Hybrid halide perovskites represent one of the most promising solutions toward the fabrication of all solid nanostructured solar cells, with improved efficiency and long-term stability. This article aims at investigating the structural properties of iodide/chloride mixed-halide perovskites and correlating them with their photovoltaic performances. We found out that, independent of the components ratio in the precursor solution, Cl incorporation in an iodide-based structure, is possible only at relatively low concentration levels (below 3–4%). However, even if the material band gap remains substantially unchanged, the Cl doping dramatically improves the charge transport within the perovskite layer, explaining the outstanding performances of meso-superstructured solar cells based on this material.

Hybrid halide perovskites represent one of the most promising solutions toward the fabrication of all solid nanostructured solar cells with improved efficiency and long-term stability. This article aims at investigating the structural properties of the iodide/chloride mixed-halide perovskites and correlating them with the photovoltaic performances of the related sensitized solar cells. We found out that, independently on the components ratio in the precursor solution, Cl incorporation, in a I-based structure, is possible only at relatively low concentration levels (below 3-4%). However, even if the material band-gap remains substantially unchanged, incorporation of Cl as a dopant dramatically improves the charge transport within the perovskite layer, explaining the outstanding performances of meso-superstructured solar cells based on this material.

By establishing magnetic order in a square lattice compound, we introduce the first magnetic “new fermion.”

Double corundum-related polar magnets are promising materials for multiferroic and magnetoelectric applications in spintronics. However, their design and synthesis is a challenge, and magnetoelectric coupling has only been observed in Ni3TeO6 among the known double corundum compounds to date. Here we address the high-pressure synthesis of a new polar and antiferromagnetic corundum derivative Mn2MnWO6, which adopts the Ni3TeO6-type structure with low temperature first-order field-induced metamagnetic phase transitions (T N = 58 K) and high spontaneous polarization (~ 63.3 μC·cm−2). The magnetostriction-polarization coupling in Mn2MnWO6 is evidenced by second harmonic generation effect, and corroborated by magnetic-field-dependent pyroresponse behavior, which together with the magnetic-field-dependent polarization and dielectric measurements, qualitatively indicate magnetoelectric coupling. Piezoresponse force microscopy imaging and spectroscopy studies on Mn2MnWO6 show switchable polarization, which motivates further exploration on magnetoelectric effect in single crystal/thin film specimens.

Cation ordering in ABO3 perovskites can lead to interesting and useful phenomena such as ferrimagnetism and high magnetoresistance by spin polarized conduction in Sr2FeMoO6. We have used high pressures and temperatures to synthesize the cation ordered AA′BB′O6 perovskites CaMnFeReO6, CaMnMnReO6, and Ca(Mn0.5Cu0.5)FeReO6. These have columnar A/A′ and rocksalt B/B′ cation orders, as found in the recently discovered double double perovskite MnNdMnSbO6, and partial Mn/Cu order over tetrahedral and square planar A′ sites in Ca(Mn0.5Cu0.5)FeReO6 demonstrates that 'triple double' cation order is possible. Neutron diffraction reveals complex ferrimagnetic orders in all three materials; CaMnFeReO6 and Ca(Mn0.5Cu0.5)FeReO6 have large room temperature magnetizations with low temperature switching of magnetoresistance in the latter material, and CaMnMnReO6 displays a high coercivity of 1.3 T at low temperatures.

We report an experimental study of the magnetic order and electronic structure and transport of the layered pnictide EuMnSb2, performed using neutron diffraction, angle-resolved photoemission spectroscopy (ARPES), and magnetotransport measurements. We find that the Eu and Mn sublattices display antiferromagnetic (AFM) order below T Eu N = 21(1) K and T Mn N = 350(2) K respectively. The former can be described by an A-type AFM structure with the Eu spins aligned along the c axis (an in-plane direction), whereas the latter has a C-type AFM structure with Mn moments along the a-axis (perpendicular to the layers). The ARPES spectra reveal Dirac-like linearly dispersing bands near the Fermi energy. Furthermore, our magnetotransport measurements show strongly anisotropic magnetoresistance, and indicate that the Eu sublattice is intimately coupled to conduction electron states near the Dirac point. 75.30.Gw, 74.70.Xa Topological semimetals can host quasiparticle excitations which masquerade as massless fermions due to the linearly-dispersing electronic bands created by interactions with the crystal lattice. The Dirac or Weyl nodes, where the conduction and valence bands meet in momentum space, are robust against small perturbations due to the protection afforded by crystalline symmetries or the topology of the electronic bands 1-5 . Topological semimetals exhibit exceptional electronic transport properties (e.g. extremely high carrier mobility and large linear magnetoresistance) and the control of these exotic charge carriers could help realize a new generation of spintronic devices with low power consumption 6-8 .Such control can potentially be realized in materials in which magnetic order coexists with non-trivial electronic band topology. Recent ARPES, quantum oscillation, neutron diffraction and ab initio band structure studies suggest that materials in the AMnSb 2 (A = Ca, Sr, Ba, Eu, Yb) family display many of the required properties 9-18 . The two-dimensional zig-zag layer of Sb atoms [ Fig. 1] in these 112-pnictides play host to fermions which can be described by the relativistic Dirac or Weyl equations. Furthermore, the electronic transport in this family of materials also displays large magnetoresistive effects, suggesting a coupling between the magnetism and charge carriers 9-17 . These effects could be driven by changes in the electronic band structure topology due to changes in the symmetry of the spin structures induced by the applied field 19 .Within the AMnSb 2 family, EuMnSb 2 is of particular interest because the conducting zig-zag layer of Sb atoms is sandwiched between two interpenetrating magnetic sublattices (Eu and Mn), as shown in Fig. 1(a). Such a structure may lead to an enhancement of the coupling between the topological quasiparticles and mag-netism, compared to that in compounds with a nonmagnetic atom on the A site. The dramatic magnetoresistive behaviour observed in a recent work 20 is evidence for the importance of this coupling. Up to now, however, the nature of the magnetic order in...

Octahedral distortion in ABO3 perovskite materials is ubiquitous because of the ionic size mismatch between A and B cations, leading to various kinds of crystal symmetry. However, such a distortion always results in centrosymmetric structures except for the covalent bond formation because of the second-order Jahn–Teller (SOJT) effect that occurs with d0 or lone-pair cations. Here, we report that an unusual combination of the layered A-site cation ordering and B-site rock salt ordering in NaYNiWO6 prepared under high-pressure and high-temperature conditions results not only in a polar (P21) structure, as revealed by the neutron diffraction analysis, but exhibits multiferroic properties below the magnetic ordering of Ni2+ ions (T N = 21 K). Analysis of the neutron diffraction data at 20 K reveals an incommensurate sinusoidal spin ordering with the propagation vector, k i = (0.471(2), 0, 0.491(4)), and a commensurate collinear spin structure with k c = (0.5, 0, 0.5) below 18 K. X-ray diffraction data confirm the polar structure in Dy, Ho, and Yb compounds. All four compounds exhibit a switchable change in electric polarization (ΔP) at the magnetic ordering temperatures, demonstrating coupling between ferroelectricity and magnetism.

Understanding structural responses of metal-organic frameworks (MOFs) to external stimuli such as the inclusion of guest molecules, temperature/pressure has gained increasing attention in many applications, for example, manipulation and manifesto smart materials for gas storage, energy storage, controlled drug delivery, tunable mechanical properties, and molecular sensing, to name but a few. Herein, neutron and synchrotron diffractions along with Rietveld refinement and density functional theory calculations have been used to elucidate the responsive adsorption behaviors of defect-rich Zr-based MOFs upon the progressive incorporation of ammonia (NH3) and variable temperature. UiO-67 and UiO-bpydc containing biphenyl dicarboxylate and bipyridine dicarboxylate linkers, respectively, were selected and the results establish the paramount influence of the functional linkers on their NH3 affinity, which leads to stimulus-tailoring properties such as gate-controlled porosity by dynamic linker flipping, disorder, and structural rigidity. Despite their structural similarities, we show for the first time the dramatic alteration of NH3 adsorption profiles when the phenyl groups are replaced by the bipyridine in the organic linker. These molecular controls stem from controlling the degree of H-bonding networks/distortions between the bipyridine scaffold and the adsorbed NH3 without significant change in pore volume and unit cell parameters. Temperature-dependent neutron diffraction also reveals the NH3-induced rotational motions of the organic linkers. We also demonstrate that the degree of structural flexibility of the functional linkers can critically be affected by the type and quantity of the small guest molecules. This strikes the delicate control in material properties at the molecular level.