MATS 3011 Lecture Notes - Ion, Schottky Defect, Fused Quartz
Document Summary
Amxp type structure (a) caf2 (fluorite structure) comes from ca2+ and f- Using radii ratio rule: rca2+rf- = 0. 75 --> coordination # = 8. Basis --> a group of 1 ca2+ + 2f- B/c coordination # of cation is 8 and coordination of anion is 4so different stoichiometry. Structure of covalently bonded ceramics (less than 1. 7 difference in electronegativity) Silicate ceramics --> composed of silicon & oxygen. Each oxygen wants to share w/ another positive charge. Based on arrangement of building blocks, can have different silicate strucutres ----> 1 dimensional, 2d, or 3d example --> silica. Every oxygen in each tetrahedra is shared w/ adjacent si atom. Silica could be crystalline (quartz) or amorphous (cristobalite, trydimite) all 3 examples are 3 polymorphs of silica. Displacive transitions: lower heat, just displace position of atoms w/in structure, less energy b/c not breaking any bonds. Reconstructive: breaking bonds to change structureneeds energy --> high t.
