Enhanced dielectric response in MWCNT blended NiCo2O4 nano-composoites

Subrata Karmakar1, a) and Dhrubananda Behera1

1Department of Physics and Astronomy, National Institute of Technology Rourkela, Rourkela-769008, Odisha, India. a) Corresponding author: 516ph1010@nitrkl.ac.in, dbehera@nitrkl.ac.in

Abstract The nano crystalline NiCo2O4 blended with MWCNT with various proportionate (5%, 10% and 15%) was synthesized via temperature dependent Co-prepation techniques with a perspective to investigate dielectric and electrical response for improvement its supercapacitor applications. The X-ray diffractometer, FESEM and TEM techniques were used to identify its phase purity, surface morphology, elemental composition and homogeneous grain growth in nm range for various compositions. The FTIR spectra exhibit the suppression of the metal oxide (Ni-O, Co-O) vibrations with the incorporation of MWCNT. The dielectric constant and loss was increased with the evolution of MWCNT percentages and the outmost value of dielectric constant was observed 8x104 at room temperature. The i-v characteristics spectacles on improved electrical current from μA to mA with inclusion of MWCNT. The electrochemical properties indicates that the specific capacitance of NiCo2O4/MWCNTs was increased 12.5% and about 97.9% of the capacitance retained after 3000 charge-discharge cycles as compared to pure NiCo2O4. The good electrochemical performances proposed that these NiCo2O4/MWCNTs composites could be promising materials for energy and ecologically related applications.

Enhanced dielectric response in MWCNT

blended NiCo2O4 nano-composites

By

Prof. D. Behera

Department of Physics and Astronomy, National Institute of Technology Rourkela,

Rourkela-769008, Odisha, India.

Outline

Introduction Experimental Techniques Result and Discussion Conclusion References

What are Cobaltites??? Cobaltite although rare is still an important and valuable ore of cobalt, a

strategically and industrially useful metal. The symmetry of cobaltite is somewhat in dispute. Its structure is very similar to the structure of pyrite, FeS2.

The general chemical formula of a inverse spinal cobaltite molecule is

(M2+Co23+O4

2-), where M2+ represents a divalent metal ion such as Zn2+, Mg2+, Mn2+, Cd2+, Ni2+ etc. In the unit cell, Co ions occupy both sites with tetrahedral (Td) and octahedral local environment, while M2+ (Ni) ions share the sites with an octahedral (Oh) local environment.

Origin of metallic behavior in spinel Cobaltite is ferrimagnetic

substances. Cobaltites are modified structures of Cobalt with its cation distribution

composed of various transition metals ( d-block elements ; transition metals).

Cobaltite

Spinel Hexagonal-114 Cobaltite

Classification of Cobaltite

MCo2O4 (where, M is the divalent cations like Co, Ni, Zn, Cd)

Example:LnBaCo4O7 Where Ln= Ca, Y, Er ,Yb etc.

Example:LnCoO3 Where Ln=Y, Nd , Sm , Ce , Tm etc

Perovskite Ortho-cobaltite

Why Nickel Cobaltite ?

NiCo2O4 inverse spinel unit cell. Ni occupies the octahedral sites and Co is distributed over both octahedral and tetrahedral sites.

Atomic model of the unit cell of NiCo2O4 in the inverse spinel crystal structure. The Td sites are occupied by Co ions and the Oh sites are shared by the Ni and Co ions. Right: the electronic configurations of Ni and Co ions on the Oh sites and Td sites respectively.

The magnetic moments of the Ni and Co ions on Oh and Td sites respectively, are believed to be anti-aligned, corresponding to a ferrimagnetic order below TN ~ 330 K.

Whereas, it is only very recently that NiCo2O4 has been used as a potential candidate for super capacitive materials.

Continued...

What are Carbon nanotubes ?

Carbon nanotubes (CNTs) are allotropes of carbon.

These cylindrical carbon molecules have

interesting properties that make them potentially useful in many applications in nanotechnology, electronics, optics and other fields of materials science, as well as potential uses in architectural fields.

They exhibit extraordinary strength and

unique electrical properties, and are efficient conductors of heat.

Their final usage, however, may be

limited by their potential toxicity.

Electrical Properties of CNT

If the nanotube structure is armchair then the electrical properties are metallic.

If the nanotube structure is chiral then the electrical properties can be either semiconducting with a very small band gap, otherwise the nanotube is a moderate semiconductor.

In theory, metallic nanotubes can carry an electrical current density of 4×109 A/cm2 which is more than 1,000 times greater than metals such as copper.

Due to their Nanoscale dimensions, electron transport in carbon nanotubes will take place through quantum effects and will only propagate along the axis of the tube. Because of this special transport property, carbon nanotubes are frequently referred to as “one-dimensional.”

Experimental Techniques Synthesis of NiCo2O4 Nano-particles :

Na2Co3

Heated in oven at 800 C and large precipitation observed

Precipated compound

filtered

Annealed at

3750 C for 3 hours

Nickel(II) acetate tetrahydrate

Cobalt(II) acetate tetrahydrate

Solution

Take XRD data to confirm its phase

formation

CNT NiCo2O4

Co-precipation Method

Result and Discussion X-Ray diffraction and FTIR analysis :

XRD analysis confirmed the single phase of both Nickel cobaltite nanoparticles and CNT blended counterpart.

The position of the peaks is assigned to Nickel Cobaltite in accordance with the JCPDS card no-73-1702).

The phase shows the pure cubic structure of NiCo2O4 (space group - Fd3m).

Result and Discussion Surface morphological analysis:

Particle size has been identified < 50 nm

Result and Discussion Continued…

The FESEM micrographs of NiCo2O4/CNT exhibits the perfect blending and homogeneous dispersion of CNT with NiCo2O4 The EDX elemental

analysis exposed the true stochiometrical ratios of fundamental element Ni, Co, O and C respectively.

The HR-TEM micrographs of NiCo2O4/15%CNT exhibits the perfect alliance and romance between NiCo2O4 and CNT

Impedance study

Impedance decreases with frequency and Conducting nature increases due to incorporation of CNT

Investigation of structural and electrical transport properties of nano-flower shaped NiCo2O4 supercapacitor electrode materials”- Journal of Alloys and Compounds Volume 757, 15 August 2018, 49-59.

Dielectric study

The Dielectric constant of NiCo2O4 gradually increases with the incorporation of CNT percentages at room temperature and it follows the Maxwell-Wagner type dipolar relaxation.

The dielectric loss follows the similar trends like permittivity.

Current-Voltage study The Current

enhance from μA to mA in NiCo2O4 due to fusion of CNT

Construction of core@shell nanostructured NiFe2O4@TiO2ferrite NAND logic gate using fluorescence quenching mechanism for TiO2 sensing”- Journal of Alloys and Compounds ,765, 2018, 527-537

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