Reduction in the physical dimension of a crystalline solid lead to regular changes in the lattice constants. The lattice expansion or contraction in nanoparticles depend on a number of factors like nature of atoms in the interior, surface atoms, surface surroundings, dangling bonds, and oxygen concentration on the surface. XRD patterns of nanoparticles of MgAl2O4 having average particle size 7 nm, 9 nm, and 19 nm show that lattice parameters undergo contraction or repulsion along different planes. The lattice contraction along with lattice expansion is possible since the morphology of the particle is not spherical which is evident from the SEM micrographs. Lattice expansion is observed mainly in nanocrystals having covalent or ionic bonds. The existence of ionic bonds is evident from the IR spectrum. Along planes where there is no deficiency of oxygen, contraction is observed while where there is deficiency of oxygen lattice expansion is observed. As the particle size increases due to heating most of the planes show lattice contraction and on further heating due to the excess oxygen accumulation in interstitial positions lattice expansion is observed along most of the planes. The reason for the observation of lattice strain or lattice expansion may be due to the electrostatic attraction or repulsion between ions along different planes.
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