Bragg condition

Quasi-Bragg condition

Comment

nλ ≈ dΘ

τ^mλ ≈ 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)

c_s = 1

c_s < 1

In quasi Bragg h' c_s < h

${d^{\prime }}_{\tau 00}$ = 0.205 ´ c_s nm

${d^{\prime }}_{100}$ = 0.205 ´ c_s ´ τ = 0.296 nm,

= a'