Study of space charge and local lattice distortion in ionic conductors by artificially synthesized superlattice structures in nanometer-scale

在这项研究中，人工层的合成，以调整质子导电钙钛矿型氧化物中的掺杂剂分布，以研究掺杂剂分布对质子动力学的影响。由于三价稀土掺杂的SrZrO_3晶体具有块体晶体的特性，因此选择其作为模型材料。在这类质子导体中，掺杂剂可能对质子动力学有重要影响，利用脉冲激光沉积（PLD）技术制备了掺杂剂在二维平面上周期性分布的人工层。基质材料SrZrO 3（SZO）和掺杂剂层Y2O3交替沉积在（001）MgO衬底上。SZO和Y_2O_3层的厚度分别为5 - 20和0.25 - 1nm，薄膜总厚度约为200nm。薄膜的HREM截面图显示形成了非常薄和平坦的Y2O3界面层，并且在原子排列上几乎没有差异 ...更多信息 SZO和Y_2O_3在体相晶体中的结构不同，但在HREM象中的结构相似。XRD分析表明，SZO晶格由于热膨胀系数的大的差异而略微扭曲。人工层与MgO衬底的外延关系为（001）//（001）和[100]//[100]。在400 ℃以下观察到了同位素效应，证实了人工层中的主要载流子是质子。结果表明，当SZO层厚度为10nm左右时，电导率最高，激活能最低。这一结果表明，有一个较好的安排，在这种材料中的掺杂剂的分布，但是，电导率是低得多，激活能是高的相比，大块晶体。人工层的带隙周围的电子结构是相同的，而与SZO和SZY薄膜的带隙周围的电子结构不同。必须考虑质子传导的不同机制来阐明人工层的结果。对质子导体异质层状结构的研究可能为解决其块状晶体中晶界区电导率很低的问题提供重要信息。少

In this study, artificial layers are synthesized to tune dopant distribution in proton-conducting perovskite-type oxides in order to investigate influence of the dopant distribution on proton dynamics. SrZrO3 doped with trivalent rare earth metal has been chosen as a model material, as its properties of bulk crystal is well known. In this type of proton conductors, it is suggested that the dopant might have a significant effect on the proton dynamics.The artificial layers, in which the dopant is distributed periodically in two-dimensional plane, are formed by Pulsed Laser Deposition (PLD). The host material, SrZrO3 (SZO) and the dopant layer, Y2O3 are alternately deposited on (001)MgO substrate. The thickness of SZO and Y2O3 layers are 5-20 and 0.25-1nm, respectively, and the total thickness of the film is about 200nm. HREM cross sectional views of the thin films show that very thin and flat interfacial layers of Y2O3 are formed and there is almost no difference in atomic arrangements … More between SZO and Y2O3 in HREM image, though their structure in bulk crystals are different. XRD analysis revealed that the SZO lattice is slightly distorted due to a large difference in thermal expansion coefficient. The epitaxial relationship of the artificial layer and the MgO substrate is (001)//(001) and [100]//[100].In-plane electrical conductivity in wet air saturated with H2O and D2O at 20℃ has been obtained by impedance spectroscopy. An isotope effect is observed and it is confirmed that the main carrier in the artificial layers is proton below 400℃. It is found that the conductivity is the highest and the activation energy is the lowest when the SZO layer thickness is about 10nm. This result suggests that there is a preferable arrangement of the dopant distribution in this material, however, the conductivity was much low and the activation energy was high compared to those of bulk crystals. The electronic structures around the band gap of artificial layers are the same irrespective of the layer structure and are different from those of SZO and SZY thin films. Different mechanisms of proton conduction must be considered to elucidate the results for the artificial layers. Studies by hetero-layered structures of proton conductors might give important information to solve the problem of very low conductivity at the grain boundary region in their bulk crystals. Less