Structure and thermal stability of Bi3NbO7 thin films grown by pulsed laser deposition

• Published in: Surface & coatings technology Vol. 302; pp. 474 - 481
• Main Authors: Szwachta, Grzegorz, Kąc, Sławomir, Moskalewicz, Tomasz
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25.09.2016
• Subjects: Crystal growth; Laser deposition; Structural modulation; Surface topography; Thin films; Thin films; Crystal growth; Surface topography; Structural modulation; Laser deposition
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2016.06.052

Bismuth oxide-based materials containing the cubic δ-phase exhibit the highest ionic conductivity of all known solid-state ion conductors. However, its thermal instability prevents its application at low and intermediate temperatures. To enhance the stability of the materials other oxides are added to the bismuth oxide. In this work the effect of the substrate temperature on the structure, morphology and phase composition of Bi2O3–Nb2O5 thin films deposited onto single-crystal sapphire via pulsed laser deposition technique is studied. The thin films are characterized using X-ray diffraction, transmission electron microscopy, and atomic force microscopy techniques. Three types of microstructures of Bi3NbO7 are achieved by growing the films at different substrate temperatures. At low temperatures the disoriented columnar structure of polycrystalline films is observed. When the substrate temperature increases the (111)-oriented columns appear in thin films. As a consequence, high temperatures lead to a heteroepitaxial growth with an intermittent presence of low-angle grain boundaries. Out-of-plane X-ray diffraction and selected area electron diffraction patterns clearly confirm an epitaxial relationship, which is found to be Bi3NbO7 (111) || α-Al2O3 (0001). An interface between the thin films and substrate is sharp and abrupt. Simultaneously, interdiffusion and a formation of new chemical compounds were not observed. The face-centred cubic Bi3NbO7 phase was detected in thin films with the absent of the tetragonal polymorphic phase. Remarkably, the as-deposited samples were stable during an ex-situ annealing up to 900°C. However, above a temperature of 1000°C, volatilization was taking place due to an uncontrollable loss of bismuth. [Display omitted] •As-deposited structure of Bi3NbO7 thin films depends on substrate temperatures.•Tetragonal phase is not observed in as-deposited thin films.•Thin films are stable in the range of room temperature to 900°C.•Deposition at high temperature leads to (111)-oriented heteroepitaxial growth.