Impedance spectroscopy and investigation of conduction mechanism in BaMnO3 nanorods

BaMnO₃ nanorods were synthesized at 200 °C and atmospheric pressure using the composite-hydroxide mediated method. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to investigate the structure, size, morphology, phase purity and elemental composition of BaMnO₃ nanorods. Electrical characterization of BaMnO₃ pellet was performed at 300-400 K and in the frequency range 200 Hz-2 MHz. Temperature dependence of AC conductivity suggests that the BaMnO₃ pellet behaves as a semiconducting material and conduction across the pellet can be explained by the correlated barrier hopping model. Impedance analysis was performed using the equivalent circuit model (R₁Q₁C₁)(R₂C₂) and it suggests a single relaxation process in the BaMnO₃ pellet at a particular temperature. The analysis reveals that the BaMnO₃ pellet behaves like an n-type semiconductor material due to the presence of oxygen vacancies and some disorder. Modulus spectroscopy also supports the impedance results.     

Specific features of the optical and electrical properties of polycrystalline CdTe films grown by the thermal evaporation method

The results of studying the physical properties of thin CdTe films obtained by the thermal evaporation method have been presented. The optical constants and the band gap of the films under study have been determined (E _g = 1.46 eV). It has been established based on the investigation of optical properties and the Raman spectrum of the films that they possess high structural quality. The activation energy of the electrical conductivity of CdTe films has been determined: E _a = 0.039 eV. The measured spectral dependences of the impedance of CdTe thin films are characteristic of the inhomogeneous medium with two time constants: τ_gb = R _gb C _gb = 1/ω_gb = 1.62 × 10^?3 s and τ_g = R _g C _g = 1/ω_g = 9.1 × 10^?7 s for grain boundaries and grains, respectively.     

Impedance spectroscopy study of Pb<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript> compound

The lead pyrophosphate, Pb₂P₂O₇, compound was prepared by conventional solid-state reaction and identified by X-ray powder diffractometer. Pb₂P₂O₇ has a triclinic structure whose electrical properties were studied using impedance spectroscopy technique. Both impedance and modulus analysis exhibit the grain and grain boundary contribution to the electrical response of the sample. The temperature dependence of the bulk and grain boundary conductivity were found to obey the Arrhenius law with activation energies E _g = 0.66 eV and E _gb = 0.67 eV, respectively. The scaling behavior of the imaginary part of the complex impedance suggests that the relaxation describes the same mechanism at various temperatures.     

Structural and electrical properties of LiCo3/5Cu2/5VO4 ceramics

The LiCo_3/5Cu_2/5VO₄ compound is prepared by a solution-based chemical method and characterized by the techniques of X-ray diffraction, scanning electron microscopy and complex impedance spectroscopy. The X-ray diffraction study shows an orthorhombic unit cell structure of the material with lattice parameters a=13.8263 (30) Å, b=8.7051 (30) Å and c=3.1127 (30) Å. The nature of scanning electron micrographs of a sintered pellet of the material reveals that grains of unequal sizes (～0.2–3 μm) present an average grain size with a polydisperse distribution on the surface of the sample. Complex plane diagrams indicate grain interior and grain boundary contributions to the electrical response in the material. The electrical conductivity study reveals that electrical conduction in the material is a thermally activated process. The frequency dependence of the a.c. conductivity obeys Jonscher’s universal law.     

Structural and dielectric properties of undoped ZnO pellets prepared by solid state route

Undoped zinc oxide has been prepared at various growth temperatures by a conventional sintering process. The crystal structures of the prepared samples were studied by X-ray diffraction. The frequency-dependent dielectric dispersion of all the sintered ZnO ceramics was investigated in the temperature range from ?100 to 30 °C and in the frequency range from 1 Hz to 10 MHz by broadband dielectric spectroscopy. An analysis of the complex permittivity and electric modulus as a function of frequency has been performed assuming a distribution of relaxation times. The pellet sintered at 900 °C showed the lowest value of the dielectric strength. The temperature dependent of the parameter α is discussed. While the charge transport through the grain and grain boundary regions was examined by impedance spectroscopy. Activation energy values extracted from conduction measurements were found to be in the range of 0.09 and 0.3 eV.     

Effect of iron doping at Mn-site on complex impedance spectroscopy properties of Nd0.67Ba0.33MnO3 perovskite

The effect of Fe-doping at Mn-site on the structural and electrical properties of Nd_0.67Ba_0.33Mn_1?xFe_xO₃ (0 ≤ x ≤ 0.05) perovskites has been investigated. X-ray diffraction patterns show that the structural parameters change slightly due to the fact that the Fe³⁺ ions replacing the Mn³⁺ have similar ionic radius. The electrical properties of these samples have been investigated using complex impedance spectroscopy technique. a function of the frequency at different temperatures. When increasing the Fe-content, a decrease of dc conductivity was observed throughout the whole explored temperature range and the deduced activation energy values are found to increase from 128 meV for x = 0 to 166 meV for x = 0.05. The curves of the imaginary part of impedance (Z″) show the presence of relaxation phenomenon in our samples. The complex impedance spectra show semicircle arcs at different temperatures and an equivalent circuit of the type of R_g + (R_gb//C_gb) has been proposed to explain the impedance results.     

Structural and electrical characterization of BiFeO3–NaTaO3 multiferroic

Using a standard high-temperature solid-state reaction technique, polycrystalline samples of (Bi_1?x , Na _x ) (Fe_1?x , Ta _x ) O₃ (x = 0.0, 0.5) were prepared. The formation of the desired materials was confirmed by X-ray diffraction. The surface texture of the prepared materials recorded by scanning electron microscope exhibits a uniform grain distribution with small voids suggesting the formation of high-density pellet samples. The impedance and dielectric properties of the materials were investigated as a function of temperature and frequency. The relative dielectric constant and loss tangent of BiFeO₃ decrease on addition of NaTaO₃ (x = 0.5). The effect of addition of NaTaO₃ on grain and grain boundary contributions in the resistive and capacitive components of BiFeO₃ was studied using complex impedance spectroscopy. The value of activation energy due to both grain and grain boundary of both the samples is nearly same. The nature of variation of dc conductivity confirms the Arrhenius behavior of the materials. Study of frequency dependence of ac conductivity suggests that the materials obey Jonscher’s universal power law and the presence of ionic conductivity.     

Bi0.5Ba0.5FeO3 陶瓷的电性能及阻抗分析

以传统的固相反应法制备了Bi_0.5Ba_0.5FeO₃陶瓷,并采用X射线衍射仪、扫描电子显微镜、直流阻温测试仪和交流阻抗分析仪测试了Bi_0.5Ba_0.5FeO₃陶瓷的微结构和电性能.分析结果表明:Bi_0.5Ba_0.5FeO₃陶瓷具有立方钙钛矿结构,颗粒尺寸约1.0 μm;在16—280 ℃范围内,Bi_0.5Ba_0.5FeO₃陶瓷表现出明显的负温度系数热敏效应,其热敏常数、活化能分别为6490 K及0.558 eV;介电温谱揭示,在280 ℃下Bi_0.5Ba_0.5FeO₃陶瓷材料没有出现相变行为.对于交流阻抗谱,采用3个串联的RQ(R与Q为并联)等效部件来拟合分析,拟合结果表明拟合数据与实验数据高度匹配,且这3个等效部件分别代表晶界、晶粒和晶壳的贡献.3个部件中,晶粒对陶瓷电阻阻值的影响最大,晶壳贡献次之,晶界最小,且3个部件电阻值都显示出负温度系数效应.在25—115 ℃范围内,电学模量虚部峰频与阻抗虚部峰频始终不匹配,意味着Bi_0.5Ba_0.5FeO₃陶瓷体内部一直表现出局域导电机理. 关键词： 0.5Ba_0.5FeO₃陶瓷')" href="#">Bi_0.5Ba_0.5FeO₃陶瓷 电性能 阻抗分析     

Ferroelectric,pyroelectric and electrical properties of new tungsten–bronze tantalate

The polycrystalline sample of Li₂Pb₂Y₂W₂Ti₄Ta₄O₃₀ was prepared by a high-temperature solid-state reaction technique. Room temperature X-ray structural analysis confirms the formation of a single-phase compound. The surface morphology of the sintered pellet sample recorded by SEM (scanning electron microscope) exhibits a uniform grain distribution with few voids. Detailed studies of dielectric constant, tangent loss and remanent and spontaneous polarization with temperature and frequency exhibit the existence of ferroelectricity in the material. The temperature and frequency dependence of impedance parameters (impedance, modulus, etc) of the material exhibits a strong correlation between these electrical parameters with its micro-structure (i.e., bulk, grain boundary, etc). The nature of variation of pyroelectric-coefficient and current with temperature suggests that material has good pyroelectric properties useful for fabrication of pyroelectric detector.     

Increase of grain boundary resistance with time by impedance spectroscopy in La0.50Ca0.50MnO3+δ at 77 K

In order to investigate the effects of grain boundaries on the electrical properties of La_0.50Ca_0.50MnO_3+δ impedance spectroscopic studies have been carried out at 77 K. With time there is irreversible formation of domains, which promotes the insulating behaviour of this charge ordered material. As time passes, the grain boundary resistance increases, showing the canted spin nature of the material. However, after 150 hours the grain boundary resistance becomes saturated, indicating that most of the metastable states have relaxed and transformed into stable charge ordered ones, most probably of antiferromagnetic nature. An equivalent circuit model, R₁(R₂C₂)(R₃C₃), i.e., a resistor–capacitor network, has been proposed to explain the impedance results.