The lattice parameter change of Nd∶GGG crystal was studied by X-ray powder diffraction and the least square fitting method.The results indicate that the lattice parameters of Nd∶GGG increase along the crystal growth direction.By analyzing the Nd∶GGG crystal structure and ions occupying site,the reason of lattice parameter change is mainly attributed to the volatilization of gallium ingredient and lead to the Ga vacancy sites(Oxygen octahedral center)were occupied by Gd^(3+)with large ionic radii,and that the substitute increases with the crystal growth direction.In addition,the Gd sites(oxygen dodecahedron center)were occupied by dopant Nd^(3+)with large ionic radii and the Nd3+distribution coefficient in GGG crystal is smaller than 1,therefore,the substitute also increased with the crystal growth direction,which is another reason led to the lattice parameter increase along the crystal growth direction.In order to decrease the lattice parameter change and improve the crystal quality,some methods were adopted to restrain effectively the Ga_(2)O_(3)volatilization and decrease the Nd^(3+)concentration change along the crystal growth direction.
Sun DunluZhang QingliWang ZhaobingSu JingZhang XiaShao ShufangGu ChangjiangYin Shaotang
During the crystal growth of Nd,Cr∶GSGG by Czochralski method,in some cases eutectic reaction occurred in the nether region of the crystal,and the boule was divided into two obvious different parts,which is upper Nd,Cr∶GSGG crystal and the nether coexisting Nd,Cr∶GSGG and GdScO_(3).By X-ray powder diffraction,the structure change of NdCr∶GSGG crystal ofΦ27 mm×120 mm with eutectic along its grown direction<111>was studied.By the least square method and extrapolation function f=sinθ-sinθ^(1-t)(t is an adjustable parameter),the lattice parameters of Nd,Cr∶GSGG and additional GdScO_(3)phase were computed.The results indicate that the lattice parameters of Nd,Cr∶GSGG increase along its growth direction,which changes from a=(1.25650±0.00007)nm of the top to(1.25798±0.00010)nm of the bottom.In the process of Nd,Cr∶GSGG growth,Gd^(3+)in Nd,Cr∶GSGG is partly replaced by Nd^(3+)with larger ionic radii,and the volatilization of Ga component results in its composition variance,which cause the lattice parameters increase along growth direction.In the eutectic section,there are the Nd,Cr∶GSGG and the second phase orthorhombic GdScO_(3).The lattice parameters of GdScO_(3)are a=0.5443±0.0007,b=0.5699±0.0005 and c=(0.7865±0.0009)nm,and that of Nd,Cr∶GSGG is(1.25798±0.00010)nm.In the final growth stage,excessive volatilization of Ga composition during the crystal growth causes the growth melt deflect of the Nd,Cr∶GSGG solid solution range seriously,and results in the eutectic reaction,and the outgrowth of Nd,Cr∶GSGG and GdScO_(3).So it is necessary to decrease the effect of gallium volatilization during the growth in order to avoid eutectic growth and obtain a high-quality Nd,Cr∶GSGG.
