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摘要: 利用X射线衍射分析和Rietveld结构精修的方法研究了固相线下Pr1-xBa2-yCax+yCu3O7体系的相关系和晶体结构。研究表明:950 ℃、空气条件下,Pr1-xBa2-yCax+yCu3O7(y=0)体系系列样品总是含有两相:Pr123(PrBa2Cu3O7)和BaCuO2;而且,随Ca含量的增加,杂相BaCuO2的含量也随之增加。Pr1-xBa2-yCax+yCu3O7(x=0)体系y=0.1、0.2、0.3、0.4的样品都只含有Pr123单相;y=0.5的样品含有3相:Pr123、Ca2CuO3和Pr4Ca10Cu24O41。另外,Pr1-xBa2-yCax+yCu3O7(x=0)系列样品(y=0.1、0.2、0.3、0.4)中Pr123相还发生了正交-四方晶系的结构转化。y=0.1和0.2的样品为正交晶系,晶胞参数分别为a=0.390 33(4)和0.389 36(1) nm,b=0.389 53(4)和0.387 73(1) nm,c=1.173 38(4) 和1.168 20(2) nm;y=0.3和0.4的样品为四方晶系,晶胞参数分别为a=b=0.387 80(0) 和0.387 67(0) nm,c=1.166 00(2) 和1.165 20(2) nm。在Pr123结构中,Ba离子可以被Pr离子代替,但不能被Ca离子所代替。Ca离子占据部分Pr离子的位置。在Pr1-xBa2-yCax+yCu3O7(x=0)体系中Pr、Ba和Ca离子间的相互替代中,离子半径比化学性质起到了更大的作用。在950 ℃、空气条件下,Ca离子在Pr1-xBa2-yCax+yCu3O7体系中的最大溶解量是当x=0时,y0.4。
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关键词:
- Pr1-xBa2-yCax+yCu3O7体系 /
- 相关系 /
- 晶体结构 /
- X射线衍射 /
- Rietveld结构精修
Abstract: Subsolidus phase relation and crystal structure in the Pr1-xBa2-yCax+yCu3O7 system were studied by X-ray diffraction combined with Rietveld structure refinement. The results indicate that all of the Pr1-xBa2-yCax+yCu3O7 (y=0) samples contain a BaCuO2 phase besides the Pr123 (PrBa2Cu3O7) phase under 950 ℃ in the air. Furthermore, the content of the BaCuO2 phase increases with increasing Ca content. The samples of Pr1-xBa2-yCax+yCu3O7 (x=0) (y=0.1, 0.2, 0.3, 0.4) contain only one phase, Pr123, except for the sample with y=0.5 which contains three phases, Pr123, Ca2CuO3 and Pr4Ca10Cu24O41. Otherwise, the Pr123 structure takes place the orthorhombic-tetragonal transition in the Pr1-xBa2-yCax+yCu3O7 (x=0) system (y=0.1, 0.2, 0.3, 0.4) with increasing Ca ion content. The structure of the Pr1-xBa2-yCax+yCu3O7 (x=0) samples with y=0.1 and 0.2 is orthorhombic. The lattice parameters are a=0.390 33(4)~0.389 36(1) nm, b=0.389 53(4)~0.387 73(1) nm, c=1.173 38(4)~1.168 20(2) nm; The structure of the Pr1-xBa2-yCax+yCu3O7 (x=0) samples with x=0.3 and 0.4 is tetragonal. The lattice parameters are a=b=0.387 80(0), 0.387 67(0) nm, c=1.166 00(2), 1.165 20 (2) nm. In the Pr123 structure, Ba ions could be replaced by Pr ions, but could not be replaced by Ca ions. Ca ions partially occupy the sites of Pr ions. The ionic radius plays a more important role than the chemical properties in the mutual substitution of Pr, Ba and Ca ions in the Pr123 structure of the Pr1-xBa2-yCax+yCu3O7. The highest content of Ca ions in the Pr1-xBa2-yCax+yCu3O7 system is x=0, y=0.4 under 950 ℃ in air. -
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