The X-ray photoelectron spectroscopy and high-temperature structural studies of Zn1−xNixO/NiO two-phase composites

Abstract

Detailed investigation of the chemical states and local atomic environment of Ni and Zn in the two‐phase composites of Zn1−xNixO/NiO was reported. The X‐ray photoelectron spectra of both Ni‐2p and Zn‐2p revealed the existence of a doublet with spin‐orbit splitting Δ∼ 17.9 and 23.2 eV, respectively confirming the divalent oxidation state of both Ni and Zn. However, the samples fabricated under oxygen‐rich conditions exhibit significant difference in the binding energy Δ∼ 18.75 eV between the 2p3/2 and 2p1/2 states of Ni. The shift in the satellite peaks of Ni‐2p with increasing the Ni composition x within the Zn1−xNixO/NiO matrix signifies the attenuation of nonlocal screening because of reduced site occupancy of two adjacent Zn ions. The temperature dependence of X‐ray diffraction analysis reveals a large distortion in the axial‐rhombohedral angle α′ for oxygen‐rich NiO. Conversely, no significant distortion was noticed in the NiO system present as a secondary phase within Zn1−xNixO. Nevertheless, the unit‐cell volume of both wurtzite h.c.p. Zn1−xNixO and f.c.c. NiO exhibits an anomalous behavior between 150 and 300° C. The origin of such unusual change in the unit‐cell volume was discussed in terms of oxygen stoichiometry.

Cationic distribution, exchange interactions, and relaxation dynamics in Zn-diluted MnCo2O4 nanostructures

“…The binding energy separation between the "Mn" doublet (Δ 11:61 eV and 11.44 eV for x B ¼ 0:2 and y A ¼ 0:1, respectively) signifies the trivalent oxidation state of "Mn" (i.e., Mn 3þ ) inside the polycrystalline samples. 19,26,27 The observed value of spin orbit splitting in these systems is slightly higher ( 0:40 eV and 0:23 eV for x B ¼ 0:2 and y A ¼ 0:1) as compared to the undiluted MnCo 2 O 4 ( 11:21 eV). 19 This could be associated with the screening of "Mn 3þ " ions by additional "Zn" ions present in the x B ¼ 0:2 and y A ¼ 0:1 matrix.…”

“…[23][24][25][26] The binding energy separation between these two peaks, often characterized as the spin-orbit splitting Δ 23:08 eV, confirms the divalent oxidation state of Zn in the Mn 0:8 Zn 0:2 Co 2 O 4 matrix. 23,26 Similar results were observed for the "Zn" in MnCo 1:9 Zn 0:1 O 4 , where a slight shift in the binding energies of the Zn-doublet towards higher binding energies [Fig. 1(v)] was observed with Δ 23:14 eV, which confirms the thin Zn 2þ state in the A-site diluted sample.…”