Crystalline solids uniform atomic structures

Using evidence presented in this demonstration, explain why crystalline solids have uniform atomic structures and glasses have disordered atomic structures. 

Unlike a molecule or complex ion, which is a finite (often small) assembly of atoms, a solid has no fixed size but can add atoms indefinitely. In a sample of uniform composition the bonding arrangements of atoms are expected to be similar throughout. For example, both crystalline and glassy forms of silica (Si02) have structures with each Si surrounded by four oxygen atoms, and... 

The sol-gel method provides uniform fine powders at lower heating temperatures and for shorter heating times than a conventional heating method of mixed oxides. The crystalline sizes of the powders are about 30-50 nm in diameter. X-ray diffraction (XRD) analysis of the prepared YIG and YAG solid solutions revealed garnet structure of A3BSO12 [II] even in the case of Y (AI, Fe) 0 = 4 4 12 starting ratio. In order to investigate where the excess Y atoms are located at, extended X-ray absorption fine structures (EXAFS) were measured. 

---