Ch 1 explores the solid state — classification of solids, crystal lattices, unit cells, close packing, voids, imperfections, and electrical/magnetic properties that arise from crystal structure.
Crystalline solids have long-range order; amorphous solids lack it. 14 Bravais lattices in 7 crystal systems. Unit cell: smallest repeating unit. Simple cubic (SC): atoms at corners only (1 atom/cell). BCC: corners + body centre (2 atoms/cell). FCC: corners + face centres (4 atoms/cell).
Close packing: HCP (ABAB) and CCP/FCC (ABCABC) — both 74% efficiency. BCC = 68%. SC = 52.4%. Tetrahedral voids = 2N (N = number of spheres). Octahedral voids = N. Radius ratio determines which void a smaller ion occupies.
Point defects: Stoichiometric — Schottky (missing cation + anion pair, density decreases) and Frenkel (ion displaced to interstitial site, density unchanged). Non-stoichiometric — metal excess (F-centres, colour) and metal deficiency.
Download: https://ncert.nic.in/textbook/pdf/lech101.pdf | Part I: https://ncert.nic.in/textbook/pdf/lech1ps.zip
Schottky defects occur when cation and anion are similar in size (NaCl: Na⁺ = 95pm, Cl⁻ = 181pm). Frenkel defects occur when there is a large difference in ion sizes (AgCl: Ag⁺ = 126pm is small enough to fit in interstitial sites). The small Ag⁺ can be displaced into voids.
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