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摘要: 本文用X射线衍射、Eu2+的发射谱与激发谱、拉曼谱以及扫描电镜(SEM)颗粒形貌,研究了常压下合成的具有正交结构的SrB2O4:Eu2+晶体在3.0~7.0 GPa压力下的晶态非晶化现象。分析结果表明,压力导致晶粒细化和晶态非晶化。晶粒尺寸由常压下的微米量级细化为几十个纳米量级,随压力的变化为:2 m(0.1 MPa),49.4 nm(3.0 GPa),29.7 nm(5.0 GPa),25.1 nm(7.0 GPa)。晶态与非晶态体积比随压力增加而减小,分别为:70/30(3.0 GPa),63/37(5.0 GPa),57/43(7.0 GPa)。在压力下Eu2+是处在晶态与非晶态两种不同的低对称的环境中。纳米级晶粒是以亚晶粒形式存在于微米级大晶粒中的,压致非晶态可能组成了纳米亚晶粒的界面区。Abstract: High pressure-induced crystallization in disordered or non-crystalline matter is well known. Pressure-induced disordering or non-crystallizing in crystals, however, has been seldom found so far. In the present paper, under the pressure of 3.0~7.0 GPa, the pressure-induced non-crystallization phenomena in Eu2+ activated orthorhombic Sr-borates crystals were investigated by using X-ray diffraction, emission and excitation spectra of Eu2+, Raman spectra and SEM topography. After treating at 3.0 GPa, the X-ray diffraction spectra of the sample exhibit a new character in which a set of clearly widened peaks of the crystal were superposed on the diffuse peaks of non-crystalline state; the intensity of the emission spectrum peaking at 370 nm, which is given by 5d4f transition of Eu2+ located in orthorhombic crystal, decreased and widened obviously, and a broad band of emission spectrum peaking at 440 nm, which is given by Eu2+ located in non-crystalline state, was also observed; the excitation spectra for the two emission bands differed with each other considerably; the intensity of Raman peaks decreased and their half width increased; the particle size observed by SEM remained in the order of micrometer of orthorhombic crystal grain synthesized under normal pressure. As the pressure increasing, the width of X-ray diffraction peaks for the crystalline state increased, but the total diffraction intensity further decreased, shile the total intensity of diffuse peaks for the non-crystalline state further increased; the emission band peaking at 370 nm was not observed, only a very low emission peak was recorded at 440 nm; Raman peaks were further decreased and widened, too; the particle size observed by SEM did not vary apparently. Analyses from the experimental results of X-ray diffraction show the pressure effects in the fining of crystal grains, the non-crystallization of crystalline state, and the grain size reduction from the order of micrometer to nanometer. They are 2 m (0.1 MPa), 49.4 nm (3.0 GPa), 29.7 nm (5.0 GPa), 25.1 nm (7.0 GPa), respectively. The volume ratio fo crystalline to non-crystalline state with increasing pressure was found, they are 70/30 (3.0 GPa), 63/37 (5.0 GPa), 57/43 (7.0 GPa), respectively. The symmetry of crystal field around Eu2+ in crystalline and non-crystalline state formed under the high pressure is different and lowering. The lowering and widening of Raman peaks result from pressure-induced fining of grain to nanometer in size. Combining the results about the grain size of SEM and X-ray diffraction, it seems that the pressure-induced nano-grains exhibits in the form that there exist sub-grains in the larger grains of micrometer. The interface zone between the sub-grain is probably in non-crystalline state.
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Key words:
- SrB2O4 /
- pressure-induced non-crystallization /
- fining of grain /
- interface /
- X-ray diffraction /
- Raman spectrum
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