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LaxSr2–xNiRuO6, LaxSr4–xNiRuO8, and LaxSr3–xNiRuO7are, respectively, then= ∞, 1, and 2 members of the (Lax/2Sr1–(x/2))nSr(Ni0.5Ru0.5)nO3n+1compositional series. Reaction with CaH2, in the case of the LaxSr2–xNiRuO6perovskite phases, or Zr oxygen getters in the case of the LaxSr4–xNiRuO8and LaxSr3–xNiRuO7Ruddlesden–Popper phases, yields the corresponding topochemically reduced (Lax/2Sr1–(x/2))nSr(Ni0.5Ru0.5)nO3n–1compounds (LaxSr2–xNiRuO4, LaxSr4–xNiRuO6, and LaxSr3–xNiRuO5), which contain Ni and Ru cations in square-planar coordination sites. Thex= 1 members of each series (LaSrNiRuO4, LaSr3NiRuO6, and LaSr2NiRuO5) exhibit insulating ferromagnetic behavior at low temperature, attributable to exchange couplings between the Ni1+and Ru2+centers they contain. Increasing the La3+concentration (x> 1) leads to a reduction of some of the Ru2+centers to Ru1+centers and a suppression of the ferromagnetic state (lowerTc, reduced saturated ferromagnet moment). In contrast, increasing the Sr2+concentration (x< 1) oxidizes some of the Ru2+centers to Ru3+centers and enhances the ferromagnetic coupling (increasedTc, increased saturated ferromagnet moment) for then= ∞ andn= 2 samples but appears to have no influence on the magnetic ordering temperature of then= 1 samples. The magnetic couplings and influence of doping are discussed on the basis of superexchange and direct exchange couplings between the square-planar Ni and Ru centers.

Topochemical reduction of the cation-disordered perovskite oxides LaCo

Topochemical reduction of the n = 1 Ruddlesden-Popper phases LaSrCo0.5Rh0.5O4 and LaSrNi0.5Rh0.5O4 with Zr yields LaSrCo0.5Rh0.5O3.25 and LaSrNi0.5Rh0.5O3.25, respectively. Magnetization and XPS data reveal that while the rhodium centers in LaSrCo0.5Rh0.5O3.25 and LaSrNi0.5Rh0.5O3.25 have an average oxidation state of Rh2+, these are actually mixed valence Rh(I,III) compounds, with the disproportionation of Rh2+ driven by the favorability of locating d8 Rh1+ and d6 Rh3+ cations within square-planar and square-based pyramidal coordination sites, respectively.

Topochemical reduction of the