Investigation of the metal-insulator transition in NdNiO3 films by site-selective X-ray absorption spectroscopy

Natalia Palina; Le Wang; Sibashisa Dash; Xiaojiang Yu; Mark B H Breese; Junling Wang; Andrivo Rusydi

doi:10.1039/c7nr00742f

Investigation of the metal-insulator transition in NdNiO₃ films by site-selective X-ray absorption spectroscopy

Nanoscale. 2017 May 11;9(18):6094-6102. doi: 10.1039/c7nr00742f.

Authors

Natalia Palina¹, Le Wang², Sibashisa Dash³, Xiaojiang Yu⁴, Mark B H Breese⁵, Junling Wang², Andrivo Rusydi⁶

Affiliations

¹ Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore. natalie.mueller@nus.edu.sg phyandri@nus.edu.sg and NUSNNI-Nanocore, National University of Singapore, Singapore 117411, Singapore.
² School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore.
³ Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore. natalie.mueller@nus.edu.sg phyandri@nus.edu.sg and School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore and Department of Applied Physics, Waseda University, Shinjuku, Tokyo 169-8555, Japan.
⁴ Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore. natalie.mueller@nus.edu.sg phyandri@nus.edu.sg.
⁵ Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore. natalie.mueller@nus.edu.sg phyandri@nus.edu.sg and Department of Physics, National University of Singapore, Singapore 117542, Singapore.
⁶ Singapore Synchrotron Light Source, National University of Singapore, Singapore 117603, Singapore. natalie.mueller@nus.edu.sg phyandri@nus.edu.sg and NUSNNI-Nanocore, National University of Singapore, Singapore 117411, Singapore and Department of Physics, National University of Singapore, Singapore 117542, Singapore.

PMID: 28447095
DOI: 10.1039/c7nr00742f

Abstract

In this work, multifunctional oxide NdNiO₃ (NNO) thin films grown on a SrTiO₃ (STO) substrate using pulsed-laser deposition are studied. Temperature dependent resistivity measurements revealed that NNO/STO samples exhibit a sharp thickness dependent metal-insulator transition (MIT) over a range of 150-200 K. It is known that the electronic properties of correlated oxides are extremely complex and sensitive to changes in orbital occupancy. To evaluate the changes in the electronic and/or crystallographic structure responsible for the MIT, a site-selective (O, Ni and Nd) X-ray absorption near edge structure (XANES) analysis is performed above and below the transition temperature. Analysis of XANES spectra suggests that: (i) in NNO films nominally trivalent Ni ions exhibit multiple valency (bond disproportionation), (ii) intermetallic hybridization plays an important role, (iii) the presence of strong O 2p-O 2p hole correlation at low temperature results in the opening of the p-p gap and (iv) the valency of Nd ions matches well with that of Nd³⁺. For NNO films exhibiting a sharp MIT, Ni 3d electron localization and concurrent existence of Ni 3d⁸ and Ni 3d⁸L[combining low line]² states are responsible for the observed transition. At temperatures below the MIT the O 2p-O 2p hole correlation is strong enough to split the O 2p band stabilizing insulating phase. Temperature and thickness dependent differences observed in the site-selective XANES data are discussed in terms of possible mechanisms for the MIT (negative charge-transfer type).