A STATISTICAL-METHOD TO DETECT ORDERING AND PHASE-SEPARATION BY APFIM

A method for evaluation of atom probe field ion microscopy (APFIM) dat a to test if a material exhibits phase separation or ordering tendenci es is presented. In this method the standard error (s) of the frequenc y distribution for a large number of block sizes is compared with the standard deviation (sigma) of the binomial distribution (BD). The ED i s expected for a solid solution, where the atoms are randomly distribu ted. For an ordered material the experimental s will be smaller than a for the ED. A large s, on the other hand, can be the consequence of p hase separation. Simulations were used to determine the probability th at an observed large or small s, indicating some feature of the materi al, could have been obtained from a random distribution. Also, simulat ions were used to reveal the influence of detection efficiency on the possibility to detect ordering. Examples from four materials are prese nted to illustrate the applicability of the method. (C) 1998 Elsevier Science B.V. All rights reserved.