Bismuth-based halide double perovskite Cs_(2)KBiCl_(6): Disorder and luminescence

A new bismuth-based halide double perovskite Cs_(2)KBiCl_(6) was isolated successfully through solid-state reactions and investigated using X-ray and neutron diffraction.Rather than an ordered structure,the crystal structure consists of shifted Cs,K,Bi,and Cl sites from the ideal positions with fractional occupancy in compensation,leading to variable local coordination of Cs^(+)ions,as revealed by^(133)Cs solid-state nuclear magnetic resonance spectroscopy.Cs_(2)KBiCl_(6) displays volume hysteresis at 5-298 K range upon heating and cooling.The Cs_(2)KBiCl_(6) has a direct bandgap of 3.35(2)eV and red-shift luminescence of around 600 nm upon Mn doping compared with the Na analogue.The stabilization of disordered structure in Cs_(2)KBiCl_(6) is related to two factors including the large-sized K^(+)cation which prefers to coordinate with more than six Cl^(-),and the Bi^(3+)with 6s^(2) lone pair which has a preference for a local asymmetric environment.These findings could have general application and help to understand the structure and property of halide perovskites.

Hybrid coating SnO_(2)for enhanced Li ions storage

Anode SnO_(2)in lithium-ion batteries suffers from volume expansion and agglomeration.Here,the SnO_(2)nanoparticles are hybrided with ZrO_(2)particles by the support of carbon nanotube networks.The obtained SnO_(2)/C/ZrO_(2)composite shows improved electrochemical performances.Investigations reveal that the carbon nanotubes shorten the transmission path of electrons and Li^(+) ions.Ball milling with ZrO_(2)promotes the formation of nanosized SnO_(2)to weaken the internal strain change,being beneficial to buffering volume change during electrochemical cycling afterwards.High-resolution 6.7Li NMR investigations indicate that conversion and alloying reactions are stepwise involved for SnO_(2)/C/ZrO_(2)anode.The strategy of designing SnO_(2)/C/ZrO_(2)composite from the morphology-controlled metal-organic frameworks for energy storage widens the possibility to fabricate promising materials with enhanced performances.

Pressure-stabilized hexagonal perovskite-related isolated tetrahedral anion silicate La_(6)Sr_(3)Si_(6)O_(24)

The discovery of new perovskite compounds under high pressure mainly focuses on the ABO_(3)compositions and the compositions highly deviated from ABO_(3)are less explored.Here we demonstrate that the La_(6)Sr_(3)Si_(6)O_(24)silicate composition can be stabilized as a hexagonal perovskite-related structure with isolated tetrahedra anions under high pressure of 6 GPa.The compound adopts 9-layer shifted hexagonal perovskite-like structure with both B-cation and oxygen deficiencies and contains pseudo-cubic(c)(La/Sr)O_(2)layers and hexagonal(h)(La/Sr)O_(3)layers stacked according to(c hh)_(3)sequence.This structure features both B-cation vacancy ordering between the two consecutive hexagonal layers and oxygen vacancy ordering in c-(La/Sr)O_(2)layers,resulting in isolated tetrahedral Si O_(4)anions and ionic conduction behavior.This work demonstrates the practicability of accessing new perovskite-related functional materials from the compositions highly deviated from ABO_(3)under high pressure.