Oxygen and strontium codoping ofLa2NiO4: Room-temperature phase diagrams

Abstract

We present a detailed room temperature x-ray powder diffraction study on La2−xSrxNiO 4+δ with 0 ≤ x ≤ 0.12 and 0 ≤ δ ≤ 0.13. For x = 0.02, 0.04 and 0.06 the oxygen content phase diagrams of the Sr-doped samples show a similar sequence of pure phases and miscibility gaps as for pure La2NiO 4+δ . We find a weak Sr doping dependence of the δ range for the pure LTO, LTT and HTT phases; but overall, the δ ranges of the different phases do not vary strongly for x ≤ 0.06. Drastic changes are observed for x = 0.08 and 0.12, where miscibility gaps successively disappear. For x = 0.12 all oxygen-doped samples are in the HTT phase. The mechanism responsible for the suppression of the phase separation seems to involves multiple factors, including the Coulomb interaction between Sr impurities and interstitial oxygens as well as the reduction of the NiO6 octahedral tilt angle. The doping dependence of the lattice parameters shows clear differences for pure Sr and pure O doping. With the exception of the LTO phase, the in-plane lattice parameters explicitly depend on the type of dopant, rather than the net hole content, p = x + 2δ. In contrast, the orthorhombic strain in the LTO phase as well as the c-axis length appears to depend only on p; however, in the case of the c-axis length this "universal" behavior turns out to be accidental. Our results also show that the chemical pressure of La-site dopants is highly anisotropic, whereas that of O interstitials appears to be more isotropic. In general, this study reveals that Sr-doped samples have to be annealed carefully to achieve δ = 0, and to permit the study of the intrinsic properties of La2−xSrxNiO4.

Charge order, dielectric response, and local structure of La5/3Sr1/3NiO4 system

“…Among the TMOs, the La 2-x Sr x NiO 4 , popularly called nickelates, construct good example of such systems with complex interplay between spin-charge-lattice degrees of freedom [5][6][7][8][9][10][11][12][13][14][15][16] . The nickelates have been studied intensively, however, a substantial amount of work is dedicated to the La 5/3 Sr 1/3 NiO 4 , merely due to the fact that the system appears with robust charge stripe ordering for this doping, making it a suitable system to address various functions of the TMO perovskites.…”

Nonstoichiometry and the Origin of Electrochemical Properties of Functional Oxides for Energy Conversion and Storage Technologies

“…[18][19][20][21][22] On the other hand, a tetragonal symmetry (I4/mmm) was suggested for La 2¹x Sr x NiO 4+¤ at higher temperatures. [20][21][22] The authors found that the diffraction patterns for all composition can be indexed by the tetragonal symmetry, I4/mmm, and no obvious advantages of orthorhombic symmetry as earlier work were suggested. 23,24 Therefore, the authors calculate the lattice parameters assuming the tetragonal symmetry by using the software TOPAS (Bruker AXS).…”

Direct evidence for the suppression of charge stripes in epitaxialLa1.67Sr0.33NiO4films

“…However, only a limited number of materials have shown appropriate diffraction peaks. The clearest cases are La 2−x Sr x NiO 4 [22] and the 1/8th doped cuprates [8,9]. Another possible candidate for stripe phases identified through diffraction is superoxygenated and phase separated La 2−x Sr x CuO 4+y [16].…”