Structure,defects,and microwave dielectric properties of Al-doped and Al/Nd co-doped Ba_(4)Nd_(9.33)Ti_(18)O_(54)ceramics

Low-loss tungsten–bronze microwave dielectric ceramics are dielectric materials with potential application value for miniaturized dielectric filters and antennas in the fifth-generation(5G)communication technology.In this work,a novel Al/Nd co-doping method of Ba_(4)Nd_(9.33)Ti_(18)O_(54)(BNT)ceramics with a chemical formula of Ba_(4)Nd_(9.33+z/3)Ti_(18−z)Al_(z)O_(54)(BNT–AN,0≤z≤2)was proposed to improve the dielectric properties through structural and defect modulation.Together with Al-doped ceramics(Ba_(4)Nd_(9.33)Ti_(18−z)Al_(4z/3)O_(54),BNT–A,0≤z≤2)for comparison,the ceramics were prepared by a solid state method.It is found that Al/Nd co-doping method has a significant effect on improving the dielectric properties compared with Al doping.As the doping amount z increased,the relative dielectric constant(εr)and the temperature coefficient of resonant frequency(τf)of the ceramics decreased,and the Q×f values of the ceramics obviously increased when z≤1.5.Excellent microwave dielectric properties ofεr=72.2,Q×f=16,480 GHz,andτf=+14.3 ppm/℃were achieved in BNT–AN ceramics with z=1.25.Raman spectroscopy and thermally stimulated depolarization current(TSDC)technique were firstly combined to analyze the structures and defects in microwave dielectric ceramics.It is shown that the improvement on Q×f values was originated from the decrease in the strength of the A-site cation vibration and the concentration of oxygen vacancies(VO××),demonstrating the effect and mechanism underlying for structural and defect modulation on the performance improvement of microwave dielectric ceramics.

Recent progress in intrinsic defect modulation of g-C_(3)N_(4)based materials and their photocatalytic properties

The application of solar-driven photocatalytic processes shows considerable potential for renewable energy production and environmental remediation.Graphitic carbon nitride(g-C_(3)N_(4))has emerged as a highly promising metal-free photocatalyst due to its outstanding electronic structure and physicochemical properties.However,the intrinsic constraints of pristine g-C_(3)N_(4),such as limited visible light absorption range,high recombination rates of photogenerated charge carriers,and a scarcity of active sites,have significantly hindered its photocatalytic performance and practical implementations.Recent studies have demonstrated that defect engineering can substantially mitigate these issues by enhancing both light absorption and charge separation efficiency,thereby improving photocatalytic performance.This reviewprovides a comprehensive overview of intrinsically defective g-C_(3)N_(4)-based materials,focusing on the types of intrinsic defects,their modification strategies,and the recent advancements in the field.It also highlights the diverse applications of defect-modified g-C_(3)N_(4),including wastewater remediation,hydrogen evolution,CO_(2)conversion,NO removal,nitrogen fixation,photocatalytic disinfection,and H_(2)O_(2)production.Finally,the current challenges and future perspectives are discussed of g-C_(3)N_(4)-based photocatalytic materials,offering insights and practical guidance for the development of advanced g-CsN4-based photocatalysts.