Electron- and Hole-Doping Effects on the Metal-Insulator Transition in “113” Nickelates [<i>R</i>NiO₃, <i>R </i>= Pr, Nd, (La,Y)] Prepared at High Oxygen Pressure*

We report x-ray diffraction, electrical resistivity, and other data on bulk polycrystalline materials prepared under high oxygen pressure (150–200 bar) at high temperature (T ≈ 1000°C). These conditions stabilize the nearly simple-perovskite “113” structure, RNiO₃. For the orthorhombic parent compounds with the largest rare-earth ions that exhibit a metal-insulator transition, R = Pr and Nd, we dope with divalent Sr and Ba (hole doping) and tetravalent Ce and Th (electron doping). Results for Nd_1–xA_xNiO₃ (A= Sr, Ce, Th) have been reported previously¹: for example, for Ce⁴⁺, the net effect on the metal-insulator transition, ∂T_MI/∂x ≈ –220 K, was corrected for size effects to obtain a bare electron-doping effect, ∂T_MI/∂x_elec ≈ –1100 K. Remarkably in our study, we find that, for Pr_1–xCe_xNiO₃, the shift in the metal-insulator transition temperature with concentration x is positive, with a net ∂T_MI/∂x ≈ +225 K. Also, we find hysteresis in the metallic resistivity of rhombohedral La_1–xCe_xNiO₃, perhaps a signature of low-T pseudogap monoclinic short-range order.^2
1J. L. García-Munoz et al., Phys. Rev. B 52, 13563 (1995). ²B. Li et al., Advanced Electronic Materials 2, 1500261 (2016).