Powder diffraction

Monochromatic beam and many small crystallites with random orientations. All reciprocal-lattice points with the same |g| form a sphere; it cuts the Ewald sphere in a circle, so diffracted beams form cones of half-angle 2θ (Debye–Scherrer rings on the detector).

Crystal system Bravais lattice

Lattice parameters

a (Å)

b (Å)

c (Å)

α (°)

β (°)

γ (°)

Range (h, k, l): min, max

h k l

Only lattice-centring extinctions are applied (no glide planes or screw axes).

Beam and sample

λ (Å) Crystallites Mosaic 1.00° B (Å²) 0.0

Ideal powder rings (infinitely many crystallites)

Each crystallite has a uniform random orientation (fixed until you ask for new ones). With few crystallites you see isolated spots; with many, or a larger mosaic spread (more crystallites close enough to the Bragg condition), they fill the Debye–Scherrer rings. Each shell of radius |g| cuts the Ewald sphere in a circle, which gives a cone of half-angle 2θ. All reflections inside the limiting sphere (|g| ≤ 2/λ) that can reach the detector are included automatically.

Display

Show only diffracting points

Diffracted beams

Limiting sphere

Detector

Distance (mm) Width (mm) Angle 2θ_D (°)

Show detector in 3D

Detector image (inset)

The angle 2θ_D swings the detector about the vertical axis, so high-angle rings can be brought onto it. Below the image: the powder pattern (stick heights = multiplicity × Lorentz–polarisation × Debye–Waller, no structure factor). Click a spot in the inset to select it; drag the inset's lower-left corner to resize it.

Integration

Integrate (accumulate spots on the detector)

Stop after (s), 0 = never

While integrating, press “New random orientations” several times: each new set of crystallites adds its spots (yellow), and the Debye–Scherrer rings fill up, as in a real powder exposure. Recorded spots stay on the detector when you move it; a new wavelength or a new lattice clears them.

Click a reciprocal lattice point.