ABSTRACT
A novel layered Na3V(PO4)2 compound was synthesized and studied as a positive electrode material for Na-ion batteries for the first time. The as-prepared material exhibits two relatively high voltage plateaus at around 3.6 and 4.0 V vs Na+/Na. Operando X-ray diffraction investigation provides insight into the mechanisms of structural transformations upon cycling.
ABSTRACT
The PbO-NiO-SeO2 ternary system was fully studied using constant hydrothermal conditions at 473 K. It yields the establishment of the corresponding phase diagram using a systematic assignment of reaction products by both powder and single-crystal X-ray diffraction. It leads to the preparation of three novel lead nickel selenites, α-PbNi(SeO3)2 (I), ß-PbNi(SeO3)2 (II), and PbNi2(SeO2OH)2(SeO3)2 (III), and one novel lead cobalt selenite, α-PbCo(SeO3)2 (IV), which have been structurally characterized. The crystal structures of the α-forms I, IV, and III are based on a 3D complex nickel selenite frameworks, whereas the ß-PbNi(SeO3)2 modification (II) consists of nickel selenite sheets stacked in a noncentrosymmetric structure, second-harmonic generation active. The pH value of the starting solution was shown to play an essential role in the reactive processes. Magnetic measurements of I, III, and IV are discussed.
Subject(s)
Hot Temperature , Lead/chemistry , Nickel/chemistry , Selenious Acid/chemistry , Hydrogen-Ion ConcentrationABSTRACT
A new layered titanoniobate, Li3Ti5NbO14, a member of the AxM2nO4n+2 family, has been synthesized using a molten salt reaction between H3Ti5NbO14 and an eutectic mixture of LiOH and LiNO3. This compound crystallizes in the P21/m space group with a = 9.273(15) Å, b = 3.788(6) Å, c = 8.871(3) Å, and ß = 114.33(1)°, as determined by 3D electron diffraction single crystal analysis. It exhibits [Ti5NbO14]3- layers similar to K3Ti5NbO14, but differs from the latter by a 'parallel configuration' of its [Ti5NbO5]3- ribbons between the two successive layers. The topotactic character of the reaction suggests that exfoliation plays a prominent role in the synthesis of this new form. This new phase intercalates reversibly 2 lithium through a first-order transformation leading to a capacity of 100 mA h g-1 at a potential of 1.67 V vs. Li/Li+.
ABSTRACT
Single crystals of a new lead cobalt phosphite, PbCo2(HPO3)3, have been synthesized using mild hydrothermal techniques and characterized by X-ray diffraction analysis, SQUID magnetic measurements, IR spectroscopy, UV/vis spectroscopy, thermogravimetric analysis, and scanning electron microscopy. PbCo2(HPO3)3 crystallizes in the non-centrosymmetric (NCS) R3m space group, a = 5.3145(15) Å, c = 25.494(7) Å, V = 623.6(4) Å3. The crystal structure of PbCo2(HPO3)3 is based upon 2D heteropolyhedral blocks built up from Co2O9 octahedral dimers and HPO3 pseudo-tetrahedra. Lead cations reside in the interlayer space of the structure. Here, the NCS character results reasonably from the cooperative Pb2+ lone electron pair arrangements, by analogy to the centrosymmetric compound (NH4)2Co2(HPO3)3 with similar but disordered blocks. A local twisting of specific HPO3 groups arises due to unreasonably short HH contacts between two phosphite oxoanions. In terms of the magnetic behavior, the new PbCo2(HPO3)3 phase demonstrates weak antiferromagnetic interactions inside the Co2O9 dimers between cobalt ions as expected from the phosphite µ-O bridges.
ABSTRACT
Chemical vapor transport (CVT) reactions were used to prepare three modular mixed-valent Cu(I)-Cu(II) compounds, (Pb2Cu(2+)9O4)(SeO3)4(Cu(+)Cl(2))Cl5 (1), (PbCu(2+)5O2)(SeO3)2(Cu(+)Cl2)Cl3 (2), and (Pb(x)Cu(2+)(6-x)O2)(SeO3)2(Cu(+)Cl2)K(1-x)Cl(4-x) (x = 0.20) (3). In their crystal structures chains of anion-centered (OCu(2+)4) and (OCu(2+)3Pb) tetrahedra form honeycomb-like double layers with cavities occupied by linear [Cu(+)Cl2](-) groups.