Effect of High Pressure on the Compressibilities of NaI, LiF, and NaF

The effect of pressure to several hundred kilobars has been measured on the compressibilities of NaI, LiF, and NaF. For NaI and LiF the semiclassical Born-Mayer-Huggins theory gives a good fit over the entire pressure range. For NaI this is not necessarily expected as the large size of the I(-) ion relative to Na(+) would indicate that next-nearest-neighbor interactions could be important. The equation is quite unsatisfactory for NaF, which is quite surprising as this should be a typical ionic crystal.