6.74 Mathematica command like Matlab blkdiag

To make a matrix, which contains on its diagonal matrices, Matlab uses the command blkdiag. In Mathematica use the following

a = {{1, 2, 3}, {4, 5, 6}} 
b = {{7, 8}, {9, 10}} 
SparseArray[Band[{1, 1}] -> {a, b}]