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Abstract: Topochemical reduction of the cation-disordered perovskite oxides LaCo0.5Rh0.5O3 and LaNi0.5Rh0.5O3 with Zr yields the partially anion-vacancy ordered phases LaCo0.5Rh0.5O2.25 and LaNi0.5Rh0.5O2.25, respectively. Neutron diffraction and Hard X-ray photoelectron spectroscopy (HAXPES) measurements reveal that the anion-deficient phases contain Co1+/Ni1+ and a 1:1 mixture of Rh1+ and Rh3+ cations within a disordered array of apex-linked MO4 square-planar and MO5 square-based pyramidal coordination sites. Neutron diffraction data indicate that LaCo0.5Rh0.5O2.25 adopts a complex antiferromagnetic ground state, which is the sum of a C-type ordering (mM5 +) of the xy-components of the Co spins and a G-type ordering (mΓ1 +) of the z-components of the Co spins. On warming above 75 K, the magnitude of the mΓ1 + component declines, attaining a zero value by 125 K, with the magnitude of the mM5 + component remaining unchanged up to 175 K. This magnetic behavior is rationalized on the basis of the differing d-orbital fillings of the Co1+ cations in MO4 square-planar and MO5 square-based pyramidal coordination sites. LaNi0.5Rh0.5O2.25 shows no sign of long-range magnetic order at 2 K − behavior that can also be explained on the basis of the d-orbital occupation of the Ni1+ centers.

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Abstract: LaSrNiIrO6 adopts a B-site cation-ordered double perovskite structure with a strong a–a–c + cooperative tilting distortion (space group P21/n a = 5.5931(1) Å, b = 5.5676(1) Å, c = 7.8850(1) Å, β = 90.01(1) o). Magnetization and neutron diffraction data indicate LaSrNiIrO6 adopts a ‘type II’ antiferromagnetic structure (TN = 70 K) in which the Ni spins are arranged in an antiferromagnetic manner with their next-nearest-neighbors, with no ordered moment observed for Ir. DFT calculations, including spin-orbit coupling effects, confirm S = 1 Ni2+ and Jeff = 0 Ir5+ local configurations and indicate strong Ni() (Kobayashi et al., 1999) [1]–O(2p)–Ir()0–O(2p)–Ni() (Kobayashi et al., 1999) [1] σ-type super-super-exchange is the dominant magnetic coupling interaction in the system.

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Abstract: Double perovskite cobaltites with the general formula BaLnLn’Co2O6-δ, (where Ln, Ln’ = La, Nd, Pr, Sm, Gd, Dy, Tb) are a widely studied group of material, that results from their application potential1,2. Materials from this group exhibit high mixed electron-ion conductivity3. Some selected compositions are also reported with a minor partial on proton conductivity3, which opens the possibility of using these compounds as cathode materials in proton ceramic fuel cells (PCFC)4. Proton conductivity is possible if the material can incorporate water into its structure. Properties of BaLnLn’Co2O6-δ may be tailored due to the transitional nature of cobalt. It may exhibit different oxidation and spin states, which affects the oxygen stoichiometry and electronic structure of the material. This, on the one hand, may be very beneficial, but on the other is very challenging because to fully understand the properties of the materials from this group a full description of oxidation and spin state is necessary. Especially, the investigation of the spin state is difficult and requires the use of sophisticated research techniques, like synchrotron studies. The structure of BaLnLn’Co2O6-δ was studied by the means of combined synchrotron radiation X-ray diffraction, and neutron powder diffraction, iodometric titration was used to determine the cobalt oxidation state at room temperature, while soft X-ray absorption spectroscopy was used to investigate the spin state of cobalt spectroscopy (measurement performed at the O K-edge and Co L23-edges at the temperature range from 80 K – RT). The methods used allowed to determine the relations between cobalt oxidation and spin state and ionic radius of lanthanide, as well as temperature.

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Abstract: We report the structures of three new materials in the MDABCO-based perovskite family. Analysis of the Goldschmidt tolerance factor and octahedral factor enable us to propose compositional limits for pseudo-cubic perovskite phase formation and suggest directions for further materials discovery in this family of new ferroelectrics.

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Abstract: Methylammonium (MA+) lead halide perovskites (MAPbX3) have been widely investigated for photovoltaic applications, with the addition of Cs improving structural and thermal stability. This study reports the complete A site miscibility of Cs+ and MA+ cations in the lead chloride and lead bromide perovskites with nominal stoichiometric formulae (CsxMA1−x)Pb(Cl/Br)3 (x = 0, 0.13, 0.25, 0.37, 0.50, 0.63, 0.75, 0.87, 1). These suites of materials were synthesized mechanochemically as a simple, cost-effective synthesis technique to produce highly ordered, single phase particles. In contrast to previous studies using conventional synthetic routes that have reported significant solubility gaps, this solvent-free approach induces complete miscibility within the dual cation Cs+/MA+ system, with the resultant structures exhibiting high short-range and long-range atomic ordering across the entire compositional range that are devoid of solvent inclusions and disorder. The subtle structural evolution from cubic to orthorhombic symmetry reflecting PbX6 octahedral tilting was studied using complementary high resolution TEM, powder XRD, multinuclear 133Cs/207Pb/1H MAS NMR, DSC, XPS and UV/vis approaches. The phase purity and exceptional structural order were reflected in the very high resolution HRTEM images presented from particles with crystallite sizes in the ∼80–170 nm range, and the stability and long lifetimes of the Br series (10–20 min) and the Cl series (∼30 s–1 min) under the 200 kV/146 μA e− beam. Rietveld refinements associated with the room temperature PXRD study demonstrated that each system converged towards single phase compositions that were very close to the intended target stoichiometries, thus indicating the complete miscibility within these dual cation Cs+/MA+ solid solution systems. The multinuclear MAS NMR data showed a distinct sensitivity to the changing solid solution compositions across the MAPbX3–CsPbX3 partition. In particular, the 133Cs shifts demonstrated a sensitivity to the cubic–orthorhombic phase transition while the 133Cs T1s exhibited a pronounced sensitivity to the variable Cs+ cation mobility across the compositional range. Variable temperature PXRD studies facilitated the production of phase diagrams mapping the Cs+/MA+ compositional space for the (CsxMA1−x)PbCl3 and (CsxMA1−x)PbBr3 solid solution series, while Tauc plots of the UV/vis data exhibited reducing bandgaps with increasing MA+ incorporation through ranges of cubic phases where octahedral tilting was absent.