Effect of the synthesis conditions on the magnetic and electrical properties of the BaFeO3−x oxide: A metamagnetic behavior

Enhanced Photoluminescence and Reduced Dimensionality via Vacancy Ordering in a 10H Halide Perovskite

Vacancy-ordered halide perovskites have received great interest in optoelectronic applications. In this work, we report the novel inorganic halide Cs₁₀MnSb₆Cl₃₀ with a distinctive 10H (10-layer hexagonal) perovskite polytype structure with (hcccc)₂ stacking. Cs₁₀MnSb₆Cl₃₀ has 30% B-site vacancies ordered at both corner- and face-sharing sites, resulting in [MnSb₆Cl₃₀]^10-_n columns, i.e., a reduction of octahedral connectivity to 1D. This results in enhanced photoluminescence in comparison to the previously reported 25% vacancy-ordered 3C polytype Cs₄MnSb₂Cl₁₂ with 2D connectivity. This demonstrates not only the existence of the 10H perovskite structure in halides but also demonstrates the degree of B-site deficiency and stacking sequence variation as a direction to tune the optical properties of perovskite polytypes via vacancy rearrangements.

Layered Hexagonal Perovskite Oxides 21R Ba7Fe5Ge2O20 and 12H Ba6Fe3Ge3O17

Two hexagonal-perovskite-structure oxides, 21R Ba₇Fe₅Ge₂O₂₀ and 12H Ba₆Fe₃Ge₃O₁₇, were obtained by synthesis with a high-pressure and high-temperature technique. The Fe-containing hexagonal-perovskite-structure units are sandwiched by nonmagnetic GeO₄ tetrahedral layers in the structures, and thus both compounds show two-dimensional ferrimagnetic behaviors due to intra- and interunit magnetic interactions. 21R Ba₇Fe₅Ge₂O₂₀ has the ionic formula Ba₇Fe1₂³⁺Fe2⁴⁺Fe3₂⁴⁺Ge4₂⁴⁺O₂₀ at room temperature, and unusually high valence Fe⁴⁺ in the trimers undergoes charge disproportionation, Fe2⁴⁺ + 2Fe3⁴⁺ → Fe2^(4+2δ)+ + 2Fe3^(4-δ)+, at low temperatures. In contrast, 12H Ba₆Fe₃Ge₃O₁₇ with ionic formula Ba₆Fe1₂³⁺(Fe2_0.5⁴⁺Ge2_0.5⁴⁺)₂Ge3₂⁴⁺O₁₇ does not show a charge transition.

Hexagonal Perovskite Ba4Fe3NiO12 Containing Tetravalent Fe and Ni Ions

BaFe _xNi_{1- x}O₃ with end members of BaNiO₃ ( x = 0) and BaFeO₃ ( x = 1), which, respectively, adopt the 2H and 6H hexagonal perovskite structures, were synthesized, and their crystal structures were investigated. A new single phase, Ba₄Fe₃NiO₁₂ ( x = 0.75), that adopts the 12R perovskite structure with the space group R3̅ m ( a = 5.66564(7) Å and c = 27.8416(3) Å), was found to be stabilized. Mössbauer spectroscopy results and structure analysis using synchrotron and neutron powder diffraction data revealed that nominal Fe³⁺ occupies the corner-sharing octahedral site while the unusually high valence Fe⁴⁺ and Ni⁴⁺ occupy the face-sharing octahedral sites in the trimers, giving a charge formula of Ba₄Fe³⁺Fe⁴⁺₂Ni⁴⁺O_11.5. The magnetic properties of the compound are also discussed.

Synthesis, DFT calculations of structure, vibrational and thermal decomposition studies of the metal complex Pb[Mn(C3H2O4)2(H2O)2]

The metallo-organic complex Pb[Mn(C3H2O4)2(H2O)2] was synthesized and characterized by IR and Raman spectroscopy and powder X-ray diffraction methods. The cell parameters for the complex were determined from powder X-ray diffraction using the autoindexing program TREOR, and refined by the Le Bail method with the Fullprof program. A hexagonal unit cell was determined with a=b=13.8366(7)Å, c=9.1454(1)Å, γ=120°. The DFT calculated geometry of the complex anion [Mn(C3H2O4)2(H2O)2](2-) is very close to the experimental data reported for similar systems. The IR and Raman spectra and the thermal analysis of the complex indicate that only one type of water molecules is present in the structure. The thermal decomposition of Pb[Mn(C3H2O4)2(H2O)2] at 700 °C in air produces PbO and Pb2MnO4 as final products. The crystal structure of the mixed oxide is very similar to that reported for Pb3O4.

Complex cation order in anion-deficient Ba(n)YFe(n-1)O(2.5n) perovskite phases

The synthesis and structural characterization of BanYFen-1O2.5n (n = 2, 3, 4) anion-deficient perovskite phases is reported. The n = 2 and n = 3 members of the series, Ba2YFeO5 and Ba3YFe2O7.5, adopt structures which consist of ordered arrays of corner-linked YO6 octahedra and FeO4 tetrahedra on the perovskite B-sites and are described in unit cells related to a simple cubic perovskite cell by respective 2√2 × √2 × 2 and 3√2 × √2 × 2 geometric expansions. The complex cation ordering schemes observed in the two phases can be described on the basis of Y2Fe2O10□2 secondary building units. A rationalization for the observed structures is presented on the basis of the need to minimize lattice strain while maintaining the integrity of the local YO6 and FeO4 coordination polyhedra. The n = 4 member of the series, Ba4YFe3O10, adopts a cation and anion-vacancy disordered structure, which is attributed to dilution of the structure directing effects at extreme Y:Fe stoichiometric ratios. Magnetization data indicate Ba2YFeO5 and Ba3YFe2O7.5 exhibit paramagnetic behavior, consistent with the lack of a long-range Fe-O-Fe network. Ba4YFe3O10 adopts an antiferromagnetic state below 50 K.