Appending Leading Zeros By If Statement With Formulas For True And False In SQL

My first question is how do I append 00001 so I can have a value for the false side of 9123400001 instead of 912341...My second question is why does it prompt me to enter parameters? It also produces all false values from the if statement...What I am trying to do is use a column that has either a Y or a N and using the if statement to correspond with different formulas depending on the Y or N.This what I have so far.

SELECT
IIF (ISRAILROAD=Y,9 & UCN & TXRTAREA, 9 & UCN & 00001 )
FROM CombinedUtility;