The nickelate Pr 4 Ni 3 O 8 features quasi-two-dimensional layers consisting of three stacked square-planar NiO 2 planes, in a similar way to the well-known cuprate superconductors. The mixed-valent nature of Ni and its metallic properties makes it a candidate for potentially unconventional superconductivity. We have synthesized Pr 4 Ni 3 O 8 by topotactic reduction of Pr 4 Ni 3 O 10 in 10% hydrogen gas, and report on measurements of powder-neutron diffraction, magnetization, and muon-spin rotation (µSR). We find that Pr 4 Ni 3 O 8 shows complicated spin-glass behavior with a distinct magnetic memory effect in the temperature range from 2 to 300 K and a freezing temperature T s ≈ 68 K. Moreover, the analysis of µSR spectra indicates two magnetic processes characterized by remarkably different relaxation rates: a slowly relaxing signal, resulting from paramagnetic fluctuations of Pr/Ni ions, and a fast-relaxing signal, whose relaxation rate increases substantially below ≈ 70 K which can be ascribed to the presence of short-range correlated regions. We conclude that the complex spin-freezing process in Pr 4 Ni 3 O 8 is governed by these multiple magnetic interactions. It is possible that the complex magnetism in Pr 4 Ni 3 O 8 is detrimental to the occurrence of superconductivity.
As a member of the Ruddlesden-Popper Ln n+1 Ni n O 3n+1 series rare-earth-nickelates, the Pr 4 Ni 3 O 10 consists of infinite quasi-two-dimensional perovskite-like Ni-O based layers. Although a metal-to-metal phase transition at ≈ 157 K has been revealed by previous studies, a comprehensive study of physical properties associated with this transition has not yet been performed. We have grown single crystals of Pr 4 Ni 3 O 10 at high oxygen pressure, and report on the physical properties around that phase transition, such as heat-capacity, electric-transport and magnetization. We observe a distinctly anisotropic behavior between in-plane and out-of-plane properties: a metal-to-metal transition at within the a-b plane, and a metal-to-insulator-like transition along the c-axis with decreasing temperature. Moreover, an anisotropic and anomalous negative magneto-resistance is observed at that we attribute to a slight suppression of the first-order transition with magnetic field. The magnetic-susceptibility can be well described by a Curie-Weiss law, with different Curie-constants and Pauli-spin susceptibilities between the high-temperature and the low-temperature phases. The single crystal X-ray diffraction measurements show a shape variation of the different NiO 6 octahedra from the high-temperature phase to the low-temperature phase. This subtle change of the environment of the Ni sites is likely responsible for the different physical properties at high and low temperatures.
A new member of the cycloparaphenylene double-nanohoop family was synthesized. Its π-framework features two oval cavities that display different shapes depending on the crystallization conditions. Incorporation of the peropyrene bridge within the nanoring cycles via bay -regions alleviates steric effects and thus allows 1:1 complexation with C 60 in the solid state. This nanocarbon adopts a lamellar packing motif, and our results suggest that the structural adjustment of this double nanohoop could enable its use in supramolecular and semiconductive materials.
The desirable development of infrared nonlinear optical (IR NLO) materials is to design new compounds which exhibit wide band gaps and strong second harmonic generation (SHG) responses. Herein, we report three new sulfides, BaGaSnS (1), BaSnS (2) and BaSnS (3), with wide band gaps of 2.90, 2.98 and 3.0 eV, respectively, which have been successfully synthesized for the first time. Significantly, compound 1 exhibited a large SHG coefficient (34 × KDP), illustrating a good balance between the band gap and the SHG response. Single crystal X-ray diffraction determined that compound 1 crystallizes in the non-centrosymmetric space group P4[combining macron]2c and it was characterized as an interesting kite-shaped linkage motif of [GaSnS]. Compounds 2 and 3 crystallize in the space groups of P2c and Pnma, respectively. In addition, compounds 2 and 3 were characterized as zero-dimensional (0D) structures comprising isolated SnS tetrahedra with Ba cations and S anions located between them. However, compound 2 contains extra disulfide S anions in its isolated structure. Moreover, the theoretical calculations demonstrated that SHG responses for compound 1 could be ascribed to the transitions from S-3p and Ga-4p states to Ba-5d, Ga-4p and Sn-5p states. By analysing the relationship between the structures and properties for PbGaGeS-type compounds, it was concluded that site disorder could be an effective way to improve optical properties.
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