR spectra were broad and the spectral b roadening is believed to be attributed to the overlapping peaks of dif ferent KiRb14-iI13(i = 0-14) structures in the unit lattice. We emphas ize that the high-field shifts of Rb-87 and K-39 nuclei were observed with increasing the lattice constants of the mixed crystals. The chemi cal shifts can be explained by considering components which involve se cond-order quadrupolar coupling tensors.