Professor Thiel's long-suffering grad student Quasimodo claims to have discovered a new phase of molybdenum disilicide (

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Professor Thiel S Long Suffering Grad Student Quasimodo Claims To Have Discovered A New Phase Of Molybdenum Disilicide 1 (88.02 KiB) Viewed 13 times

Professor Thiel's long-suffering grad student Quasimodo claims to have discovered a new phase of molybdenum disilicide (MoSi₂). He states the structure has a base-centered tetragonal lattice (a = 4.54 Å, c = 7.845 Å) with the atomic motif coordinates given in the chart below. His argument rests on the observation that indexing an X-ray diffraction pattern (2= 1.54 Å) using this structure confirms a systematic absence of the (110) reflection at 13.87°. You, of course, know that base-centered tetragonal is not one of the 14 Bravais lattices; therefore, this description of the structure must be wrong. Atom Mo Mo Si Si Si Si 0 1/2 y 0 0 0 0 0 0 1/2 0 1/2 0 z 0 1/2 1/3 2/3 1/6 5/6 a) Give the correct Bravais lattice and new lattice parameters. b) Give the coordinates of the atoms in the new unit cell. c) Prove that there is still a systematic absence at 13.87° and give the indices of the forbidden reflection.