Strain-Assisted Topochemical Synthesis of La-Doped SrVO₂H Films

Abstract

Perovskite oxyhydride SrVO 2 H (V 3+ , d 2 ) is a Mott insulator with a strong two-dimensional correlation due to anion ordering. In this study, we attempted electron doping by aliovalent substitution. Although Sr 1−x La x VO 3 thin films (x ≤ 0.4) on a SrTiO 3 substrate were topochemically reduced using CaH 2 , vanadium of the reduced films retained the trivalent state. Combined with the results of secondary ion mass spectroscopy, we conclude that Sr 1−x La x VO 2+x H 1−x is obtained, where the apical oxygen site is partially replaced by hydride anions. First-principles theoretical calculations highlight the role played by compressive biaxial strain in stabilizing the charge-compensated Sr 1−x La x VO 2+x H 1−x phase, rather than the electron-doped Sr 1−x La x VO 2 H. The present study demonstrates that topochemical reactions combined with substrate strain provide various opportunities to widen the compositional space in mixed-anion compounds.

Large Perpendicular Magnetic Anisotropy Induced by an Intersite Charge Transfer in Strained EuVO2H Films

“…As shown in Figure a, the precursor EuVO 3 film with a thickness of 15 nm deposited on an STO substrate exhibits 001 and 002 peaks with distinct fringes around 2θ = 23° and 47°, which are shifted to 25.4° and 52.3° after the CaH 2 reaction (yielding lattice spacings of d 001 = 3.50 Å and d 002 = 1.75 Å, respectively). This indicates a substantial contraction of the c -axis, as also seen in SrVO 2 H thin films obtained from SrVO 3 . − Together with the out-of-plane peak shift, the XRD peak intensities of the EuVO 3 film do not show substantial changes before and after the CaH 2 reaction, which suggests that the EuVO 3 thin film is (almost) completely converted to EuVO 2 H. Here, a CaO capping on top of the thin film is advantageous in providing protection against additional damage from the formation of amorphous and crystalline impurities. The epitaxial growth is further confirmed by X-ray reciprocal space mapping (RSM) (Figure a, inset), yielding a = 3.90 Å and c = 3.50 Å for a 15 nm thick film, while scanning transmission electron microscopy (STEM) images showed a large contrast derived from the alternate EuH and VO 2 layers (Figure b and Figure S10).…”

Intersite Charge Transfer through Eu 4f Band Engineering in Eu1–xSrxVO2H Oxyhydride Films

“…The observed ICT is closely associated with the extended empty V 3d xy orbitals (Figure 1b), leading to electron transfer from the Eu 4f band (Figure 1c). 10 Despite unsuccessful attempts to inject carriers through cation substitution, 11,12 the electron doping driven by ICT enables the metallization of the Mott insulating VO 2 layers. In EuVO 2 H thin films, the concentration of doped electrons decreases with an increase in film thickness (e.g., 0.38 per V ion at 9 nm, 0.29 per V ion at 12 nm, and 0.17 per V ion at 34 nm).…”