Infiltration-growth of Superconductive REBCO Oxide and Simulation of Faceted Peritectic Crystal Growth

在<7-x>空气和Ar-1%O_2气氛中，采用熔渗生长法和定向凝固法制备了REBCO（RE=Y，Nd）和REBCO/Ag氧化物中RE_（123）（REBa_2Cu_3O_）晶体，并对其生长过程和结构进行了实验和分析研究，以阐明小面123晶体的生长和结构形成机制。为了获得无收缩、组织细小的浸渗生长样品，将Ba-Cu-O（-RE，Ag）液相浸渗到烧结好的多孔Y211（/Ag）或Nd 422（/Ag）固体中，然后冷却至周温（Tp），在温度梯度下生长123晶体。利用R-ΔT（生长过冷度）和ΔT（新晶形成过冷度）-Vc（ 关于我们 采用二维数值模拟方法，考虑了晶体取向和晶体在液相中形核的影响，较好地模拟了小面123晶体定向凝固过程中柱状和等轴组织等宏观组织的形成过程。在此基础上，利用高温原位观察装置和放大型光学显微镜，原位观察了RE 123（RD=Nd，Sm，Gd）晶体在MgO（100）衬底上的成核和生长过程。在不同的过冷度下，RE 123晶体成核生长，并测定了生长速率（u）和成核孕育时间（t<inc>）。u用ΔTr的函数u=A_<gp>ΔTr^2/η（T）表示，其中A_<gp>为常数，ΔTr=ΔT/Tp，η（T）为粘度，成核速率I_v由成核时间与成核晶体数的关系求得，用指数函数I_V={A_n/η（T）}exp（-B/ΔTr^2）表示，其中An和B为常数。结果表明，u和Iv不仅与RE 123的ΔT有关，还与Tp有关。少

Growth process and structures of RE123(REBa_2Cu_3O_<7-x>) crystals in superconductive REBCO(RE=Y,Nd) and REBCO/Ag oxides fabricated by infiltration-growth and unidirectional solidification in the atmosphere of air or Ar-1%O_2 were studied experimentally and analytically to clarify the growth and structure-formation mechanism of faceted 123 crystals. To get a sample without shrinkage and with fine microstructure by the infiltration-growth, Ba-Cu-O(-RE,Ag) liquid was infiltrated into sintered porous Y211(/Ag) or Nd422(/Ag) solid, and then cooled under the peritectic temperature(Tp) to grow 123 crystal under a temperature gradient. The critical transition conditions of macrostructures from columnar to equiaxed structures and the change in freezing front temperature of 123 phase during solidification were analyzed to clarify the effects of growth rate(R), temperature gradient(G) and sample size(cross section) by using R-ΔT(undercooling for growth) and ΔT(for formation of a new crystal)-Vc( … More cooling rate) relations.The formation processes of macrostructure such as columnar and/or equiaxed structures of faceted 123 crystals during unidirectional solidification were well simulated by two-dimensional numerical method, in which the effects of crystallographic orientations and the nucleation of crystals in the liquid were considered. Further, the nucleation and growth processes of faceted RE123 (RD=Nd,Sm,Gd) crystals were observed in-situ on MgO(100) by using a high temperature in-situ observation apparatus with zoom-type optical microscope. RE123 crystals nucleated and grew at various undercooling, and the growth rate (u) and incubation time (t_<inc>) for nucleation were measured. u was approximated by a function of ΔTr: u=A_<gp>ΔTr^2/η(T), where A_<gp> is a constant, ΔTr=ΔT/Tp and η(T) is viscosity.Nucleation rate (I_v) was obtained from the relationship between time and number of nucleated crystals, and it was approximated by an exponential function: I_V={A_n/η(T)}exp(-B/ΔTr^2), where An and B are constants. It was clarified that u and Iv depend on not only ΔT but also Tp of RE123. Less