. The Bell System technical journal . , the unit length of each of the aaxes is said to be 1; that of the c axis and a face that cuts the caxis at from the origin is said to have the c intercept of 1. (Thisunit axial length is different for different substances but the same for allcrystals of the same substance.) For example, the front cap face in has the axial intercepts 1, co, â1, 1, naming the axes in the orderfli, (12, as, c. The indices for this face are written (lOll) (general formhkil). The front vertical face has the intercepts 1, x, â 1, co and the 300 BELL
. The Bell System technical journal . , the unit length of each of the aaxes is said to be 1; that of the c axis and a face that cuts the caxis at from the origin is said to have the c intercept of 1. (Thisunit axial length is different for different substances but the same for allcrystals of the same substance.) For example, the front cap face in has the axial intercepts 1, co, â1, 1, naming the axes in the orderfli, (12, as, c. The indices for this face are written (lOll) (general formhkil). The front vertical face has the intercepts 1, x, â 1, co and the 300 BELL SYSTEM TECHNICAL JOURNAL indices (lOlO). The first two digits of the indices of any vertical prismplane are the same as those of the adjacent cap faces: the final digit is alwayszero because they are parallel to the Z (or c) axis. Since the intercepts onfli and Qi uniquely determine the intercept on a^,, the third digit of the sym-bol may be omitted. The omission is sometimes indicated by a dot, as(10-1) (general form hk-C). 0001. + a. Fig. âMiller-Bravais indices of certain crystallographic planes in quartz The use of indices instead of the actual intercepts simplifies the mathe-matics of crystallography in many ways. For example, the sum of theindices of two planes forms the indices of an intermediate plane that isparallel to the line of intersection of the first two. Thus the sum of (00-1),the atomic plane which is normal to c, and (10-0), prism face, is (10-1),the indices of the cap face directly above the (10-0) prism face. X-RAVS AXD OR/KXTATIOX OF QUARTZ CRYSTALS 301 Further, in llie equation ;/X = Id sin 9, the intcrplanar spacing d of theatomic planes (hk-C) is yuif + hk + k) + d,,.f = / -^ () Where the axial ratio c/a is l.(WW7 in quartz and ao, the distance betweenatoms along the a axis, is (KSA.^ The ti order reflection from the hk-f plane is sometimes spoken of asthe reflection from the n{hk-() plane as in Table I and Pig. where, forexample, the sec
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
