Adding overscore to character in a cell in an Excell spreadsheet

[DrJoe]

Can you do this?

I know how to do this for a floating object (insert object, equation editor,
add overscore) text box, but not how to do this within a cell.

I would like to create a column in a table with a reference to
crystallography. I would like to type <one one one bar> as <111> with a bar
over the third one (or the second, or the first). Some of the crystals have
indices other than 1 (i.e. <1122> with a bar over the first 2).

Is this possible to do?

Thanks,

Joe