Atomic Structure of a Spinel-Like Transition <math xmlns='http://www.w3.org/1998/Math/MathML' display='inline'><mrow><msub><mrow><mi>Al</mi></mrow><mrow><mn>2</mn></mrow></msub><msub><mrow><mi mathvariant='normal'>O</mi></mrow><mrow><mn>3</mn></mrow></msub><mo stretchy='false'>(</mo><mn>100</mn><mo stretchy='false'>)</mo></mrow></math> Surface