The values for the crystallite size and microstrain of the undoped and Ni-doped CeO₂-NPs obtained from the Rietveld and Halder–Wagner (H–W) methods.

	Crystallite size (nm)			Strain ×103 (no unit)
	Scherrer's method	Rietveld method	(H–W) method	Scherrer's method	Rietveld method	(H–W) method
Undoped CeO2-NPs	5.66	5.42	4.62	—	0.86	0.64
1% Ni-CeO2-NPs	5.44	4.98	4.10	—	0.63	0.58
3% Ni-CeO2-NPs	5.20	4.71	3.98	—	0.59	0.53
5% Ni-CeO2-NPs	5.00	4.32	3.56	—	0.51	0.48