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Amisha posted an Question

December 25, 2020 • 18:55 pm 30 points

Here p is number of atoms per ui find accoustical & optical branches in following solids graphite2 &c) ne (in) diamond 3 () graphene 2) n 2 in diatomic there ar

here p is Number of atoms per ui Find accoustical & optical branches in following solids Graphite2 &C) NE (in) Diamond 3 () Graphene 2) N 2 In diatomic there are two atoms basic thus p 2 (ii) Sol. () 8otems pPerwt ul in diomendl Total branches = 3p 3 x 2 6 So, (3 accoustical + 3 optical) Graphite is 2D structure with 4 atomsin primitive unit cell. (i) Total branches p 4 So, (6 optical + 2 accoustical) (ii) Graphene is 2D structure with 2 atom basis thus total branches = 2 x 2 =4 (2 accoustical + 2 optical) A linear diatomic lattice of lattice constant a with masses M as m, (M> m) are coupled E constant C. The dispersion relation is given by Q. (GATE o=CM+m Mm 1/2 M+m 4C Kka leradnda Mm Mm 2 Which one of the following statement is incorrect? (A) The atoms vibrating in transverse mode correspond to the optical branch. (B) The maximum frequency of the acoustic branch depends on the mass of the lig. m. (C)The dispersion of frequency in the optical branch is smaller than in the acousi (D) No normal modes exist in the acoustic branch for anv frequency greater than tne frequency at k = a Contact Us: Wehsite 10

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