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The search for novel lead-free materials with potential optoelectronic applications is a main research topic nowadays for an environment-friendly energy transition. Based on promising all-inorganic CsPbBr3 perovskite, we tested here the substitution of toxic Pb2+ with Cu2+ and explored the understudied CsCuBr3 halide. We present a mechanically-synthesized CsCuBr3 specimen obtained by ball milling, consisting of a well-crystallized and pure sample. Calorimetric measurements revealed a thermal event suggesting a structural phase transition around 422 K, immediately below the decomposition of the sample due to Br loss. A detailed structural analysis was carried out using neutron powder diffraction data from 20 to 420 K, focusing on the evolution of the orthorhombic phase (space-group: C2221) up to 400 K; this crystal arrangement consists of dimer units of face-sharing [CuBr6] octahedra containing Cu–Cu dimers with conspicuously short distances that account for the magnetic coupling between Cu2+ spins described before. Additionally, at 420 K, we identified a novel high-temperature phase as described in the hexagonal P6522 space group, where infinite chains of [CuBr4] square-planar units were observed. An additional study considering the Debye model was carried out, providing information on the relative Cs–Br and Cu–Br chemical bonds. From diffuse reflectance UV-Vis measurements, an optical gap of ∼1.8 eV was estimated for the orthorhombic phase at room temperature. Magnetic measurements indicate that the effective magnetization behavior versus temperature appears close to linear and seems to extrapolate to zero (smaller than 10−5 μB/Cu atom) at temperatures above 420 K, coinciding with onset of phase transition. [ABSTRACT FROM AUTHOR]

Hybrid organic–inorganic perovskites, MAPbX3 (MA: methylammonium, CH3–NH3+; X = halogen), are active absorption materials in the new generation of solar cells. The triiodide specimen (MAPbI3) remains the most widely studied perovskite due to its ability to absorb broadband light below its band gap of 1.6 eV, but its degradation in a humid atmosphere has remained a major obstacle for commercialization. Here we found that CH3NH3PbI3−xBrx (x = 0.0, 1.0) perovskites, prepared by ball milling, exhibit superior stability, showing no signs of degradation after several months of exposure to humid air. A synchrotron X-ray diffraction (SXRD) investigation was useful to determine some peculiar structural features that may account for the improved stability. The crystal structure was analysed to be in the I4/mcm and acentric I4cm space groups, yielding similar agreement factors. In both, the inorganic framework presents a conspicuously lower tilting effect than that observed in samples prepared by wet methods; an additional difference arises since the tetragonal structure is stable down to 140 K. The orientation of the organic MA units may play an important role in the properties, given the degrees of freedom for internal motion of MA groups within the PbX6 network. From the refined C/N positions, the MA+ units lie along the c axis with 25% probability. The structure at 140 K shows that the MA+ contribution along the c axis vanishes at this temperature. By contrast, MAPbI2Br crystallizes in the cubic phase with the space group Pm3¯m, also with a larger unit-cell volume than that previously described. The absence of phase transitions down to 120 K suggests that the anion disorder prevents the localization of MA units upon cooling. [ABSTRACT FROM AUTHOR]

A series of isostructural cobalt hydroxychloride salts with the formula Co2(OH)4- xCl x were fabricated by using a precipitation method from aqueous solutions of CoCl2 and NaOH with different mixing ratios. The crystal structure was resolved from neutron powder diffraction data, including the location of H atoms of the hydroxide groups. The structure (space group R 3 m) consists of an open network of edge-sharing CoO6 and CoO6-2 xCl2 x octahedra, forming intercrossed 1D channels where the hydrogen atoms reside. Unusually high values of the magnetic entropy change were observed for all samples, probably due to the geometrically frustrated magnetic structure; for example, the magnetic entropy change was 8.3 J/kg K for the sample with Co/Cl > 2.5 at 10 K in a magnetic field change of 20 kOe. [ABSTRACT FROM AUTHOR]

A series of isostructural cobalt hydroxychloride salts with the formula Co2(OH)4- xCl x were fabricated by using a precipitation method from aqueous solutions of CoCl2 and NaOH with different mixing ratios. The crystal structure was resolved from neutron powder diffraction data, including the location of H atoms of the hydroxide groups. The structure (space group R 3 m) consists of an open network of edge-sharing CoO6 and CoO6-2 xCl2 x octahedra, forming intercrossed 1D channels where the hydrogen atoms reside. Unusually high values of the magnetic entropy change were observed for all samples, probably due to the geometrically frustrated magnetic structure; for example, the magnetic entropy change was 8.3 J/kg K for the sample with Co/Cl > 2.5 at 10 K in a magnetic field change of 20 kOe. [ABSTRACT FROM AUTHOR]

Prussian blue analogs with an open framework are ideal cathodes for Na‐ion batteries. A superior high‐rate and highly stable monoclinic nickel hexacyanoferrate (NiHCF‐3) is synthesized via a facile one‐step crystallization‐controlled co‐precipitation method. It gives a high specific capacity of 85.7 mAh g−1, nearly to its theoretical value. It also exhibits an excellent rate capability with a high capacity retention ratio of 78% at 50 C and a stable cycling performance over 1200 cycles. Through the ex situ X‐ray diffraction and pair distribution function measurements, it is found that the monoclinic structure with distorted framework is greatly related to the high Na content. The electronic structure studies by density functional theory (DFT) calculation demonstrate that NiHCF‐3 deformation promotes the framework conductivity and improves the electrochemical activity of Fe, which results in an ultrahigh‐rate performance of monoclinic phase. Furthermore, the high‐quality monoclinic (NiHCF‐3) exhibits excellent compatibility with both hard carbon and NaTi2(PO4)3 anodes in full cells, which shows great prospects for the application in the large‐scale energy storage systems. A performance optimization induced by the structure distortion caused by Na content is described. The high‐Na‐content monoclinic nickel hexacyanoferrate exhibits a large specific capacity of 85.7 mAh g−1 at 0.1 C, a high rate capability of 66.2 mAh g−1 at 50 C, and a long cycling life of 1200 cycles without apparent decay. [ABSTRACT FROM AUTHOR]

A mixed oxide with the crystal structure of the DyMn 2 O 5 family, namely NdMn 1.5 Ru 0.5 O 5 , is reported active for the oxygen evolution reaction (OER) in acidic media. NdMn 1.5 Ru 0.5 O 5 displays high OER activity of 500 A g Ru −1 at 1.5 V. Moreover, is more stable than most Ru oxides reported to date, remaining active for more than 500 cycles between 1.1. and 1.7 V at low scan rate of 10 mV s−1. The high activity and stability are attributed to the Ru cations, as NdMn 2 O 5 exhibits very low OER activity. NdMn 1.5 Ru 0.5 O 5 has particularly short Ru–Ru distances of 2.60 Å, a value close to the Ru–Ru metallic distances around 2.642 Å. The high activity and durability of NdMn 1.5 Ru 0.5 O 5 for the OER are also demonstrated in a proton exchange membrane water electrolysis cell by producing a low-loaded anode electrode with 0.5 mg Ru cm−2. The cell achieves 1.97 V at 0.5 A cm−2, consistent with the performances reported for Ru-based catalysts but with lower Ru loading. This performance is maintained during 100 h of operation. Additionally, NdMn 1.5 Ru 0.5 O 5 displays visible ORR activity in acidic media, recording an onset potential of 0.85 V at 0.1 mA cm−2. It is noteworthy to highlight the extreme rarity of bifunctional ORR/OER catalysts acidic media. [Display omitted] • NdMn 1.5 Ru 0.5 O 5 exhibits OER activity in acidic media of 500 A g Ru −1@1.5 V. • Stable PEMWE with NdMn 1.5 Ru 0.5 O 5 anode (0.5 mg Ru cm−2) achieved 1.97 V@0.5 A cm−2 • NdMn 1.5 Ru 0.5 O 5 shows bifunctional OER/ORR activity, with a BI of 0.88 V. [ABSTRACT FROM AUTHOR]

Na 0.5 Bi 0.5 TiO 3 (NBT) and its acceptor-doped perovskites, as lead-free piezoelectric materials before, have been found to be excellent oxygen-ion conductors with potential applications in intermediate-temperature solid oxide fuel cells (SOFCs). Among them, the Bi deficient and B-site Mg doped sodium bismuth titanate (Na 0.5 Bi 0.49 Ti 0.98 Mg 0.02 O 2.965 , NBTM) exhibits a remarkable oxygen ionic conductivity. Here, we report a structural analysis on NBT and NBTM ceramics using high-temperature in situ neutron diffraction (NPD) to gain insight into the effects of Mg doping on ionic conductivity and structure. Both perovskite oxides exhibit two consecutive phase transformations from R 3 c to P 4 bm at ∼400 °C and from P 4 bm to Pm 3 ¯ m at ∼600 °C. The effects of Bi deficiency and Mg substitution on oxygen vacancy concentration and ion displacements are revealed. In addition, a NBTM supported single cell consisting of Ag-NBTM cathode and Ni-NBTM anode is fabricated to evaluate the possibility of its application in intermediate-temperature SOFCs. The structural stability of NBTM is still a major concern that hinders its utilization at high temperature and under reducing atmosphere. [ABSTRACT FROM AUTHOR]

LaNiO 3 perovskite is a promising electrocatalyst for the oxygen reduction reaction (ORR). In this work we study the effects of several key structural and morphological features on the performance of LaNiO 3 perovskites for the ORR. We have prepared a series of LaNiO 3 oxides via soft chemistry and calcined the final materials at different temperatures from 500 to 1000 °C. With the aim of obtaining morphological and structural information relevant to their performance the prepared oxides have been thoroughly characterized by BET, Power Neutron Diffraction (PND), XRD, HRTEM, STEM-HAADF and XPS. We have analysed the effect of extrinsic (surface area and particle size) and intrinsic factors (formation of oxygen vacancies, Ni oxidation states and occupancy of the e g levels) on the current densities and specific activity, respectively, of several samples of LaNiO 3 . The catalysts with higher catalytic activity are those in which the perovskite structure is properly formed, but display high surface areas. [ABSTRACT FROM AUTHOR]

R2NiMnO6 (R = Tb, Ho, Er, Tm) perovskites have been prepared by soft-chemistry techniques followed by high oxygen-pressure treatments; they have been investigated by X-ray diffraction, neutron powder diffraction (NPD), and magnetic measurements. In all cases the crystal structure is defined in the monoclinic P21/n space group, with an almost complete order between Ni2+ and Mn4+ cations in the octahedral perovskite sublattice. The low temperature NPD data and the macroscopic magnetic measurements indicate that all the compounds are ferrimagnetic, with a net magnetic moment different from zero and a distinct alignment of Ni and Mn spins depending on the nature of the rare-earth cation. The magnetic structures are different from the one previously reported for La2NiMnO6, with a ferromagnetic structure involving Mn4+ and Ni2+ moments. This spin alignment can be rationalized taking into account the Goodenough-Kanamori rules. The magnetic ordering temperature (TCM) decreases abruptly as the size of the rare earth decreases, since TCM is mainly influenced by the superexchange interaction between Ni2+ and Mn4+ (Ni2+-O-Mn4+ angle) and this angle decreases with the rare-earth size. The rare-earth magnetic moments participate in the magnetic structures immediately below TCM. [ABSTRACT FROM AUTHOR]