COMPREHENSIVE COMPUTERIZED SURVEY OF THE SLICE CONFIGURATIONS OF NH4H2PO4 (ADP) TYPE STRUCTURES

A thorough analysis of the surface configurations of NH4H2PO4 (ADP) at the atomic/molecular level has revealed a much larger number of PBCs and F-slices than obtained previously by Aquilo and Woensdregt (AW) in 1984 [J. Crystal Growth 69 ( 1984) 527] and 1987 [J. Crystal Growth 8 3 (1987) 549] by means of visual inspection of structure projections. The computational results of these relatively early applications of th e Hartman-Perdok (WP) theory may be called into question insofar as th ey arise from an incomplete set of theoretical data. Specifically, the ADP forms {031} and {211}, {21 $$($) over bar 1} classified earlier b y AW as S and K forms, respectively, are here demonstrated to be genui ne F forms. The present theoretical results improve agreement with exp eriment: (i) The theoretical F character of {031}, a form thought by A W to be important in connection with tapering, is reconciled with the experimental observation by AW, according to which (031) grows as flat faces. (ii) The interpretation of an experimental observation by Dam et al, in 1986 [J. Crystal Growth 74 (1986) 118] of a series of small flat faces on zone [1 $($) over bar$$ 11] was dismissed by AW in 1987 as theoretically impossible, on the grounds that only one F face, the (022), was known to occur on that zone. The fact established here that (121) = {21 $$($) over bar 1} is also an F face located on the same z one invalidates that objection. The theoretical F character of (121) a grees with the recent experimental observation of Verheijen et al., ac cording to which (121) is located on the [1 $($) over bar$$ 11] Bat fa ce band. The aim of the present work is to (i) remove some degree of c onfusion currently in the literature as regards interpretation of expe rimental results, and (ii) provide a tool enabling a more accurate and adequate investigation of the growth mechanism and morphology of ADP type structures than has thus far been available.