Understanding of the Mechanism and Kinetics of the Fast Solid-State Reaction between NaF and VPO4 to Form Na3V2(PO4)2F3

The solid-state reaction between NaF and VPO₄ is widely used to produce Na₃V₂(PO₄)₂F₃, a promising cathode material for sodium-ion batteries. In the present work, the mechanism and kinetics of the reaction between NaF and VPO₄ were investigated, and the effect of preliminary high-energy ball milling (HEBM) was studied using in situ time-resolved synchrotron powder X-ray diffraction, in situ transmission electron microscopy, differential scanning calorimetry, etc. The reaction was attributed to a "dimensional reduction" formalism; it proceeds quickly with the unilateral diffusion of Na⁺ and F^- ions into VPO₄ particles as a limiting stage. The use of HEBM leads to the mechanism corresponding to the third-order reaction model and accelerates the interaction. The rate constant k increases from 3.5 × 10^-5 to 3.4 × 10^-3 s^-1, and diffusion coefficient D increases from 2 × 10^-14 to 4 × 10^-13 cm² s^-1 when HEBM is used. The calculated apparent activation energy is ∼290 kJ mol^-1. The electrochemical properties of the as-prepared Na₃V₂(PO₄)₂F₃ are not inferior to the properties of the materials prepared by conventional solid-state synthesis.

Ba2.5Pb1.5B12O22: structural transformation from a centrosymmetric to a noncentrosymmetric space group by introducing Pb into Ba2B6O11

A new congruent-melting lead barium borate, Ba_2.5Pb_1.5B₁₂O₂₂, was synthesized via a high-temperature solid-state reaction under atmospheric pressure. It crystallizes in the noncentrosymmetric space group Cmc2₁ with a unit cell of a = 19.051(8) Å, b = 10.726(3) Å, c = 8.612(3) Å, and Z = 4. It features a new functional building block (FBB), [B₁₂O₂₆]^16-, that is made up of five [B₃O₈]^7- and one [BO₃]^3- connected by sharing vertex O atoms. It is derived by introducing Pb into Ba₂B₆O₁₁, which leads to a structural transformation from a centrosymmetric to a noncentrosymmetric space group. Its second harmonic generation response (SHG) is approximately 0.9 times that of KDP at the fundamental wavelength of 1064 nm and is also phase-matchable. It has a wide transparent region with a UV cutoff edge of about 250 nm according to the reflectance spectra and high thermal stability, which illustrates that it is a potential candidate for ultraviolet nonlinear optical materials.

ACs5Bi4(PO4)2(P2O7)3 (A = K, Rb and Cs) with two kinds of isolated P–O groups designed by dimensional reduction theory

ACs5Bi4(PO4)2(P2O7)3 (A = K, Rb and Cs) were successfully designed and synthesized by dimensional reduction theory with a system of A2O–Bi2O3–P2O5.

Ba3Ca4(BO3)3(SiO4)Cl: a new non-centrosymmetric complex alkaline-earth metal borosilicate chloride with a deep-ultraviolet cut-off edge

The first complex alkaline-earth metal borosilicate chloride, Ba₃Ca₄(BO₃)₃(SiO₄)Cl, as a potential ultraviolet nonlinear optical material.

Ba3B10O17Br2: a new barium borate halide with B–O layered structure

A new barium borate halide, Ba₃B₁₀O₁₇Br₂, has been obtained, and is the first barium borate halide with a B–O layered structure.

Structure comparison and optical properties of Na7Mg4.5(P2O7)4: a sodium magnesium phosphate with isolated P2O7 units

The crystal structure of Na₇Mg_4.5(P₂O₇)₄ comprises a parallelogram channel composed of corner/edge-sharing isolated [P₂O₇] dimers and a Na(2)O₅ polyhedra to form a 3D framework and has an ultraviolet (UV) cut-off edge of about 210 nm.

Application of the dimensional reduction formalism to Pb9−xBax[Li2(P2O7)2(P4O13)2] (x = 0, 2, 6, 7): a series of phosphates with two types of isolated polyphosphate groups

Dimensional reduction is used to design and synthesise Pb₉[Li₂(P₂O₇)₂(P₄O₁₃)₂] by using Li₂O to dismantle Pb₃P₄O₁₃.