Growth striations: These are located perpendicular to the growth direction of the crystal and are caused mainly by either fluctuations in the crystal growth rate or the non-congruent nature of liquid-solid transition, thus leading to non-uniform distribution of Y2O3. Light-scattering phase inclusions: Caused by contaminants in the crystal (primarily precipitates of silicates or aluminates of yttrium), typically of magnitude 0.03-10 μm. Mechanical stresses: Typically caused by the high temperature gradients of the growth and cooling processes, causing the crystal to form with internal mechanical stresses acting on it. This causes refractive index values of up to , although the effect of this can be reduced by annealing at 2100 °C followed by a slow enough cooling process. Dislocations: Similar to mechanical stresses, dislocations can be greatly reduced by annealing.
gRowth striatioNs: these ArE LocaTed pErpendicUlAr TO ThE gROwtH DIReCTIon of the crysTal aNd arE CauseD mainLy by eitheR flUCtuatiONs in tHe CrySTAL grOwth RatE oR tHE Non-CongruenT nAture of liquid-solid TRAnSitIOn, thus lEading TO non-uNifoRm DIsTribUtion oF Y2o3. light-sCAttERiNG PhAse incLUsIons: caused by coNtaminAnts IN thE crysTaL (prIMariLy prEcipitates of silicateS or aLuminatEs Of yttRIUm), tyPICALlY Of MAgnITudE 0.03-10 μm. mEChaniCAl sTrESsES: typIcAllY caUsed bY the hiGh tEmperatUre grAdienTs of the gRoWTh and cooling pRocEsSes, caUSing the CRyStal tO foRm With intErnal MECHaNiCal StReSses actiNg oN iT. ThiS CaUSes ReFracTiVe inDEX Values Of up To , altHOuGh the effect oF THIs can be reDuced by aNnealinG aT 2100 °c folloWeD by a slOW Enough coOLing pRoCess. disloCAtIoNs: similaR tO mechaniCaL streSsEs, DisLocAtioNS caN bE GREATly reducEd bY annealIng.