Question

can anyone explain me about tetragonal and orthorhombic voids

Answer 1

These are just the shapes created by the space between balls packed together in different ways. I'm not sure what context this is since you can approach this from all sorts of directions including Advanced Inorganic chemistry, linear algebra, geometry, or general chemistry, topology,...

http://www.youtube.com/watch?v=5oxJoUmlfvw

there's a nice little example for you though!