Research ArticlePHYSICS

Spontaneous phase segregation of Sr2NiO3 and SrNi2O3 during SrNiO3 heteroepitaxy

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Science Advances  05 Mar 2021:
Vol. 7, no. 10, eabe2866
DOI: 10.1126/sciadv.abe2866
  • Fig. 1 Epitaxial synthesis of SrNiO3−δ (SNO) films with a 1:1 Sr/Ni ratio.

    (A) Schematic crystal structures for bulk NdNi3+O3 and SrNi4+O3. Tolerance factor t=rA+rO2(rB+rO), where rA, rB, and rO are the ionic radius of A and B cations and oxygen, respectively, in a set of ABO3 crystal structures. Sr doping in NdNiO3 (Nd1−xSrxNiO3) would increase t due to the larger ionic radius of Sr2+ ion. (B) XRD θ-2θ scan of SNO films. The left inset shows the RHEED pattern for an as-grown SNO film on LSAT(001) viewed along the [100] zone axis. The right inset shows the magnified 004 peak with clear thickness fringes. # indicates that the peak originated from our XRD setup. a.u., arbitrary units.

  • Fig. 2 Phase segregation occurs in SNO films.

    (A) Cross-sectional STEM image of SNO/LSAT along the [110] LSAT direction. Dashed circles clearly show phase segregation. (B) Magnified images of the Sr2NiO3 phase and the SrNi2O3 phase marked by green and blue rectangles in (A). (C and D) Cross-sectional STEM images of two different phases in SNO/LSAT along the [100] LSAT direction. EELS maps (right) from the area marked with a yellow rectangle in the STEM images (left). Scale bar, 2 nm. (E) APT tip reconstruction for SNO/LSAT. (F) A 3D volume rendering showing regions with greater than 13.5% Ni2+ (upper, gray scale). 2D Ni2+ (middle) and Sr2+ (lower) concentration maps highlighting where spatially localized Ni and Sr enrichment occurs.

  • Fig. 3 Spectroscopy results of SNO films.

    Ni 2p XPS (A) and Ni L edge XAS (B) of SNO films. The reference spectra for Ni2+ and Ni3+ were measured using a vacuum-annealed NdNiO3−δ film (VA-NNO) and a plasma-annealed NdNiO3 film (PA-NNO), respectively, both grown on SrTiO3(001). The spectrum for a NiO film grown on MgO (001) is included for comparison. The blue dashed lines in (A) denote the Ni 2p1/2 and Ni 2p3/2 peak positions of SNO films. The purple and blue dashed lines in (B) are guidelines for peak positions.

  • Fig. 4 O K edge XAS and electrical transport of SNO.

    (A) O K edge XAS for PA-NNO, SNO, and VA-NNO films measured at room temperature. (B) Temperature-dependent resistivity of these three samples. The purple arrow denotes the metal-insulator transition point (TMI).

  • Fig. 5 Orbital polarization in SNO films.

    (A) Polarization-dependent XAS across the Ni L edge for SNO/LSAT(001). The inset shows a sketch of the engineered orbital and spin states, which forms the electronic configuration (Ni2+, 3d8) and orbital polarization (ndx2 y2> nd3z2 r2). (B) Schematic of the crystalline structures of Sr2NiO4 (SNO_214), pyramid Sr2NiO3 (SNO_213 pyramid), planar Sr2NiO3 (SNO_213 planar), and SrNi2O3 (SNO_123). (C) Partial density of states (PDOS) of these four different systems. The Fermi level (the black dashed line) is placed at 0 eV. The black arrows denote the spin state.

Supplementary Materials

  • Supplementary Materials

    Spontaneous phase segregation of Sr2NiO3 and SrNi2O3 during SrNiO3 heteroepitaxy

    Le Wang, Zhenzhong Yang, Xinmao Yin, Sandra D. Taylor, Xu He, Chi Sin Tang, Mark E. Bowden, Jiali Zhao, Jiaou Wang, Jishan Liu, Daniel E. Perea, Linda Wangoh, Andrew T. S. Wee, Hua Zhou, Scott A. Chambers, Yingge Du

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