应力对LaAlO_3/BaTiO_3超晶格结构及性能的影响

采用激光脉冲分子束外延技术,在(100)取向SrTiO3或Nb:SrTiO3单晶基片上成功外延生长不同结构的LaAlO3/BaTiO3超晶格。利用高能电子衍射技术和X射线衍射技术对LaAlO3/BaTiO3超晶格的生长过程和微结构进行了表征。发现由于LaAlO3和BaTiO3晶格常数的不匹配,在LaAlO3/BaTiO3超晶格中存在应变,该应变又对超晶格的铁电性能具有很大的影响。而不同的结构存在的应变不同,非对称结构的LaAlO3/BaTiO3超晶格的应变随每个周期中LaAlO3层厚度的增加、BaTiO3层厚度的减少而增大,其剩余极化强度不仅未减少,反而增加。

Effect of Stress on the Structure and Ferroelectric Properties of LaAlO_3/BaTiO_3 Superlattices

LaAlO3/BaTiO3 superlattices were prepared on (100) oriented SrTiO3 or Nb-doped SrTiO3 substrates by laser molecular beam epitaxy. The change of diffraction streaks observed in reflection high-energy electron diffraction during the growth of LaAlO3 and BaTiO3 illustrated the different epitaxial growth for LaAlO3 and BaTiO3 . The X-ray diffraction spectra of the superlattices with different thickness of LaAlO3 and BaTiO3 layers within a period showed that the c-axis lattice constants changed with layer thickness due to the strain induced by lattice mismatch between LaAlO3 and BaTiO3. The remanent polarization of the superlattices increased with decreasing the thickness of BaTiO3 layers and increasing the thickness of LaTiO3 layers. This suggests that the remanent polarization is closely related with the lattice strain in the superlattices.