Abstract
This chapter gives a general overview of synthesis and recent development of nickel oxide as a nonstoichiometric compound. We establish the synthesis chemistry of nickel oxide as a nonstoichiometric material, and hence successively introduce definitions and classifications of nonstoichiometric compounds as well as their point defects. The samples of nonstoichiometric nickel oxide are synthesized by thermal decomposition method. The nonstoichiometry of samples was then studied chemically by iodometric titration, and the results are further corroborated by excess oxygen obtained from the thermo-gravimetric analysis (TGA). X-ray diffraction (XRD) and Fourier transformed infrared (FTIR) techniques are used to analyze structural phase of nonstoichiometric nickel oxide. The change in oxidation state of nickel was studied by X-ray photoelectron spectroscopy (XPS) analysis. The shift in antiferromagnetic ordering and transition temperature due to nonstoichiometry is studied by magnetic and specific heat capacity analysis.
Highlights
In solid-state chemistry, the study of compound has been expanded to the crystal structure level
While nonstoichiometric compounds are the chemical compounds deviated from stoichiometry, namely their elemental composition cannot be represented by a ratio of well-defined natural numbers, and violate the law of definite proportions, a nonstoichiometric compound is a type of special solid-state compound with definite structure and thermodynamic characteristics, which differs from its stoichiometric counterpart and a mixture
The samples of different oxygen contents of nickel oxide were synthesized by thermal decomposition method
Summary
In solid-state chemistry, the study of compound has been expanded to the crystal structure level. The unique properties are determined by their solid phase composition, thermodynamic properties, and crystal defect structure These properties depend upon the structure and phase of the crystal; the unit cell parameter plays an important role in nonstoichiometric compound, which varies in a definite manner. The X-ray diffraction study reveals that as the composition of the nonstoichiometric compound changes, the cell parameter and other property continuously changes, which is different from crystalline stoichiometric compound. An abrupt change in thermodynamical conditions, such as specific volume, entropy, or specific heat, changes the derivatives of free energy These parameters can be used as a helpful indicator of phase transitions. The defect that is introduced by sudden change in conditions, changes the physical properties of a material It is quite different from the abrupt variation in physical properties that arises from symmetry or ordering change in a conventional phase transition. The effect of nonstiochiometry on oxidation state, bonding between oxygen and nickel, magnetic property, specific heat, and structural property were studied
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