PRESSURE-INDUCED DISTORTIONS OF PB(NO3)(2) ISOMORPHS

Energy-dispersive and angle-dispersive x-ray-diffraction (EDXD and ADX D) measurements show that when compressed by pressures above 10.0 GPa isostructural Pb(NO3)(2), Ba(NO3)(2), and Sr(NO3)(2) transform reversi bly to highly disordered structures. Raman measurements under compress ion suggest that the transformation occurs via reorientation of the ni trate ions to multiple sites and movement of the metal ions from the c rystal positions. Our main conclusion is that EDXD and ADXD measuremen ts give different meanings to the notion ''x-ray amorphous.'' Thus, wh enever this phrase is used, the method used and the conditions that pr evail must be specified. We also suggest that our results show that Ra man spectroscopy can be used to distinguish nonrandom nitrate and cati on environments in metal nitrate glasses.