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The enhancement in photoconduction under below-band gap light illumination is attributed to the transition from defect levels (e.g., oxygen vacancies). These nonstoichiometric compounds exhibit different properties such as conductivity, magnetism, catalytic nature, color, and other unique solid-state properties, which have important technological applications.Įxperimental and calculated results demonstrate that the migration of anion and cation vacancies and the formation of insulating vacancy clusters near the vicinity of the interface are the fundamental switching mechanism.
![nickel xps peak nickel xps peak](https://www.researchgate.net/publication/336598298/figure/download/fig3/AS:941641061908489@1601516132739/XPS-spectrum-of-a-Co-2p-and-b-Ni-2p-in-Ni-Co-2-4-MOF.png)
Beside some unusual information on solid-state chemistry, stability, and dynamics can be explore through their structure and characteristic. Due to defect structure in a continuous manner, these compounds are different with stoichiometric compounds. 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 therefore violate the law of definite proportions, hence 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. All chemical compounds obeying these laws are called as stoichiometric compounds. The law of definite proportions, the law of constant composition, and the law of conservation of mass state that a chemical compound always contains exactly the same proportion of elements by mass. In solid-state chemistry, the study of compound has been expanded to the crystal structure level. The shift in antiferromagnetic ordering and transition temperature due to nonstoichiometry is studied by magnetic and specific heat capacity analysis.
![nickel xps peak nickel xps peak](https://minio.scielo.br/documentstore/1678-7064/XHTmyptL63FrMwZtPL6ZsdL/0083fc31a856cfcfc54e25e024fea38bf50f901b.jpg)
The change in oxidation state of nickel was studied by X-ray photoelectron spectroscopy (XPS) analysis. X-ray diffraction (XRD) and Fourier transformed infrared (FTIR) techniques are used to analyze structural phase of nonstoichiometric nickel oxide. 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). The samples of nonstoichiometric nickel oxide are synthesized by thermal decomposition method. 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. This chapter gives a general overview of synthesis and recent development of nickel oxide as a nonstoichiometric compound.