•Self-assembled 3D Co3(PO4)2·8H2O architecture at room temperature.•The method is green, low-cost, time-saving and large-scale yield.•The electrode exhibits good specific capacitance of 350 F/g at 1 A/g.•The electrode exhibits good rate capability and cycling stability.Hierarchical 3D cobalt phosphate octahydrate (Co3(PO4)2·8H2O) architecture with flower-like morphologies assembled from 2D microsheets are successfully synthesized at room temperature by a green precipitate process without adding any surfactant. The as-prepared architecture with an interconnecting 2D microsheets structure provide large nanoscale pore channels for ion transport, exhibits remarkable pseudocapacitive activities including good specific capacitance (350 F/g at 1 A/g), rate capability (227 F/g at 10 A/g), and excellent cycling stability (capacitance increase to retention 102% after 1000 cycles).

Bicrystalline materials have wide applications from silicon chips to photocatalysis, but the controlled synthesis of nanocrytals with ordered phase junction has been challenging, in particular via chemical synesthetic routes. Here, we propose a general strategy to design biphase crystals formed via partial solid-to-solid phase transition with perfect phase junction, e.g., being atomically sharp and built of two particular sets of epitaxially joined planes of the two component phases, and present such an example by designing, synthesizing, and characterizing the interface of two TiO2 phases, namely, TiO2-B/anatase biphase nanocrystals that are obtained conveniently via one-pot chemical synthesis. Our design strategy classifies the common solid-to-solid phase transition into three types that are distinguishable by using the newly developed stochastic surface walking (SSW) method for unbiased pathway sampling. Only Type-I crystal is predicted to possess perfect phase junction, where the phase transition involves one and only one propagation direction featuring single pathway phase transition containing only one elementary kinetic step. The method is applicable for the understanding and the design of heterophase materials via partial phase transition in general.Keywords: heterophase crystal; orientation relation; phase junction; photocatalysis; solid-to-solid phase transition; TiO2-B/anatase;

A new method has been explored to synthesize zeolite ANA crystals with regular icositetrahedron in aqueous media via transformation of zeolite Y under the conditions of low temperature, short reaction time, and without organic template. The products are perfect, almost 100% crystals. The samples prepared at different crystallization stages are measured by XRD, TEM, and SEM to investigate the transformation mechanism from zeolite Y to zeolite ANA. It has been demonstrated for the first time that the mechanism of forming a zeolite ANA polycrystal with sphere or shell morphologies is the in situ solid phase iso-structure transformation (Is-SPIST) of zeolite Y. The Is-SPIST mechanism is also supported by the results of steam-induced crystallization experiments and other assistant means, including the same Si/Al ratio, the same weight, the same particle size, and the same morphology before and after transformation of zeolite Y to zeolite ANA. It is also observed that a spherical or shell ANA polycrystal is constructed via the reconstruction from its exterior to interior, to form an ANA single crystal with a solid or hollow icositetrahedron. The main driving force of the reconstruction is considered to be the grain boundary energy existing between polycrystalline grains. This process also obeys the mechanism of in situ solid phase reconstruction (Is-SPR). Furthermore, the size and morphology of the zeolite ANA single crystal can be modified by surfactants.