A SYNCHROTRON-RADIATION STUDY OF POTASSIUM ZINC FLUORIDE PEROVSKITE

Vibration amplitudes and electron-deformation densities, DELTArho, hav e been determined for KZnF3 from diffraction data measured using focus ed synchrotron radiation with lambda = 0.7000 (2) angstrom at the Phot on Factory, KEK, Japan. The lack of systematic variation of intensity with path length indicates that secondary extinction is not significan t, a result confirmed when the strong intensities measured using a wea ker parallel beam with lambda = 0.5000 (2) angstrom showed no dependen ce on lambda. The 0.7 angstrom study is generally concordant with, but more precise (R = 0.008, wR = 0.006) than earlier analyses with Mo Ka lpha radiation. The charge of +0.47 (4) e determined for the Zn atom i s larger than that calculated with extinction corrections which minimi ze differences between observed and calculated structure factors. Near the Zn nucleus DELTArho is mildly anisotropic, with a topography simi lar to that found for closed-shell atoms in related perovskite structu res.