Abstract

Composites with the (Bi, Fe, ◻)₂(Fe, W)₂O₆O'_δ composition (pyrochlore, hereinafter BFWO)/amorphous phase were obtained by hydrothermal-microwave synthesis in the Bi₂O₃–Fe₂O₃–WO₃–(H₂O) system and characterized. The degree of the amorphous phase transformation into crystalline BFWO was found to increase from ~0.08 to ~0.82 with an increase in isothermal exposure duration at 180°C from 1 s to 5 min. The type of this dependence correlates well with the nature of the change in the BFWO phase crystallites average size (estimated by the Williamson–Hall graphical method), which increases from 270(20) to ~600 nm. It is shown that two morphological motifs are found in all samples, one of which is represented by particles whose average size correlates with the average size of the BFWO phase crystallites, and the other is represented by agglomerates sized at ~100 nm and composed of particles of the amorphous phase. Large particles have a core-shell type structure, in which BFWO crystallites form the core, and the shell is composed of the amorphous phase. The band gap (E_g) of the obtained composite materials for direct allowed electronic transitions is in the range of 2.26‒2.40 eV and decreases with an increase in the fraction of the BFWO crystal phase in the composite.

中文翻译：

---

Bi2O3–Fe2O3–WO3–(H2O) 体系中的烧绿石相：水热-微波合成的形成和光学性质

摘要

_{在Bi 2} O ₃ -Fe ₂ O ₃中通过水热-微波合成得到(Bi, Fe, ◻) ₂ (Fe, W) ₂ O ₆ O' _δ组成（烧绿石，以下简称BFWO）/无定形相的复合材料–WO ₃ –(H ₂O) 系统和特征。发现非晶相转变为结晶BFWO的程度从~0.08增加到~0.82，180°C下的等温暴露持续时间从1秒增加到5分钟。这种依赖性的类型与 BFWO 相微晶平均尺寸（通过 Williamson-Hall 图解法估计）的变化性质密切相关，从 270(20) 增加到 ~600 nm。结果表明，在所有样品中都发现了两种形态基序，其中一种由平均尺寸与 BFWO 相微晶的平均尺寸相关的颗粒表示，另一种由尺寸约为 100 nm 且由颗粒组成的团聚体表示的非晶相。大颗粒具有核壳型结构，其中BFWO微晶形成核，壳由非晶相组成。带隙 (所获得的用于直接允许电子跃迁的复合材料的E _g ) 在 2.26-2.40 eV 的范围内，并且随着复合材料中 BFWO 晶相比例的增加而减小。