Phase evolution of Ba2YCu3O6+x films during the BaF2 process
Phase evolution of Ba2YCu3O6+x films during the BaF2 process
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DOI：
10.1088/0953-2048/17/9/018
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发表时间：
2004-09
影响因子：
3.6
通讯作者：
W. Wong-Ng;I. Levin;R. Feenstra;L. Cook;M. Vaudin
中科院分区：
文献类型：
--
作者：
W. Wong-Ng;I. Levin;R. Feenstra;L. Cook;M. Vaudin
采用高温X射线衍射和透射电镜研究了BaF 2非原位转化生成Ba 2 YCu 3 O 6 +x（Y-213）过程中的物相演变和反应动力学。在这项研究中，前体膜与对应于Y-213的组合物沉积在单晶SrTiO 3基板上使用电子束共蒸发技术。两种不同的前体，（BaF 2 +Y +Cu）和（BaF 2 + YF 3 +Cu），使用，并在所得系列样品的相演变进行了比较。对于（BaF 2 +Y +Cu）膜，在转化过程的中间阶段，非晶前体部分结晶成BaF 2样氟氧化物相（其中BF表示BaF 2）和CuO的混合物。在接近700 °C的温度下，观察到Y2 Cu 2 O 5和BaF 2相关的超结构（，，）。对于这一系列的薄膜，非原位过程涉及几个水合/氧化反应，最终转化成Y-213相的前体。总反应方案可以表示为：其中Ba（OxFy）表示BaF 2-类氟氧化物和BaF 2-相关的超结构相。Y-213相的生长和BaF 2类相的消耗在时间上近似线性。所得Y-213薄膜主要是c轴织构，沿着具有较小体积分数的a轴织构和随机取向区域。对于所研究的（BaF 2 + YF 3 +Cu）薄膜，我们观察到类似的Ba（OxFy）相和BaF 2相关的超结构的演化，沿着CuO的结晶;然而，没有观察到Y2 Cu 2 O 5（s）。YF 3组分保持非晶（从X射线衍射结果）并与Ba（OxFy）、CuO和H2O反应以形成Y-213和Y2 O3。在735 °C下长时间（>2小时）退火后，膜中存在未反应的Ba（OxFy）、Y2 O3和CuO表明Y-213转化不完全。我们的结论是，（BaF 2 +Y F3+Cu）的前体是不太适合相对于（BaF 2 +Y +Cu）在目前的工艺条件下。
High-temperature x-ray diffraction and transmission electron microscopy were used to study the phase evolution and reaction kinetics during the ex situ BaF2 conversion process to form Ba2YCu3O6+x (Y-213). For this study, precursor films with compositions corresponding to Y-213 were deposited on single crystal SrTiO3 substrates using an e-beam co-evaporation technique. Two different precursors, (BaF2+Y +Cu) and (BaF2+Y F3+Cu), were used, and the phase evolution in the resulting series of samples was compared. For the (BaF2+Y +Cu) films, at intermediate stages of the conversion process, the amorphous precursor partially crystallized into a mixture of a BaF2-like oxyfluoride phase (, where BF denotes BaF2) and CuO. At temperatures close to 700 °C, Y2Cu2O5 and a BaF2-related superstructure (, , ) were observed. For this series of films, the ex situ process involved several hydration/oxidation reactions which ultimately transformed the precursor into the Y-213 phase. The overall reaction scheme can be represented as: , where Ba (OxFy) represents both the BaF2-like oxyfluoride and the BaF2-related superstructure phases. The growth of the Y-213 phase and the consumption of BaF2-like phases were approximately linear in time. The resulting Y-213 films were predominantly c-axis textured, along with smaller volume fractions of a-axis textured and randomly oriented regions. For the (BaF2+Y F3+Cu) films investigated, we observed a similar evolution of the Ba (OxFy) phase and the BaF2-related superstructure, along with crystallization of CuO; however, Y2Cu2O5(s) was not observed. The Y F3 component remained amorphous (from x-ray diffraction results) and reacted with Ba (OxFy), CuO and H2O to form Y-213 and Y2O3. The presence of unreacted Ba (OxFy), Y2O3 and CuO in the film after prolonged (>2 h) annealing at 735 °C indicates incomplete Y-213 conversion. We conclude that the (BaF2+Y F3+Cu) precursor was less suitable relative to (BaF2+Y +Cu) under the present processing conditions.