Bragg condition

Quasi-Bragg condition

Comment

nλ ≈ dΘ

τmλ ≈ d'Θ'

Including metric, ('), n, m integral

m = −infinity, −1, 0 1, 2, 3… or

h' = 0, τ−1, 1,τ, τ−1, τ−2, τ−3

d = a/h

d' = a'/h'

r is fixed within known models

Diffraction depends on harmonic r. h in SF for Equation (1) & QSF for (2)

cs = 1

cs < 1

In quasi Bragg h' cs < h

d τ 00 = 0.205 ´ cs nm

d 100 = 0.205 ´ cs ´ τ = 0.296 nm,

= a'