Single-crystal growth of sapphire

Czochralski growth of oxides

“…The first reported oxide material grown using the Czochralski technique (CaWO 4 ) was in 1960 [5]. This initial paper was followed quickly by numerous other papers dealing with the growth of a variety of oxide materials such as LiNbO 3 [6], LiTaO 3 [7], BGO [8], YAG (Y 3 Al 5 O 12 ) [9], Nd:YAG [10] and Al 2 O 3 (Sapphire) [11,12]. By the mid-1960s, the Czochralski process for the growth of oxide materials was becoming well established.…”

Gas bubbles in shaped sapphire

“…They [17] also show that the optical quality of the crystals decreases because of the presence of gas bubbles when the concentration of impurities in the raw material increases. Cockayne [18] used cracked crystals, high quality powder or cracked Verneuil crystals as raw materials. But he does not comment on the influence on the density of the bubbles in the crystals thus obtained; however the critical pulling rate from which bubbles are incorporated increases when the quality of the raw material is better.…”

“…An area highly concentrated in impurities appears close to the solidification interface and due to the large difference of density when sapphire solidifies, micro-bubbles are formed. According to Cockayne [18], the bubbles are formed by the incorporation of the impure liquid which will create cavities during its cooling. The impurities which cause this effect have a coefficient of segregation lower than unity and can be those which are dissolved in the raw material, or those which are added as doping agent (in the case of ruby) or the gases coming from the growth atmosphere.…”

Sapphire Crystal Growth and Applications

“…In [17] resistance heating by an Ir ribbon in an argon-oxygen or a nitrogen-oxygen environment has been used. A ribbon-shaped conductor penetrated the molten zone.…”

“…In particular, from the crystals obtained in [23] laser rods were fabricated. In [17] crystals of good quality 100 mm long by 15 mm diameter were grown at pull rates of 6 to 50 mm h −1 .…”