Jonscher indices for dielectric materials

Two parameters are proposed as Jonscher indices,named after A.K.Jonscher for his pioneering contribution to the universal dielectric relaxation law.Time domain universal dielectric relaxation law is then obtained from the asymptotic behavior of dielectric response function and relaxation function by replacing parameters in Mittag–Leffler functions with Jonscher indices.Relaxation types can be easily determined from experimental data of discharge current in barium stannate titanate after their Jonscher indices are determined.

RELAXOR FERROELECTRIC MATERIALS FOR MICROWAVE TUNABLE APPLICATIONS

With strong dependences of dielectric constant on external applied electric fields,relaxor barium zirconium titanate(BaZr_(x)Ti_(1-x)O_(3)or BZT)and barium stannate titanate(BaS_(n)xTi_(1-x)O_(3)or BTS),in both bulk ceramic and thinfilm forms,are increasingly being recognized as potential candidates of microwave tunable materials for device applications.This paper is aimed to review the recent progress in understanding the dielectric properties(such as tunability,dielectric loss and dielectric constant)of these relaxor materials.However,due to their relatively high dielectric constant and loss tangent,pure Ba(Zr,Ti)O_(3) and Ba(Sn,Ti)O_(3) do not fully satisfy the requirements of practical device applications.Therefore,various strategies have been developed to improve the dielectric properties of these two groups of relaxor materials.In this paper,wefirst discussed the dielectric tunability characteristics of pure Ba(Zr,Ti)O_(3) and Ba(Sn,Ti)O_(3) and then summarized the strategies that have been used,including(i)small amount acceptor or donor doping(such as rare-earth ions and transition metal ions)and(ii)forming composites with low loss and low dielectric constant microwave dielectric materials(such as MgO,MgTiO_(3) and so on).At the same time,the relationship between relaxor behavior and dielectric tunability was also discussed.

Dielectric tunable characteristics of compositional-gradient BaTi_(1-x)Sn_(x)O_(3)thin films

Compositional-gradient BaTi_(1-x)Sn_(x)O_(3)thin films on Pt(100)/Ti/SiO_(2)/Si substrates are fabricated with sol-gel using spin coating.All of the structures of the prepared thin films are of single-phase crystalline perovskite with a dense and crack-free surface mor-phology.BTS10/15/20 thin film exhibits enhanced temperature stability in its dielectric behavior.The temperature coefficient of capacitance TCC_(20-150)in the temperature range from 20°C to 150°C is−0.9×10^(−4)/°C and that of TCC20-(-95)in the temperature range from 20°C to−95°C is−3.8×10^(−4)/°C.Furthermore,the thin films show low leakage current density and dielectric loss.High and stable dielectric tunable performances are found in BTS10/15/20 thin films:the dielectric tunability of the thin films is around 20.1%under a bias voltage of 8 V at 1 MHz and the corresponding dielectric constant is in the range between 89 and 111,which is beneficial for impedance matching in circuits.Dielectric tunability can be obtained under a low tuning voltage,which helps ensure safety.The simulated resonant frequency of the compositional-gradient BTS thin films depends on the bias electric field,showing compositional-gradient BTS thin films could be used in electrically tunable components and devices.These prop-erties make compositional-gradient BTS thin films a promising candidate for dielectric tuning.

Accelerating electron transport in Eosin Y by bidentately bridging on BaSnO_(3)for noble-metal-free photocatalytic H 2 production

The separation and transport of photogenerated carriers is regarded as a curial factor in photocatalytic H_(2)pro-duction.As known in solar cells and photoelectron-chemistry,to strengthen the electron conduction for effective utilization of carriers,the electron transport material(ETM)is widely applied.Herein,inspired by the function of ETM,we adopted barium stannate(BaSnO_(3),labeled as BSO)as an excellent ETM which had the merits of high electron mobility,suitable conduction band position and simple preparation,to adjust the carrier kinetics of dye Eosin Y(EY)-sensitized photocatalytic system.Detailly,the photocatalytic system with the spatial sepa-ration sites of photogenerated carriers excitation and water reduction reaction was elaborately constructed,that was,dye EY-sensitized BSO(EY/BSO)for photocatalytic H_(2)production.The photocatalytic H_(2)-production rate of EY/BSO(257𝜇mol·h^(−1)·g EY^(−1))in the absence of noble metals was 28.6 times higher than that of single EY(∼9𝜇mol·h^(−1)·g EY^(−1))under visible-light irradiation.With systematic and comprehensive characterizations,the formed electron transport channel by the bidentate bridging of EY on BSO could accelerate the transfer of photogenerated electrons from EY to BSO,promoting the effective separation of photogenerated carriers for the enhanced pho-tocatalytic performance.Moreover,the water reduction reaction for H_(2)production proceeded on the surface of BSO that acted as the H_(2)-evolution cocatalyst,avoiding the use of high-cost noble metals.Furthermore,based on the well-proved ETM-based concept in the EY/BSO system,La-doped BaSnO_(3)(LBSO)with better electron trans-port ability was adopted to construct EY/LBSO system(344𝜇mol·h^(−1)·g EY^(−1))which showed better photocatalytic activity than EY/BSO.