Nanorods of Potassium Tantalum Niobate Tetragonal Tungsten Bronze Phase Grown by Pulsed Laser Deposition

Abstract

International audienceK−Ta−Nb−O tetragonal tungsten bronze phase was grown on (11̅02) Al2O3 (R-plane sapphire) by pulsed laser deposition. The microstructure, structure, and chemical composition of the deposit were studied by scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectrometry, and transmission electron microscopy. The crystal structure was solved by precession electron diffraction as being tetragonal tungsten bronze-type structure with space group P4/mbm, refined cell parameters a = 12.537 ± 0.003 Å, c = 3.975 ± 0.001 Å, and composition K5.06(Ta0.57Nb0.43)10.99O30. The tetragonal potassium tantalum niobate growth follows two modes with respect to the substrate surface: (i) as single vertical right parallelepiped-shaped nanorods (50 to 100 nm wide and up to 1 μm in length) along the [001] direction and (ii) as in-plane attached crystals along the ⟨310⟩ direction. These two growth modes are understood as being governed by the plane termination of the substrate. This new phase is of potential interest due to the physical (dielectric, catalytic, etc.) properties evidenced for tetragonal tungsten bronze phases in numerous systems

Tetragonal tungsten bronze phase thin films in the K–Na–Nb–O system: Pulsed laser deposition, structural and dielectric characterizations

“…To favor the growth of the TTB phase, the alkaline target composition was further decreased down to (K 0.5 Na 0.5 ) 0.7 NbO 3 (target T2). The film obtained at 600°C using this target (F3) leads to the formation of the TTB phase on Nb:(110)SrTiO 3 as displayed by XRD (Figure 3a The parallelepiped-shape long crystal elongation is along the [001] direction, as commonly observed for TTB phases [16,36]. As for the two previous phases, this direction corresponds to a slight distortion of the octahedra.…”

“…However, in the KNN system, many other phases of potential interest exist without being thoroughly investigated. In many chemical systems, such as K-Nb-O (KN), K-Ta-O, K-Li-Nb-O (KLN) or K-Ta-Nb-O, chemically close to the KNN system, Tetragonal Tungsten Bronze (TTB) phases have been reported either as thin films or bulk [16][17][18][19][20]. The TTB structure can be described along the [001] direction by two cationic octahedral sites B1 and B2 and three cationic tunnels A1, A2…”

“…Finally, the C sites can only be occupied by small cations and are often found to be empty. , and C, and the cationic octahedral sites B1 and B2 [16].…”

Structural analysis of strained LaVO3thin films

“…Using XRD, partial structural studies focused on the determination of the amplitude of octahedral tiltings in thin films were achieved [13][14][15][16][17]. Dealing with the structure determination of unknown phases deposited in the form of thin films, precession electron diffraction (PED) [18] has proved to be one valuable technique [19,20] not limited by the size of the probe nor the small volume of diffracting material. This technique was thus retained as a good tool to investigate the structure of our LaVO 3 (LVO) thin films grown on (001)-oriented SrTiO 3 (STO) substrates.…”

Precession electron diffraction tomography on twinned crystals: application to CaTiO3thin films

“…Electron diffraction tomography (Kolb et al, 2007(Kolb et al, , 2008Mugnaioli et al, 2009), combined or not with precession electron diffraction (PED) (Vincent & Midgley, 1994), appears to be the ideal technique to investigate the structure of nanomaterials and has already proved its efficiency for solving the structure of unknown materials deposited in the form of thin films (Boullay et al, 2009;Simon et al, 2013;Zhang et al, 2016;Li et al, 2017;Veis et al, 2018). With this technique, the kinematical approximation is a good hypothesis for quantitative analysis of the intensities, and structure solution methods such as the 'charge flipping' algorithm (Palatinus & Chapuis, 2007) can be used.…”