Electrical Transport Properties of Large, Individual NiCo₂O₄ Nanoplates

Abstract

Understanding the electrical transport properties of individual semiconductor nanostructures is crucial to advancing their practical applications in high‐performance nanodevices. Large‐sized individual nanostructures with smooth surfaces are preferred because they can be easily made into nanodevices using conventional photolithography procedures rather than having to rely on costly and complex electron‐beam lithography techniques. In this study, micrometer‐sized NiCo2O4 nanoplates are successfully prepared from their corresponding hydroxide precursor using a quasi‐topotactic transformation. The Co/Ni atomic arrangement shows no changes during the transformation from the rhombohedral LDH precursor (space group R$ \bar 3 $m) to the cubic NiCo2O4 spinel (space group Fd $ \bar 3 $m), and the nanoplate retains its initial morphology during the conversion process. In particular, electrical transport within an individual NiCo2O4 nanoplate is further investigated. The mechanisms of electrical conduction in the low‐temperature range (T < 100 K) can be explained in terms of the Mott's variable‐range hopping model. At high temperatures (T > 100 K), both the variable‐range hopping and nearest‐neighbor hopping mechanisms contribute to the electrical transport properties of the NiCo2O4 nanoplate. These initial results will be useful to understanding the fundamental characteristics of these nanoplates and to designing functional nanodevices from NiCo2O4 nanostructures.

Is NiCo2S4 Really a Semiconductor?

“…24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59It has been reported that thiospinel NiCo 2 S 4 has a much higher conductivity than its oxide counterpart (NiCo 2 O 4 ) and that it is a semiconductor with a direct band gap of 1.2 eV based on UV-Vis measurements. 6 Yet, the reported UV-Vis spectra 6,19 showed a nearly straight line, unlike the UV-Vis spectra of typical semiconductors, 20 implying that no absorption has actually occurred during the measurement. We observe a similar behavior in our material and find it hard to make any definite conclusion from UV-Vis measurements ( Figure S3).…”

Nickel Cobaltite Nanostructures for Photoelectric and Catalytic Applications

“…It has been demonstrated that Ni x Co 3-x O 4 and polycrystalline NiCo 2 O 4 fi lms at 300 °C exhibit an electrical conductivity of 0.1-0.3 S cm −1 and 0.6 S cm −1 , respectively, while that of hexagonal NiCo 2 O 4 nanoplates reaches up to 62 S cm −1 , which are all much higher than the 3.1 × 10 −5 S cm −1 of Co 3 O 4 . [11][12][13][14][15] The high electronic conductivity, which favors fast electron transfer in NiCo 2 O 4 materials, facilitates their application as electrodes. Meanwhile, simultaneous contributions from both redox couples of Co 3+ / Co 2+ and Ni 3+ /Ni 2+ offer richer redox reactions than those of the two corresponding single metallic oxides, resulting in a notable catalytic and electrocatalytic activity.…”

Atomic layer deposition of nickel–cobalt spinel thin films

“…[12][13][14][15][16][17][18] Formally, it is an inverse spinel with Ni 2+ ions occupying the octahedral site (O h ) and Co 3+ ions distributed over the O h and tetrahedral site (T d ) but the real cation distribution may significantly differ from this, depending on the preparation method. 19 The conduction mechanism is still a subject of discussion and a large variation in the resistivity values is reported in literature.…”