The high pressure phase transitions in KF and RbF

The high pressure B1 ? B2 transitions in KF at ~ 40 kbar and RbF at ~ 30 kbar have been studied using hydrostatic X-ray diffraction. No other transitions have been observed. The addition of the $\text{ΔV}\text{V}$ for these transitions to the already existing body of literature on B1–B2 transitions in alkali halides permits an extension of Pauling's theory to larger values of radius ratios. It also permits the modified Born criterion for predicting phase transitions to be further verified. Values of ionic radii for 8 coordination we suggest are 1.33 Å for F^?, 1.84 Å for Cr^?, 2.00 Å for Br^? and 2.27 Å for I^?.