Applied Surface Science 376 (2016) 209–218 Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Thin (111) oriented CoFe 2 O 4 and Co 3 O 4 films prepared by decomposition of layered cobaltates Josef Burˇ sík a,∗ , Miroslav Soroka a , Róbert Uhreck ´ y a , Radomír Kuˇ zel b , Filip Mika c , ˇ Stˇ epán Huber d a Institute of Inorganic Chemistry of the Academy of Sciences of the Czech Republic, v.v.i., 250 68 Husinec- ˇ Reˇ z 1001, Czech Republic b Charles University in Prague, Faculty of Mathematics and Physics, Ke Karlovu 5, 121 16 Praha 2, Czech Republic c Institute of Scientific Instruments, Academy of Sciences of the Czech Republic, v.v.i., Královopolská 147, 612 64 Brno, Czech Republic d University of Chemistry and Technology, Faculty of Chemical Technology, Technická 5, 166 28 Prague 6, Czech Republic a r t i c l e i n f o Article history: Received 22 December 2015 Received in revised form 16 March 2016 Accepted 16 March 2016 Available online 19 March 2016 Keywords: Layered cobaltates Spinels Chemical solution deposition Thin films Oriented growth a b s t r a c t The formation and structural characterization of highly (111)-oriented Co 3 O 4 and CoFe 2 O 4 films pre- pared by a novel procedure from 00l-oriented NaCoO 2 and Na(CoFe)O 2 is reported. The Na(CoFe)O 2 films were deposited on MgO, SrTiO 3 , LaAlO 3 , and Zr(Y)O 2 single crystals with (100) and (111) orientations by chemical solution deposition method and crystallized at 700 ◦ C. Subsequently they were transformed into (111)-oriented spinel phase during post-growth annealing at 800–1000 ◦ C. Morphology and struc- ture of the films was investigated by means of scanning electron microscopy and X-ray diffraction. While all spinel films exhibit pronounced out-of-plane orientation irrespective of substrate, the rate of in-plane orientation strongly depend on lattice misfit values. Different epitaxial phenomena ranging from true one-to-one epitaxy to the existence of many-to-one epitaxy involving two or more orientations were determined by full 3D texture analysis. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Iron and cobalt oxides form an important class of materials [1]. CoFe 2 O 4 is a good candidate for applications in magneto- optical technology [2–4] and more recently it has also been used in multiferroic composite materials [5]. Considering the need in today’s technologies to downsize the components in electronic and telecommunication devices, the most urgent step is to pre- pare ferrite materials in a form of thin films. CoFe 2 O 4 and Co 3 O 4 crystallize in cubic spinel structure with a face-centered cubic (fcc) oxide anion sublattice. The crystal structure of spinels along the [111] direction is the hexagonal primitive (oblique) and the O 2− sublattice in spinels presents in the [111] direction an fcc stacking sequence ABCA. Layered transition metal oxides with -NaFeO 2 or -NaCoO 2 type structures have been thoroughly investigated due to their possible use as materials in rechargeable ion batteries and ther- moelectric energy conversion devices [6]. Due to their structural ∗ Corresponding author. E-mail addresses: bursik@iic.cas.cz (J. Burˇ sík), soroka@iic.cas.cz (M. Soroka), uhrecky@iic.cas.cz (R. Uhreck ´ y), kuzel@karlov.mff.cuni.cz (R. Kuˇ zel), filip.mika@isibrno.cz (F. Mika), stepan.huber@vscht.cz ( ˇ S. Huber). complexity, these compounds are systematized according to the anion environment around the alkali metal and the size of the repeat unit perpendicular to the alkali metal layer [7]. For example, O3 refers to a structure with octahedrally coordinated alkali ions and a stacking of three CoO 2 − layers. Similarly, P2 refers to a struc- ture with trigonal prismatic coordinated alkali ions and a stacking of two CoO 2 − layers. Na(CoFe)O 2 compound crystallizes in rhombohedral structure, space group R ¯ 3m(a = 0.2975 nm, c = 1.595 nm [8]). The crystal struc- ture consists of two-dimensional triangular lattice of (CoFe)O 2 − layers of edge sharing (CoFe)O 6 octahedra separated by sodium ions. Adjacent (CoFe)O 2 − layers are offset laterally to create a three- layer O3 structure. The sodium atoms occupy the octahedral holes between these layers. Four different phases have been reported in the thermodynamic NaCoO 2 chemical system. Among the known three NaCoO 2 phases forming the O3 structures the so called - NaCoO 2 phase crystallizes in rhombohedral structure, space group R ¯ 3m. The coordination of sodium ions in these structures is octahe- dral. Only one thermodynamic phase delineated as -phase phase exhibits a two-layer P2 structure. Its crystal structure consists of layers of edge-sharing rhombohedrally distorted CoO 6 3− octahedra separated by an insulating layer of Na + ions forming trigonal NaO 6 prisms. Along the [001] direction, the O 2− sublattice in Na(CoFe)O 2 and -NaCoO 2 form ABCA sequence with ccp symmetry, while the http://dx.doi.org/10.1016/j.apsusc.2016.03.130 0169-4332/© 2016 Elsevier B.V. All rights reserved.