"In metallic hydrides , hydrogen occupies interstitial sites in the metal lattice producing distortion without changing the type of lattice."

Explain the above statement.
And also tell what does these terms mean
i) Lattice
ii) Interstitial sites
iii) Distortion

Dear User,
In metallic hydrides, small interstices are present. The hydride ions get deposited in these interstitial sites as they are small in size. This causes a distortion in the lattice but the type of lattice is maintained. This was first assumed but later it has been found that except for some transition metals, the type of lattice also gets changed. 
(i) Lattice :It is a regular arrangement of particles i.e. atoms, molecules or ions. 
(ii) Interstitial sites : These are small voids present between atoms in a lattice which can be filled by other atoms or ions.
(iii)Distrortion :It is the alteration in the original shape or any other characteristic.