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Structural,optical,electrical,and dielectric relaxation properties of rare earth containing sodium bismuth titanate Na_(0.5)Bi_(0.5)TiO_(3) perovskite:Effect of ionic radius

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Journal of Rare Earths 2024年第2期42卷 383-391,I0006页

作者： Rajdip Roy Abhigyan Dutta Department of Physics The University of BurdwanBurdwan713104India

The main focus of this work is to study the effect of the ionic radius of different rare earth dopant cations RE^(3+)(RE=La,Sm,Dy,and Ho) on structural and various physical properties of sodium bismuth titanate(Na_(0.5)B_(0.5)TiO_(3),NBT) based perovskite *** X-ray diffraction data indicate the successful formation of the rhombohedral phase(space group R3c) of NBT nano perovskite incorporated with various rare earth ions in *** lattice parameters were found to increase linearly with the ionic radius of the dopant *** ionic radii and atomic mass of rare earth dopants appear to be essential factors in the grain growth of the prepared *** grain growth results in better crystallinity of the sample by reducing the microstrain with the increase of dopant ionic *** emission scanning electron microscopy and energy-dispersive X-ray spectra confirm the prepared compositions' phase purity and *** UV-Vis spectra reveal that La-doped NBT composition exhibits the lowest optical band gap,which unfolds the application of NBT-based perovskite as photoactive *** ac conductivity and complex impedance spectra unveil that the composition with the largest ionic radius,i.e.,La-doped NBT compound,exhibits the highest dc and bulk conductivity with the lowest activation *** frequency-dependent dielectric data follows Havriliak-Negami(HN) formalism and non-Debye type relaxation *** also indicate that La-doped NBT composition exhibits the highest dielectric strength ***,this study first elaborates that the increasing ionic radius of the rare earth dopant cation in the Bi-site of NBT perovskite improves its microstructural,optical,and electrical properties.

关键词： Rare earth doped NBT Microstructural analysis Optical band gap AC Conductivity dielectric relaxation Rare earths

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dielectric relaxation of interfacial polarizable molecules in chitosan ice-hydrogel materials

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Journal of Materiomics 2018年第1期4卷 35-43页

作者： Y.Q.Li C.X.Zhang P.Jia Y.Zhang L.Lin Z.B.Yan X.H.Zhou J.-M.Liu Laboratory of Solid State Microstructures and Innovative Center of Advanced Microstructures Nanjing UniversityNanjing 210093China Institute for Advanced Materials Hubei Normal UniversityHuangshi 435002China

The functionalities of hydrogel-based smart materials are highly related to the electrostatic interactions and molecular polarization associated with the polymer networks and encapsulated water droplets,and therefore the dielectric responses of the polarizable molecules in the polymer,water,and polymer-water interfaces are particularly attractive,where the properties of polymer-water interfacial molecules remain *** from extensive dielectric relaxation spectroscopy studies on polymer hydrogel solutions,in this work we investigate the dielectric response of chitosan hydrogels below the water solidifying point(ice-hydrogels)so that the contribution of chitosan-water interfacial molecules can be *** is revealed that the chitosan-water interfacial polarizable molecules have slow dielectric relaxation but large polarization compared with the chitosan chains and water molecules,and the dielectric relaxations beyond~10^(4)Hz are substantially *** thermal activation energy of the dielectric relaxation for these interfacial polarizable molecules can be as large as 0.93 eV,i.e.89.73 kJ/*** present work provides a platform for characterizing the polymer-water electrostatic interactions and interfacial polarizable molecules,informative to understand the microstructure-property relationships of chitosan-based hydrogel materials.

关键词： Chitosan hydrogels dielectric relaxation Polymer-water interfacial polarizable molecules Thermal activation energy

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dielectric relaxation and scaling of AC conductivity observed in mixed valence perovskite Eu_(2)CoMnO_(6)

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Journal of Advanced dielectrics 2021年第6期11卷 52-58页

作者： Md.G.Masud B.K.Chaudhuri Department of Physics Basanti Devi College147B Rash Behari AvenueKolkata 700029India Center for Rural and Cryogenic Technologies Jadavpur UniversityKolkata 700032India Formerly at Solid State Physics Department Indian Association for the Cultivation of Science Kolkata 700032India

Monophasic and polycrystalline double perovskite Eu_(2)CoMnO_(6)has been synthesized,and its structural characterization,fre-quency and temperature-dependent dielectric relaxation have been *** thermally activated dielectric relaxation was explained using the empirical Havriliak-Negami(HN)dielectric relaxation function with an estimated activation energy E~0.22 eV and attempt frequency f0~2.46×10^(9)*** frequency-dependent AC conductivity data,over a wide range of tempera-ture(100-325 K),followed the empirical universal power law behavior(~f n,n is the constant exponent)showing two different frequency exponents,respectively,in the high-and low-temperature *** high-temperature(>275 K)conductivity data followed the continuous time random walk(CTRW)approximation model proposed by ***,this model failed to repro-duce the observed conductivity spectra in the low-temperature side(<200 K).Interestingly,both the high-and low-temperatures’conductivity data can be scaled to the master curve with suitably chosen scaling parameters.

关键词： dielectric relaxation AC conductivity scaling perovskite

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AC Conductivity and dielectric relaxation Behavior of Sol-gel Ba_xSr_(1-x)TiO_3 Thin Films

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Journal of Materials Science & Technology 2011年第9期27卷 802-808页

作者： Ala eddin A. Saif P. Poopalan Microfabrication Cleanroom School of Microelectronic Engineering University Malaysia Perlis (UniMAP)

BaxSr1-xTiO3 sol-gel thin films with x--0.5, 0.7 and 0.8 have been fabricated as AI/BST/Pt capacitor. The AC conductivity and dielectric properties over a frequency rang of 10 Hz and I MHz have been studied in order to explore the ion dynamics and relaxation mechanisms in the films. The frequency dependent conductivity plots show three regions of conduction processes. dielectric results show that ε＇ at low frequencies increases as Sr content decreases, whereas at high frequencies, it shows opposite variation, which is attributed to the dipole dynamics. The electric modulus plots reveal the relaxation peaks which are not observed in the ε＂ plots and the contribution of the grains, grain boundaries and electrode to the relaxation mechanisms.

关键词： Barium strontium titanate (BST) thin film AC conductivity dielectric relaxation Electric modulus

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Progress in the study of molecular organized assemblies by dielectric relaxation spectroscopy

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Progress in Natural Science:Materials International 2006年第3期16卷 221-230页

作者： ZHAO Kongshuang, HE Kejuan and WEI Suxiang (Department of Chemistry, Beijing Normal University, Beijing 100875, China Department of Chemistry, South China Normal University, Guangzhou 510631, China) Department of Chemistry Beijing Normal University Beijing 100875 China Department of Chemistry South China Normal University Guangzhou 510631 China

Because dielectric spectroscopy covers a great many problems in physical and chemical systems occurring in an extremely wide frequency range, the study of this method plays an important role in physical chemistry. As an effective tool to detect inner properties of substance systems, the dielectric spectroscopy method is widely used in chemical systems and has been dramatically developed in recent decade. This review paper describes the applications of the dielectric spectroscopy in the chemical field, and main concentrations are focused on the micelle, microemulsion and other so-called molecular organized assemblies. Some dielectric principles and models proposed for these systems are introduced. In addition, recent technical developments in dielectric spectroscopy and developing trend of this method in other chemical systems are reviewed.

关键词： dielectric relaxation micelle microemulsion vesicle relaxation time.

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STUDIES ON THE CHAIN STRUCTURAL EFFECT OF PVDF AND VDF (52)/TrFE(48) COPOLYMER BY MEANS OF THE METHOD OF dielectric relaxation

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Chinese Journal of Polymer Science 1994年第1期12卷 12-21页

作者：张兴元 FURUKAWA Takeo Department of Materials Science and Engineering University of Science and Technology of China Hefei 230026 Department of Chemistry Science University of Tokyo Japan

Through improvements on a fully commercial and automatic system measuring frequency andtemperature spectra of the complex elastic, dielectric, and piezoelectric constants of polymerfilms, the precision for measuring complex dielectric constants achieved 2‰ from original 1%.The complex dielectric constants of PVDF, VDF （95 ）/VF （5）, VDF （52）/TrFE （48） and VDF（47. 5）/TrFE（47. 5）/HeFP （5） over a range of-120-140℃, 10-2-10;Hz were measured bythe described system. The diminution of chain regularity due to 5mol% vinyl fluoride in the chainof PVDF led to disappearing of α-relaxation and increase in T;（3℃） of VDF （95）/VF （5）.Because of the spatial impediment of 5mol% HeFP in copolymer chain, the Curie point of VDF（52）/TrFE（48） decreased by 30℃ and T;by 3℃. The behavior of dielectric relaxation indicatedthat 5mol% vinyl fluoride and HeFP made the relaxation strength of noncrystalline regionreduced, the activation energy of local relaxation increased and the relaxation time prolonged respectively.

关键词： Polyvinylidene fluoride VDF(52)/TrFE(48) Chain structure effect dielectric relaxation

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dielectric relaxation in Bi_2BaNb_2O_9 Ceramic

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Journal of Materials Science & Technology 1993年第6期9卷 461-463页

作者： Xiaoli WANG Xi YAO Electronic Materials Research Laboratory,Xi’an Jiaotong University,Xi’an,710049,China

A very strong dielectric relaxation was observed in Bi_2BaNb_2O_9 *** temperature difference between the maximum dielectric constant temperatures T_m measured at 1 kHz and 100 kHz is 65℃. which is about 2-4 times tha... 详细信息

关键词： dielectric relaxation ceramic temperature

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Phases confirmation of cloudy Silwet L-77 aqueous solution by dielectric relaxation spectroscopy

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Chinese Chemical Letters 2010年第6期21卷 734-737页

作者： Wei Zhou Wei Da Xu Yu Mei Sun Ya Wen Zhou School of Chemistry and Environmental Engineering Beijing Technology and Business UniversityBeijing 100048China

The phase transition of Silwet L-77(a kind of siloxane surfactant) dilute aqueous solution with temperature was investigated by dielectric relaxation *** the initial heating process,a dielectric relaxation was found at about 10~6 Hz,which was considered as the interface polarization ascribed to the interface between water and liquid phases(W and L_1).With the temperature increasing further,a new dielectric relaxation was observed at about 10~4 Hz,which was assigned to the appearance of liquid crystal phase(L_α).According to the dielectric parameters fitted by Cole-Cole equation,the coexistence temperature of W,L_1 and L_αwas determined at about 37.0℃.

关键词： dielectric relaxation Silwet L-77 Phase transition

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dielectric relaxation and phase structure in PZN based ferroelectric ceramics

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Progress in Natural Science:Materials International 1998年第3期 3-5页

作者：樊慧庆张良莹姚熹 China Electronic Materials Research Laboratory Xi’an 710049 Xi’an Jiaotong Univeristy

dielectric behavior of lead zinc niobate (PZN) based ferroelectric ceramics is carefully studied be-tween-100 and 200℃ in cooling and heating measurements. The zero-field spontaneous and field-induced relaxor-normal ferroelectric transitions are observed in this ferroelectric system. X-ray diffraction examinations under differenttemperatures demonstrate that the micro-macrodomain transition corresponds to rhombohedral-tetragonal first-orderphase switching. The region of the (0.9-x)Pb(Zn1/3Nb2/3)O3-0.1BaTiO3-xPbTiO3(0.0≤x≤0.2) phase dia-gram is established through analysis of structure and dielectric behavior associated with changes in temperature andcomposition

关键词： relaxor ferroelectrics dielectric relaxation rhombohedral-tetragonal phase switching micromacrodomain

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Oxygen-vacancy-related dielectric relaxation and conduction mechanisms in Bi5TiNbWO15 ceramics

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Chinese Physics B 2007年第7期16卷 2131-2135页

作者：王晓娟龚志强钱亚峰朱骏陈小兵 College of Physics Science and Technology Yangzhou University Yangzhou 225002 China The National Laboratory of Solid State Microstructure Nanjing University Nanjing 210008 China

This paper reports that the intergrowth ceramics Bi5TiNbWO15 （BW-BTN） have been prepared with the conventional solid-state reaction method. The dielectric and conductivity properties of samples were studied by using the dielectric relaxation and AC impedance spectroscopy in detail. Two distinct relaxation mechanisms were detected both in the plots of dielectric loss （tanδ） and the imaginary part （Z″） versus frequency in the frequency range of 10 Hz-13 MHz. We attribute the higher frequency relaxation process to the hopping process of the oxygen vacancies inside the grains, while the other seems to be associated with the space charges bound at the grain boundary layers. The AC impedance spectroscopy indicates that the conductivities at 625 K for bulk and grain boundary are about 1.12 × 10^-2 S/m and 1.43 × 10^-3 S/m respectively. The accumulation of the space charges in the grain boundary layers induces a space charge potential of 0.52 eV.

关键词： intergrowth dielectric relaxation impedance spectroscopy oxygen vacancies

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