热辐射透过百分数对界面形状的影响

Affect of Crystal Transmission for Heat Radiation of Melt on Shape of Interface

从同一引上法生长装置，在完全相同的生长条件下，生长了不同掺质的凸界面的钇铝石榴石系列晶体：ＹＡＧ，Ｔｍ∶ＹＡＧ，Ｎｄ∶ＹＡＧ，（Ｃｅ，Ｎｄ∶ＹＡＧ），（Ｃｒ，Ｔｍ∶ＹＡＧ）和（Ｃｒ，Ｔｍ，Ｈｏ∶ＹＡＧ）。晶体的凸度（凸界面锥体的高度和晶体半径之比）与晶体对熔体热辐射透过百分数有关，透过百分数大，通过晶体辐射出的能流大，对流熔体进入晶体下方冷却快，液流弯曲大，晶体凸度大；透过百分数小，晶体凸度就小。相应于这个透过百分数的透过系数大的晶体，由于Ｔ／ｘ大，仅能以大的凸度（自然对流）或大的凹度（强迫对流）生长，在转速适当时，易于在晶体首部出现明显的界面翻转。在温度时间特性曲线拐点之前，随晶体长度的增加，由于透过百分数的增大，将使界面凸度变小。

A series of yttrium aluminium garnet crystals(YAG,Tm∶YAG,Ce:Nd∶YAG,Cr:Tm∶YAG and Cr:Tm:Ho∶YAG)with deflection of the interface toward the melt and shape of interface into a cone were grown using one equipment and same grown condition.The convex degree(the ratio of highnese of the cone to the radius of the crystal)depends on the crystal transmission for heat rediation of melt.When transmission of crystal is large,energy flow through crystal is large,flud flow is curved and crystal of large convex degree was grown.When transmission is small, crystal of small convex degree was grown.Due to large tramsmission coefficient crystal led high abscissa temperature gradieut,the crystal only with large convex degree(natural convection)or with large concave degree(forced convection)was grown,so that obvious interface inversion is able to appear and it is located in the top of the crystal when rotation rate is suitable.Because the length of crystal or the transmission of crystal is increased during the growth process,the convex degree of crystal is decreased before the turn point of the temperature time characteristica curve.