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In the solid form FeO, CoO and NiO all has the NaCl-structure (simple cubic). In a series of diffraction experiments with x-rays ([tex]\lambda = 0.15406~\text{nm}[/tex]) one found reflexes from the (111), (200) and (220)-planes with the following [tex]\theta[/tex]-values ([tex]\theta[/tex] is the angle in Bragg's law, [tex]2d\sin\theta=\lambda[/tex]):

FeO: 18.04 20.95 30.28

CoO: 18.26 21.20 30.77

NiO: 18.63 21.64 31.45

The first number is the angle corresponding to the reflection from the (111)-plane, the second number corresponds to reflection from the (200)-plane and the third from the (220)-plane.

Question: What are the axis length for the three unit cells? Any hints?

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# Bragg diffraction

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