Improved polaronic transport under a strong Mott-Hubbard interaction in Cu-substituted NiO

• Published in: Inorganic chemistry frontiers Vol. 7; no. 4; pp. 853 - 858
• Main Authors: Park, Seong Gon, Lee, Kyu Hyoung, Lee, Jae-Hoon, Bang, Geukchan, Kim, Junghwan, Park, Hee Jung, Oh, Min Suk, Lee, Suyoun, Kim, Young-Hoon, Kim, Young-Min, Hosono, Hideo, Bang, Joonho, Lee, Kimoon
• Format: Journal Article
• Language: English
• Published: London Royal Society of Chemistry 21.02.2020
• Subjects: Antiferromagnetism; Conduction bands; Copper; Density functional theory; Energy gap; Hopping conduction; Inorganic chemistry; Materials substitution; Nickel oxides; Optical properties; Polarons; Substitution reactions; Transition temperature; Valence band
• ISSN: 2052-1553; 2052-1545; 2052-1553
• DOI: 10.1039/c9qi01052a

The origin of the electrical and optical properties of Cu-substituted NiO (Cu : NiO) polycrystalline bulks synthesized via a solid-state reaction is reported. The partial substitution of Ni sites with Cu led to a drastic decrease of the electrical resistivity from 7.73 × 10 8 to 6.51 × 10 4 Ω·cm and a reduction in the energy for the self-trapping barrier from 0.58 to 0.24 eV in accordance with small polaron hopping conduction. The well-sustained band gap of 3.1 eV and antiferromagnetic transition temperature of 453 K demonstrate that the strength of the electron correlation in NiO can persist even at a high Cu concentration up to 22 atomic percent. Density functional theory calculations confirm that the Cu 3d orbital encourages d - p hybridization between metal cations and oxygen anions at the valence band maximum. As a consequence, this hybridization plays a critical role in improving the polaron hopping efficiency without much suppression of the Mott-Hubbard interaction and thus retaining the wide band gap nature. We report the origin of improved hole conduction without band-gap collapse in Cu-doped NiO.