Tetrahedral rotation and interlayer region

The dimensions of an ideal octahedral sheet in the (001) plane are commonly less than those of an ideal and unconstrained tetrahedral sheet. Thus, to obtain congruence, the difference in size of the tetrahedral and octahedral sheets must be adjusted by any one or more of the following (i) in-plane rotation of adjacent tetrahedra in opposite directions about c (parameter a) (ii) thickening of the tetrahedra (parameter x), and (iii) a flat- 

McCauley and Newnham (1971) specified by multiple regression analysis that, although the a value is largely controlled by the tetrahedral-octahedral sheet lateral misfit ( 90%), it also reflects the field strength of the interlayer cation. Toraya (1981) observed 

Symbols as in Figiue 2. The plot reports only structures pubhshed after 1992, i.e., structures not considered in the predictive equation of Weiss etal. (1992). 

The calculated a values using the equation of Weiss et al. (1992) and data published after 1992 (i.e., not used to derive the equation) vs. observed a values are consistent mostly in the range of 7-9°, whereas the correspondence is lower for smaller and larger angles (Fig. 12). Weiss et al. (1992) also predicted the a value from sheet composition using a vector-representation grid. They calculated a mean tetrahedral distance, d (T-0), and a mean octahedral bond distances, d (M-A) (where A is any anion), from equations 

To better understand the role of tetrahedral-octahedral lateral misfit for M, TMi, 

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