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The family of rare earth (RE) nickelate perovskites RENiO3 has emerged over the past two decades as an important platform for quantum matter physics and advanced applications. The parent compounds from this family are strongly correlated insulators or metals, in most cases with long-range spin order. In the past few years, carrier doping has been achieved using different approaches and has been proven to be a powerful tuning parameter for the microscopic properties and collective macroscopic states in RENiO3 compounds. In particular, a series of recent studies has shown that carrier doping can be responsible for dramatic but reversible changes in the long-range electronic and magnetic properties, underscoring the potential for use of nickelates in advanced functional devices. In this review, we discuss the recent advancements in our description, understanding and application of electron-doped rare earth nickelates. We conclude with a discussion of the developments and outlook for harnessing the quantum functional properties of nickelates in novel devices for sensing and neuromorphic computation.

A heterojunction Mott field effect transistor (FET) is proposed that consists of an epitaxial channel material that exhibits an electron correlation induced Mott metal-to-insulator transition. The Mott material is remotely (modulation) doped with a degenerately doped conventional band insulator. An applied voltage modulates the electron transfer from the doped band insulator to the Mott material and produces transistor action by inducing an insulator-to-metal transition. Materials parameters from rare-earth nickelates and SrTiO3 are used to assess the potential of the “modulation-doped Mott FET” (ModMottFET or MMFET) as a next-generation switch. It is shown that the MMFET is characterized by unique “charge gain” characteristics as well as competitive transconductance, small signal gain, and current drive.

The rare earth nickelate La 2 Ni 0.9 Co 0.1 O 4+ δ (LNCO) was synthesized via the citrate/EDTA method. X-ray powder diffraction confirmed that the material is single-phase and crystallizes in the orthorhombic K 2 NiF 4 -type structure. In-situ dc-conductivity and conductivity relaxation measurements on a bar-shaped sample were applied to determine the electronic conductivity as well as the chemical surface exchange coefficient and chemical diffusion coefficient of oxygen from 600 °C to 850 °C and 0.01 ≤ p O 2 / bar ≤ 0.1. The results indicate that substitution of nickel with cobalt in La 2 Ni 0.9 Co 0.1 O 4+ δ leads to significantly higher values of the surface exchange coefficient compared to La 2 NiO 4+ δ , while the electronic conductivity is somewhat reduced. The oxygen non-stoichiometry of LNCO was studied by thermogravimetry in the same temperature and oxygen partial pressure range. The measured thermal expansion coefficients of LNCO fit well with those of common solid electrolytes such as GDC and YSZ. Self-diffusion coefficients of oxygen and ionic conductivities were calculated from the experimentally determined diffusivities and the thermodynamic factor of oxygen by using the Nernst-Einstein relation. The results indicate that LNCO offers an attractive option for application as air electrode in solid oxide cells. • First-order Ruddlesden-Popper phase La 2 Ni 0.9 Co 0.1 O 4+ δ successfully synthesized. • Oxygen exchange kinetics of La 2 Ni 0.9 Co 0.1 O 4+ δ was studied at 600–800 °C. • Substitution of Ni with Co leads to higher chemical surface exchange coefficient. • Substitution of Ni with Co decreases activation energy of surface exchange process. • The ionic conductivity of oxygen was calculated using the Nernst-Einstein relation. [ABSTRACT FROM AUTHOR]

Abstract: A new approach to synthesis of epitaxial thin film of lanthanide nickelates, LnNiO3 (Ln=La, Pr, Nd, Sm), on single crystal surfaces using solutions of heterometallic complexes as precursors has been developed. The precursors of two types were selected: (1) the complexonates LnNi(DTPA)∙nH2O (H5DTPA — diethylenetriaminepentaacetic acid) and (2) complexes Ni(mosalen)Ln(piv)3 (H2mosalen — N,N′-ethylene-bis(3-metoxy-salicylaldiimin), Hpiv — pivalic acid). The use of heterometallic complexes as precursors allowed to deposit epitaxial films of rare earth nickelates with annealing at low temperature–low oxygen conditions. The LaNiO3 film deposited from LaNi(DTPA)∙nH2O precursor solution on (001)SrTiO3 substrate was successfully used as sublayer for highly textured KNbO3 film grown by MOCVD. [Copyright &y& Elsevier]