Potassium tert-butoxide K(OtBu)

     Potassium tert-butoxide K(OtBu) (M = 112.21) is white hygroscopic powder, having bulk density 500g/l, melting point 170-190°C (by other data 220°C [34], 256°C dec. [39], 256-258°C [69])), boiling point 275°C (with decomposition) [34], sublimable 140°C/10-3 Torr, Vapor pressure 1 Torr / 220°C.

     K(OtBu) is soluble in THF (220g/l), tert-butanol (140g/l), boiling alcohols (17%), hydrocarbons (hexane 1.8g/l),   α = 4 (MS, Toluene, THF), 1 (ROH).

   K(OtBu) is safe to handle in air for few minutes, but for longer periods is hygroscopic and transforms completely to hydroxide KOH + carbonate K2CO3 after air exposure for couple of hours.

Molecular strucutre of KOtBu

Fig. Molecular structure of [KOtBu]4

   Potassium tert-butoxide has tetrameric structure [KOtBu]4  (cubic molecule with μ3-bridging OtBu groups)  [K4(μ3-OtBu)4] (Fig.) , according to single crystal XRD [[i],[ii]]

[i] M. H. Chisholm, S. R. Drake, A. A. Naiini, W. E. Streib, Polyhedron, 1991, 10, 337–345

[ii] E. Østreng, H. H. Sønsteby, S. Øien, O. Nilsen, H. Fjellvåg, Dalton Trans., 2014, 43, 16666-16672, « Atomic layer deposition of sodium and potassium oxides: evaluation of precursors and deposition of thin films "

KOtBu (+Nb(OiPr)4(thd)) for KNbO3 by MOCVD

     Potassium tert-butoxide KOtBu, combined with Nb(OiPr)4(thd), was applied as potassium MO precursor for single-source powder flash evaporation MOCVD growth of epitaxial KNbO3 thin films for potential applications in surface acoustic wave (SAW) and nonlinear optic devices. Substrate type (MgO or SrTiO3) and deposition temperature were influencing KNbO3 film microstructure. Device quality of the prepared KNbO3 films was verified by the high second harmonic generation (SHG) output; the oxygen non-stoichiometry was shown to influence the phase transition temperature.[i]

[i] M.V. Romanov, I.E. Korsakov, A.R. Kaul, S.Yu. Stefanovich, I.A. Bolshakov, G. Wahl, Chem. Vapor Dep., 2004, Vol.10, Iss.6, p.318-324, « MOCVD of KNbO3 Ferroelectric Films and their Characterization », https://doi.org/10.1002/cvde.200306302, https://onlinelibrary.wiley.com/doi/abs/10.1002/cvde.200306302 

KOtBu (+Nb(OEt)5) for KNbO3 by MOCVD

       Potassium tert-butoxide K(OtBu) in combination with Nb(OEt)5 was applied as volatile  K precursor for the in situ deposition of epitaxial [110]-oriented KNbO3 thin films on single crystal LaAlO3 (100) substrates.by low pressure MOCVD at 800 °C deposition temperature.  The obtained layers had smooth, featureless morphology with <2nm root-mean-square roughness by AFM. The grown KNbO3 layers produced second harmonic generation of 1.064 μm incident light, the effective second order nonlinear susceptibility d of the as-deposited films was as high as 13 pm/V. [i] Another report of same authors reported K(OtBu)-based growth of epitaxial KNbO5 layers with c-axis oriented normal to the substrate; the layers had surface roughness of 1 - 4 nm by AFM, and film/substrate interface was shown by TEM to be semi-coherent with lattice misfit accommodated by misfit dislocations.[ii] In yet another report of KNbO3 growth by MOCVD using K(OtBu) combined with Nb(OEt)5, the microstructure of (001) p-oriented layers on (100)p LaAlO3 (subscript p indicates the choice of a pseudocubic unit cell); their large second-order nonlinear optical response was studied. The grown KNbO3 layers were demonstrated by TEM to be epitaxial , having abrupt and semicoherent film/substrate interface. The strain between layer and substrate due to 5% lattice constant mismatch was accommodated by formation of an array of misfit dislocations and by 60° and 120° ferroelectric microdomains located in a 20 nm region adjacent to the interface; the layers were shown to be free of significant defects beyond the multidomain region.[iii]

[i] M. J. Nystrom,  B. W. Wessels, D. B. Studebaker,  T. J. Marks, W. P. Lin,  G. K. Wong, Appl. Phys. Lett. 1995, 67, 365; https://doi.org/10.1063/1.114630 , « Epitaxial potassium niobate thin films prepared by metalorganic chemical vapor deposition », https://aip.scitation.org/doi/abs/10.1063/1.114630

[ii] M. J. Nystrom, B. W. Wessels, J. Chen, D. Studebaker, T. J. Marks, W. P. Lin, G. K. Wong, MRS Symp. Proc., vol. 392 (Symposium U – Thin Films for Integrated Optics Applications),  1995, 183, « Deposition of Potassium Niobate Thin Films by Metalorganic Chemical Vapor Deposition and their Nonlinear Optical Properties », https://doi.org/10.1557/PROC-392-183, https://www.cambridge.org/core/journals/mrs-online-proceedings-library-archive/article/deposition-of-potassium-niobate-thin-films-by-metalorganic-chemical-vapor-deposition-and-their-nonlinear-optical-properties/8D474174BF39673E5B70D205CADBAE40

[iii] M.J. Nystrom, B.W. Wessels, J. Chen, T.J. Marks, Appl. Phys. Lett. , 1996, 68, 761; « Microstructure of epitaxial potassium niobate thin films prepared by metalorganic chemical vapor deposition »,    https://doi.org/10.1063/1.116734

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