Epitaxial growth and cationic exchange properties of layered KNb3O8 thin filmsElectronic supplementary information (ESI) available: RBS spectrum of KNb3O8 film on sapphire; XRD, SEM (film D); cross-sectional SEM (films B and D); phi-scan (film E); rocking-curves (films B and E); IR spectra (film F2); EDXS spectra (films F, F2, F3); brightfield micrograph and electron diffraction pattern (film F2); XRD of KNb3O8 film on SiO2; HRTEM (films F, F2). See DOI: 10.1039/c7ra00261k

• Main Authors: Waroquet, A, Demange, V, Hakmeh, N, Perrière, J, Freslon, S, Députier, S, Guilloux-Viry, M
• Format: Journal Article
• Language: English
• Published: 08.03.2017
• ISSN: 2046-2069
• DOI: 10.1039/c7ra00261k

The KNb 3 O 8 potassium triniobate phase is a layered compound that shows excellent photocatalytic activity, intercalation properties and electrochemical performances. In this study, we report the synthesis of this niobate in thin film form. Thin films of layered KNb 3 O 8 phase were grown by pulsed laser deposition on (100)-oriented strontium titanate SrTiO 3 substrates using targets with different compositions and various deposition parameters. Samples were analyzed by X-ray diffraction, scanning and transmission electron microscopy, X-ray energy dispersive and Rutherford backscattering spectroscopies. This work shows that KNb 3 O 8 films are obtained in a narrow composition range, close to K 1.13 Nb 3 O 8.7 that can be achieved with several combinations of the elaboration parameters (target composition, deposition temperature, target-substrate distance, laser fluence). Slight potassium amount variations in the film composition lead to the growth of other niobates ( i.e. K 2 Nb 8 O 21 , K 6 Nb 10.88 O 30 , K 3 Nb 7 O 19 , K 4 Nb 6 O 17 ). The KNb 3 O 8 films are either made of elongated crystals (500 nm long, 50-75 nm wide, and 40 nm thick) or of flat lamellas. In both cases, they are (010)-preferentially oriented with epitaxial relationships with the substrate, namely (010)KNb 3 O 8 //(100)SrTiO 3 , [100]KNb 3 O 8 //[010]SrTiO 3 and [001]KNb 3 O 8 //[001]SrTiO 3 . Protonation of the KNb 3 O 8 films leads to a complete exchange of K + ions by H 3 O + ions that are themselves exchanged by Sn 2+ ions after immersion in a tin chloride solution confirming the exchange reaction capabilities also in thin films. Exchange of K + by Sn 2+ leads to the band gap reduction of 0.33 eV. The KNb 3 O 8 potassium triniobate phase is a layered compound that shows excellent photocatalytic activity, intercalation properties and electrochemical performances. K-Sn exchange of KNb 3 O 8 films leads to decrease the optical gap towards visible range.