Spin gap in quasi-one-dimensional S=3/2 antiferromagnet CoTi2O5

Quasi-one-dimensional(1D)antiferromagnets are known to display intriguing phenomena especially when there is a spin gap in their spin-excitation spectra.Here we demonstrate that a spin gap exists in the quasi-1D Heisenberg antiferromagnet CoTi2O5 with highly ordered Co2+/Ti4+occupation,in which the Co2+ions with S=3/2 form a 1D spin chain along the a-axis.CoTi2O5 undergoes an antiferromagnetic transition at TN~24 K and exhibits obvious anisotropic magnetic susceptibility even in the paramagnetic region.Although a gapless magnetic ground state is usually expected in a quasi-1D Heisenberg antiferromagnet with half-integer spins,by analyzing the specific heat,the thermal conductivity,and the spin-lattice relaxation rate(1/T1)as a function of temperature,we found that a spin gap is opened in the spin-excitation spectrum of CoTi2O5 around TN,manifested by the rapid decrease of magnetic specific heat to zero,the double-peak characteristic in thermal conductivity,and the exponential decay of 1/T1 below TN.Both the magnetic measurements and the first-principles calculations results indicate that there is spin-orbit coupling in CoTi2O5,which induces the magnetic anisotropy in CoTi2O5,and then opens the spin gap at low temperature.

Research Progress in the Fabrication of Covalent Organic Framework Membranes for Chemical Separations

Membrane technology has become one of the most promising separation technologies for its energy saving, high separation efficiency, environmental friendliness, and economic feasibility. Covalent organic frameworks(COFs) with intrinsically high porosity, controllable pore size, uniform pore size distribution and long-range ordered channel structure, have emerged as next-generation materials to fabricate advanced separation membranes. This feature article summarizes some latest studies in the development of pure COF membranes in our lab, including their fabrication and applications in chemical separations. Finally, current challenges facing high-performance COF separation membranes are discussed.

Advanced sodium-ion capacitor based on antimony-carbon composite anode

Alloy-type materials with the characteristics of high theoretical capacity,low sodiation/desodiation potential,and good conductivity are considered as one of the most promising anodes for sodium-ion batteries or capacitors.However,the large volume change during the sodiation leads to poor cyclability and slow kinetics,thus presenting the main issue impeding the practical application.Herein,we propose a facile wet chemistry and pyrolysis method to synthesize Sb-carbon composite that Sb nanoparticles or single atoms are confined and/or dispersed in the wrinkled carbon framework with high nitrogen content.This unique architecture of Sb-carbon composite increases atomic interface contact/interaction with Na~+,facilitating ion diffusion and alleviating the volume change of Sb during the charge/discharge process.Half-cell test shows that Sb-carbon composite exhibits a high-rate capability and stable cycling life.Furthermore,sodium-ion capacitors fabricated by employing Sb-carbon composite as anode and home-made active carbon as cathode,deliver both high-energy density of 157 Wh·kg^(-1)and high-power density of 25 kW·kg^(-1)as well as excellent cycling performance exceeding 4000 cycles.