LEED ANALYSES REVISITED FOR 2 STRUCTURES FORMED BY ZR(0001) - THE SURFACE WHEN CLEAN AND WHEN CONTAINING SUFFICIENT OXYGEN TO JUST EXTINGUISH THE HALF-ORDER BEAMS

LEED crystallographic analyses have been made for two structures forme d by the (0001) surface of zirconium and which show (1 x 1)-type diffr action patterns. An analysis with eight diffracted beams for clean Zr( 0001) supports an earlier conclusion that this surface has a regular h cp-type structure, and that the first interlayer spacing shows a contr action hem the bulk spacing by about 1.6%. A surface formed by O, at t wice the coverage applying for the best-developed half-monolayer (2x2) diffraction pattern, is analyzed using tensor LEED for nine diffracte d beams, including the use of the average t-matrix approximation. It i s concluded that the 1 monolayer (ML) structure is actually disordered with 0.5 ML of O distributed statistically over octahedral holes betw een the first and second Zr layers, and another 0.5 ML of O similarily distributed between the second and third metal layers.