Atomic disorder of Li_0.5Ni_0.5O thin films caused by Li doping: estimation from X-ray Debye–Waller factors

Abstract

Cubic type room-temperature (RT) epitaxial Li 0.5 Ni 0.5 O and NiO thin films with [111] orientation grown on ultra-smooth sapphire (0001) substrates were examined using synchrotron-based thin-film X-ray diffraction. The 111 and 222 rocking curves including six respective equivalent reflections of the Li 0.5 Ni 0.5 O and NiO thin films were recorded. The RT B 1 factor, which appears in the Debye-Waller factor, of a cubic Li 0.5 Ni 0.5 O thin film was estimated to be 1.8 (4) Å 2 from its 111 and 222 reflections, even though the Debye model was originally derived on the basis of one cubic element. The corresponding Debye temperature is 281 (39) K. Furthermore, the B 2 factor in the pseudo-DebyeWaller factor is proposed. This parameter, which is evaluated using one reflection, was also determined for the Li 0.5 Ni 0.5 O thin film by treating Li 0.5 Ni 0.5 O and NiO as ideal NaCl crystal structures. A structural parameter for the atomic disorder is introduced and evaluated. This parameter includes the combined effects of thermal vibration, interstitial atoms and defects caused by Li doping using the two Debye-Waller factors.

Lattice distortion and electronic structure of magnesium-doped nickel oxide epitaxial thin films

“…It is difficult to visualize the transformation of the lattice structures of these films with increasing Mg content. The calculated atomic order parameter of Mg 0.52 Ni 0.48 O (0.61) is smaller than that of Li 0.5 Ni 0.5 O (0.66) [28], which demonstrates the increased effect of the Mg 2+ ions when compared with that of the Li + on the atomic-scale disorder. This may imply that the preferred occupation of some of the cationic sites when the Mg content is high enough is sufficient to form an ordered solid solution similar to that of Li x Ni 1−x O with x > 0.…”

“…The above discussion shows that the doped Mg plays an important role in the lattice distortion of the Mg x Ni 1−x O films. To describe the resulting atomic disorder quantitatively, we attempted to evaluate the Debye temperature ( M ) and the Debye-Waller factor (D w i ) of these Mg x Ni 1−x O films from the x-ray diffraction intensities of the 111 Bragg points [28]. The relationship between M and D w i has been described as [29]…”

“…(7) from Ref. [28] and the average integrated intensity of the 111 and 222 Bragg peaks [28], which is suitable for the [28]. The results are listed in Table I.…”

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“…The phase transition from the solid-solution (-phase) to hydride (-phase) of Pd was reported using pressure -composition-temperature (PCT) measurement even in NPs in the diameter range of 2 to 3 nm. Kobayashi et al reported that absorbed hydrogen atoms are strongly trapped and stabilized in the lattice of Pd NPs, compared to bulk Pd, resulting the incomplete recovery in the reversing absorption and desorption process of the PCT measurement [1]. Hydrogen-absorption properties of metal NPs are strongly correlated with the atomic scale structure and the electronic states.…”

“…PbTiO3 perovskite was carried out in the wide temperature range 298-928 K[1]. A transition from a tetragonal (P4mm) to a cubic (Pm3__ _ m) phase has been revealed near 753 K. In the acentric P4mm symmetry group, the difference in relative displacement between Pb and O along the c-axis is much larger than that between Ti and O.…”