Effect of quenching rate on crystalline and impedance properties of NiO nanoparticles

NiO nanopowder is produced through plasma-chemical synthesis in a low-pressure arc reactor in an atmosphere of 80% Ar + 20% O
₂
at a pressure of 40 (sample 1) and 180 Pa (sample 2). The crystalline, morphological, and impedance properties are studied by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and impedance spectroscopy. It is shown that an increase in pressure leads to the synthesis of nanomaterials with fundamentally different crystalline and electrical properties. Sample 1 shows a non-stoichiometric composition (Ni
₄₂
O
₅₈
), a face-centered cubic lattice, and a size of coherent scattering regions (CSR) of 16 nm. The impedance studies shows that the frequency dependences are well described by the Debye relaxation model, at low frequencies the real part of the dielectric constant is equal to 35, and thermal studies show a negative temperature coefficient of resistance (NTCR). Sample 2 has an amorphous structure, almost stoichiometric composition (Ni
₄₈
O
₅₂
). At low frequencies, the real and imaginary parts of the dielectric constant reaches 10
⁵
. The anomaly is explained by the formation of a double electric layer near the electrodes due to proton-ion conductivity.