CHARACTERIZATION OF OH-F SHORT-RANGE ORDER IN POTASSIUM-FLUOR-RICHTERITE BY INFRARED-SPECTROSCOPY IN THE OH-STRETCHING REGION

The infrared spectrum of a sample of potassium-fluor-richterite (PFR) is compared with that of a synthetic ''potassium-richterite'' having a similar OH-F content. The PFR spectrum shows an additional absorption band with respect to the synthetic sample, and this is assigned to a configuration involving Al-[Tl]. The spectra show that there is strong short-range order of OH in the structure of PFR, that involves coupli ng between H and (Si, Al) rings of tetrahedra in response to the bond- valence requirements on the bridging atoms of oxygen in Al-O-Si dimers of tetrahedra.