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Six new AA′BB′O6 perovskites KLaMnWO6, NaLaMnWO6, NaNdMnWO6, NaTbMnWO6, NaNdCoWO6, and NaNdMgWO6 have been prepared. Each possesses the unusual combination of layered ordering of the A-site cations and rock-salt ordering of the B-site cations. The structure and properties of these samples have been characterized using monochromatic X-ray and neutron powder diffraction, UV–vis diffuse reflectance spectroscopy, and SQUID magnetometry. NaLaMnWO6, NaNdMnWO6, and NaTbMnWO6 adopt a structure with monoclinic P21 symmetry arising from the combination of cation ordering and a–a–c+ octahedral tilting. The structures of the other three compounds are similar, but the presence of satellite reflections in the neutron diffraction data suggests a more complicated superstructure. Each of the four AA′MnWO6 samples shows a paramagnetic to antiferromagnetic transition with Néel temperatures ranging from 6 to 15 K. The NaTbMnWO6 compound shows a second magnetic transition at ∼9 K. The origin of two magnetic phase transitions appears to arise from coupling between the Mn2+ sublattice and the Tb3+ sublattice.

Electron, neutron, and synchrotron X-ray diffraction together with transmission electron microscopy studies reveal the spontaneous formation of a complex superlattice in bulk samples of the perovskite KLaMnWO 6 . The superlattice structure, which possesses P42m space group symmetry with a = 40.0637(7) A ˚and c = 8.1306(3) A ˚, results from a two-dimensional compositional modulation of the A-site cations (K þ and La 3þ ), combined with a complex pattern of tilts involving the corner connected octahedra. The basic pattern of octahedral tilting involves out-of-phase tilts of neighboring octahedra about the pseudocubic a and b axes (aac 0 tilting). Unexpectedly, the out-of-phase tilting is disrupted in both directions by an in-phase tilt once every five octahedra. The occurrence of regularly repeating, well-separated in-phase tilts helps to alleviate strains that arise from formation of the compositionally modulated chessboard superlattice.

Transmission electron microscopy studies of the perovskite NaLaMgWO 6 reveal the formation of a complex, compositionally modulated structure. Annular dark field scanning transmission electron microscopy images and scanning transmission electron microscopy-electron energy-loss spectroscopy scans show that this modulation involves a repeating pattern of La-rich and La-poor stripes, each stripe 6 a p or approximately 24 A wide (where a p is the edge length of the simple cubic perovskite unit cell). High-resolution transmission electron microscopy images clearly show, and electron diffraction patterns confirm, a periodicity of 12 a p along either the [100] p or [010] p direction. Available evidence suggests a spontaneous separation into stripes that possess the nominal stoichiometry, NaLaMgWO 6, alternating with Na-poor/La-rich stripes that have a stoichiometry of (La x Na 1-3 x )LaMgWO 6. X-ray powder diffraction measurements are insensitive to this intricate structural complexity, which may be a more widespread feature of (A (+)Ln (3+))MM'O 6 perovskites than previously appreciated.

Aqueous zinc (Zn) chemistry features intrinsic safety, but suffers from severe irreversibility, as exemplified by low Coulombic efficiency, sustained water consumption and dendrite growth, which hampers practical applications of rechargeable Zn batteries. Herein, we report a highly reversible aqueous Zn battery in which the graphitic carbon nitride quantum dots additive serves as fast colloid ion carriers and assists the construction of a dynamic & self-repairing protective interphase. This real-time assembled interphase enables an ion-sieving effect and is found actively regenerate in each battery cycle, in effect endowing the system with single Zn2+ conduction and constant conformal integrality, executing timely adaption of Zn deposition, thus retaining sustainable long-term protective effect. In consequence, dendrite-free Zn plating/stripping at ~99.6% Coulombic efficiency for 200 cycles, steady charge-discharge for 1200 h, and impressive cyclability (61.2% retention for 500 cycles in a Zn | |MnO2 full battery, 73.2% retention for 500 cycles in a Zn | |V2O5 full battery and 93.5% retention for 3000 cycles in a Zn | |VOPO4 full battery) are achieved, which defines a general pathway to challenge Lithium in all low-cost, large-scale applications.