George K C, Kurien Siby, Mathew Jose
Department of Physics, St. Berchmans' College, Changanassery, Kerala 686104, India.
J Nanosci Nanotechnol. 2007 Jun;7(6):2016-9. doi: 10.1166/jnn.2007.760.
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.
晶体固体物理尺寸的减小会导致晶格常数发生规律性变化。纳米颗粒中的晶格膨胀或收缩取决于许多因素，如内部原子的性质、表面原子、表面环境、悬空键以及表面的氧浓度。平均粒径为7纳米、9纳米和19纳米的MgAl2O4纳米颗粒的XRD图谱表明，晶格参数在不同平面上会发生收缩或排斥。由于颗粒形态不是球形（这从SEM显微照片中很明显），晶格收缩和晶格膨胀都是可能的。晶格膨胀主要在具有共价键或离子键的纳米晶体中观察到。红外光谱表明存在离子键。在没有氧缺乏的平面上观察到收缩，而在有氧缺乏的地方观察到晶格膨胀。随着加热导致粒径增大，大多数平面显示晶格收缩，进一步加热时，由于间隙位置存在过量氧积累，大多数平面观察到晶格膨胀。观察到晶格应变或晶格膨胀的原因可能是不同平面上离子之间的静电吸引或排斥。
