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Ca0.64WO4：Eu0.24陶瓷的高温相变机理及其对发光性能的影响
Mechanism of phase transition induced by high temp eratures and its influences on the luminescence of Ca0.64WO4:Eu0.24 ceramics
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摘要: 纯的CaWO4具有优异的耐压、耐热稳定性，化学组成为Ca0.64WO4：Eu0.24的陶瓷也具有CaWO4结构，但Ca2+晶格位置含有12 mol%的肖特基缺陷.这种缺陷浓度高的CaWO4相是否具有良好的高温稳定性还有待研究.本文探讨了过度烧结对Ca0.64WO4：Eu0.24陶瓷相结构的影响，揭示了在高温下产生相变的可能原因，并研究了该相变对材料发光性能的影响.研究表明，当烧结温度超过1100?C时，被肖特基缺陷束缚的部分氧离子会解离，造成Ca0.64 WO4：Eu0.24陶瓷体相中氧元素含量严重不足，诱发CaWO4相发生相变，析出单斜晶系的Eu2WO6；研究还发现， CaWO4相的晶面间距在高温相变后会增大；这可能是导致Ca0.64WO4：Eu0.24陶瓷发光强度显著降低的一个重要原因.Abstract: Ca0.64WO4:Eu0.24 also crystallizes in the phase of CaWO4 with about 12 mol% of Schottky defects on Ca2+-sites in the crystal lattice of CaWO4. The question whether such a phase is well stable at high temperatures remains to be studied, so the impacts of over-sintering on the structure of Ca0.64WO4:Eu0.24 ceramics are examined. The probable origins resulting in the phase transition at high temperatures are discussed, and the influences of such a phase transition on the luminescence properties are also studied. Observations reveal that some oxygen ions bonded to Schottky defects may be released when the sintering temperature is over 1100 ?C. This leads to the shortage of oxygen element for the bulk Ca0.64WO4:Eu0.24 ceramics, and a phase transition in CaWO4 may have occurred. A monoclinic phase of the formula Eu2WO6 is generated. It is found that the distance between crystal planes in CaWO4 becomes larger after the phase transition. This may be one of the primary reasons accounting for the sharp decrease of luminescent intensities of Ca0.64WO4:Eu0.24 ceramics.
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