基于组分Ca_2Pr_2Cu_5O_(10)三元固溶区的范围和晶体结构

The Extent and Crystal Structure of the Solid Solution Based on Ca_2Pr_2Cu_5O_(10)

利用X射线衍射分析和Rietveld结构精修方法研究了基于组分Ca2Pr2Cu5O10三元固溶区的范围和晶体结构。根据X射线分析结果和相消失法,为了保持Ca2+xPr2-xCu5O10结构单位晶胞中恒定的氧含量和电价平衡,基于组分Ca2Pr2Cu5O10的三元固溶区的范围可确定为:在Ca2+xPr2-xCu5O10固溶区的富Ca区(Ca/Pr>1),其表达式仍可以表示为一般的化学计量式Ca2+xPr2-xCu5O10(x=0.4,0.2,0);在富Pr区(Ca/Pr<1),其表达式为Ca1.7Pr2.2·Cu5O10、Ca1.4Pr2.4Cu5O10,即:Ca2+xPr2-xCu5O10固溶区范围从Ca2.4Pr1.6Cu5O10至Ca1.4Pr2.4·Cu5O10。研究表明:基于组分Ca2Pr2Cu5O10的三元固溶体晶体结构可以看作是正交晶系NaCuO2型亚晶胞的无公度相;Ca2.4Pr1.6Cu5O10亚晶胞的点阵常数为a0=0.28246(7)nm,b0=0.63693(1)nm,c0=1.06794(1)nm;其正交超结构的点阵常数为a=5a0,b=b0,c=5c0。Ca2.4Pr1.6Cu5O10的结构也可以用单斜超晶胞来表述,该单斜超晶胞的空间群为P21/c,Z=4,a=5a0,b=b0,c=c0/sinβ,β=104.79°或136.60°,V=5a0b0c0。在基于组分Ca2Pr2Cu5O10的三元固溶体晶体结构中,Ca和Pr之间在一定范围内是可以相互替代的,而且它们在结构中的占位是无序的。

The extent and crystal structure of the solid solution based on Ca_2Pr_2Cu_5O_(10) were studied by X-ray diffraction combined with Rietveld structure refinement. According to the principle of valence neutralization and the disappearing-phase method, in the Ca-rich region (i.e. Ca/Pr>1) the composition of solid solution can be expressed as the general stoichiometry Ca_(2+x)Pr_(2-x)Cu_5O_(10), and in the Pr-rich region (i.e. Ca/Pr<1) as Ca_(1.7)Pr_(2.2)Cu_5O_(10)、 Ca_(1.4)Pr_(2.4)Cu_5O_(10),i.e., the solid solubility of the Ca_2Pr_2Cu_5O_(10)-based solid solution can be determined as from Ca_(2.4)Pr_(1.6)Cu_5O_(10) to Ca_(1.4)Pr_(2.4)Cu_5O_(10). The crystal structure of Ca_2Pr_2Cu_5O_(10) based solid solution is an incommensurate phase based on the orthorhombic NaCuO_2-type subcell. The lattice parameters of Ca_(2.4)Pr_(1.6)Cu_5O_(10) subcell are a_0=0.28246(7) nm,b_0=0.63693(1) nm,c_0=1.06794(1) nm,and its orthorhombic superstructure is with a=5a_0,b=b_0,c=5c_0.The Ca_(2.4)Pr_(1.6)Cu_5O_(10) structure is also determined by using a monoclinic supercell with space group P2_1/c, Z=4,a=5a_0,b=b_0,c=c_0 /sinβ and β=104.79 °or 136.60 °,V=5 a_0b_0 c_0.In the structure of the solid solution based on Ca_2Pr_2Cu_5O_(10), the mutual substitution between Pr and Ca is possible in some bound. Furthermore, they are distributed disorderly in the structure.