A heterogrammic word square (one containing no repeated letters) is limited to size three or four; a size five square containing 25 different alphabetic letters is impossible to achieve. In Making the Alphabet Dance (St. Martin's , 1996), heterogrammic 4-squares by George Lopes, Jeremy Morse and Jeff Grant are given.
Eckler, A. Ross
"Heterogrammic Word Squares,"
Word Ways: Vol. 39
, Article 12.
Available at: http://digitalcommons.butler.edu/wordways/vol39/iss3/12