During sintering of my 2 pellets for 12 hours at 1200 degrees on two seperate crucibles, there is a formation of green layer below the surface. I made sure to clean the crucible twice before sintering, still this layer has been formed. Also in one of the samples, the above surface layer has become black. I don't know what caused them to be like this. Will this effect my dielectric properties and should I do the XRD for the two to be sure that no other phase has been araised.

Note- I used PVA to form the pellet and used 5 tone force to make the pellets.