Cationic structure and charge transport in sol–gel-derived nickel-cobaltite thin films

Abstract

Conductive nickel-cobaltite (Ni x Co 3-x O 4 ) thin films were synthesized on Al 2 O 3 substrates by using a solgel process for varying Ni composition x (B 1.0). X-ray diffraction data indicated that the polycrystalline Ni x Co 3-x O 4 samples have cubic spinel (Fd 3m) structure with the lattice constant increasing slightly with increasing Ni composition (by 0.5 % for x = 1.0 compared to that of Co 3 O 4 ). X-ray photoelectron spectroscopy data indicated that the Ni ions in nickel-cobaltite have multi-valence (Ni 2? and Ni 3? ). The temperature-dependent electrical resistivity (q) data of the nickel-cobaltite samples were measured in the 4-300 K range in comparison with Co 3

Inkjet Printing as High-Throughput Technique for the Fabrication of NiCo2O4 Films

“…According to the quantitative XPS analysis and calculated areas from 2p3/2 peaks of cobalt and nickel, the surface atomic content is 13.9, 15.1, 6.1, and 4.4% for Co 2+ , Co 3+ , Ni 2+ , and Ni 3+ , respectively. This means that the mixed oxidation states of cobalt and nickel favor the charge neutrality and structural stability of the inkjet-printed NiCo 2 O 4 film, as previously observed for a sol-gel film [2]. The electronic absorption spectra obtained from 5 different zones along the NiCo 2 O 4 film are presented in Figure 7.…”

“…On the other hand, the nickel 2p spectrum contains peaks associated with 2p3/2 (854 eV) and 2p1/2 (872 eV) as well as their respective satellite peaks at 861 and 880 eV. The main peak at 854 eV is assigned to octahedral Ni 2+ ions, whereas the small shoulder at 856 eV has been ascribed to Ni 3+ present in NiCo 2 O 4 oxide [2,6]. The contribution of every metallic cation was determined by a curve-fitting analysis of their respective XPS spectra.…”

“…NiCo 2 O 4 oxide has recently been a motivating topic from the viewpoint of materials science because of its interesting catalytic, electrical, and optical properties. These properties are related to important technological applications such as electrodes for fuel cells [1,2], electrodes in sodiumand lithium-ion batteries [2][3][4], optoelectronic [5,6] and magnetic devices [7,8], supercapacitors [4,[9][10][11][12][13], flat-panel displays [2,14], infrared transparent conducting materials [2,5,14], glucose sensors [15], and several electrochemical reactions [1,6,7,[16][17][18][19][20]. In particular, the production of clean energy from renewable sources as in the electrocatalytic water splitting process is an attractive alternative for an energy economy based on hydrogen [20,21].…”

“…Many of the above-mentioned applications of NiCo 2 O 4 require its fabrication in thin film form; moreover, taking into consideration a possible scale-up, the surface dimensions of the film is an important issue. In this respect, NiCo 2 O 4 films have been principally prepared by physical deposition processes such as pulsed laser deposition [16,[23][24][25] and radio frequency magnetron sputtering [5,8], as well as by means of chemical routes including electrodeposition [6,14,15], sol-gel [2], hydrothermal synthesis [26], spray pyrolysis [4], and chemical vapor deposition [27]. In general, if cost of the process and equipment requirements are considered, the solution-based chemical methods are more appropriate than physical routes.…”

Magnetic and Electrical Properties of Spinel Copper Ferrite Thin Films

“…The binding energy of a Cu 2p electron under a crystal field of eight (octahedral) O 2− ions is expected to be smaller than that under the field of four (tetrahedral) O 2− ions. The ratio of line intensity [16] between α 1 and β 1 obtained by estimating their curve-fitted areas is 4:1 for the x = 1.0 specimen, implying that ~20 % of the Cu 2+ ions are located at the tetrahedral sites.…”